pros and cons of S2 tranny in 951?
11-25-2003, 07:33 PM
#1
Racer
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pros and cons of S2 tranny in 951?
what are the cons besides lower top speed and the debate of strenth?
anybody have one that can speak from experience?
anybody have one that can speak from experience?
11-26-2003, 02:03 AM
#2
Three Wheelin'
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Moderately modified, the 951's 1st gear is useless. 2nd is questionable. If you shorten them, you just increase that. Your 3rd - 5th gear accelleration may be better though.
11-26-2003, 02:51 AM
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I have a S2 tranny in my 86 951. The shorter gears make the turbo lag a lot less noticeable. I would say that this is one of the best mods I have done and have been very glad I did the swap. The overall feel is that the car lost 300lbs of weight.
john
john
11-26-2003, 03:01 AM
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Shorter gears may make the lag down low less noticeable, but they "ride the tourque curve" shorter of a time then the slightly taller gears would, decreacing the top end power to make up for the added pull down low. I dont have any real numbers but this is the same principal with putting a 968 tranny in a 951. All in all your going to lose to someone with a 951 gear box unless its a 1/4th of a mile or something. Even if the lag area down low pulls a little harder due to the short gears.
11-26-2003, 10:45 AM
#5
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I agree with John, but we both live at high altitude where lag is more pronounced. Smooth 1st gear starts are much easier, but 2nd gear is a bit short to build full boost. 3rd-5th are much better in my opinion.
But I'm concerned about the durability of the S2 box. Mine has LSD but no oil cooler, and even with Redline heavyweight shockproof oil, it does not sound happy after a track session. If (when) I pull it off for a rebuild, I'm going to see about fitting the oil cooler.
But I'm concerned about the durability of the S2 box. Mine has LSD but no oil cooler, and even with Redline heavyweight shockproof oil, it does not sound happy after a track session. If (when) I pull it off for a rebuild, I'm going to see about fitting the oil cooler.
11-26-2003, 11:13 AM
#6
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so its not just top speed i would sacrafice, its also power in higher gears?
would a 951 win in a freeway race against a 951 with an s2 tranny, assuming they didn't go higher than say 135mph?
would a 951 win in a freeway race against a 951 with an s2 tranny, assuming they didn't go higher than say 135mph?
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11-26-2003, 09:11 PM
#9
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And to put to rest the part about the S2/torque curve issue Craig 88 and myself have very similar GT3S cars. I've driven both on the same track same day and Craig's is better sutied to me. On a track like Putnam I only use 3-4 in my car. With Craig's I used 3-4-5, nice box.
Alan C.
Craig, load up on food tomorrow I need a weight advantage
Alan C.
Craig, load up on food tomorrow I need a weight advantage
11-27-2003, 11:02 AM
#11
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I dont have an S2 box and have not run one in my Turbos, but Ive known guys that have for years in track/race cars with both stock and modified power, with no reliability or strength problems. I dont think the oil coolers are that necessary unless you are running endurance races or prolonged run groups on very high speed tracks.
Shorter gearing does nothing to the power the engine makes, nor does it change the rpm/torque curve. The car will accelerate slightly faster because its pulling a shorter gear. A car accelerates a lot faster in 3rd than it does in 4th, because 3rd is a much shorter gear than 4th is. So if you make 4th a slightly shorter ratio, it will accelerate slightly quicker than stock.
In an acceleration test between a stock turbo and a turbo w/ an S2 trans, the car with the S2 trans will be quicker all the way through the gears, actually through 4th. 5th gear comparitive acceleration might be much closer because the S2 trans has a taller 5th gear set than the turbo, not really an overdrive ratio, but taller than the turbo gear set ratio (although the overall S2 final drive ratio is still slightly shorter than the turbos final drive).
Because of that, some guys will put the S2 ring and pinion in a turbo trans, or put the turbo 5th gear set in an S2 trans. The S2 ring/pinion with the turbo 5th gear limits the car to about 140mph I recall. With full S2 trans, its probably closer to 150 or so. I think the factory top speed on the S2 is 149 and there are probably a few rpms left at that point.
For those of you with straight S2 gear boxes, what rpms do you run at 60mph in 5th? A turbo will be at 2300 rpm, a turbo with an S2 ring/pinion (w/ the turbo 5th gear) will be at 2800 rpm.
Shorter gearing does nothing to the power the engine makes, nor does it change the rpm/torque curve. The car will accelerate slightly faster because its pulling a shorter gear. A car accelerates a lot faster in 3rd than it does in 4th, because 3rd is a much shorter gear than 4th is. So if you make 4th a slightly shorter ratio, it will accelerate slightly quicker than stock.
In an acceleration test between a stock turbo and a turbo w/ an S2 trans, the car with the S2 trans will be quicker all the way through the gears, actually through 4th. 5th gear comparitive acceleration might be much closer because the S2 trans has a taller 5th gear set than the turbo, not really an overdrive ratio, but taller than the turbo gear set ratio (although the overall S2 final drive ratio is still slightly shorter than the turbos final drive).
Because of that, some guys will put the S2 ring and pinion in a turbo trans, or put the turbo 5th gear set in an S2 trans. The S2 ring/pinion with the turbo 5th gear limits the car to about 140mph I recall. With full S2 trans, its probably closer to 150 or so. I think the factory top speed on the S2 is 149 and there are probably a few rpms left at that point.
For those of you with straight S2 gear boxes, what rpms do you run at 60mph in 5th? A turbo will be at 2300 rpm, a turbo with an S2 ring/pinion (w/ the turbo 5th gear) will be at 2800 rpm.
11-27-2003, 01:39 PM
#12
Three Wheelin'
For those of you with straight S2 gear boxes, what rpms do you run at 60mph in 5th?
Transmission --------------- rpm at -------------- speed at
----------------------------- 60 mph ------------- 6450 rpm
951 ------------------------- 2,330 ---------------- 166
944S2 ---------------------- 2,510 ---------------- 154
951 with 944S2 R&P ------- 2,680----------------- 145
944S2 with 9515th gear --- 2,680 ---------------- 145
Through an odd coincidence (conspiracy?) a 951 R&P and 944S2 5th give exactly the same overall ratio (3.21:1) as a 944S2 R&P with 951 5th gear. Hmmmmmm....
11-27-2003, 03:06 PM
#13
Racer
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[QUOTE]Originally posted by Waterguy
[B]Calculated for 225/50-16 tires, 5th gear statistics:
Transmission --------------- rpm at -------------- speed at
----------------------------- 60 mph ------------- 6450 rpm
i don't understand this. are you saying the rpm would be 6450 at 60mph?
[B]Calculated for 225/50-16 tires, 5th gear statistics:
Transmission --------------- rpm at -------------- speed at
----------------------------- 60 mph ------------- 6450 rpm
i don't understand this. are you saying the rpm would be 6450 at 60mph?
11-27-2003, 07:37 PM
#14
Three Wheelin'
Those are column headings. I am giving the engine rpm for each transmission at 60 mph in 5th gear. I am also giving the speed of a car with each transmission at redline (6450 rpm) in 5th gear.