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> Taller final drive ratio available?
Mid_Engine_914
post Dec 30 2006, 05:16 PM
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I was looking through the PET catalogs for the early 911/912s and later 911s and saw that there is a ring gear and pinion shaft listed with a ratio of 7:27 or 3.857:1 which is taller than the 914's stock 7:31 (4.429:1) ratio. Will this ring gear and pinion shaft work in the 914's 901 tranny?
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Crazyhippy
post Dec 30 2006, 05:30 PM
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i know 8:31 has been done, not sure what trans it's out of originally...

You have the HP to pull a taller gear?, a stockish motor needs the rpm to keep cool

BJH
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Mid_Engine_914
post Dec 30 2006, 06:22 PM
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I'm hoping to put a VR6 in my car this year and maybe in the future put a turbo kit on it. I've been playing with Drag Racing Analyzer and according to DRA a 245 whp motor would do 0-60 in 5.2s with the stock final drive ratio and 0-60 in 4.8s with the taller ratio.
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Crazyhippy
post Dec 30 2006, 07:01 PM
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and the 1st time you try to duplicate those #'s, you will be mopping tranny parts up off the street... LOL

BJH
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Mid_Engine_914
post Dec 30 2006, 08:28 PM
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Those acceleration numbers were based on a 4000 rpm launch, 'typical' shift time of 0.4s and full lift of throttle during shifts. I then reviewed the recommendations (below) on Renegade Hybrids' site and used DRA to estimate the acceleration times without using first gear, stock final drive ratio, soft compound 205/50-15 street tires and 50% posi and it estimates 0-60 in 4.9s and the quarter mile in 13.2. So I'm assuming it should be ok with a fresh tranny rebuild.

QUOTE
By now, you have probably been well educated on the limitations of the stock 914 transaxle. If not, here is a quick recap...

1. Don't use 1st gear period.

2. 300 HP and 300 FPT are the streetable limitations.

3. Shock loading will kill the tranny in no time.

4. No speed shifting or excessive abuse.

5. Have your 914 tranny converted to a four speed with taller gears by Renegade if the following scares you!
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Crazyhippy
post Dec 30 2006, 08:41 PM
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4000rpm launch on sticky street tires...

Thanks for directing me to the website... i worked there for 4 years, and have DESTROYED a few transaxles... 4000 rpm launches will do it.

And the 300hp # can be bumped if you are a VERY smooth driver. 400 HP has been done, but one mistake is enough to kill it.

BJH
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Mueller
post Dec 30 2006, 08:49 PM
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QUOTE
So I'm assuming it should be ok with a fresh tranny rebuild.


that makes me laugh and wonder after how many miles/launches will the transmission still be a "fresh rebuild"??? (IMG:style_emoticons/default/biggrin.gif)

at some point, the transmission will no longer be "fresh", do you limit your 4000rpm launches to 5, 10* or ???

or will you just do it once to measure the numbers to never repeat them again??

*bmw has an electronic counter that only allows 10 "F1" style starts in thier SMG equipped cars....supposedly the clutch turns to jelly after that number..
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Mid_Engine_914
post Dec 30 2006, 08:50 PM
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So I guess you don't recommend that people use the stock 901 with a V8 engine swap either?
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Mueller
post Dec 30 2006, 08:55 PM
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QUOTE(Mid_Engine_914 @ Dec 30 2006, 06:50 PM) *

So I guess you don't recommend that people use the stock 901 with a V8 engine swap either?



not if they are planning to do 4K rpm clutch drops (IMG:style_emoticons/default/burnout.gif) (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/burnout.gif)
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scotty914
post Dec 30 2006, 08:58 PM
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QUOTE(Mueller @ Dec 30 2006, 09:55 PM) *

QUOTE(Mid_Engine_914 @ Dec 30 2006, 06:50 PM) *

So I guess you don't recommend that people use the stock 901 with a V8 engine swap either?



not if they are planning to do 4K rpm clutch drops (IMG:style_emoticons/default/burnout.gif) (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/burnout.gif)



no, but a stock tranny handles pre loaded first gear suby powered launches (IMG:style_emoticons/default/bootyshake.gif)
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Crazyhippy
post Dec 30 2006, 09:00 PM
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depends on the appliction, ther are NO 2 v-8 cars that are built the same, or will be driven the same. If you want to drag race (which is what you are implying) the 901 gearbox does not belong in the car.

If you want to cruise and go to car shows, it will be fine.
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Mid_Engine_914
post Dec 30 2006, 09:00 PM
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No problem, I changed it to a 1500 rpm launch (everything else same as above) and the 0-60 time went to 5.0s and the quarter mile at 13.3. Problem solved. (IMG:style_emoticons/default/drunk.gif)
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Mueller
post Dec 30 2006, 09:04 PM
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QUOTE(scott thacher @ Dec 30 2006, 06:58 PM) *

QUOTE(Mueller @ Dec 30 2006, 09:55 PM) *

QUOTE(Mid_Engine_914 @ Dec 30 2006, 06:50 PM) *

So I guess you don't recommend that people use the stock 901 with a V8 engine swap either?



not if they are planning to do 4K rpm clutch drops (IMG:style_emoticons/default/burnout.gif) (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/burnout.gif)



no, but a stock tranny handles pre loaded first gear suby powered launches (IMG:style_emoticons/default/bootyshake.gif)


what the heck is "pre loaded"?? (IMG:style_emoticons/default/screwy.gif) (IMG:style_emoticons/default/biggrin.gif)

how many times have you done this? are you traction limited?

NOBODY has said the transmission will blow up the 1st time from being abused.....yes, it is coping with the abuse, but for how long??
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Crazyhippy
post Dec 30 2006, 09:10 PM
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i'm traction limited (IMG:style_emoticons/default/biggrin.gif)

Also have another trans ready to go....

BJH
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Mid_Engine_914
post Dec 30 2006, 09:12 PM
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I just changed it back to an open diff. (no posi) and the acceleration numbers basically didn't change so that may take some additional stress of the tranny. I won't be drag racing it constantly just dusting a few ricers (and Boxsters?) every now and then.
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Crazyhippy
post Dec 30 2006, 09:14 PM
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You have a few People that have done this before warning you.... but have fun...

BJH
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Mid_Engine_914
post Dec 30 2006, 09:40 PM
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You may be right but the information on Renegade's site seems to say that the 901 is fine for motors up to 300 hp (mine would have at most 280) as long as you're not constantly thrashing it. I'm going to gamble that the tranny will be fine with 1500 rpm launches and normal shifting.

(IMG:http://img220.imageshack.us/img220/1413/renegadetrannyinfovy4.jpg)
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jmmotorsports
post Dec 31 2006, 08:48 AM
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I bought a 911 sportomatic transmission a couple months ago. Plan to use the 7:27 ring and pinion out of it in my V8 car. Should be a nice ratio for a v8.

Jerry







;
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Mid_Engine_914
post Jan 5 2007, 10:45 AM
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QUOTE(jmmotorsports @ Dec 31 2006, 06:48 AM) *

I bought a 911 sportomatic transmission a couple months ago. Plan to use the 7:27 ring and pinion out of it in my V8 car. Should be a nice ratio for a v8.

Jerry



Jerry, so the 7:27 ring and pinion is a bolt-in replacement for the stock 7:31 ring and pinion?
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topatrout914
post Jan 5 2007, 11:22 AM
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My first 914 was a 1970 with D-jet and I sheared the bolts and roll pins at CV joint flange after multiple high RPM clutch drops. So the tranny may be the least of your worries if I can break it with a stock motor. (IMG:style_emoticons/default/confused24.gif)


(IMG:style_emoticons/default/smash.gif)
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