2.20 vs 2.54 ratio?
01-07-2005, 11:41 AM
#46
928 Collector
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Originally Posted by SharkSkin
That's really the bottom line. ........... moving gear ratios around is about being able to be in the right gear at the right RPM at the right time .....
With a 2.54 rear end, torque comes to the ground for every gear, same as for 2.20. It just goes by faster. So, in a 2.2 you are at the "sweet spot" (aka torque peak) for longer, if you are able to select the right gear. Which I am.
I found the GT's frustrating because I'd just be getting to the sweet spot when it would fly by and I'd be needing to row to the next gear already. In my 2.2, I let her rip and the more revs I build, the more torque and the more acceleration I experience.
AUTOS
.... are a different ball game. They are able to change gears in an instant, so they really do not care or lose any time between shifts.
HOWEVER
.... autos don't usually shift after their torque peak. THey usually shift BEFORE their torque peak, which gives the common misbelief that autos are made of bacon. A properly-adjusted auto with shorter gearing (ie 2.54 and higher) will usually eat any and all other cars for breakfast, given the same engine and weight.
01-07-2005, 01:39 PM
#47
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Drag racing is a bit like having sex, the first few times you do it you may think you are doing great! but everyone else involved knows better 
The first 60 feet of a drag race is where most are won or lost. In the world of Drag racing a tenth of a second is a big deal. The quicker you can get the engine up to 5,000-6,000 rpm range for that launch the quicker that first 60 feet time should be. My wife just scored tickets for the NHRA Winternationals at Pomona , I think I will go tell John Force he needs to start out in second gear
The first 60 feet of a drag race is where most are won or lost. In the world of Drag racing a tenth of a second is a big deal. The quicker you can get the engine up to 5,000-6,000 rpm range for that launch the quicker that first 60 feet time should be. My wife just scored tickets for the NHRA Winternationals at Pomona , I think I will go tell John Force he needs to start out in second gear
01-07-2005, 03:21 PM
#48
Race Director
Thread Starter
Man did this turn into a much bigger post than I thought! After reading through the posts it appears that acceleration equates to power to weight ratio with traction and gearing factored in. The lower geared cars do seem to have an advantage in lower speed accelertation, at higher speeds the taller geared cars should do better. Either way a few mods to a 2.2 car would make up the difference!
01-07-2005, 03:25 PM
#49
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Jim B wrote:
>>>The first 60 feet of a drag race is where most are won or lost.
Most but not all Jim. The 5 speed S4's really put power down late in the quarter. The Pac NW group goes drag racing every summer, and on many occasions the 5 speeds would pull their competitors right before the finish line. I don't know if that's more of a launch issue (them 5 speeds are tough to get rolling) , or is a result gearing/HP. Watching from the stands behind the tree, it is weird seeing what appears to be the 5 speed 928 taking a loss, only to have the announcer give it the win. One of our guys after coming from behind said it all, "These things have got long legs". Damn truth.
>>>The first 60 feet of a drag race is where most are won or lost.
Most but not all Jim
. The 5 speed S4's really put power down late in the quarter. The Pac NW group goes drag racing every summer, and on many occasions the 5 speeds would pull their competitors right before the finish line. I don't know if that's more of a launch issue (them 5 speeds are tough to get rolling) , or is a result gearing/HP. Watching from the stands behind the tree, it is weird seeing what appears to be the 5 speed 928 taking a loss, only to have the announcer give it the win. One of our guys after coming from behind said it all, "These things have got long legs". Damn truth.
01-07-2005, 04:03 PM
#50
Rennlist Member
OK DEEP breath.......
Lets go back to basics. Newtons 2nd law. but, since we are accelerting a mass at different speeds, you have to look at the FINAL RESULTANT torque to the wheels through the gears over the speed range. when we increase a gear reduction, all we are doing is shifting the mechanical advantages down the speed scale. If we were talking about comparing two cars in 1st gear running 0- 40mph and then one car changed gear boxes to a higher ratio and the test became 0-35mph, then yes, the torque would be 14% higher the speed 88%as fast and the time would decrease. Not because we have added any power. the power would be uneffected the work done would be the same (if the same amount of power was used) we just got to a slower speed faster.
(ive given up with the HP discussion where I was trying to help simplify the explanation)
Now, if the top speed goal remained at 40mph, then the higher numerical rear end would have to shift into 2nd for the last 5mph, giving it a much lower torque for the last 5mph vs the car with the taller rear end still in first gear. the net result should be "no change" (or little differnce) average rate of acceleration would be the same because the work was the same. Work = force x displacement.
yes, Force = mass X acceration. In telling you that you were using it in the wrong context, I created even more confusion.. yes, at any part of an acceleration profile, torque is key. the reason i wanted you to also look at force over time (ie work), as this shows the entire picture. Again, torque without speed is 0 work, Speed without torque is 0 work.
yes, gearing is leverage and mutiplies torque. however, lets take a simple example of why this doesnt relate to increased acceleration in our cars in itself. taking the 2.2 :1 trannie and then changing to a 2.72 rear end does increase the mechanical advangtage for each gear respectively. However, when you match the mechanical advantages to the torques available on a stock S4 engine, you can see what happens.
Take 60mph to 75mph. S4 vs GT who has better acceleration (assume same weighs, hp, redlines)? well if you look at this example the S4 would be in 2nd gear with a final ratio of 5.9:1 producing 5.9 x the torque of the engine while the GT would now be in 3rd at 4.8:1 producing only 4.8 x the torque of the engine at 4500rpm or so. so, here you have a clear area where a 2.72 rear end is making less torque to the wheels, correct????? does this make sense???? if an engine makes 300ftlbs of torque at 4500 (resultant rpm after the 60mph 2-3gear shift , to equal 1440ftlbs of torque!!!!!!!!!!!!!!!!!!!!!!!!!!
Now, the S4 with the taller rear end is still in 2nd running from 5000rpm to 6400rpm to the target speed of 75mph. the engine is making an close to 300ftlbs here, and the net torque throught the gears is 1770ft lbs!!!!!!!!!!!!
DOES everyone see that from 60-75mph, that the S4 with a taller rear end makes 330ft lbs more to the rear wheels ??? This is the torque you are talking about and there is more of it over this range. a lot more. however, now to be fair, what happend from the 40mph to 60mph range. yes, the GT was enjoying a 15% torque advantage 2040ftlbs compared to the S4's 1770flt lbs. . (but just before that, the s4 had the longer duration in 1st gear.......... you see how this works?????)
The problem you are getting into is thinking the rear end is a torque multiplier. its really a torque shifter. the torque multiplication is based on speed and gear selection. it does not increase "OVERALL" torque. again, and ill keep on saying it, it depends!!!!!!! (lots of factors)
you quote my comparisons of the S4 automatic gear boxes and state, "clearly more force under the curve" wrong again. there are trade offs there as well. Again, you shift the torque curve, but you dont increase hp. if you dont know the range of operation, or if it is infinitely variable, then statistically, there would be no difference in acceleratoin with these two gear boxes. (see example above for a 60mph to 75mph race)
Ok, now some details of you other comments>>>>you said,
"NO. NO Force over time means nothing. (Force / mass) * time means velocity. FORCE / MASS means Acceleration. Force over time means zip."
Force x distance is work. Power = force x velocity. again, as you can see from example above, to get "torque" (mass x acceleration) you multiply the engine torque at a particular speed . the speed of the car will determine what gear you will be in so that you can multiply the torque to get the total "force" .
If you want to talk torque, you have to incorporate the range of speeds to be operating in. An s4 engine can make 300ftlbs to 275ftlbs over the operational range (ie 4500rpm to 6400rpm) by having a numerically higher ratio rear end, all you do is shift the multiplication curve up or down the speed curve. the average torque to the wheels willl not change. why, because it CANT.
#1 law of physics energy can not be destroyed or created. you cannot create energy by gearing. you cannot make hp by gearing. however, you CAN make more effient your application of the torque/hp to the wheels by gearing by knowing the range of application speeds and applying them.
yes, mass x acceleration is torque, but if speed is ignored, you loose the major component of being able acclerate a mass. DISPLACEMENT now work is done with a torque applied to a wall. the torque is there, but no work is done. Definition: 1hp is equal to 550lbs lifted 1 foot in 1 second. If we have 550ftlbs of torque on a wrench and it aint moving, nothing is being done, there is no acceleration of the mass!!!!!!!! however, if we move the 550lbs in 1foot in 1 second , we use 1hp. if we gear it down to 2:1 and move the same weight half the distance, but it will be 550bs in 1/2foot in 1/2second, we still have used 1hp. You can see where this is going.
Hp is everything , as it incorporates all that we are discussing. by just focusing on torque, you can still arrive at the corrrect answers, but it requires one more step (speed) that is already incorporated in to HP by defalt. it is not marketing.
it is the pure answer. but, if you want to talk torque, i can shift and do more work if it will help you understand.
going to your last comments, you clearly have to pull out some real numbers and digest them. the comparison i did above mainly done with the S4 and GT due to the familarity of the ratios. the points remain the same. gearing doesnt make hp. it doensnt nessarily have to improve or degrade accleration of our cars. Illl say it still again, it depends. It depends on the application of speeds . Ive given you a range speeds where the S4 clearly has more rear wheel torque than the higher numerically ratio'ed GT. but, there are also wider ranges where the GT has torque advantages . If ole Newton is correct, and i believe he is, then the net difference over many ranges of speed applicaton should be nil!! try it. pick your speed range, plug in the numbers and get back to me.
its all about maximixing the average Hp to the wheels over the operating range.
if it was "all" about torque, then with an infinitely variable gear box, where would the engine rpm rest??? max torque or max HP??????? i think you know the answer now! max HP!!!!!!!!!!!
Mark
Lets go back to basics. Newtons 2nd law. but, since we are accelerting a mass at different speeds, you have to look at the FINAL RESULTANT torque to the wheels through the gears over the speed range. when we increase a gear reduction, all we are doing is shifting the mechanical advantages down the speed scale. If we were talking about comparing two cars in 1st gear running 0- 40mph and then one car changed gear boxes to a higher ratio and the test became 0-35mph, then yes, the torque would be 14% higher the speed 88%as fast and the time would decrease. Not because we have added any power. the power would be uneffected the work done would be the same (if the same amount of power was used) we just got to a slower speed faster.
(ive given up with the HP discussion where I was trying to help simplify the explanation)
Now, if the top speed goal remained at 40mph, then the higher numerical rear end would have to shift into 2nd for the last 5mph, giving it a much lower torque for the last 5mph vs the car with the taller rear end still in first gear. the net result should be "no change" (or little differnce) average rate of acceleration would be the same because the work was the same. Work = force x displacement.
yes, Force = mass X acceration. In telling you that you were using it in the wrong context, I created even more confusion.. yes, at any part of an acceleration profile, torque is key. the reason i wanted you to also look at force over time (ie work), as this shows the entire picture. Again, torque without speed is 0 work, Speed without torque is 0 work.
yes, gearing is leverage and mutiplies torque. however, lets take a simple example of why this doesnt relate to increased acceleration in our cars in itself. taking the 2.2 :1 trannie and then changing to a 2.72 rear end does increase the mechanical advangtage for each gear respectively. However, when you match the mechanical advantages to the torques available on a stock S4 engine, you can see what happens.
Take 60mph to 75mph. S4 vs GT who has better acceleration (assume same weighs, hp, redlines)? well if you look at this example the S4 would be in 2nd gear with a final ratio of 5.9:1 producing 5.9 x the torque of the engine while the GT would now be in 3rd at 4.8:1 producing only 4.8 x the torque of the engine at 4500rpm or so. so, here you have a clear area where a 2.72 rear end is making less torque to the wheels, correct????? does this make sense???? if an engine makes 300ftlbs of torque at 4500 (resultant rpm after the 60mph 2-3gear shift , to equal 1440ftlbs of torque!!!!!!!!!!!!!!!!!!!!!!!!!!
Now, the S4 with the taller rear end is still in 2nd running from 5000rpm to 6400rpm to the target speed of 75mph. the engine is making an close to 300ftlbs here, and the net torque throught the gears is 1770ft lbs!!!!!!!!!!!!
DOES everyone see that from 60-75mph, that the S4 with a taller rear end makes 330ft lbs more to the rear wheels ??? This is the torque you are talking about and there is more of it over this range. a lot more. however, now to be fair, what happend from the 40mph to 60mph range. yes, the GT was enjoying a 15% torque advantage 2040ftlbs compared to the S4's 1770flt lbs. . (but just before that, the s4 had the longer duration in 1st gear.......... you see how this works?????)
The problem you are getting into is thinking the rear end is a torque multiplier. its really a torque shifter. the torque multiplication is based on speed and gear selection. it does not increase "OVERALL" torque. again, and ill keep on saying it, it depends!!!!!!! (lots of factors)
you quote my comparisons of the S4 automatic gear boxes and state, "clearly more force under the curve" wrong again. there are trade offs there as well. Again, you shift the torque curve, but you dont increase hp. if you dont know the range of operation, or if it is infinitely variable, then statistically, there would be no difference in acceleratoin with these two gear boxes. (see example above for a 60mph to 75mph race)
Ok, now some details of you other comments>>>>you said,
"NO. NO Force over time means nothing. (Force / mass) * time means velocity. FORCE / MASS means Acceleration. Force over time means zip."
Force x distance is work. Power = force x velocity. again, as you can see from example above, to get "torque" (mass x acceleration) you multiply the engine torque at a particular speed . the speed of the car will determine what gear you will be in so that you can multiply the torque to get the total "force" .
If you want to talk torque, you have to incorporate the range of speeds to be operating in. An s4 engine can make 300ftlbs to 275ftlbs over the operational range (ie 4500rpm to 6400rpm) by having a numerically higher ratio rear end, all you do is shift the multiplication curve up or down the speed curve. the average torque to the wheels willl not change. why, because it CANT.
#1 law of physics energy can not be destroyed or created. you cannot create energy by gearing. you cannot make hp by gearing. however, you CAN make more effient your application of the torque/hp to the wheels by gearing by knowing the range of application speeds and applying them.
yes, mass x acceleration is torque, but if speed is ignored, you loose the major component of being able acclerate a mass. DISPLACEMENT now work is done with a torque applied to a wall. the torque is there, but no work is done. Definition: 1hp is equal to 550lbs lifted 1 foot in 1 second. If we have 550ftlbs of torque on a wrench and it aint moving, nothing is being done, there is no acceleration of the mass!!!!!!!! however, if we move the 550lbs in 1foot in 1 second , we use 1hp. if we gear it down to 2:1 and move the same weight half the distance, but it will be 550bs in 1/2foot in 1/2second, we still have used 1hp. You can see where this is going.
Hp is everything , as it incorporates all that we are discussing. by just focusing on torque, you can still arrive at the corrrect answers, but it requires one more step (speed) that is already incorporated in to HP by defalt. it is not marketing.
it is the pure answer. but, if you want to talk torque, i can shift and do more work if it will help you understand.
going to your last comments, you clearly have to pull out some real numbers and digest them. the comparison i did above mainly done with the S4 and GT due to the familarity of the ratios. the points remain the same. gearing doesnt make hp. it doensnt nessarily have to improve or degrade accleration of our cars. Illl say it still again, it depends. It depends on the application of speeds . Ive given you a range speeds where the S4 clearly has more rear wheel torque than the higher numerically ratio'ed GT. but, there are also wider ranges where the GT has torque advantages . If ole Newton is correct, and i believe he is, then the net difference over many ranges of speed applicaton should be nil!! try it. pick your speed range, plug in the numbers and get back to me.
its all about maximixing the average Hp to the wheels over the operating range.
if it was "all" about torque, then with an infinitely variable gear box, where would the engine rpm rest??? max torque or max HP??????? i think you know the answer now! max HP!!!!!!!!!!!
Mark
Originally Posted by 928Quest
Wow, I am not even sure where to start.
'The confusion runs rampant when folks start thinking that a numerically higher rear end increases torque overall, and it clearly doesnt. "
What?? Wrong. It does increase torque overall, by defintion. Its a torque multiplier. Given the same transmission gearing and then changing the rear ratio DOES increase the torque overall.
"...Now, your 4 speed automatic with the 2.2 vs the 2.54:1
2.2 1st 8.1 2nd 5.3 3rd 3.0 4th 2.2 (spacing of .65.56.73 ) (.64ave)
2.54 1st 9.8 2nd 5.7 3rd 3.65 4th 2.54 (spacing of .58.64.69) (.64 ave)..."
Yes, clearly the 2.54 AT has a torque advantage troughout the range as compared to the 2.2 AT, which why they are typically quicker that the 2.2 boxes. Clearly more Force under the curve, therefore more acceleration over time, even if the horsepower is the same.
"...torque without speed ( RPMS) is meaningless. speed (rpm) without torque is meaningless. torque x speed is HP it takes hp to make a car acclerate over a distance. when you "loosely " use acceleration, we are not talking about just acceleration as in the term F=MA, we are talking about work. we are talking about force over time! when you are talking about acceleration from 0-60mph torque has little meaning unless speed is attached ot it so, yes, i talk about hp to remove some of the simple math. now, if you want to talk torque, we can talk torque. Here is an example with some real values...."
..."we are talking about force over time! ..." NO. NO Force over time means nothing. (Force / mass) * time means velocity. FORCE / MASS means Acceleration. Force over time means zip.
How can you even write this paragraph. Heck I am not even sure what you are saying. ""...torque without speed ( RPMS) is meaningless. speed (rpm) without torque is meaningless..."????
That noise you hear is every dead Physics teacher revolving at 1000rpm, with considerable torque I might add. Mr. Newton says A=F/M. Force is not horsepower, it is force. That combined with mass IS EVERYTHING. It is "A". Nowhere in F=MA is speed mentioned. Yes, horse power is a measure of work, but that isn't directly applicable to acceleration.
".. Loosly use acceleration..."?? You must be joking, as I said acceleration is everything. It what this whole thread is about. That acceleration multiplied by time, instant by instant gives you ever increasing velocity. HP does not even enter the picture. HP is tripe that the marketing managers hang there hat on. Power whether in watts, hp or whatever is tricky thing and can be misleading. You would not be the first to be confused by it. The force that the wheels push against the ground with from instant to instant and the weight of the car is what matters. That force is directly controlled by the gearing. Torque of the engine * tranny gear ratio * rear ratio. Change the rear ratio higher and the whole curve shifts up. And yes the wheels turn slower, That way horsepower remains constant.
"...at this point 75mph, the S4 shifts into 4th..."
HUH??? My S4 shifts into 4 at about 130mph. You must mean shifts into 3rd. We are talking automatics here right??? The whole thread is about changing a 2.2 AT to 2.54 AT. This whole monolog comparing these two cars is interesting, but dubious.
"...Even still, you can see if you plot out the TORQUE, since you guys are getting so hung up on it, TORQUE to the rear wheels through the gear boxes of different values, have many trade offs. The net should in theory be the SAME acceleration rate at certain target speeds and favorable to each depending on the starting and ending speed...."
No, and until you realize this you will continue to be slightly short of spectacular.
"...Folks over these periods, the mechanical advantage is clearly in the hands of the taller rear end..."
I can't believe you trying to say that the GT with the torque shoved higher and the torque advantage of the 2.73 gears is going to have its clocked cleaned by an AT S4, or even a 5spd S4. This is clearly not the case by anybody's measure, I must be misunderstanding you.
'The confusion runs rampant when folks start thinking that a numerically higher rear end increases torque overall, and it clearly doesnt. "
What?? Wrong. It does increase torque overall, by defintion. Its a torque multiplier. Given the same transmission gearing and then changing the rear ratio DOES increase the torque overall.
"...Now, your 4 speed automatic with the 2.2 vs the 2.54:1
2.2 1st 8.1 2nd 5.3 3rd 3.0 4th 2.2 (spacing of .65.56.73 ) (.64ave)
2.54 1st 9.8 2nd 5.7 3rd 3.65 4th 2.54 (spacing of .58.64.69) (.64 ave)..."
Yes, clearly the 2.54 AT has a torque advantage troughout the range as compared to the 2.2 AT, which why they are typically quicker that the 2.2 boxes. Clearly more Force under the curve, therefore more acceleration over time, even if the horsepower is the same.
"...torque without speed ( RPMS) is meaningless. speed (rpm) without torque is meaningless. torque x speed is HP it takes hp to make a car acclerate over a distance. when you "loosely " use acceleration, we are not talking about just acceleration as in the term F=MA, we are talking about work. we are talking about force over time! when you are talking about acceleration from 0-60mph torque has little meaning unless speed is attached ot it so, yes, i talk about hp to remove some of the simple math. now, if you want to talk torque, we can talk torque. Here is an example with some real values...."
..."we are talking about force over time! ..." NO. NO Force over time means nothing. (Force / mass) * time means velocity. FORCE / MASS means Acceleration. Force over time means zip.
How can you even write this paragraph. Heck I am not even sure what you are saying. ""...torque without speed ( RPMS) is meaningless. speed (rpm) without torque is meaningless..."????
That noise you hear is every dead Physics teacher revolving at 1000rpm, with considerable torque I might add. Mr. Newton says A=F/M. Force is not horsepower, it is force. That combined with mass IS EVERYTHING. It is "A". Nowhere in F=MA is speed mentioned. Yes, horse power is a measure of work, but that isn't directly applicable to acceleration.
".. Loosly use acceleration..."?? You must be joking, as I said acceleration is everything. It what this whole thread is about. That acceleration multiplied by time, instant by instant gives you ever increasing velocity. HP does not even enter the picture. HP is tripe that the marketing managers hang there hat on. Power whether in watts, hp or whatever is tricky thing and can be misleading. You would not be the first to be confused by it. The force that the wheels push against the ground with from instant to instant and the weight of the car is what matters. That force is directly controlled by the gearing. Torque of the engine * tranny gear ratio * rear ratio. Change the rear ratio higher and the whole curve shifts up. And yes the wheels turn slower, That way horsepower remains constant.
"...at this point 75mph, the S4 shifts into 4th..."
HUH??? My S4 shifts into 4 at about 130mph. You must mean shifts into 3rd. We are talking automatics here right??? The whole thread is about changing a 2.2 AT to 2.54 AT. This whole monolog comparing these two cars is interesting, but dubious.
"...Even still, you can see if you plot out the TORQUE, since you guys are getting so hung up on it, TORQUE to the rear wheels through the gear boxes of different values, have many trade offs. The net should in theory be the SAME acceleration rate at certain target speeds and favorable to each depending on the starting and ending speed...."
No, and until you realize this you will continue to be slightly short of spectacular.
"...Folks over these periods, the mechanical advantage is clearly in the hands of the taller rear end..."
I can't believe you trying to say that the GT with the torque shoved higher and the torque advantage of the 2.73 gears is going to have its clocked cleaned by an AT S4, or even a 5spd S4. This is clearly not the case by anybody's measure, I must be misunderstanding you.
01-07-2005, 04:13 PM
#51
Rennlist Member
The "sweet spot" you speak of i hope is max hp!! all the gear boxes manual and auto, have the same sweetspots. the gear spacing determines how long you stay in the sweetspot. autos , by my numbers above, are not in the sweet spot as long as the manuals, due to there being 5 gears and the gear spacing being closer together.
if you plot out the actual torque to the wheels over a range , say 0-100mph, you will be surprised how close the net torque to the wheels is for all cars either comparing manual to manual (up to 4th gears due to the 5th in the 2.2 being way out of the range of the other gears) and the autos to auto comparison.
by the way, do autos really shift at max torque??? (ie 4500rpm) I doubt it, but i could be wrong. i would think that they shift at near redline under WOT. if they dont, that could be part of your problem. (or anyone else running and loosing against a 2.54 with a 2.2 auto over certain speed ranges)
this is the reason and purpose of the discussion to show that rear end ratios have little to do with net acceleration over a varied speed range.
mk
if you plot out the actual torque to the wheels over a range , say 0-100mph, you will be surprised how close the net torque to the wheels is for all cars either comparing manual to manual (up to 4th gears due to the 5th in the 2.2 being way out of the range of the other gears) and the autos to auto comparison.
by the way, do autos really shift at max torque??? (ie 4500rpm) I doubt it, but i could be wrong. i would think that they shift at near redline under WOT. if they dont, that could be part of your problem. (or anyone else running and loosing against a 2.54 with a 2.2 auto over certain speed ranges)
this is the reason and purpose of the discussion to show that rear end ratios have little to do with net acceleration over a varied speed range.
mk
Originally Posted by heinrich
Agreed. Having driven GT's and extensively my 2.2 5spd, I know that whether you're on a track or the freeway, the answer is ... are you putting torque to the ground.
With a 2.54 rear end, torque comes to the ground for every gear, same as for 2.20. It just goes by faster. So, in a 2.2 you are at the "sweet spot" (aka torque peak) for longer, if you are able to select the right gear. Which I am.
I found the GT's frustrating because I'd just be getting to the sweet spot when it would fly by and I'd be needing to row to the next gear already. In my 2.2, I let her rip and the more revs I build, the more torque and the more acceleration I experience.
AUTOS
.... are a different ball game. They are able to change gears in an instant, so they really do not care or lose any time between shifts.
HOWEVER
.... autos don't usually shift after their torque peak. THey usually shift BEFORE their torque peak, which gives the common misbelief that autos are made of bacon. A properly-adjusted auto with shorter gearing (ie 2.54 and higher) will usually eat any and all other cars for breakfast, given the same engine and weight.
With a 2.54 rear end, torque comes to the ground for every gear, same as for 2.20. It just goes by faster. So, in a 2.2 you are at the "sweet spot" (aka torque peak) for longer, if you are able to select the right gear. Which I am.
I found the GT's frustrating because I'd just be getting to the sweet spot when it would fly by and I'd be needing to row to the next gear already. In my 2.2, I let her rip and the more revs I build, the more torque and the more acceleration I experience.
AUTOS
.... are a different ball game. They are able to change gears in an instant, so they really do not care or lose any time between shifts.
HOWEVER
.... autos don't usually shift after their torque peak. THey usually shift BEFORE their torque peak, which gives the common misbelief that autos are made of bacon. A properly-adjusted auto with shorter gearing (ie 2.54 and higher) will usually eat any and all other cars for breakfast, given the same engine and weight.
01-07-2005, 04:21 PM
#52
Rennlist Member
Chuck, you must be able to see that there is no free ride, and if you want to go faster, acclerate faster, you need more hp PERIOD . And that ride cost money!!
gearing is leverage, but with given HP , a certain amount of work can be done (force x displacement) or torque x speed, etc. if you look at the final drive ratio, you are missing most of the picture. each of the 5 gears have ratios mutiplied by the rear end. the engine redlines at 6400rpm, and the gear spacing is close to the same for most all 928s (except 5th gears, so use gears 1-4 and speeds ranging from 0-155mph) if you look at the torque available over the entire speed range, with multiple gear boxes, the answer becomes very clear. If you just drive in the fog of (F=MA) and dont consider the other factors, you are going to stay confused.
Because we have gears, you can do one of two things. take HP and look at the average put to the wheels over the operatonal range, or use Torque and multiply it out over the same speed range. either way, the answer will be the same.
Mk
gearing is leverage, but with given HP , a certain amount of work can be done (force x displacement) or torque x speed, etc. if you look at the final drive ratio, you are missing most of the picture. each of the 5 gears have ratios mutiplied by the rear end. the engine redlines at 6400rpm, and the gear spacing is close to the same for most all 928s (except 5th gears, so use gears 1-4 and speeds ranging from 0-155mph) if you look at the torque available over the entire speed range, with multiple gear boxes, the answer becomes very clear. If you just drive in the fog of (F=MA) and dont consider the other factors, you are going to stay confused.
Because we have gears, you can do one of two things. take HP and look at the average put to the wheels over the operatonal range, or use Torque and multiply it out over the same speed range. either way, the answer will be the same.
Mk
Originally Posted by 928Quest
"...torque increase by increasing the rear end doesnt produce increased acceleration, HP does this..."
No, increased torque does increase acceleration. And like everything in physics there is no free ride. The price you pay for this is decreased top end.
It is like a lever, A lever can greatly multiply your force, but the price you pay is is in greatly increased input displacement and decreased output displacment. Input power is the same because you move further with less force on the input side.
You certainly must see this.
No, increased torque does increase acceleration. And like everything in physics there is no free ride. The price you pay for this is decreased top end.
It is like a lever, A lever can greatly multiply your force, but the price you pay is is in greatly increased input displacement and decreased output displacment. Input power is the same because you move further with less force on the input side.
You certainly must see this.
01-07-2005, 04:24 PM
#53
928 Collector
Rennlist Member
Rennlist Member
Originally Posted by mark kibort
The "sweet spot" you speak of i hope is max hp!!
Originally Posted by mark kibort
this is the reason and purpose of the discussion to show that rear end ratios have little to do with net acceleration over a varied speed range.
In my opinion, rear-end ratios have everything to do with acceleration, all other things being equal. MARK:
If rear-end ratios do not affect acceleration .... what do they affect, in your humble opinion?
01-07-2005, 04:38 PM
#54
Rennlist Member
Dave, this stuff is pretty simple, and I know that there are some great minds on the list. however, this is an area that i am painfully familar with and have relative to this topic discussions (on a regular basis) with PHD'ed scientists that have forgoten more than ill ever learn about science /physics. However, with this discussion, im talking to folks that are trying to think this out intuitively, with just a rememberance of physics from highschool or college to make them dangerous. Heck, its really simple stuff . all you need is a hp curve(and torque curve, and the gear ratos and you can actually make a very accurate acceleration chart of any of the cars and ratios we are discussing. just plug in the numbers and you will have the answer.
you talk about hp and the comparisons of a 4.1 vs a 3.0:1 rear end. you think that in every gear at every speed , the 4.1 has a torque advantage??? think again. plot it out for several gear shifts. let me know some real data, not just guess work. I know you understand basic gearing , if you have raced all you mention . but, many racers still dont understand the basics here. some of these basics are well understood by the crew chiefs, and they make the decisions to change rear ends either up or down. Yes, sometimes faster is a taller rear end, and it dont always mean top speed of the vehicle.
you also mention the higher hp , the higher the rate of acceleration , which is correct. but you go on to attach gearing and torque to gain this energy which is wrong. gearing only increases or decreases the effeciency of the applicatoin of HP/torque over an operating range. it doesnt create energy to accelerate faster. read my recent long post about why.
I you or anyone disagrees with the math, let me know . we can talk about it. but trust me, the math dont lie
yes, its all about torque and how its applied through the gears over the operational range. otherwise, all race teams would just put in lower rear ends until the car would move.
Mk
you talk about hp and the comparisons of a 4.1 vs a 3.0:1 rear end. you think that in every gear at every speed , the 4.1 has a torque advantage??? think again. plot it out for several gear shifts. let me know some real data, not just guess work. I know you understand basic gearing , if you have raced all you mention . but, many racers still dont understand the basics here. some of these basics are well understood by the crew chiefs, and they make the decisions to change rear ends either up or down. Yes, sometimes faster is a taller rear end, and it dont always mean top speed of the vehicle.
you also mention the higher hp , the higher the rate of acceleration , which is correct. but you go on to attach gearing and torque to gain this energy which is wrong. gearing only increases or decreases the effeciency of the applicatoin of HP/torque over an operating range. it doesnt create energy to accelerate faster. read my recent long post about why.
I you or anyone disagrees with the math, let me know . we can talk about it. but trust me, the math dont lie
yes, its all about torque and how its applied through the gears over the operational range. otherwise, all race teams would just put in lower rear ends until the car would move.
Mk
Originally Posted by Ketchmi
To reuse my drag gearing anaology........
If you have two vehicles with the exact same mass and horsepower running the quarter mile:
The one with the lower geared rear end will be able to expend more energy during the same given distance thusly produce more average power during the run which equals a quicker ET. (up to a point where the gearing is too low and you lose efficiency)
A quicker ET is directly related to the amount of average torque/horsepower produced during the given distance. Both vehicles have say 300 hp. If one has 3:00/1 rear gears versus one with say 4:10/1, it is averageing a lower rpm during the run thusly producing less average horsepower and torque for the given distance. It will not have the same rate of acceleration as the vehicle with the 4:10/1 ratio.
Torque multiplication is done by the transmission and the differential gearing. Lower differential gears will multiply the available engine's torque to produce more applied torque. How else could an engine with 300#' of torque ever get a 3500# vehicle to move at all?
I hope I have succeded in explaining this without too many numbers. You know how simple all of "us" out here are. BTW, actual application.......I have an 89' GT in the shop and two 87's and one 88' 5-speed available. I have driven all them extensivly. The GT is much quicker to any given speed short of it's max than any of the stock 5-speed 2.2 geared S4's. I don't think the additional 14 horsepower is the answer as it's much quicker than 14 horsepower would allow for. I also have a couple of post 89' auto's available with the 2:54 gears that I have compared to my 86.5' and to a couple of 87' auto's. The 89' and up auto's are considerably quicker during acceleration. Practical application.
Simply put, the more energy expended during a given distance will increase the rate of acceleration (disregarding wheel spin). The more energy expended, the more energy produced. The higher average horsepower for a given distance, the higher rate of acceleration. The lower the gearing, the higher the torque multiplication, the higher applied torque, the greater mass acceleration. It's true that a fixed horsepower/mass will give a general maximum velocity during a given distance but that doesn't mean that it cannot accelerate to it's maximum velocity in a fixed distance much quicker thusly producing a faster rate of acceleration and a quicker ET.
Oh yeah, I'm not driving a calculator here, it's all been proven in applied science. I've raced almost everything under the sun for decades. Motorcycles, snowmobiles, Formula V, Formula Atlantic, autocross, road racing, drag racing, open road racing, pretty much everything but Bonneville. I live close to the salt but have not yet gotten the urge to play on it. Do not be so quick to shun the intelligence of the masses.
We all appreciate what you do and have done for the 928 but this ain't NASCAR, we ain't sittin' in the stands with a bud in both hands cheering blindly for our driver de jour. There are some great minds playing with 928's and many of them are right here on Rennlist. Don't be blind enough to not question your own math.
Dave
Motorsport
If you have two vehicles with the exact same mass and horsepower running the quarter mile:
The one with the lower geared rear end will be able to expend more energy during the same given distance thusly produce more average power during the run which equals a quicker ET. (up to a point where the gearing is too low and you lose efficiency)
A quicker ET is directly related to the amount of average torque/horsepower produced during the given distance. Both vehicles have say 300 hp. If one has 3:00/1 rear gears versus one with say 4:10/1, it is averageing a lower rpm during the run thusly producing less average horsepower and torque for the given distance. It will not have the same rate of acceleration as the vehicle with the 4:10/1 ratio.
Torque multiplication is done by the transmission and the differential gearing. Lower differential gears will multiply the available engine's torque to produce more applied torque. How else could an engine with 300#' of torque ever get a 3500# vehicle to move at all?
I hope I have succeded in explaining this without too many numbers. You know how simple all of "us" out here are. BTW, actual application.......I have an 89' GT in the shop and two 87's and one 88' 5-speed available. I have driven all them extensivly. The GT is much quicker to any given speed short of it's max than any of the stock 5-speed 2.2 geared S4's. I don't think the additional 14 horsepower is the answer as it's much quicker than 14 horsepower would allow for. I also have a couple of post 89' auto's available with the 2:54 gears that I have compared to my 86.5' and to a couple of 87' auto's. The 89' and up auto's are considerably quicker during acceleration. Practical application.
Simply put, the more energy expended during a given distance will increase the rate of acceleration (disregarding wheel spin). The more energy expended, the more energy produced. The higher average horsepower for a given distance, the higher rate of acceleration. The lower the gearing, the higher the torque multiplication, the higher applied torque, the greater mass acceleration. It's true that a fixed horsepower/mass will give a general maximum velocity during a given distance but that doesn't mean that it cannot accelerate to it's maximum velocity in a fixed distance much quicker thusly producing a faster rate of acceleration and a quicker ET.
Oh yeah, I'm not driving a calculator here, it's all been proven in applied science. I've raced almost everything under the sun for decades. Motorcycles, snowmobiles, Formula V, Formula Atlantic, autocross, road racing, drag racing, open road racing, pretty much everything but Bonneville. I live close to the salt but have not yet gotten the urge to play on it. Do not be so quick to shun the intelligence of the masses.
We all appreciate what you do and have done for the 928 but this ain't NASCAR, we ain't sittin' in the stands with a bud in both hands cheering blindly for our driver de jour. There are some great minds playing with 928's and many of them are right here on Rennlist. Don't be blind enough to not question your own math.
Dave
Motorsport
01-07-2005, 04:45 PM
#55
Rennlist Member
You must have not read my post. rear end ratios. or better said, total gear ratios tell you how effecient the engine HP/torque will be put to the wheels over an operational range.
HP does move the car forward, BY DEFINITION!!! torque x speed is HP. without speed, you aint moving!!
sure, torque is as important as the speed, in fact, equally important.
Its not opinion, its fact.
ive already worked a couple of senareos for you . what do you disagree with as far as the GT vs S4 accelerating from 60 to 75mph. I gave you the torques, speeds and times and in this range, it is a classic example of what im talking about. Gearing doesnt buy hp. gearing doesnt even buy overall, average torque put to the wheels . it buys where you have that torque over a speed range.
Mk
HP does move the car forward, BY DEFINITION!!! torque x speed is HP. without speed, you aint moving!!
sure, torque is as important as the speed, in fact, equally important.
Its not opinion, its fact.
ive already worked a couple of senareos for you . what do you disagree with as far as the GT vs S4 accelerating from 60 to 75mph. I gave you the torques, speeds and times and in this range, it is a classic example of what im talking about. Gearing doesnt buy hp. gearing doesnt even buy overall, average torque put to the wheels . it buys where you have that torque over a speed range.
Mk
Originally Posted by heinrich
Thought I was clear. MAX TORQUE. Horsepower does not move the car forward and is calculated from torque anyway.
In your opinion it is In my opinion, rear-end ratios have everything to do with acceleration, all other things being equal.
MARK:
If rear-end ratios do not affect acceleration .... what do they affect, in your humble opinion?
In your opinion it is
In my opinion, rear-end ratios have everything to do with acceleration, all other things being equal. MARK:
If rear-end ratios do not affect acceleration .... what do they affect, in your humble opinion?
01-07-2005, 04:54 PM
#56
Rennlist Member
Someone please plug in the speeds and torque on a chart to show what the rear wheel torque is from 0-100mph
THIS WILL ANSWER ALL WHO QUESTION!!!!
Use: 300ftlbs at peak torque 4500rpm 275ftlbs of torque at redline 6400rpm. (good general model not far off proportional from most all S4s) with those numbers, you can now plot out from 0-100mph what TORQUE is put to the wheels and used for acceleration!!
CDs of the 2004 race season for anyone with close to the right story to the gearing question based on ACTUAL numbers and actual comparative torque values over the acceleration range.
HERE ARE THE GEAR RATIO NUMBERS.
S4 1st 8.9:1 2nd 5.9:1 3rd 4.2 4th 3.2 5th 2.2 (spacing of .66.71.76) .71ave
GT 1st 10.2:1 2nd 6.8:1 3rd 4.8 4th 3.6 5th 2.72 (spacing of .66.71.75)
the GT compared to the S4 has these mechanical advantages per gear (114%,115%,113%112% and a rear end difference of 124%)
Mark
PS, if you want to do it for the Automatics, those numbers again, are posted below. I think the above is best as the comparisons of the gear boxes have uniform differnces.
Now, your 4 speed automatic with the 2.2 vs the 2.54:1
(and yes, the actual ratios are different between the two gear boxes, but ive listed the final results of the ratios here)
2.2 1st 8.1:1 2nd 5.3 3rd 3.0 4th 2.2 (spacing of .65.56.73 ) (.64ave)
2.54 1st 9.8:1 2nd 5.7 3rd 3.65 4th 2.54 (spacing of .58.64.69) (.64 ave)
compared to the 2.2, the 2.54 trannie has these mechanical advantages per gear ( 120%, 107%, 121%, and final drive difference of 115%)
THIS WILL ANSWER ALL WHO QUESTION!!!!
Use: 300ftlbs at peak torque 4500rpm 275ftlbs of torque at redline 6400rpm. (good general model not far off proportional from most all S4s) with those numbers, you can now plot out from 0-100mph what TORQUE is put to the wheels and used for acceleration!!
CDs of the 2004 race season for anyone with close to the right story to the gearing question based on ACTUAL numbers and actual comparative torque values over the acceleration range.
HERE ARE THE GEAR RATIO NUMBERS.
S4 1st 8.9:1 2nd 5.9:1 3rd 4.2 4th 3.2 5th 2.2 (spacing of .66.71.76) .71ave
GT 1st 10.2:1 2nd 6.8:1 3rd 4.8 4th 3.6 5th 2.72 (spacing of .66.71.75)
the GT compared to the S4 has these mechanical advantages per gear (114%,115%,113%112% and a rear end difference of 124%)
Mark
PS, if you want to do it for the Automatics, those numbers again, are posted below. I think the above is best as the comparisons of the gear boxes have uniform differnces.
Now, your 4 speed automatic with the 2.2 vs the 2.54:1
(and yes, the actual ratios are different between the two gear boxes, but ive listed the final results of the ratios here)
2.2 1st 8.1:1 2nd 5.3 3rd 3.0 4th 2.2 (spacing of .65.56.73 ) (.64ave)
2.54 1st 9.8:1 2nd 5.7 3rd 3.65 4th 2.54 (spacing of .58.64.69) (.64 ave)
compared to the 2.2, the 2.54 trannie has these mechanical advantages per gear ( 120%, 107%, 121%, and final drive difference of 115%)
01-07-2005, 05:02 PM
#57
928 Collector
Rennlist Member
Rennlist Member
Originally Posted by mark kibort
.... HP does move the car forward, BY DEFINITION!!! torque x speed is HP. without speed, you aint moving!!
01-07-2005, 05:30 PM
#58
Rennlist Member
acceleration is the 2nd derivative of distance and the 1st derivative of speed.
what this means , is if you have an acceleraton , with out some type of displacement attached to it it is just force. there is no acceleration. force is meaningless without speed.
now, what do you mean, by " that is just wrong?"
to move something (a mass) from point a to point b requires work. work is force x displacement and then over time, you get HP.
What part of this is not sinking in?
MK
Mk
what this means , is if you have an acceleraton , with out some type of displacement attached to it it is just force. there is no acceleration. force is meaningless without speed.
now, what do you mean, by " that is just wrong?"
to move something (a mass) from point a to point b requires work. work is force x displacement and then over time, you get HP.
What part of this is not sinking in?
MK
Mk
Originally Posted by heinrich
DUDE that is just wrong
01-07-2005, 05:49 PM
#59
Drifting
Gee, here we go again Mark.
If you are running a 4:10/1 rear gear ratio, every #' of torque produced by the engine is multiplied by 4.1! There are points of difference during which a higher geared car will be producing more applied torque, for instance when a 4:10 geared car has just shifted into a higher gear and the 3:00 geared car is building up to a shift but that is not going to be as significant as you say. Simply put for every '# of torque produced by a given engine, the torque will be multiplied by the differential (and transmission) gearing to give you a value of applied torque.
I am comparing apples to apples here, same engines and transmissions. Only change is rear gearing. Side by side exactly equipped cars with different differential gearing prove my point. Do the math, for every rpm point in every gear the lower geared car will have more applied torque. Will it have better acceleration? Damn right, (within the limits of adhesion) Will it have a lower top speed, Damn right (within horsepower and aerodynamic drag limits). Will it have better acceleration in any gear at any rpm (as long as the other vehicle is in the same gear at the same rpm), Damn right. I'm not sure what you are missing here but you are right, it's all simple math. That's not saying it would be quicker on any given road course, there are way too many variables to account for that. This is just to prove that lower gearing benefits acceleration.
Hmmmmm, simple. If gearing didn't effect acceleration then your car would accelerate at the same rate from a dead stop in 3rd gear as it would in first? The engine is producing the exact same horsepower and torque in third as it is in first isn't it? (I know, too simple but it makes a point)
Dave
If you are running a 4:10/1 rear gear ratio, every #' of torque produced by the engine is multiplied by 4.1! There are points of difference during which a higher geared car will be producing more applied torque, for instance when a 4:10 geared car has just shifted into a higher gear and the 3:00 geared car is building up to a shift but that is not going to be as significant as you say. Simply put for every '# of torque produced by a given engine, the torque will be multiplied by the differential (and transmission) gearing to give you a value of applied torque.
I am comparing apples to apples here, same engines and transmissions. Only change is rear gearing. Side by side exactly equipped cars with different differential gearing prove my point. Do the math, for every rpm point in every gear the lower geared car will have more applied torque. Will it have better acceleration? Damn right, (within the limits of adhesion) Will it have a lower top speed, Damn right (within horsepower and aerodynamic drag limits). Will it have better acceleration in any gear at any rpm (as long as the other vehicle is in the same gear at the same rpm), Damn right. I'm not sure what you are missing here but you are right, it's all simple math. That's not saying it would be quicker on any given road course, there are way too many variables to account for that. This is just to prove that lower gearing benefits acceleration.
Hmmmmm, simple. If gearing didn't effect acceleration then your car would accelerate at the same rate from a dead stop in 3rd gear as it would in first? The engine is producing the exact same horsepower and torque in third as it is in first isn't it? (I know, too simple but it makes a point)
Dave
01-07-2005, 06:05 PM
#60
Rennlist Member
Torque is a static measure. Horsepower is a measure of work done that incorporates torque, but is a measure indicating acceleration of mass over time. Straightforward enough.
One thing I'll say here, this from personal experience.... and it is simply another way of saying the same thing as many of the statements above. Lower gearing can increase acceleration in certain circumstances. These are old numbers and I'm a tad fuzzy on them, but this ought to be close enough.
I used to have a 1967 Dodge R/T... a buddy had a near-identical car. Main difference between the cars was I had 2.72:1 gears, he had 3.54:1.
I did the 1/4 mile in about 13 at 130, using only first and second gear.
He did the 1/4 in about 12 at ~135, but he used most of 3rd gear.
Why the difference? IMHO it's because with 1 more gear at his disposal he was able to keep to "the area under the curve" longer, on average. Additionally, with his lower first gear, he was able to launch a lot harder. I didn't have major traction issues, but I didn't accelerate hard till 30+ MPH. He DID have major traction issues, and he only brought it under 12 secs with drag slicks. His car didn't make any more power, his advantage was due to spending more time, on average, in the "sweet spot". I'll say it again... gearing serves only to move the sweet spot around. In my buddie's case, the sweet spot was the 1/4 mile. However, on the open road, his car would start to wheeze at about 125, while I could still kickdown into 2nd and walk all over him. My sweet spot was over 40 MPH, suited for highway use and not 1/4 mile.
Another way we used to state it was, gears could make your car quick, or fast... pick one.
One thing I'll say here, this from personal experience.... and it is simply another way of saying the same thing as many of the statements above. Lower gearing can increase acceleration in certain circumstances. These are old numbers and I'm a tad fuzzy on them, but this ought to be close enough.
I used to have a 1967 Dodge R/T... a buddy had a near-identical car. Main difference between the cars was I had 2.72:1 gears, he had 3.54:1.
I did the 1/4 mile in about 13 at 130, using only first and second gear.
He did the 1/4 in about 12 at ~135, but he used most of 3rd gear.
Why the difference? IMHO it's because with 1 more gear at his disposal he was able to keep to "the area under the curve" longer, on average. Additionally, with his lower first gear, he was able to launch a lot harder. I didn't have major traction issues, but I didn't accelerate hard till 30+ MPH. He DID have major traction issues, and he only brought it under 12 secs with drag slicks. His car didn't make any more power, his advantage was due to spending more time, on average, in the "sweet spot". I'll say it again... gearing serves only to move the sweet spot around. In my buddie's case, the sweet spot was the 1/4 mile. However, on the open road, his car would start to wheeze at about 125, while I could still kickdown into 2nd and walk all over him. My sweet spot was over 40 MPH, suited for highway use and not 1/4 mile.
Another way we used to state it was, gears could make your car quick, or fast... pick one.