2.20 vs 2.54 ratio?
01-07-2005, 06:09 PM
#61
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you finally are one to concede that there are gains after shift. they are much more significant than you are describing. why??? because, gearing doesnt produce hp, just the ablity to maximize its application over the speed range. do your test with real numbers 0-60 with at least a 2 gear shift. look at the values and get back to me. there are speed targets and ranges that will favor a lower or higher rear end. (all other things being equal)
This is basic, and you are dead wrong!
sorry, but read what I have posted in detail and get back to me if you still disagree.
to your last point, com' mon, thats what ive been talking about. in 3rd gear vs 1st gear, the difference is the torque multiplied by the gear ratio. 3rd gear start wouldnt be the best use of max (or near max, or max average hp) would it? you are going to confuse matters by comparing differnt gears in a gear box, as the speeds are entirely different. and, we are trying to accelerate a mass (your car) over a speed range. (ie 0-60 60-100, 40-75mph, etc)
so, you say, "better acceration at any rpm" ??? really?? you havent even done my test. GT vs S4 at 60mph to 75mph . let me know what you come up with.
I just wonder what this group is going to do when the "light" finally comes on.
I just passes a couple of these posts on to a PHDed engineer and he got a laugh out of the discussion. He pointed to that i was not only correct, but " dead on right" . better do some intraspective review here!
Mk
This is basic, and you are dead wrong!
sorry, but read what I have posted in detail and get back to me if you still disagree.
to your last point, com' mon, thats what ive been talking about. in 3rd gear vs 1st gear, the difference is the torque multiplied by the gear ratio. 3rd gear start wouldnt be the best use of max (or near max, or max average hp) would it? you are going to confuse matters by comparing differnt gears in a gear box, as the speeds are entirely different. and, we are trying to accelerate a mass (your car) over a speed range. (ie 0-60 60-100, 40-75mph, etc)
so, you say, "better acceration at any rpm" ??? really?? you havent even done my test. GT vs S4 at 60mph to 75mph . let me know what you come up with.
I just wonder what this group is going to do when the "light" finally comes on.
I just passes a couple of these posts on to a PHDed engineer and he got a laugh out of the discussion. He pointed to that i was not only correct, but " dead on right" . better do some intraspective review here!
Mk
Originally Posted by Ketchmi
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
... no offense.
01-07-2005, 06:25 PM
#63
Drifting
cant believe this thread has run to over 5 pages and most of it is just plain bull s$%t!!
gearing DOES affect aceleration. not only do we see the cars with higher rear end ratios getting to 60 mph quicker we also see the last generation of the 16v S2 run out of steam before reaching max power, due to its 2.2 back end. and what did porsche think? they saw fit to change to a 2.54 rear end for the last model years for better acceleration.
carry on and argue physics and numbers some more then...
gearing DOES affect aceleration. not only do we see the cars with higher rear end ratios getting to 60 mph quicker we also see the last generation of the 16v S2 run out of steam before reaching max power, due to its 2.2 back end. and what did porsche think? they saw fit to change to a 2.54 rear end for the last model years for better acceleration.
carry on and argue physics and numbers some more then...
01-07-2005, 06:30 PM
#64
Rennlist Member
Ok folks, just ran some crude numbers, rather than digging deep and doing the calculus. we are just going to use averages. averages like. max torque is 300ftlbs at 4500rpm and 275ftlbs at 6400rpm assuming a straight line (which is close enough) average the torque in that range and call it 290ftlbs.
we are talking about the max acceleration potential of a 290ftlb , 4500rpm to 6400rpm engine with either S4 manual gears or GT manual gears from speeds of 0 to 105mph. I used 105mph, becuase it would be unfair to use 100mph to the S4 and unfair to the GT to use 112mph.
what we have is the ave torque (since you guys love torque so much) in all gear shifts from 0-105mph
here is the time line as close as I can get it from my data and from Road and track.
0-35 35-40 40-60 60-75 75-96 96-105mph
2sec 1sec 3 sec 2 sec 3sec 3 sec
(Given 6seconds 0-60 8secs 60-105 or 7seconds 60-100mph)
net torque over the operational range is pretty close to even for the S4 if the test is to 105mph (and even better if it is to 111mph, and 2% less than the GT if the test is to 100mph
ill put in the values in a bit . totals are: 3982 ftlbs/seconds average for the GT and 3944ftlbs/seconds for the S4. a difference of+ 2% for the S4 (to a top speed of 105mph) if the target speed is 100mph, the numbers are 3808 ftlbs and 3740ftlbs in favor of the GT also only 2% diff.
This is the total amount of accelerating torque available over the operational range. there are the numbers. they are very very close to what would be if we actually used area under the curves. and the times in those gears are also very close to actual.
so, that really is the net net of a S4 with a 2.2 compared to the GT with the 2.72
Proof in the NUMBERS!!!!!
MK
we are talking about the max acceleration potential of a 290ftlb , 4500rpm to 6400rpm engine with either S4 manual gears or GT manual gears from speeds of 0 to 105mph. I used 105mph, becuase it would be unfair to use 100mph to the S4 and unfair to the GT to use 112mph.
what we have is the ave torque (since you guys love torque so much) in all gear shifts from 0-105mph
here is the time line as close as I can get it from my data and from Road and track.
0-35 35-40 40-60 60-75 75-96 96-105mph
2sec 1sec 3 sec 2 sec 3sec 3 sec
(Given 6seconds 0-60 8secs 60-105 or 7seconds 60-100mph)
net torque over the operational range is pretty close to even for the S4 if the test is to 105mph (and even better if it is to 111mph, and 2% less than the GT if the test is to 100mph
ill put in the values in a bit . totals are: 3982 ftlbs/seconds average for the GT and 3944ftlbs/seconds for the S4. a difference of+ 2% for the S4 (to a top speed of 105mph) if the target speed is 100mph, the numbers are 3808 ftlbs and 3740ftlbs in favor of the GT also only 2% diff.
This is the total amount of accelerating torque available over the operational range. there are the numbers. they are very very close to what would be if we actually used area under the curves. and the times in those gears are also very close to actual.
so, that really is the net net of a S4 with a 2.2 compared to the GT with the 2.72
Proof in the NUMBERS!!!!!
MK
Last edited by mark kibort; 01-07-2005 at 10:13 PM.
01-07-2005, 06:30 PM
#65
928 Collector
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Originally Posted by mark kibort
.... HP does move the car forward, BY DEFINITION!!! torque x speed is HP. without speed, you aint moving!!
Horsepower is torque over time (1 horsepower equals 33,000 foot-pounds of work per minute ). It does not move the car.
Speed is distance moved over time.
01-07-2005, 06:32 PM
#66
Drifting
Mark, read. I am not considering your "test". As I stated, at a given rpm in a given gear, (BOTH CARS BEING IN THE SAME GEAR AT THE SAME RPM!) the lower geared car will accelerate quicker. Where does this take into account a GT vs. an S4? Something tells me that the two cars would be in different gears at your "test". "do your test with real numbers 0-60 with at least a 2 gear shift." Once again, I am comparing apples to apples. Both cars equipped with auto transmissions would benefit the lower geared car significantly. The rotational mass at speed would also effect the acceleration curve during a shift with an auto transmission. The time taken to shift a 5-speed car skews the whole thing. I'm quite sure that the way you stated it to your PHD'ed engineer could also be debated...........
You missed my point completely. "there are speed targets and ranges that will favor a lower or higher rear end. (all other things being equal)" I can agree with that but that still is not my point. Reread my post then reply. I can really appreciate a good debate whereas everyone involved gains something from it but this is not the case. As I said, reread my post and you will eventually agree with what I have stated.
Dave
You missed my point completely. "there are speed targets and ranges that will favor a lower or higher rear end. (all other things being equal)" I can agree with that but that still is not my point. Reread my post then reply. I can really appreciate a good debate whereas everyone involved gains something from it but this is not the case. As I said, reread my post and you will eventually agree with what I have stated.
Dave
01-07-2005, 06:38 PM
#67
Rennlist Member
Look at the total ratios and get back to me
mk
mk
Originally Posted by heinrich
Torque is the force it takes to turn the wheels to move the car, with gearing factored-in. THIS LAST FACT MEANS TALLER GEARS ACCELERATE MORE SLOWLY AT THE SAME FORCE DRIVING THEM.
Horsepower is torque over time (1 horsepower equals 33,000 foot-pounds of work per minute ). It does not move the car.
Speed is distance moved over time.
Horsepower is torque over time (1 horsepower equals 33,000 foot-pounds of work per minute ). It does not move the car.
Speed is distance moved over time.
01-07-2005, 06:41 PM
#69
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Brian,
Just so you don't loose it with all the debate, the 2.54 90+ S4
was .3 seconds faster to 60 and had a 3 mph higher top end.
This is with the same hp and same areodynamics. The 316/317
hp/torque output of the engine seems to perform better with the
2.54 transaxle. But you're right with a few mods (more power)
the 2.20 would be great. In fact I'm planning on a 2.54 to 2.20
swap in the future. I can already spin the wheels in the first 2 gears,
so I'm loosing traction. I'll also top out at 186 mph. With the 2.20,
I hope to spin the wheels less and have a top end over 200...
Just so you don't loose it with all the debate, the 2.54 90+ S4
was .3 seconds faster to 60 and had a 3 mph higher top end.
This is with the same hp and same areodynamics. The 316/317
hp/torque output of the engine seems to perform better with the
2.54 transaxle. But you're right with a few mods (more power)
the 2.20 would be great. In fact I'm planning on a 2.54 to 2.20
swap in the future. I can already spin the wheels in the first 2 gears,
so I'm loosing traction. I'll also top out at 186 mph. With the 2.20,
I hope to spin the wheels less and have a top end over 200...
01-07-2005, 07:53 PM
#70
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Mark,
I hope everyone is finding this as interesting as I am. I still take issue with alot of what you have to say.
I think we agree on some points. Certainly closer spacing would be great
Here are my sticking points
"...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!!..."
That is EXACTLY the point, I want better acceleration but I am willing to loose the "go faster" (top speed). Obviously if you want both things, horse power needs to go up. That was not the point of this thread. The point of this thread is will a 2.54 rear end accelerate faster than a 2.2. The answer is yes.
I have been extremly clear in multiple posts that I know there is no free ride. In fact I have made the point that HP is constant no matter what gearing is like. I don't particulary care for you to be pinning that misunderstanding on me.
I have also been clear that HP does not tell you squat about acceleration. Acceleration is what this thread is all about. If you had two identical 928's with identical HP and weight. One with a high ratio rear end and one with a low ratio rear end, the HP delevered wold be identical but the acceleration would be way different. The price payed would be top end. You on the other hand have stated multiple times that rear end ratios have no impact on acceleration and this is just WRONG.
The above is the crux of our disgreement
I like to look at HP as being a good comparison of what an engines potential is, but without looking at torque, total gearing and weight to find acceleration you can't know what a cars potential is.
I, like others on this board, would not mind trading some high speed capability for more mid speed acceleration. In fact it was this very thing that Porsche did when they switched from 2.2 rear end to 2.54 rear end. Theoretical top speed went down and torque went up. Going to 2.7 - 2.9 aould make me a very satisfied customer, I would get better low-mid speed acceleration and loose useless top end.
I hope everyone is finding this as interesting as I am. I still take issue with alot of what you have to say.
I think we agree on some points. Certainly closer spacing would be great
Here are my sticking points
"...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!!..."
That is EXACTLY the point, I want better acceleration but I am willing to loose the "go faster" (top speed). Obviously if you want both things, horse power needs to go up. That was not the point of this thread. The point of this thread is will a 2.54 rear end accelerate faster than a 2.2. The answer is yes.
I have been extremly clear in multiple posts that I know there is no free ride. In fact I have made the point that HP is constant no matter what gearing is like. I don't particulary care for you to be pinning that misunderstanding on me.
I have also been clear that HP does not tell you squat about acceleration. Acceleration is what this thread is all about. If you had two identical 928's with identical HP and weight. One with a high ratio rear end and one with a low ratio rear end, the HP delevered wold be identical but the acceleration would be way different. The price payed would be top end. You on the other hand have stated multiple times that rear end ratios have no impact on acceleration and this is just WRONG.
The above is the crux of our disgreement
I like to look at HP as being a good comparison of what an engines potential is, but without looking at torque, total gearing and weight to find acceleration you can't know what a cars potential is.
I, like others on this board, would not mind trading some high speed capability for more mid speed acceleration. In fact it was this very thing that Porsche did when they switched from 2.2 rear end to 2.54 rear end. Theoretical top speed went down and torque went up. Going to 2.7 - 2.9 aould make me a very satisfied customer, I would get better low-mid speed acceleration and loose useless top end.
01-07-2005, 08:16 PM
#71
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Chuck,
Don't what to start another war of words, but one point I guess that was
missed in my post was that the 2.54 S4 had a higher top end. This was
becasue the hp available at the rpms when going 165 with the 2.20 final
drive ratio was too low to go any faster. With the 2.54 rear end the rpms
were higher, and the engine made enough power to go to 168... So the lower
drive ratio doesn't always mean more top end.
I think the 2.20 final drive was for fuel economy or maybe noise.
Again just a minor point, but you won't want to mislead anyone. If you
have enough power, then the 2.20 would eventully go faster.
Don't what to start another war of words, but one point I guess that was
missed in my post was that the 2.54 S4 had a higher top end. This was
becasue the hp available at the rpms when going 165 with the 2.20 final
drive ratio was too low to go any faster. With the 2.54 rear end the rpms
were higher, and the engine made enough power to go to 168... So the lower
drive ratio doesn't always mean more top end.
I think the 2.20 final drive was for fuel economy or maybe noise.
Again just a minor point, but you won't want to mislead anyone. If you
have enough power, then the 2.20 would eventully go faster.
01-07-2005, 08:49 PM
#73
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The automatic the pinion gear is bolted to the output of the automatic portion of the transaxle. The 5 speed the pinion gear is the main shaft and changing means a full rebuild. So the automatic is much easier. However it probably is more cost effective to buy a complete transaxle. In addition there are variations from years to years which prevent using some gears in some transmissions.
