2.20 vs 2.54 ratio?
01-06-2005, 08:56 PM
#31
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Having the ability to spin the tires does not mean you do spin the tires ! just as with braking ,cornering ,when accelerating being just under the threshold of wheel spin is the sweet spot.
01-06-2005, 09:01 PM
#32
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Jim,
This is the area of driver skill being important in the equation... If the tires do spin, there will not be any effective application of the force to move the car further.... (Unless this was not the goal to begin with... a la burnout..
)
You said it yourself with balancing on the limit of adhesion... In essence, controlling the net drag on the car for optimal speed.... science, science, science....
This is the area of driver skill being important in the equation... If the tires do spin, there will not be any effective application of the force to move the car further.... (Unless this was not the goal to begin with... a la burnout..
)You said it yourself with balancing on the limit of adhesion... In essence, controlling the net drag on the car for optimal speed.... science, science, science....
01-07-2005, 12:21 AM
#33
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Man, this really gets old. Everytime someone brings up the differences in rear ends and how much more accerlation one could get with a higher ratio rear end there is all of this confusion.
Mark certainly has his view, but Marks view has no application to my or most of our daily driving experiance. In two years of 928 ownership I have only exceeded 100mph only a few times and then only for a few seconds.
Tony's bike analogy is right on, assuming of coarse that Tony is happy with the max velocity he can acheive in first gear. In fact Tony's analogy is close to most of our realities.
The vast majority of my driving is at street speed. Being a the good upstanding citizen that I am, I rarely exceed the posted limit. Also not wanting to be an impediment to my fellow drivers I always try to reach the posted limit as quickly as possible, hey, I am just being a good citizen.
To this end a higher ratio 2.54, 2.74, 3.xx would be better then 2.2. GlenL is correct when he says that a 2.54 will accelerate faster then a 2.2. Mark is correct that the 2.2 will could eventually acheive a higher velocity. Mark is also correct that we could all benefit from closer spaced gears. Heck, the ideal setup would be an engine tuned to operate at one specific rpm speed mated to a countinuously variable transmission that could hold the engine at that perfectly tuned rpm for any velocity. Pigs will fly first.
The reality is that for most of us the velocities the 928 is capable of is several times faster than the posted limit.
Mark, higher ratio's are the way for most of us to achieve what we want from these cars, it does affect acceleration. Yes, gearing does not affect horsepower, but is does affect torque.
Torque is force. the weight of cars is mass, a is the acceleration, F=MA rules, or in this case a=f/m. Velocity is V=at. Increasing the gear ratio multiplies the force, which increases the acceleration which gets you to your good citizen velocity quicker, thats what most of us are looking for. Saying that rear end ratio has no effect on acceration is just silly.
Mark certainly has his view, but Marks view has no application to my or most of our daily driving experiance. In two years of 928 ownership I have only exceeded 100mph only a few times and then only for a few seconds.
Tony's bike analogy is right on, assuming of coarse that Tony is happy with the max velocity he can acheive in first gear. In fact Tony's analogy is close to most of our realities.
The vast majority of my driving is at street speed. Being a the good upstanding citizen that I am, I rarely exceed the posted limit. Also not wanting to be an impediment to my fellow drivers I always try to reach the posted limit as quickly as possible, hey, I am just being a good citizen.
To this end a higher ratio 2.54, 2.74, 3.xx would be better then 2.2. GlenL is correct when he says that a 2.54 will accelerate faster then a 2.2. Mark is correct that the 2.2 will could eventually acheive a higher velocity. Mark is also correct that we could all benefit from closer spaced gears. Heck, the ideal setup would be an engine tuned to operate at one specific rpm speed mated to a countinuously variable transmission that could hold the engine at that perfectly tuned rpm for any velocity. Pigs will fly first.
The reality is that for most of us the velocities the 928 is capable of is several times faster than the posted limit.
Mark, higher ratio's are the way for most of us to achieve what we want from these cars, it does affect acceleration. Yes, gearing does not affect horsepower, but is does affect torque.
Torque is force. the weight of cars is mass, a is the acceleration, F=MA rules, or in this case a=f/m. Velocity is V=at. Increasing the gear ratio multiplies the force, which increases the acceleration which gets you to your good citizen velocity quicker, thats what most of us are looking for. Saying that rear end ratio has no effect on acceration is just silly.
01-07-2005, 12:46 AM
#34
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Like Chuck says, I think the real question is "Is the 2.54 better than the 2.20" (for street driving)?
For automatics, I say a big YES. You are kind of stuck with the 4 ratios you have and how it shifts (unless you do it yourself). For 5 speeds (2.20 vs 2.63 or 2.73), I don't think it's the same kind of issue.
For automatics, I say a big YES. You are kind of stuck with the 4 ratios you have and how it shifts (unless you do it yourself). For 5 speeds (2.20 vs 2.63 or 2.73), I don't think it's the same kind of issue.
01-07-2005, 01:12 AM
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Oh, I also noticed nobody even took a stab at answering the original point of this thread. I'll be brave and venture a guess. The gearing multiplies the force. So the percent change between 2.2 and 2.54 is 15.45%. F=MA is a completely linear equation so...increase your acceleration, g, curve at each point by 15.45% and you have your answer. For instance if at one particular part of your g curve you have 0.5g's with the 2.2 rear end you might have 0.577g's with the 2.54 rear end. This is a pretty signifcant change.
Why do I think this is the right answer???? Because I am brilliant. Ok, maybe not. But I will give a reason.
On my GTEC graph if you look at the number of g's I am pulling shortly after the shift to second you will a value of about 0.33g's, the g reading shortly after the shift to third (about the same rpm) is about 0.20 g's. On my 91 S4 the total gear ratio in 2nd is 5.715:1, the fianl gear ratio in 3rd is 3.657:1 the percent change is -36.00%. If I deduct 36% from the above 2nd gear g's of 0.33g I get a g of 0.211. HE SHOOTS HE SCORES. Please no autographs.
Why do I think this is the right answer???? Because I am brilliant. Ok, maybe not. But I will give a reason.
On my GTEC graph if you look at the number of g's I am pulling shortly after the shift to second you will a value of about 0.33g's, the g reading shortly after the shift to third (about the same rpm) is about 0.20 g's. On my 91 S4 the total gear ratio in 2nd is 5.715:1, the fianl gear ratio in 3rd is 3.657:1 the percent change is -36.00%. If I deduct 36% from the above 2nd gear g's of 0.33g I get a g of 0.211. HE SHOOTS HE SCORES. Please no autographs.
01-07-2005, 01:30 AM
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I do not think the 2.20 and 2.54 trannys only differ by the final drive. It's not just a math problem using those two numbers. Someone here will be able to figure out speed at redline in gears 1 through 4, and that may give some numerical description of the difference. Before I picked up my '87 S4 5 speed, several people gave me their opinion of GT vs. S4 (2.20) gearing, and Dave C. figured out speed/RPM in each gear. His numerical breakdown gave me a very accurate idea of how it would be, and it was.
As for the 2.54 a/t, the "seat of the pants" is good enough for me. I have 20+ years of racing motorcycles, and I understand how gearing can affect how you go fast. At the track, even small changes will let you run certain gears in different situations and either work well or not.
As for the 2.54 a/t, the "seat of the pants" is good enough for me. I have 20+ years of racing motorcycles, and I understand how gearing can affect how you go fast. At the track, even small changes will let you run certain gears in different situations and either work well or not.
01-07-2005, 02:01 AM
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Carl, I think you are correct that the 2.2 years and 2.54 years also had slightly different transmission ratios. YMMV. But I believe the method used in my second email is valid for predicting the performance differnece with any gear changes, and that was the point of the question in this threads first post. Do you know what the tranny ratios are for a 87 or 88??
01-07-2005, 02:52 AM
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Originally Posted by 928andRC51
At the track, even small changes will let you run certain gears in different situations and either work well or not.
So yeah, moving gear ratios around [Edit]is about[/Edit] being able to be in the right gear at the right RPM at the right time in certain situations. With closer gears you have better odds of being in that sweet spot or near enough. This also depends heavily on driving style. In short... I don't think there is ever going to be a consensus on the "one" "right answer".
Oh, and YMMV
Last edited by SharkSkin; 01-07-2005 at 03:09 AM.
01-07-2005, 02:55 AM
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There should be no confusion. The math is quite simple. The confusion runs rampant when folks start thinking that a numerically higher rear end increases torque overall, and it clearly doesnt. This is why i tend to simplify the equation by only using HP and better said, average hp to the wheels over the operating range. My view has EVERY application to daly driving. what i telling you is that a small change in rear end or even gear ratios will have no difference on a wide range of acceleration, especially in daly driving as your limits of acceleration ranges are infinite!! You may need to go 0-70mph, 20 to 40mph, 40 to 75mph merging on a highway, or 50 to 100mph to get some kicks . either way, gearing its much more important on a race track where every ounce of HP is needed to give the best lap times possible.
Now, TONY'S analogy is WaY WAY off from being "right on". he is comparing 1st gear to 16th gear???? one bike is using a huge mechanical advantage of torque to acclerate 0-5mph and the other is using a fraction of the torque to acclerate over this low range of speed. remember, i said AVERAGE HP OVER THE OPERATIONAL RANGE. if you are going to compare accelerations, you have to have gear boxes that have the same gear spacing and number of gears. So, the reason that the analogy is meaninless and further confuses the issues, is that you are only using one gear. Remember, if we all had infinitely variable gear boxes, our engines would hit max hp (5500rpm or so) and stay there until the gear box hit max speed.
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.
0-75mph. real live speed range (without breaking too many laws) 2.75 rear end vs 2.2 rear end. and then maybe look at 40 to 110mph.
GEAR RATIOS LISTED FOR 3 928s. US 84 , S4 and a GT/GTS/79
84US 1st 9.3:1, 2nd 6.3:1 3rd 4.58
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%)
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%)
Now, the real truth of the rate of acceleration lies in the mix of gears and HP produced by the engine and the shape of the HP curve over the operating range. at first glance you can look at these ratios and say, "heck, the GT has better, and more torque in each gear, so the GT is the higher torque gear box" BUT WAIT!!!!! , again , it depends!
THE RACE! (assume 2 seconds in 1st gear, 4 seconds in 2nd gear, and 6 seconds in 3rd for totals of 6 second 0-60, 6 seconds 60-100mph)
the S4 out of the shoot in 1st gear, has 83% of the torque of the GT 2.72 rear end and 1st gear ratio up to the GTs redline (assume same redlines of 6400rpm), but after a shift to 2nd the S4 continues on in 1st for 120% faster speed before its shift to 2nd . during this time, it was enjoying a 130% mechanical advantage (auto would have a 142% mechanical advantage) before its shift to second where it is back to 85% of the mechanical torque. as the GT with the 2.72 hits its redline in 2nd, shifting to 3rd at about 60mph where time elapse is close to 5.5 seconds, the S4 now continues in 2nd gear with a 22% mechanical advantage for the next 1000rpms , or 2 seconds or so, before it hits target speed of 75mph. (now, the race should be acutally won by the S4 to 75mph)
at this point 75mph, the S4 shifts into 4th and the GT has a 12% advantage again. until the trade off happens again at near 95mph where about 3 seconds has transpired and then an even greater advantage is had by the S4 for an even longer period (ie 95mph to 110mph) where the s4 would have a wopping 30% advantage for an even LONGER period of time (in fact, the longest of the entire test if it was a race to 110mph, on the order of 5 seconds or so.).
Folks over these periods, the mechanical advantage is clearly in the hands of the taller rear end. sure, most 4500-4800rpm to 6400rpm post shift averages of engine torque are about average 5% less than torque up to redline.
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.
as far as the automatics, the spacing of the gears in both boxes are close to the same with an average spacing of .61 or so for all the gears and close to that from 1st to 2nd. this means that the difference of these gear boxes is also very subtle as far as accelerating torque.
So, sure, if you pick a target test of acceleration of the hightest ratio from 0-to the redline in that gear, sure, the rate of acceleration willl be greatest in the lowest gear to its individual redline. however, at any speed beyond that, a series of trade offs occur, showing explicitly as i have given the total ratios that no one gear box final drive assures by any streatch, the fastest acceleration profiles for our cars. ive picked the target speeds that favor the S4. by selecting different speeds you could find advantages for the GTS gear box as well. This just proves for street driving, there is certainly no differnce due to the varied applicatoins and speed ranges.
Now, we have been over this time and time again, and it still seems that many dont understand the basics here. Does this help???? Hope so!
MK
If you still are in the dark about HP vs torque. remember the other example of two cars , both with 500hp, same shaped hp curves, same gear box spacing, but one with max torque of 500ftlbs and the other at 250ft lbs. Of course, the max hp rpms of both of these cars are differnet, one at 5000rpm and the other at 10,000rpm. both are 5 speeds. they are both coming off the corner in 2nd gear at 40mph, and they accelerate. who , if any, will be faster, and why?
remember these are two cars with GROSSLY differerent engine torques.
answer: because the engines HP are the same, the acceleration rates will be the same, exactly the same due to gearing one 2x of the other to match mechanical torques to the wheels in every gear.
So, in summary, gearing effects efficiency of the hp put to the wheels over the operating range. it does not , in itself, create or destroy HP (accelerating forces)
Now,
Now, TONY'S analogy is WaY WAY off from being "right on". he is comparing 1st gear to 16th gear???? one bike is using a huge mechanical advantage of torque to acclerate 0-5mph and the other is using a fraction of the torque to acclerate over this low range of speed. remember, i said AVERAGE HP OVER THE OPERATIONAL RANGE. if you are going to compare accelerations, you have to have gear boxes that have the same gear spacing and number of gears. So, the reason that the analogy is meaninless and further confuses the issues, is that you are only using one gear. Remember, if we all had infinitely variable gear boxes, our engines would hit max hp (5500rpm or so) and stay there until the gear box hit max speed.
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.
0-75mph. real live speed range (without breaking too many laws) 2.75 rear end vs 2.2 rear end. and then maybe look at 40 to 110mph.
GEAR RATIOS LISTED FOR 3 928s. US 84 , S4 and a GT/GTS/79
84US 1st 9.3:1, 2nd 6.3:1 3rd 4.58
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%)
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%)
Now, the real truth of the rate of acceleration lies in the mix of gears and HP produced by the engine and the shape of the HP curve over the operating range. at first glance you can look at these ratios and say, "heck, the GT has better, and more torque in each gear, so the GT is the higher torque gear box" BUT WAIT!!!!! , again , it depends!
THE RACE! (assume 2 seconds in 1st gear, 4 seconds in 2nd gear, and 6 seconds in 3rd for totals of 6 second 0-60, 6 seconds 60-100mph)
the S4 out of the shoot in 1st gear, has 83% of the torque of the GT 2.72 rear end and 1st gear ratio up to the GTs redline (assume same redlines of 6400rpm), but after a shift to 2nd the S4 continues on in 1st for 120% faster speed before its shift to 2nd . during this time, it was enjoying a 130% mechanical advantage (auto would have a 142% mechanical advantage) before its shift to second where it is back to 85% of the mechanical torque. as the GT with the 2.72 hits its redline in 2nd, shifting to 3rd at about 60mph where time elapse is close to 5.5 seconds, the S4 now continues in 2nd gear with a 22% mechanical advantage for the next 1000rpms , or 2 seconds or so, before it hits target speed of 75mph. (now, the race should be acutally won by the S4 to 75mph)
at this point 75mph, the S4 shifts into 4th and the GT has a 12% advantage again. until the trade off happens again at near 95mph where about 3 seconds has transpired and then an even greater advantage is had by the S4 for an even longer period (ie 95mph to 110mph) where the s4 would have a wopping 30% advantage for an even LONGER period of time (in fact, the longest of the entire test if it was a race to 110mph, on the order of 5 seconds or so.).
Folks over these periods, the mechanical advantage is clearly in the hands of the taller rear end. sure, most 4500-4800rpm to 6400rpm post shift averages of engine torque are about average 5% less than torque up to redline.
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.
as far as the automatics, the spacing of the gears in both boxes are close to the same with an average spacing of .61 or so for all the gears and close to that from 1st to 2nd. this means that the difference of these gear boxes is also very subtle as far as accelerating torque.
So, sure, if you pick a target test of acceleration of the hightest ratio from 0-to the redline in that gear, sure, the rate of acceleration willl be greatest in the lowest gear to its individual redline. however, at any speed beyond that, a series of trade offs occur, showing explicitly as i have given the total ratios that no one gear box final drive assures by any streatch, the fastest acceleration profiles for our cars. ive picked the target speeds that favor the S4. by selecting different speeds you could find advantages for the GTS gear box as well. This just proves for street driving, there is certainly no differnce due to the varied applicatoins and speed ranges.
Now, we have been over this time and time again, and it still seems that many dont understand the basics here. Does this help???? Hope so!
MK
If you still are in the dark about HP vs torque. remember the other example of two cars , both with 500hp, same shaped hp curves, same gear box spacing, but one with max torque of 500ftlbs and the other at 250ft lbs. Of course, the max hp rpms of both of these cars are differnet, one at 5000rpm and the other at 10,000rpm. both are 5 speeds. they are both coming off the corner in 2nd gear at 40mph, and they accelerate. who , if any, will be faster, and why?
remember these are two cars with GROSSLY differerent engine torques.
answer: because the engines HP are the same, the acceleration rates will be the same, exactly the same due to gearing one 2x of the other to match mechanical torques to the wheels in every gear.
So, in summary, gearing effects efficiency of the hp put to the wheels over the operating range. it does not , in itself, create or destroy HP (accelerating forces)
Now,
Originally Posted by 928Quest
Man, this really gets old. Everytime someone brings up the differences in rear ends and how much more accerlation one could get with a higher ratio rear end there is all of this confusion.
Mark certainly has his view, but Marks view has no application to my or most of our daily driving experiance. In two years of 928 ownership I have only exceeded 100mph only a few times and then only for a few seconds.
Tony's bike analogy is right on, assuming of coarse that Tony is happy with the max velocity he can acheive in first gear. In fact Tony's analogy is close to most of our realities.
The vast majority of my driving is at street speed. Being a the good upstanding citizen that I am, I rarely exceed the posted limit. Also not wanting to be an impediment to my fellow drivers I always try to reach the posted limit as quickly as possible, hey, I am just being a good citizen.
To this end a higher ratio 2.54, 2.74, 3.xx would be better then 2.2. GlenL is correct when he says that a 2.54 will accelerate faster then a 2.2. Mark is correct that the 2.2 will could eventually acheive a higher velocity. Mark is also correct that we could all benefit from closer spaced gears. Heck, the ideal setup would be an engine tuned to operate at one specific rpm speed mated to a countinuously variable transmission that could hold the engine at that perfectly tuned rpm for any velocity. Pigs will fly first.
The reality is that for most of us the velocities the 928 is capable of is several times faster than the posted limit.
Mark, higher ratio's are the way for most of us to achieve what we want from these cars, it does affect acceleration. Yes, gearing does not affect horsepower, but is does affect torque.
Torque is force. the weight of cars is mass, a is the acceleration, F=MA rules, or in this case a=f/m. Velocity is V=at. Increasing the gear ratio multiplies the force, which increases the acceleration which gets you to your good citizen velocity quicker, thats what most of us are looking for. Saying that rear end ratio has no effect on acceration is just silly.
Mark certainly has his view, but Marks view has no application to my or most of our daily driving experiance. In two years of 928 ownership I have only exceeded 100mph only a few times and then only for a few seconds.
Tony's bike analogy is right on, assuming of coarse that Tony is happy with the max velocity he can acheive in first gear. In fact Tony's analogy is close to most of our realities.
The vast majority of my driving is at street speed. Being a the good upstanding citizen that I am, I rarely exceed the posted limit. Also not wanting to be an impediment to my fellow drivers I always try to reach the posted limit as quickly as possible, hey, I am just being a good citizen.
To this end a higher ratio 2.54, 2.74, 3.xx would be better then 2.2. GlenL is correct when he says that a 2.54 will accelerate faster then a 2.2. Mark is correct that the 2.2 will could eventually acheive a higher velocity. Mark is also correct that we could all benefit from closer spaced gears. Heck, the ideal setup would be an engine tuned to operate at one specific rpm speed mated to a countinuously variable transmission that could hold the engine at that perfectly tuned rpm for any velocity. Pigs will fly first.
The reality is that for most of us the velocities the 928 is capable of is several times faster than the posted limit.
Mark, higher ratio's are the way for most of us to achieve what we want from these cars, it does affect acceleration. Yes, gearing does not affect horsepower, but is does affect torque.
Torque is force. the weight of cars is mass, a is the acceleration, F=MA rules, or in this case a=f/m. Velocity is V=at. Increasing the gear ratio multiplies the force, which increases the acceleration which gets you to your good citizen velocity quicker, thats what most of us are looking for. Saying that rear end ratio has no effect on acceration is just silly.
Last edited by mark kibort; 01-07-2005 at 03:58 AM.
01-07-2005, 03:04 AM
#41
Rennlist Member
[bzzzzzzt. wront answer! see my post and see if you can find out where you are missing the point.
you start throwing out F=MA and you are using it incorrectly.
read my post and read it carefully. i have pulled out all the ratios.
i could break it down further and give times and speeds, but I dont think it is nessesary, if you understand the basic points. However, with this group, i may need to .
Please, pull out a basic physics book and read the first chapter. this is getting out of control!!!
torque increase by increasing the rear end doesnt produce increased acceleration, HP does this, and better said, by maximizing HP over the operational range, you gain the greatest acceleration.
MK
QUOTE=928Quest]Oh, I also noticed nobody even took a stab at answering the original point of this thread. I'll be brave and venture a guess. The gearing multiplies the force. So the percent change between 2.2 and 2.54 is 15.45%. F=MA is a completely linear equation so...increase your acceleration, g, curve at each point by 15.45% and you have your answer. For instance if at one particular part of your g curve you have 0.5g's with the 2.2 rear end you might have 0.577g's with the 2.54 rear end. This is a pretty signifcant change.
Why do I think this is the right answer???? Because I am brilliant. Ok, maybe not. But I will give a reason.
On my GTEC graph if you look at the number of g's I am pulling shortly after the shift to second you will a value of about 0.33g's, the g reading shortly after the shift to third (about the same rpm) is about 0.20 g's. On my 91 S4 the total gear ratio in 2nd is 5.715:1, the fianl gear ratio in 3rd is 3.657:1 the percent change is -36.00%. If I deduct 36% from the above 2nd gear g's of 0.33g I get a g of 0.211. HE SHOOTS HE SCORES. Please no autographs.[/QUOTE]
you start throwing out F=MA and you are using it incorrectly.
read my post and read it carefully. i have pulled out all the ratios.
i could break it down further and give times and speeds, but I dont think it is nessesary, if you understand the basic points. However, with this group, i may need to .
Please, pull out a basic physics book and read the first chapter. this is getting out of control!!!
torque increase by increasing the rear end doesnt produce increased acceleration, HP does this, and better said, by maximizing HP over the operational range, you gain the greatest acceleration.
MK
QUOTE=928Quest]Oh, I also noticed nobody even took a stab at answering the original point of this thread. I'll be brave and venture a guess. The gearing multiplies the force. So the percent change between 2.2 and 2.54 is 15.45%. F=MA is a completely linear equation so...increase your acceleration, g, curve at each point by 15.45% and you have your answer. For instance if at one particular part of your g curve you have 0.5g's with the 2.2 rear end you might have 0.577g's with the 2.54 rear end. This is a pretty signifcant change.
Why do I think this is the right answer???? Because I am brilliant. Ok, maybe not. But I will give a reason.
On my GTEC graph if you look at the number of g's I am pulling shortly after the shift to second you will a value of about 0.33g's, the g reading shortly after the shift to third (about the same rpm) is about 0.20 g's. On my 91 S4 the total gear ratio in 2nd is 5.715:1, the fianl gear ratio in 3rd is 3.657:1 the percent change is -36.00%. If I deduct 36% from the above 2nd gear g's of 0.33g I get a g of 0.211. HE SHOOTS HE SCORES. Please no autographs.[/QUOTE]
01-07-2005, 04:17 AM
#42
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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, 04:19 AM
#43
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"...read my post and read it carefully. i have pulled out all the ratios.
i could break it down further and give times and speeds, but I dont think it is nessesary, if you understand the basic points. However, with this group, i may need to .
Please, pull out a basic physics book and read the first chapter. this is getting out of control!!!
torque increase by increasing the rear end doesnt produce increased acceleration, HP does this, and better said, by maximizing HP over the operational range, you gain the greatest acceleration...."
...However, with this group, i may need to...
Wow, you are right this is getting out of control, the whole group is stupid???
Please, Based what you are saying I am positive that I and others here have a good deal of book time in Physics.
Stop embarrassing yourself.
i could break it down further and give times and speeds, but I dont think it is nessesary, if you understand the basic points. However, with this group, i may need to .
Please, pull out a basic physics book and read the first chapter. this is getting out of control!!!
torque increase by increasing the rear end doesnt produce increased acceleration, HP does this, and better said, by maximizing HP over the operational range, you gain the greatest acceleration...."
...However, with this group, i may need to...
Wow, you are right this is getting out of control, the whole group is stupid???
Please, Based what you are saying I am positive that I and others here have a good deal of book time in Physics.
Stop embarrassing yourself.
01-07-2005, 04:40 AM
#44
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"...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, 11:28 AM
#45
Drifting
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