2.20 vs 2.54 ratio?
02-09-2005, 01:24 PM
#181
Rennlist Member
Ketchmi,
you are giving it the biggest twist of all below in your post. I can tell you are getting some of it, but much of it seems to be passing you by.
there is no new math here, its just average torque over the operating range. yes, there are shorter times where the lower rear end ratio will have an advantage over a given speed range, AND, I didnt shorten the time for that advantage either, so its all been equal in the comparison. SO, look at the times of the mechanical advantages over a particular speed range and you can see there are trade offs. folks always seem to mock, what they dont understand. right now, i just think you have just missed a few key elements of the comparison.
If you look at the speed range YOU want to accelerate fastest too, you have to look closer to just putting a larger numerical ratio on the rear end. I have NEVER even talked about the advantage to a higher tops speed overall. Ive also given the advantage to the 2.75 boxes at speeds over 155mph, due to the much larger and spacing of the 2.2 between 4-5th gears, where the spacing of all the gears of the 2.75 is relatively the same. however, the two gear boxes are only 15% different from each gear 1-4th, through the most common operational range for ALL 928s with less that 400hp flywheel. (ie 155mph)
So, if you are a road racer or a drag racer, you have to look at the target speed and see if the gear box matches what will give you the most amount of AVE torque over the speed range. (yes, there are trade offs, and it isnt any "new Math") . go back to the numbers and add the torque advantages to the speed range times for both gear boxes and you will see that that the tend to cancel eachother out.
yes this is getting old. why the resistance to grasp the simple concepts?
Your quote below
"THE LOWER GEARED CAR WIILL OUT ACCELERATE THE HIGHER GEARED ONE TO DISTANCE!!!!!!!!!!! "
As i have been saying, it depends what that distance is and the speed range achieved by a given HP and set of gears.
again, want an example, look at the torque numbers for 0-60 vs 0-75 or 0-90 vs 0-115mph or ESPECIALLY 0-125 vs 0-155. those are real life numbers that you will have to reach in racing or drag racing. you really think a GT 2.75 has an advantage to 75mph, 115, or especially 115mph??? try again it will not. however, there are just as much advantages for the other speeds for the GT. this is why the gear box DOESNT make hp.
force (rotational torque) x distance is the work
work over the time is the HP
HP x the time is the energy.
One can also say that work = force x distance x time is the HP.
Or, since force = mass x accel, you can say that
work=mass x accel x distance x time
torque by gearing is only one factor of what it takes to accelerate a car. this is why there are trade offs with gearing. go ahead, take my numbers or the ones from the computer program and see the total torque produced over the time and distance (ie speed range). Actually, the spacing i used also is not favoring the S4, I actually found a speed that is neutral. If i wanted to find a speed that is in favor of the s4, i would have selected 75mph or 115mph, NOT the 105 that was fair for both cars, and this is why the times are so close (and the average torques to the wheels are so close!!)
again, does a taller rear end ratio help all ranges of accelerations?
No, it depends.
Mk
you are giving it the biggest twist of all below in your post. I can tell you are getting some of it, but much of it seems to be passing you by.
there is no new math here, its just average torque over the operating range. yes, there are shorter times where the lower rear end ratio will have an advantage over a given speed range, AND, I didnt shorten the time for that advantage either, so its all been equal in the comparison. SO, look at the times of the mechanical advantages over a particular speed range and you can see there are trade offs. folks always seem to mock, what they dont understand. right now, i just think you have just missed a few key elements of the comparison.
If you look at the speed range YOU want to accelerate fastest too, you have to look closer to just putting a larger numerical ratio on the rear end. I have NEVER even talked about the advantage to a higher tops speed overall. Ive also given the advantage to the 2.75 boxes at speeds over 155mph, due to the much larger and spacing of the 2.2 between 4-5th gears, where the spacing of all the gears of the 2.75 is relatively the same. however, the two gear boxes are only 15% different from each gear 1-4th, through the most common operational range for ALL 928s with less that 400hp flywheel. (ie 155mph)
So, if you are a road racer or a drag racer, you have to look at the target speed and see if the gear box matches what will give you the most amount of AVE torque over the speed range. (yes, there are trade offs, and it isnt any "new Math") . go back to the numbers and add the torque advantages to the speed range times for both gear boxes and you will see that that the tend to cancel eachother out.
yes this is getting old. why the resistance to grasp the simple concepts?
Your quote below
"THE LOWER GEARED CAR WIILL OUT ACCELERATE THE HIGHER GEARED ONE TO DISTANCE!!!!!!!!!!! "
As i have been saying, it depends what that distance is and the speed range achieved by a given HP and set of gears.
again, want an example, look at the torque numbers for 0-60 vs 0-75 or 0-90 vs 0-115mph or ESPECIALLY 0-125 vs 0-155. those are real life numbers that you will have to reach in racing or drag racing. you really think a GT 2.75 has an advantage to 75mph, 115, or especially 115mph??? try again it will not. however, there are just as much advantages for the other speeds for the GT. this is why the gear box DOESNT make hp.
force (rotational torque) x distance is the work
work over the time is the HP
HP x the time is the energy.
One can also say that work = force x distance x time is the HP.
Or, since force = mass x accel, you can say that
work=mass x accel x distance x time
torque by gearing is only one factor of what it takes to accelerate a car. this is why there are trade offs with gearing. go ahead, take my numbers or the ones from the computer program and see the total torque produced over the time and distance (ie speed range). Actually, the spacing i used also is not favoring the S4, I actually found a speed that is neutral. If i wanted to find a speed that is in favor of the s4, i would have selected 75mph or 115mph, NOT the 105 that was fair for both cars, and this is why the times are so close (and the average torques to the wheels are so close!!)
again, does a taller rear end ratio help all ranges of accelerations?
No, it depends.
Mk
Originally Posted by Ketchmi
Give up Heinrich, there will always be an excuse for the given times according to Mark. It's like "New Math" and can be conformed to his way of thinking. For example, why even put down the difference between 35 and 40 mph other than to show a large advantage for the S4 gearing for HOW LONG? His speed spacing is set up to make it appear much better for the S4, let's see........35 mph, 5 mph, 20mph, 15mph, 21mph, 9mph. He also refuses to realize that the given times in each gear, to each speed will differ, not the same between the two cars. (2 sec, 1 sec, 3 sec, 2 sec, 3 sec, 3 sec.) They cannot be the same with greater amounts of torque applied by the GT gearing.........
I gave up. He does have some points to make but........this is getting really old, really fast. Almost everyone else on here is talking about straight line acceleration, not track configuration. As far as pure straight acceleration to high gear redline (or as close as the horsepower limit will push it) THE LOWER GEARED CAR WIILL OUT ACCELERATE THE HIGHER GEARED ONE TO DISTANCE!!!!!!!!!!! YES the higher geared one will have a higher top speed but the lower geared one will out accelerate it to it's limit. Hmmmm, according to Mark's math, the higher geared car will out accelerate the lower one to 180mph (because the lower geared one redlines at 170mph!) It's all how you twist the math.
And I told myself I was done with this post, sheesh!
Let's all have a drink!
Dave
Motorsport
I gave up. He does have some points to make but........this is getting really old, really fast. Almost everyone else on here is talking about straight line acceleration, not track configuration. As far as pure straight acceleration to high gear redline (or as close as the horsepower limit will push it) THE LOWER GEARED CAR WIILL OUT ACCELERATE THE HIGHER GEARED ONE TO DISTANCE!!!!!!!!!!! YES the higher geared one will have a higher top speed but the lower geared one will out accelerate it to it's limit. Hmmmm, according to Mark's math, the higher geared car will out accelerate the lower one to 180mph (because the lower geared one redlines at 170mph!) It's all how you twist the math.
And I told myself I was done with this post, sheesh!
Let's all have a drink!
Dave
Motorsport
02-09-2005, 01:32 PM
#182
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You know sometimes if someone doesnt agree with you, trying to make them see your point is pointless. The best thing is to let it go and go to a happy place. Honestly I cannot believe this thread is still going on and on and on and on and on. You guys need to agree to disagree and move on. You guys will never get each other to agree your (Mark and Ketchmi) method of thinking.
LOL Andy
LOL Andy
02-09-2005, 01:43 PM
#183
Rennlist Member
actual spacing, for which i used some ball park numbers to make a point, now you are getting beyond the point. However, here are the REAL numbers using the gear ratios for the s4 and GT
lets use 6400rpm redline to keep things even.
54mph 82mph, 115mph, 153mph for the S4 2.2 ratio
48mph 71mph, 102mph, 135mph and 5th of 180mph for the GT 2.75 ratio box
DIFF BETWEEN GTS AND S4
0-48 48mph 15% advantage GTS
48-54 mph= 6mph 30% advantage S4
54-71 mph = 17mph 15% advantage GTS
71-82 mph =11mph 30% adv. S4
82-102 mph =20mph 15% adv GTS
102-115 mph = 13mph 30%adv S4
115-135 mph = 20mph 15% adv GTS
135-153 mph= 18mph 30% adv S4
obviously, to most to this discussion, the big advantage is 0-48, no question. but through the gears, there are trade offs. also keep in mind, those advantages are weighted by the longer and longer time spent in those gears as you go faster. since the WHOLE goal here is to accelerate fastest over time, the above gives you a clear picture of what I have been speaking of.
(note: the reason that there is a 30% s4 advantage, is due to mechanical advantage in that gear for those speeds vs the GTS. there are some differences in ave hp over those ranges due to the different rpms being used, and those differences are even more trade offs. Even if the S4 advantages were only 20%, you can see the trade offs)
now, all the math is right here! Its not my spacing, its whats given for each car! For every space between the two speeds in any gear, there will be an advantage and trade off. up to 48mph, the gts has a 15% advantage , but from 48 to 54mph, the S4 has a greater advantage even though the time spent is shorter. where it really matters is 102 vs 115mph, where there is no way that the GTS can keep any advantages that it had up to 102mph. (and also to 71mph). look at the tiimes all you want. shade them in favor with each of the gear ratios, you end up with the same result as the computer program that Vihuer posted. NO DIFFERENCE OVERALL< but certainly advantages for each at different speeds .
Again, if we had infinitely variably gear boxes, the engine would run at max hp not max torque! (and we would not be having this discussion)
Mk
lets use 6400rpm redline to keep things even.
54mph 82mph, 115mph, 153mph for the S4 2.2 ratio
48mph 71mph, 102mph, 135mph and 5th of 180mph for the GT 2.75 ratio box
DIFF BETWEEN GTS AND S4
0-48 48mph 15% advantage GTS
48-54 mph= 6mph 30% advantage S4
54-71 mph = 17mph 15% advantage GTS
71-82 mph =11mph 30% adv. S4
82-102 mph =20mph 15% adv GTS
102-115 mph = 13mph 30%adv S4
115-135 mph = 20mph 15% adv GTS
135-153 mph= 18mph 30% adv S4
obviously, to most to this discussion, the big advantage is 0-48, no question. but through the gears, there are trade offs. also keep in mind, those advantages are weighted by the longer and longer time spent in those gears as you go faster. since the WHOLE goal here is to accelerate fastest over time, the above gives you a clear picture of what I have been speaking of.
(note: the reason that there is a 30% s4 advantage, is due to mechanical advantage in that gear for those speeds vs the GTS. there are some differences in ave hp over those ranges due to the different rpms being used, and those differences are even more trade offs. Even if the S4 advantages were only 20%, you can see the trade offs)
now, all the math is right here! Its not my spacing, its whats given for each car! For every space between the two speeds in any gear, there will be an advantage and trade off. up to 48mph, the gts has a 15% advantage , but from 48 to 54mph, the S4 has a greater advantage even though the time spent is shorter. where it really matters is 102 vs 115mph, where there is no way that the GTS can keep any advantages that it had up to 102mph. (and also to 71mph). look at the tiimes all you want. shade them in favor with each of the gear ratios, you end up with the same result as the computer program that Vihuer posted. NO DIFFERENCE OVERALL< but certainly advantages for each at different speeds .
Again, if we had infinitely variably gear boxes, the engine would run at max hp not max torque! (and we would not be having this discussion)
Mk
Originally Posted by Ketchmi
For example, why even put down the difference between 35 and 40 mph other than to show a large advantage for the S4 gearing for HOW LONG? His speed spacing is set up to make it appear much better for the S4, let's see........35 mph, 5 mph, 20mph, 15mph, 21mph, 9mph. He also refuses to realize that the given times in each gear, to each speed will differ, not the same between the two cars. (2 sec, 1 sec, 3 sec, 2 sec, 3 sec, 3 sec.) They cannot be the same with greater amounts of torque applied by the GT gearing.........
Dave
Motorsport
Dave
Motorsport
Last edited by mark kibort; 02-09-2005 at 02:00 PM.
02-09-2005, 04:02 PM
#184
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Brian Iceman innocently asks...."How much of a difference does the 89+ 2.54 axle ratio make in terms of acceleration vs the 87-88 2.20 axle ratio (automatic)? My 2.20 seems fairly strong, the 2.54 must really fly!'..... FINALLY after much verbiage (kind of rhymes with garbage) Mr Kibort states....."obviously, to most to this discussion, the big advantage is 0-48, no question. " .......... Seems to me that in the stop light wars, 1/8 or 1/4 drags 0-48MPH is pretty darn important. It is also pretty obvious that the more gears you have to use between 0-150 mph the closer you get to having the holey grail of the constantly variable transmission running at maximum horsepower with less RPM drop between gears. It is also worth noting that in 5th gear it is DIRECT drive you no longer transfer power from 5th down to the lay shaft then back from the layshaft to the pinion as you do in all the lower gears. That forcing the power to turn corners move from one shaft to another and back again is inefficient and turns power into heat. So it would be nice if 5th gear were usable on most tracks.
02-13-2005, 02:32 AM
#185
Rennlist Member
Jim,
that is right! if you could take the 2.75, and make it an S4 box (this is done by going from a GTS box and putting a 3.09 on it, that would be the best box for the tracks and power i have. It would give me mostly the same gear box i have now, and allow my 4th gear now, to run on 5th gear with a very high numerical rear end (3.09 vs my current 3.2 in 4th). 1st gear would probably not be used then, as i have shown before. However, it would be one way to allow for reduction of those eff. losses. BUT, 3.09 for my car would have a 5th gear top rpm of 160+mph, and i cant get to that speed at most tracks, so it really wouldnt help at a track like road america. (the loss off torque of 3.09vs 3.2 wouldnt be overcome with the greater gear train eff of the 1:1. at best, it would probably be a wash. However, if there was such a thing as a 3.2 rear end, that would make your point valid!)
Again, going back to the original question, i think NO ONE ever just races to 48mph. in fact, from the charts provided, an S4 has a 1st gear of 50+ mph , and i would be willing to bet that most folks race until about 75mph whether they admit it or not. heck, that is a burning rubber 1st gear a quick shift to 2nd for one second and cool the jets!!!!
So, the answer again lies in what target speed you want to end up with , and how that matches your final gear ratios, rpm limits, and HP.
You do make a very interesting point, that is yet to be shown. what is the difference in running a dyno run in 5th gear vs 4th??? ive done 3rd vs 4th and seen a 10hp difference. wonder if it is more. i know most dynos are speed limited to a point, but even if someone did a 3000rpm to 5000rpm run in 5th, it would be interesting.
mk
that is right! if you could take the 2.75, and make it an S4 box (this is done by going from a GTS box and putting a 3.09 on it, that would be the best box for the tracks and power i have. It would give me mostly the same gear box i have now, and allow my 4th gear now, to run on 5th gear with a very high numerical rear end (3.09 vs my current 3.2 in 4th). 1st gear would probably not be used then, as i have shown before. However, it would be one way to allow for reduction of those eff. losses. BUT, 3.09 for my car would have a 5th gear top rpm of 160+mph, and i cant get to that speed at most tracks, so it really wouldnt help at a track like road america. (the loss off torque of 3.09vs 3.2 wouldnt be overcome with the greater gear train eff of the 1:1. at best, it would probably be a wash. However, if there was such a thing as a 3.2 rear end, that would make your point valid!)
Again, going back to the original question, i think NO ONE ever just races to 48mph. in fact, from the charts provided, an S4 has a 1st gear of 50+ mph , and i would be willing to bet that most folks race until about 75mph whether they admit it or not. heck, that is a burning rubber 1st gear a quick shift to 2nd for one second and cool the jets!!!!
So, the answer again lies in what target speed you want to end up with , and how that matches your final gear ratios, rpm limits, and HP.
You do make a very interesting point, that is yet to be shown. what is the difference in running a dyno run in 5th gear vs 4th??? ive done 3rd vs 4th and seen a 10hp difference. wonder if it is more. i know most dynos are speed limited to a point, but even if someone did a 3000rpm to 5000rpm run in 5th, it would be interesting.
mk
Originally Posted by Jim bailey - 928 International
Brian Iceman innocently asks...."How much of a difference does the 89+ 2.54 axle ratio make in terms of acceleration vs the 87-88 2.20 axle ratio (automatic)? My 2.20 seems fairly strong, the 2.54 must really fly!'..... FINALLY after much verbiage (kind of rhymes with garbage) Mr Kibort states....."obviously, to most to this discussion, the big advantage is 0-48, no question. " .......... Seems to me that in the stop light wars, 1/8 or 1/4 drags 0-48MPH is pretty darn important. It is also pretty obvious that the more gears you have to use between 0-150 mph the closer you get to having the holey grail of the constantly variable transmission running at maximum horsepower with less RPM drop between gears. It is also worth noting that in 5th gear it is DIRECT drive you no longer transfer power from 5th down to the lay shaft then back from the layshaft to the pinion as you do in all the lower gears. That forcing the power to turn corners move from one shaft to another and back again is inefficient and turns power into heat. So it would be nice if 5th gear were usable on most tracks.
