FINAL DRIVE R&P SWAP?
04-20-2005, 02:29 PM
#31
Addict & Guru
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Martin
Just a point of clarification. Your reference to $8,000 to change the gear set is, I assume, based on a custom rebuild. My admittedly not as perfect swap to a (used) G50/21 closer ratio box cost about $1,500 net after the sale of the stock G50/20. For my daily driver 90/10 street/DE use I find the Euro box to be a big improvement every day whether on the track or the street. It's among the most enjoyable mods I've done & certainly the most performance bang for the buck. Your empirical data differs with mine. Neither is objective since, as Grant said, no 2 production cars & no 2 drivers are identical.
This thread was started by an inquiry about changing R&P for greater acceleration in a street driven, not a track driven car. There should be no debate that acceleration w/in each gear will be improved. Whether more frequent shifts offset the gains depends on the desired terminal speed. If e.g., the goal is street drags to 50 mph (1-2 gear) changing the R&P would be a plus.
IMO, changing R&P alone is not a balanced approach & for me would not be my choice, but since Michael never defined his specific goals we don't know if he cares about improving the gaps that already exist in the stock box. However, on a practical level, I find 1st gear (38 mph top) to be marginally useless other than to get the car moving. For city driving I'd find a R&P changed 1st gear w/a 22 mph top to be a real pita. Other than that & worse gas mileage, changing R&P should provide better pull within each gear w/o any degradation of the stock box's existing gearing gaps.
Just a point of clarification. Your reference to $8,000 to change the gear set is, I assume, based on a custom rebuild. My admittedly not as perfect swap to a (used) G50/21 closer ratio box cost about $1,500 net after the sale of the stock G50/20. For my daily driver 90/10 street/DE use I find the Euro box to be a big improvement every day whether on the track or the street. It's among the most enjoyable mods I've done & certainly the most performance bang for the buck. Your empirical data differs with mine. Neither is objective since, as Grant said, no 2 production cars & no 2 drivers are identical.
This thread was started by an inquiry about changing R&P for greater acceleration in a street driven, not a track driven car. There should be no debate that acceleration w/in each gear will be improved. Whether more frequent shifts offset the gains depends on the desired terminal speed. If e.g., the goal is street drags to 50 mph (1-2 gear) changing the R&P would be a plus.
IMO, changing R&P alone is not a balanced approach & for me would not be my choice, but since Michael never defined his specific goals we don't know if he cares about improving the gaps that already exist in the stock box. However, on a practical level, I find 1st gear (38 mph top) to be marginally useless other than to get the car moving. For city driving I'd find a R&P changed 1st gear w/a 22 mph top to be a real pita. Other than that & worse gas mileage, changing R&P should provide better pull within each gear w/o any degradation of the stock box's existing gearing gaps.
04-20-2005, 03:17 PM
#32
King of Cool
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Guys, I got it!
That there is no drop in rmp when changing R&P only.
Thanks to Grant's spreadsheets I was thinking about it more an realized why:
When changing R&P only, it's a change between the gearbox and the rear tyres, not between the gearbox and the engine.
That's why there's less difference in speed between two gears when you change R&P but not change in rpm.
And when you change gears, you change "everything" meaning there's change in speed & rmp between two gears.
Still, car is faster (if not counting more gear changes) because in every gear, in a way you're in a slightly "lower gear" than what you would be with stock R&P.
Dan,
You're example is what I've always though would be the "best bang for the buck"; buying first an Euro tranny and then selling your existing one.
That there is no drop in rmp when changing R&P only.
Thanks to Grant's spreadsheets I was thinking about it more an realized why:
When changing R&P only, it's a change between the gearbox and the rear tyres, not between the gearbox and the engine.
That's why there's less difference in speed between two gears when you change R&P but not change in rpm.
And when you change gears, you change "everything" meaning there's change in speed & rmp between two gears.
Still, car is faster (if not counting more gear changes) because in every gear, in a way you're in a slightly "lower gear" than what you would be with stock R&P.
Dan,
You're example is what I've always though would be the "best bang for the buck"; buying first an Euro tranny and then selling your existing one.
04-20-2005, 04:49 PM
#33
Racer
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Bored today sitting here at work, so just for kicks decided to start up good old cartest. For those of you who aren't familiar, it's a free car acceleration simulator, and pretty damned accurate if set up right. I have a 95 993 speced out fairly accurately with a real dyno curve plugged in. Did one run with the standard 3.44 R&P (#1) , and another with a 4.00 R&P (#2). Run is a 20mph rolling start in 1st gear, all parameters same between the two cars except R&P. Shift time is 1/2 second. Here are the results -
seconds----speed #1---distance #1----speed #2----distance #2
1------------35.8-----------40---------------34.2-----------41
2------------41.3-----------97---------------41.4-----------95
3------------50.8-----------168--------------52.7-----------168
4------------60.5-----------254--------------62.9-----------257
5------------66.3-----------339--------------64.8-----------340
6------------72.9-----------444--------------72-------------441
7------------77.4-----------554 --------------79------------551
8------------83.6-----------678--------------85.7-----------678
9------------89.4-----------805--------------91.4-----------808
10-----------94.5-----------933--------------92.9-----------936
Notice how both cars lead each other at different times in the run - the #2 car pulls harder, but loses distance when it shifts, then gains ground, then shifts again. In the end, after 10 seconds of WOT, it's only 3 feet ahead.
seconds----speed #1---distance #1----speed #2----distance #2
1------------35.8-----------40---------------34.2-----------41
2------------41.3-----------97---------------41.4-----------95
3------------50.8-----------168--------------52.7-----------168
4------------60.5-----------254--------------62.9-----------257
5------------66.3-----------339--------------64.8-----------340
6------------72.9-----------444--------------72-------------441
7------------77.4-----------554 --------------79------------551
8------------83.6-----------678--------------85.7-----------678
9------------89.4-----------805--------------91.4-----------808
10-----------94.5-----------933--------------92.9-----------936
Notice how both cars lead each other at different times in the run - the #2 car pulls harder, but loses distance when it shifts, then gains ground, then shifts again. In the end, after 10 seconds of WOT, it's only 3 feet ahead.
04-20-2005, 04:51 PM
#34
Rennlist Member
Gear Box and R&P
Dan writes, "Your empirical data differs with mine. Neither is objective since, as Grant said, no 2 production cars & no 2 drivers are identical." I can't argue with that.... 
From personal experience, I learned how much fun the close ration box can be. This was in fact a total gear change operation, built from scratch.
Let me summarize my only point..................for dedicated track drivers, a change to a close ration box may not necessarily "rock your world"
when it comes time to compare your lap times against those 993 cars with comparable drivers with standard G 50 transmissions. Then again, on certain tracks, it may.
I close with, a good consistent driver in a standard G50 tranny car will nearly always, if not always, be faster than a lesser driver with a close ration tranny. Seat time, instruction and talent will take you a long ways, IMHO. I am spent on this topic...
From personal experience, I learned how much fun the close ration box can be. This was in fact a total gear change operation, built from scratch.
Let me summarize my only point..................for dedicated track drivers, a change to a close ration box may not necessarily "rock your world"
when it comes time to compare your lap times against those 993 cars with comparable drivers with standard G 50 transmissions. Then again, on certain tracks, it may. I close with, a good consistent driver in a standard G50 tranny car will nearly always, if not always, be faster than a lesser driver with a close ration tranny. Seat time, instruction and talent will take you a long ways, IMHO. I am spent on this topic...
02-15-2007, 04:23 PM
#35
Rennlist Member
Any more recent thoughts on changing the final drive ratios on our cars? I notice that I can change the final drive ratio in NASA's time trials without having any additional points assessed against my car, whereas if I changed the gear ratios then I would be assessed three points.
02-15-2007, 04:52 PM
#36
Weathergirl
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In that specific circumstance it might work for you. Need to look at what gears you use at what speeds. If you're only using, say 3rd and 4th now and barely getting into 5th, a shorter R&P could make your effective 2-speed a 3-speed.
Would be really annoying to drive on the street, though, with the short 1st.
Would be really annoying to drive on the street, though, with the short 1st.
02-15-2007, 06:42 PM
#37
You can see the difference between a properly setup race trans(/30), street trans(/20 stock and w/ short cwp) and sport trans(/31) by examining the following
G50/20 stock
g50/20 w/ 8:32
G50/30 Cup
G50/31 RS
G50/20 stock
g50/20 w/ 8:32
G50/30 Cup
G50/31 RS
04-09-2007, 05:54 PM
#40
Rennlist Member
Thanks to advice from this board, I immediately knew what I had found when I located a 96 C4S with LWF, RS Clutch, and updated gears. I subsequently found the gear set was provided by Paul Guard's. I was fortunate to pick up this car without paying any extra for the upgrade (and they gave me the OEM gears as well).
Bill was kind enough to plug my ratios into his spreadsheet and generate a very interesting chart. I'd love to do something about the 1st / 2nd gear ratio but they are fixed on my particular car.
http://forums.pelicanparts.com/showt...hreadid=333081
Bill was kind enough to plug my ratios into his spreadsheet and generate a very interesting chart. I'd love to do something about the 1st / 2nd gear ratio but they are fixed on my particular car.
http://forums.pelicanparts.com/showt...hreadid=333081
