FINAL DRIVE R&P SWAP?
04-19-2005, 10:56 AM
#16
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Don't dismiss the R&P change out of hand. While it is not as beneficial as changing all 6 gearsets, it provides a significant acceleration advantage over the stock gearing.
The argument of losing time while shifting more is meaningless. On the street, a tenth or two lost to shifting is not important. What counts is the improvement to the snap and feel of the car. On the track, it is unlikely that you will be shifting more. Instead, it is more likely that you will just always have 14% more and 14% more torque at the wheels.
It is true that the R&P change does not reduce the RPM drops between gears, which are critcial. This is why swapping all the gearsets is better. However, the lower final drive does help the engine overcome the large gaps without getting bogged down so much. Certainly it feels as if the gaps are smaller.
All road racing cars should be set up to put the engine on the rev limiter a few meters before the end of the longest straight. Running gears taller than this is a waste of acceleration. The gears should be able to cover the anticipated speed range of the car and not one mph more. On a stock 993, the gear limited top speed is 187mph. Since the engine does not produce enough power to attain this speed, this choice results in sub-optimal acceleration. Obviously a street car requires other considerations such as crusing rpm, fuel economy etc.
Chris Cervelli
Premier Motorsports
The argument of losing time while shifting more is meaningless. On the street, a tenth or two lost to shifting is not important. What counts is the improvement to the snap and feel of the car. On the track, it is unlikely that you will be shifting more. Instead, it is more likely that you will just always have 14% more and 14% more torque at the wheels.
It is true that the R&P change does not reduce the RPM drops between gears, which are critcial. This is why swapping all the gearsets is better. However, the lower final drive does help the engine overcome the large gaps without getting bogged down so much. Certainly it feels as if the gaps are smaller.
All road racing cars should be set up to put the engine on the rev limiter a few meters before the end of the longest straight. Running gears taller than this is a waste of acceleration. The gears should be able to cover the anticipated speed range of the car and not one mph more. On a stock 993, the gear limited top speed is 187mph. Since the engine does not produce enough power to attain this speed, this choice results in sub-optimal acceleration. Obviously a street car requires other considerations such as crusing rpm, fuel economy etc.
Chris Cervelli
Premier Motorsports
04-19-2005, 05:00 PM
#17
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The argument of losing time while shifting more is meaningless. On the street, a tenth or two lost to shifting is not important. What counts is the improvement to the snap and feel of the car. On the track, it is unlikely that you will be shifting more. Instead, it is more likely that you will just always have 14% more and 14% more torque at the wheels.
04-19-2005, 05:13 PM
#18
Originally Posted by flatair
Code:
The argument of losing time while shifting more is meaningless. On the street, a tenth or two lost to shifting is not important. What counts is the improvement to the snap and feel of the car. On the track, it is unlikely that you will be shifting more. Instead, it is more likely that you will just always have 14% more and 14% more torque at the wheels.
04-19-2005, 05:19 PM
#19
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Originally Posted by Flying Finn
Guys, I don't necessarily disagree just changing R&P is "halfass" solution and for sure you'll get better results with changing gears.
However, surely by changing R&P only will shorten the "gap" between gears, or am I missing something here?
Just thinking it mathemathically, when you calculate the final ratio of one certain gear, you need to know the gear and R&P, and calculate them both, no?
When you take difference between two gears alone, that of course is still the same but when you combine that difference with different ratio R&P, the total is different.
Result: gap between two gears is different with only changing R&P.
However, surely by changing R&P only will shorten the "gap" between gears, or am I missing something here?
Just thinking it mathemathically, when you calculate the final ratio of one certain gear, you need to know the gear and R&P, and calculate them both, no?
When you take difference between two gears alone, that of course is still the same but when you combine that difference with different ratio R&P, the total is different.
Result: gap between two gears is different with only changing R&P.
When you change the R&P, the speed at which redline is achieved in 2nd is lowered. At this lowered speed (and lower gearing for 3rd gear with the lower R&P), 3rd gear picks up at exactly the same Xrpm as it did with the standard R&P. I have an Excel spreadsheet that allows one to experiment with the numbers.
All those who said that the lower R&P will give better acceleration are correct, since the gearing will be lower overall and the overall gearing of the 993 is too tall, but it will not improve the rpm drop on upshifts (very important on the track).
04-19-2005, 06:21 PM
#20
Originally Posted by GrantG
Finn - your analysis makes sense to a point, but it does not pan out in terms of rpm drop on upshift. If you shift at redline in 2nd gear and drop into 3rd, the engine will be turning Xrpm in 3rd at the vehicle speed at which redline is achieved in 2nd.
When you change the R&P, the speed at which redline is achieved in 2nd is lowered. At this lowered speed (and lower gearing for 3rd gear with the lower R&P), 3rd gear picks up at exactly the same Xrpm as it did with the standard R&P. I have an Excel spreadsheet that allows one to experiment with the numbers.
All those who said that the lower R&P will give better acceleration are correct, since the gearing will be lower overall and the overall gearing of the 993 is too tall, but it will not improve the rpm drop on upshifts (very important on the track).
When you change the R&P, the speed at which redline is achieved in 2nd is lowered. At this lowered speed (and lower gearing for 3rd gear with the lower R&P), 3rd gear picks up at exactly the same Xrpm as it did with the standard R&P. I have an Excel spreadsheet that allows one to experiment with the numbers.
All those who said that the lower R&P will give better acceleration are correct, since the gearing will be lower overall and the overall gearing of the 993 is too tall, but it will not improve the rpm drop on upshifts (very important on the track).
04-19-2005, 06:39 PM
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The time off full throttle on a fast upshift should be about .35 seconds. .25 if you are really fast and in a hurry. I find that if I try to beat .35 I miss more often than I like.
Chris Cervelli
Premier Motorsports
Chris Cervelli
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04-19-2005, 06:39 PM
#22
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Rant: I agree with Flatair...he writes...
Although he is speaking to changing the R&P, based on my experience, I feel the same may be true (is true in my experience) with the widely praised merits of changing over to close ratio gears. "In a street driven car, changing your R&P will make your car *feel* quicker and more responsive, and in-gear acceleration will be greatly improved....BUT you're going to have to shift more. That will negate most of your in-gear acceleration gains - given you shift pretty quickly you'll end up getting to 100mph at the same rate."
My neighbor and I have nearly identically prepared 993 cars. We run the same tires. We both run PSS9s, he has 993RS bars, I have TRG bars. The big difference between the two cars, he has a close ratio (Jeff Gamroth built) tranny with a Porsche Motorsports LSD. I have a stock tranny with a standard Porsche LSD. We are very close in driving ability...and post very similar times wherever we go.
This weekend in Buttonwillow, I could pull him in a few spots, he me in a few...bottom line, overall, the performance of the cars was nearly identical. Coming on to the front straight through the S turns, he could take it in 3rd, I had to go down to second...I noted at the exit of the turn, he could pull me by a bit, but I would soon carch up going down the front straight.
Steve Weiner says the short gears feel like 50 HP...they very well may as the car is hitting the maximum torque curve and HP more frequently on the way to 100 + MPH, and the Varioram is firing off its unique 5,000 RPM "song" one additional time, but the trade off, the short gear guy will be shifting more.
Would I spend the money to re-gear my tranny knowing what I know now, and based on feedback from my neighbor, probably not. Would I replace the factory LSD that has 30,000 miles on it with a Porsche Motorsports or Guard LSD, it would be nice but my old "piece of $%&" standard LSD seems to be working well. My car with its "piece of $%&*" standard LSD just hooks up, and does so well out of sharp corners such as the Buttonwillow "Off Ramp" and coming out of the "Star Mazda Turn" as well as my neighbors car with the Porsche Motorsports LSD. How can this be?
Based on my personal experience, I do agree that driving a close ratio geared car would probably be more fun to drive around town, and it could feel that it has an additional 50 HP...but considering that a tranny rebuild with close ration gears is probably $8,000 or more, I'll just stay with my factory long gears for now.
You may feel that based on the collective wisdom and shared opinions on the Board, "everyone" just knows that a close ration tranny is better, and that the standard factory LSD is a "piece of $%&": It just is, don't argue! Well everyone, with a few exceptions, thought the earth was flat once upon a time. That did not make it true, did it.
I could probably be sold a Guard LSD...I just like the look of those well engineered marvels.
My neighbor and I have nearly identically prepared 993 cars. We run the same tires. We both run PSS9s, he has 993RS bars, I have TRG bars. The big difference between the two cars, he has a close ratio (Jeff Gamroth built) tranny with a Porsche Motorsports LSD. I have a stock tranny with a standard Porsche LSD. We are very close in driving ability...and post very similar times wherever we go.
This weekend in Buttonwillow, I could pull him in a few spots, he me in a few...bottom line, overall, the performance of the cars was nearly identical. Coming on to the front straight through the S turns, he could take it in 3rd, I had to go down to second...I noted at the exit of the turn, he could pull me by a bit, but I would soon carch up going down the front straight.
Steve Weiner says the short gears feel like 50 HP...they very well may as the car is hitting the maximum torque curve and HP more frequently on the way to 100 + MPH, and the Varioram is firing off its unique 5,000 RPM "song" one additional time, but the trade off, the short gear guy will be shifting more.
Would I spend the money to re-gear my tranny knowing what I know now, and based on feedback from my neighbor, probably not. Would I replace the factory LSD that has 30,000 miles on it with a Porsche Motorsports or Guard LSD, it would be nice but my old "piece of $%&" standard LSD seems to be working well. My car with its "piece of $%&*" standard LSD just hooks up, and does so well out of sharp corners such as the Buttonwillow "Off Ramp" and coming out of the "Star Mazda Turn" as well as my neighbors car with the Porsche Motorsports LSD. How can this be?
Based on my personal experience, I do agree that driving a close ratio geared car would probably be more fun to drive around town, and it could feel that it has an additional 50 HP...but considering that a tranny rebuild with close ration gears is probably $8,000 or more, I'll just stay with my factory long gears for now.
You may feel that based on the collective wisdom and shared opinions on the Board, "everyone" just knows that a close ration tranny is better, and that the standard factory LSD is a "piece of $%&": It just is, don't argue! Well everyone, with a few exceptions, thought the earth was flat once upon a time. That did not make it true, did it.
I could probably be sold a Guard LSD...I just like the look of those well engineered marvels.
Last edited by Martin S.; 04-19-2005 at 06:48 PM. Reason: I have seen the light and the error of my wicked ways!
04-19-2005, 09:32 PM
#24
Originally Posted by flatair
Code:
If it takes You a second to shift a G50 box I would recommend letting Chris rebuild it...
04-20-2005, 09:06 AM
#25
King of Cool
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Originally Posted by GrantG
Finn - your analysis makes sense to a point, but it does not pan out in terms of rpm drop on upshift. If you shift at redline in 2nd gear and drop into 3rd, the engine will be turning Xrpm in 3rd at the vehicle speed at which redline is achieved in 2nd.
When you change the R&P, the speed at which redline is achieved in 2nd is lowered. At this lowered speed (and lower gearing for 3rd gear with the lower R&P), 3rd gear picks up at exactly the same Xrpm as it did with the standard R&P. I have an Excel spreadsheet that allows one to experiment with the numbers.
All those who said that the lower R&P will give better acceleration are correct, since the gearing will be lower overall and the overall gearing of the 993 is too tall, but it will not improve the rpm drop on upshifts (very important on the track).
When you change the R&P, the speed at which redline is achieved in 2nd is lowered. At this lowered speed (and lower gearing for 3rd gear with the lower R&P), 3rd gear picks up at exactly the same Xrpm as it did with the standard R&P. I have an Excel spreadsheet that allows one to experiment with the numbers.
All those who said that the lower R&P will give better acceleration are correct, since the gearing will be lower overall and the overall gearing of the 993 is too tall, but it will not improve the rpm drop on upshifts (very important on the track).
I will do something, either R&P or gears at some point so it would be interesting to compare different solutions.
I still believe I'm right (
), even though far more experienced guys tell me I'm not, stubborn Finn... Way I understand it the "final final" ratio that the rear wheels turn is defined by the gear, and the R&P, is it not?
If it is and you change one element, the overall should change.. For example:
Gear 2 = 2, gear 3 = 3, stock R&P = 5, Modified R&P = 4. So:
-Stock situation: "Final final" of gear 2 is 10 (2x5) and gear 3 is 15, that gives us difference of 5
-Modified situation: "Final final" ratio of gear 2 is 8 and gear 3 is 12, difference being 4., which is different from modified R&P.
Am I totally "out" here?. I need that excel sheet...
OK, anyway, in my opinion benefit of re-gearing or changing R&P is more when you're at track and your gears don't suit so well. I have two turns in Sebring where 2nd is too short and 3rd is too long, I take them with 3rd but with shorter gears or R&P, I could take them with 3rd and acceleration would be better.
04-20-2005, 10:14 AM
#26
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Finn - I've sent it to you - please experiment and report back - maybe I've misunderstood something...
04-20-2005, 10:46 AM
#27
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Mr, Finn, Flying,
First of all, I am assuming that you have a street car that you are taking to the track. If I am wrong here and you have a dedicated track car...go at it, change out the gears and or R&P. I think you will find that the Final Solution for those with a huge budget, is to have gears for every track.
In reality, who can afford that? Put in the R&P, about $4,000 installed, or the close gears, around $8,000, don't be surprised to discover that you have opened a new can of worms on other turns.
In the case where "I have two turns in Sebring where 2nd is too short and 3rd is too long", you may re-gear or install a new R&P and now discover turns that were optimal before, you now have created a new mismatch.
In closing, my comments are based on personal obvservations at the track, both California Speedway and Byttonwillow Raceway. The short gears on my neighbors cars and my stock gears seemed to even out over the track, he was quicker in some sections, I was quicker in others.
I will admit his car is more fun to drive around town by a wee bit...a little more shifting but always in the power band. Good luck with your project whichever way you decide to go.
First of all, I am assuming that you have a street car that you are taking to the track. If I am wrong here and you have a dedicated track car...go at it, change out the gears and or R&P. I think you will find that the Final Solution for those with a huge budget, is to have gears for every track.
In reality, who can afford that? Put in the R&P, about $4,000 installed, or the close gears, around $8,000, don't be surprised to discover that you have opened a new can of worms on other turns.
In the case where "I have two turns in Sebring where 2nd is too short and 3rd is too long", you may re-gear or install a new R&P and now discover turns that were optimal before, you now have created a new mismatch.
In closing, my comments are based on personal obvservations at the track, both California Speedway and Byttonwillow Raceway. The short gears on my neighbors cars and my stock gears seemed to even out over the track, he was quicker in some sections, I was quicker in others.
I will admit his car is more fun to drive around town by a wee bit...a little more shifting but always in the power band. Good luck with your project whichever way you decide to go.
04-20-2005, 11:46 AM
#28
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Martin - I understand your point about re-gearing the box and then having new concerns about being between gears on turns that were properly geared before. However, with a close-ratio box, you should always have the right gear, or if not, the wrong gear should be much closer to optimal than the stock gearbox (on average). The stock gearbox is so widely spaced that I can't imagine that a re-gear wouldn't make a sizable improvement on virtually any track. If you and your neighbor are running the same lap times, I can only imagine one or more of the following must be true:
1. Your neighbor did not choose his ratios very wisely
2. Your car's motor must be running stronger than his
3. Your car's suspension must be better tuned
4. You must be modest about your driving ability relative to his
Have you ever swapped cars at the track? Would be interesting to see if your times are still the same...
1. Your neighbor did not choose his ratios very wisely
2. Your car's motor must be running stronger than his
3. Your car's suspension must be better tuned
4. You must be modest about your driving ability relative to his
Have you ever swapped cars at the track? Would be interesting to see if your times are still the same...
04-20-2005, 12:29 PM
#29
King of Cool
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Grant,
I'll take a look at it. Thanks for sending it.
Martin,
My car is similar to yours (I believe), it's a street car that I take it to DEs.
I'm thinking of starting to race with PBOC (Porsche BMW club down here) but am still hesitant... Should get a dedicated track car for that but we'll see...
I've modified it somewhat; it has PSS-9, RS sways, monoballs, some RS bits (wing, splitters, washer fluid reservoir, short shifter etc.), RSR steering wheel, supercups & no cats, no sound deadening, no rear seats and some other weight saving things (I've saved little under 300 lbs, including roll bar that's been added) etc.
I'm nowhere near done with my modifications but slowly I'm getting closer to what I believe is a Porsche as it should be.
Someone might concider my car kinda "rough" for street use but that's the way I like my Porsches.
I'll never sell it, instead I'll pass it to my son once I'm too old to drive and my goal with the modifications is to have Porsche that's just the way I want it to be so paying big $$$ for modifications is not so big deal as in a car that will be sold innext five years.
I agree with you, R&P or even more so, re-gearing is pretty damn expensive and is not on top of my "remaining modifications" list at the moment.
I think finding euro tranny and then selling existing US tranny would be much more cost effective (~$3000 or so?).
And yes, like you said, perfecting those two corners at Sebring might end up screwing some others, probably not but turns 14 & 16 might be close.
I disagree though that re-gearing doesn't improve the car, in my opinion 993 US tranny is not so well geared, especially between 2-3 but also rest of them are too widely spaced.
Maybe I will just learn to drive faster so those two corner will be good with 3rd gear!
I'll take a look at it. Thanks for sending it.
Martin,
My car is similar to yours (I believe), it's a street car that I take it to DEs.
I'm thinking of starting to race with PBOC (Porsche BMW club down here) but am still hesitant... Should get a dedicated track car for that but we'll see...
I've modified it somewhat; it has PSS-9, RS sways, monoballs, some RS bits (wing, splitters, washer fluid reservoir, short shifter etc.), RSR steering wheel, supercups & no cats, no sound deadening, no rear seats and some other weight saving things (I've saved little under 300 lbs, including roll bar that's been added) etc.
I'm nowhere near done with my modifications but slowly I'm getting closer to what I believe is a Porsche as it should be.
Someone might concider my car kinda "rough" for street use but that's the way I like my Porsches.
I'll never sell it, instead I'll pass it to my son once I'm too old to drive and my goal with the modifications is to have Porsche that's just the way I want it to be so paying big $$$ for modifications is not so big deal as in a car that will be sold innext five years.
I agree with you, R&P or even more so, re-gearing is pretty damn expensive and is not on top of my "remaining modifications" list at the moment.
I think finding euro tranny and then selling existing US tranny would be much more cost effective (~$3000 or so?).
And yes, like you said, perfecting those two corners at Sebring might end up screwing some others, probably not but turns 14 & 16 might be close.
I disagree though that re-gearing doesn't improve the car, in my opinion 993 US tranny is not so well geared, especially between 2-3 but also rest of them are too widely spaced.
Maybe I will just learn to drive faster so those two corner will be good with 3rd gear!
04-20-2005, 01:25 PM
#30
Rennlist Member
All good points you have raised...
Bottom line...its your car, you will do what you think is best. I get the sense that some Rennlisters feel that a change to the Euro gears will be a night and day difference. The car will certainly feel different on the street, and the track too. But the question remains, will it be any faster in relation to overall lap times in contrast to a standard geared car? Maybe, maybe not...but it will be more fun to drive. Personally, I am not about to pay $8,000 for a maybe. Now a kick *** LSD, that could be a different story.
I have been told by many track junkies, that a Porsche Motorsports or Guard LSD will make a difference; they are seeing 1 to 2 seconds a lap improvement. I have also been told that my stock LSD is a piece of garbage...yet it continues to work for me. I just don't get it, how can that be?
You mention that neighbor and I should swap cars....I don't want to take the risk he'd break mine or I'd break his...that could be the end of a friendship, and I'd have to find a new racing, fishing and hunting buddy, not an easy task. We'll just continue having fun and chasing each other around the track.
Good luck with your car. It sounds like a would be a real blast to drive, with 300 Lbs. out of the car and the other mods. Now taking 300 Lbs. out of the car, there is no refuting that this mod will result in significantly increased performance.
I have been told by many track junkies, that a Porsche Motorsports or Guard LSD will make a difference; they are seeing 1 to 2 seconds a lap improvement. I have also been told that my stock LSD is a piece of garbage...yet it continues to work for me. I just don't get it, how can that be?
You mention that neighbor and I should swap cars....I don't want to take the risk he'd break mine or I'd break his...that could be the end of a friendship, and I'd have to find a new racing, fishing and hunting buddy, not an easy task. We'll just continue having fun and chasing each other around the track.
Good luck with your car. It sounds like a would be a real blast to drive, with 300 Lbs. out of the car and the other mods. Now taking 300 Lbs. out of the car, there is no refuting that this mod will result in significantly increased performance.