Transmissions
05-16-2004, 11:14 PM
#1
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Transmissions
Alright fellas. I would like to start a thread about transmissions. I am trying to learn the intricacies of the 944 trannies and which ones are best, cheapest, easiest to find these days, strongest, fastest top ends, best for urban driving, best LSD type, etc. I would like to hear everyone's current opinions on LSD units and what is being used, how it's holding up to abuse, what was the factory LSD type. etc. Get the idea? I think everyone would benefit on some current info and opinions on transmissions. So let's here it. Step to the plate and chime in, I want everyone's 2 cents.
Chris
Chris
05-16-2004, 11:26 PM
#2
Three Wheelin'
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I think the 924 transmission is a great untapped resource. It has a 4.11 final drive. The 5th gear is a .62 ratio, which is very very tall to counteract the short 4.11 final drive. Pop this 5th gear into a 951 tranny (3.375 final drive) and you'll have a theoretical top speed (HP limiting) of over 210 mph. Not to mention low rpms for those interstate speeders. 
I plan on picking one of these up and putting the 4.11 R&P into my NA to see if I can give it some more "Pep". I'll also try out the 5th in my turbo.
Thats my contribution.
I plan on picking one of these up and putting the 4.11 R&P into my NA to see if I can give it some more "Pep". I'll also try out the 5th in my turbo.
Thats my contribution.
05-17-2004, 02:07 PM
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hobojoe: I had my '86 951 trans. rebuilt while adding a lsd. $1k in bearings alone! (just the parts, excluding labor!), you're WAY better off to just buy a good used 951S trans.
05-17-2004, 03:08 PM
#7
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I always thought (and dreamt of) installing a 968 6-speed gearbox. I thought that was the quickest in terms of acceleration and top speed that is (almost) bolt on to the 951. You SERIOUSLY think, sorry, seriously calculated that the 924 tranny would be able of speeds of 210+? how about more specific info for the amount of power it can take and acceleration specs?
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05-17-2004, 03:43 PM
#8
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You SERIOUSLY think, sorry, seriously calculated that the 924 tranny would be able of speeds of 210+?
Lets take for example the 1980 924 turbo transmission.
"Gear Ratio" for this equation = Final drive x ratio for individual gear
Final Drive: 4.71
5th Gear: .60
mph = (rpm x tire diameter) / (gear ratio x 336)
mph= (6200 x 24.5) / ([4.71 x .60] x 336)
In a 924 turbo, 6200 rpm in 5th gear would be right at 159.97 mph.
Now take the 5th gear from this 924 turbo (.60 ratio) and pop it into the 951 tranny (3.375 final drive)
mph = (rpm x tire diameter) / (gear ratio x 336)
mph= (6200 x 24.5) / ([3.375 x .60] x 336)
In a 944 turbo transmission with a 924T 5th gear, at 6200 rpm you would be at 223.25 mph.
05-17-2004, 05:03 PM
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Here's my contribution.
The 951 tranny's 1st and 2nd gear are pretty weak. If you launch at high rpms and drop the clutch for a drag launch, eventually, 1st gear will break, even with a low powered car (in my case, stock 951 with autothority chip).
If you baby the launch and the shift into 2nd gear, you can slam into 3rd, 4th and 5th without breaking anything. Because 1st and 2nd is part of the mainshaft, it's a costly replacement item.
The 951 tranny's 1st and 2nd gear are pretty weak. If you launch at high rpms and drop the clutch for a drag launch, eventually, 1st gear will break, even with a low powered car (in my case, stock 951 with autothority chip).
If you baby the launch and the shift into 2nd gear, you can slam into 3rd, 4th and 5th without breaking anything. Because 1st and 2nd is part of the mainshaft, it's a costly replacement item.
05-17-2004, 05:17 PM
#10
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If you launch at high rpms and drop the clutch eventually first gear in any car will break
Has anyone put a quaife or similar in an 86? Experiences? I heard its not an easy fit.
Has anyone put a quaife or similar in an 86? Experiences? I heard its not an easy fit.
05-17-2004, 05:36 PM
#11
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This has some useful info:
http://www.clarks-garage.com/shop-manual/trans-04.htm
Thats why I am looking into having a 4340 Steel mainshaft and removable 1st and 2nd gears made.
http://www.clarks-garage.com/shop-manual/trans-04.htm
If you launch at high rpms and drop the clutch eventually first gear in any car will break
05-17-2004, 07:17 PM
#13
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I wouldn't mess with the stock gear ratios. Porsche did it right. Our 5th gear is the perfect combination between able to accelerate and reach top speed in a timely fashion. The rest of the gears are spaced nicely downward. If you have a really tall 5th gear, the car will feel like a dog and you'll destroy that nice feeling of being able to pull away briskly from cruise mode in high gear; something that very few high hp cars can match. If you go with a shorter 968 trans, you'll run out of revs before you reach a high top speed.
A heavily modded engine favoring torque over RPM (usually the case with us) can go with taller gearing via final drive ratio only, or taller tires.
A heavily modded engine favoring torque over RPM (usually the case with us) can go with taller gearing via final drive ratio only, or taller tires.
05-18-2004, 12:00 AM
#15
What about changing 3rd gear... my friend that's looking to get his 951S trans rebuilt complained that 3rd gear is to long and brings revs to low coming out of a turn...