S2 ring & pinion vs stock ring & pinion question
08-16-2005, 11:20 AM
#1
S2 ring & pinion vs stock ring & pinion question
Forgive me for taking the easy way out on this (asking here instead of looking it up myself), but does anyone know what the threshhold point is between an S2 vs stock ring & pinion is? At what point does the gear ratio of the stock r&p start to out perform an S2?
Regards,
Regards,
08-16-2005, 11:31 AM
#2
Rennlist Member
Im not clear what you mean by threashold and one out performing the other? By performance, do you mean acceleration? The shorter gearing will always be faster.
And are you asking about an S2 ring and pinion installed in a turbo trans, or an S2 trans versus a turbo tran - the S2 has a taller 5th gear than the turbo 5th gear. So an S2 trans with a turbo 5th gear set is the same as a turbo trans with an S2 ring and pinion.
And are you asking about an S2 ring and pinion installed in a turbo trans, or an S2 trans versus a turbo tran - the S2 has a taller 5th gear than the turbo 5th gear. So an S2 trans with a turbo 5th gear set is the same as a turbo trans with an S2 ring and pinion.
08-16-2005, 12:41 PM
#3
I'll try to clarify my question.
I have an '86 951 LSD tranny with a S2 r&p in it. Is there a point of diminishing returns on the gearing advantage (which you are saying no), aside from loss of top end speed potential where the gearing from a stock box would maybe correlate better to it hp/torque curves, or will it always be faster? I guess what I am asking is how did the factory determine the gear ratio on the turbo vs the S2. Was it just a gas mileage/top end bragging rights thing, or were they looking at mating the powerband to the gear ratio?
Regards,
I have an '86 951 LSD tranny with a S2 r&p in it. Is there a point of diminishing returns on the gearing advantage (which you are saying no), aside from loss of top end speed potential where the gearing from a stock box would maybe correlate better to it hp/torque curves, or will it always be faster? I guess what I am asking is how did the factory determine the gear ratio on the turbo vs the S2. Was it just a gas mileage/top end bragging rights thing, or were they looking at mating the powerband to the gear ratio?
Regards,
08-16-2005, 12:51 PM
#4
Burning Brakes
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the shorter gearbox is not necessarily faster and may even be bit slower if you have to shift too much. for example, if it's so short you have to shift into 4th at the end of the 1/4 mile, rather than winding out 3rd, i bet it will have a slower et than the taller gearbox. same thing with 0-60 if you have to shift to 3rd rather than stay in 2nd, i think your time will be slower. someone else on the 928 web board explains this pretty well. it's a popular misconception that shorter gears are always faster except at top end. i believe this is incorrect.
08-16-2005, 12:52 PM
#5
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Hello Scott,
If this is for racing - there are two cars in our team, ours with stock 951 ratios and R&P, and a friend's, which has a 951 with S2 R&P. Any turn where we are forced to go below 3,500 rpm, he has an advantage over us - he is on boost, and we are not. If you have a slow track (with a few of these slower turns), he has a definite advantage. On faster tracks (like the Spa/Francorchamps track in Europe), we have an advantage. In terms of top speed: his car does not go much over 250 kmh (around 155 mph) before the rev limiter cuts in, whereas ours can go beyond this. His gets there quicker, though.
Hope this helps somewhat. Guess in the US you would not need the top speed?
If this is for racing - there are two cars in our team, ours with stock 951 ratios and R&P, and a friend's, which has a 951 with S2 R&P. Any turn where we are forced to go below 3,500 rpm, he has an advantage over us - he is on boost, and we are not. If you have a slow track (with a few of these slower turns), he has a definite advantage. On faster tracks (like the Spa/Francorchamps track in Europe), we have an advantage. In terms of top speed: his car does not go much over 250 kmh (around 155 mph) before the rev limiter cuts in, whereas ours can go beyond this. His gets there quicker, though.
Hope this helps somewhat. Guess in the US you would not need the top speed?
08-16-2005, 01:39 PM
#6
Dr Ron has said this very well. I have both. The S2 is currently in the car.
I can only go about 155-160.
I blew the doors off of an STI (on track, of course) a couple weeks ago - I hit the limiter in third and had to change to 4th while I was passing him. That's annoying.
That said - the S2 box is 10,000 times better street box for USA cars that travel on 25-35 MPH roads. The gearing is perfect.
I can only go about 155-160.
I blew the doors off of an STI (on track, of course) a couple weeks ago - I hit the limiter in third and had to change to 4th while I was passing him. That's annoying.
That said - the S2 box is 10,000 times better street box for USA cars that travel on 25-35 MPH roads. The gearing is perfect.
08-16-2005, 02:18 PM
#7
My wife will be relieved to know that I can only hit 155 mph... lol
Thanks for the great answers, guys!
Regards,
Thanks for the great answers, guys!
Regards,
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08-16-2005, 04:34 PM
#9
Rennlist Member
If the question is, which allows for faster acceleration: the shorter the gears, the faster the car will accelerate. Pure physics.
With 245/45/16 tires, here are approx speeds at 6500 rpm for a Turbo vs S2 transmission
Gear / Turbo / S2
1st / 40mph / 35
2nd / 69mph / 60
3rd / 101mph / 88
4th / 137mph / 119
5th / 171mph / 158
The S2 5th gear is a 0.778 ratio, and the Turbo has a 0.829 ratio 5th gear set. So if you put an S2 R/P in a turbo trans or the Turbo 5th Gear set in an S2 Trans, the top speed is 149 mph at 6500 rpm.
You can see from the table above where the taller geared car would have the advantage, and vice versa. Side by side at 60mph, the Turbo trans could still be in 2nd gear, but the S2 trans would have to be in 3rd, so from 60-69 mph, the Turbo trans would have better acceleration since it is in a lower gear. Same logic for each gear comparison. But below the shift points (when the cars are in the same gear), the shorter geared car would accelerate quicker, ie from 0-35, 40-60, 69-88, 101-119, 137-158 (or 149) mph compared to 35-40, 60-69, 88-101, 119-137 for the turbo trans.
Other considerations:
For a street car, the S2 R/P will be at a higher RPM in top gear at freeway cruising speeds.
For the track, you also want to consider what a shorter R/P would do for shift points, and this will be track specific. For example, at Brainerd International (my home track), I can run the complete backside of the track in 3rd gear with a standard Turbo transmission. If I put in an S2 trans or R/P, I would have to shift to 4th between two of the turns then downshift back to 3rd while braking for the next corners. So the trade off is better acceleration versus the increased time and braking distance it may take to perform the upshift, then downshift in the braking zones. I would also be buzzing through turn 1 and into 2 at redline in 5th, and we all know what high rpm right hand turns can do to the #2 rod bearing. So for BIR, I would likely prefer the Turbo trans. But for Road America, I would absolutely prefer the S2 trans. In general, which is better/faster will be driver, car, and track specific for any given stretch of track, series of corners, or full lap.
Pro race teams do this analysis all the time. They will have different gear boxes for different tracks, trying to maximize the choice between shorter gears (more acceleration) and taller gearing (less shifting). Especially for endurance racing, less shifting can be a big benefit of less wear and tear on the trans and clutch and less fatigue for the driver.
With 245/45/16 tires, here are approx speeds at 6500 rpm for a Turbo vs S2 transmission
Gear / Turbo / S2
1st / 40mph / 35
2nd / 69mph / 60
3rd / 101mph / 88
4th / 137mph / 119
5th / 171mph / 158
The S2 5th gear is a 0.778 ratio, and the Turbo has a 0.829 ratio 5th gear set. So if you put an S2 R/P in a turbo trans or the Turbo 5th Gear set in an S2 Trans, the top speed is 149 mph at 6500 rpm.
You can see from the table above where the taller geared car would have the advantage, and vice versa. Side by side at 60mph, the Turbo trans could still be in 2nd gear, but the S2 trans would have to be in 3rd, so from 60-69 mph, the Turbo trans would have better acceleration since it is in a lower gear. Same logic for each gear comparison. But below the shift points (when the cars are in the same gear), the shorter geared car would accelerate quicker, ie from 0-35, 40-60, 69-88, 101-119, 137-158 (or 149) mph compared to 35-40, 60-69, 88-101, 119-137 for the turbo trans.
Other considerations:
For a street car, the S2 R/P will be at a higher RPM in top gear at freeway cruising speeds.
For the track, you also want to consider what a shorter R/P would do for shift points, and this will be track specific. For example, at Brainerd International (my home track), I can run the complete backside of the track in 3rd gear with a standard Turbo transmission. If I put in an S2 trans or R/P, I would have to shift to 4th between two of the turns then downshift back to 3rd while braking for the next corners. So the trade off is better acceleration versus the increased time and braking distance it may take to perform the upshift, then downshift in the braking zones. I would also be buzzing through turn 1 and into 2 at redline in 5th, and we all know what high rpm right hand turns can do to the #2 rod bearing. So for BIR, I would likely prefer the Turbo trans. But for Road America, I would absolutely prefer the S2 trans. In general, which is better/faster will be driver, car, and track specific for any given stretch of track, series of corners, or full lap.
Pro race teams do this analysis all the time. They will have different gear boxes for different tracks, trying to maximize the choice between shorter gears (more acceleration) and taller gearing (less shifting). Especially for endurance racing, less shifting can be a big benefit of less wear and tear on the trans and clutch and less fatigue for the driver.