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Old 11-07-2010, 11:30 AM   #1
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2,5 gearbox instead of 2,7

Would a gearbox from a 2,5 engine improve acceleration on my 2,7 ?
Topspeed is only theoretical to me as I visit Gemany very seldom. On the other hand I desperately need better acceleration during the few trackdays I do every year. Another benefit would be that the annoying 3k rpm vibration would be out of my cruising range.
Anyone tried this ?
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Old 11-07-2010, 11:46 AM   #2
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Not sure what the gear ratio differences are. I have been SERIOUSLY thinking about this, though...

http://www.gboxweb.com/
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Old 11-08-2010, 02:36 AM   #3
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Gearbox

According to the Bentley Manual the ratios in the g/box are the same for 1st, 2nd, and 3rd. The main difference is in 4th, 5th and the final drive.
------ 2.5 vs. 2.7
1st - 3.50
2nd - 2.12
3rd - 1.43
4th - 1.03 vs. 1.09
5th - 0.79 vs. 0.84
Final drive 3.89 vs. 3.56
You'll have to do your own math, I might screw it up.

Last edited by Spinnaker; 11-08-2010 at 02:53 AM. Reason: appended
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Old 11-09-2010, 10:59 AM   #4
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Quote:
Originally Posted by Spinnaker
According to the Bentley Manual the ratios in the g/box are the same for 1st, 2nd, and 3rd. The main difference is in 4th, 5th and the final drive.
------ 2.5 vs. 2.7
1st - 3.50
2nd - 2.12
3rd - 1.43
4th - 1.03 vs. 1.09
5th - 0.79 vs. 0.84
Final drive 3.89 vs. 3.56
You'll have to do your own math, I might screw it up.
That is from where I got the idea.
This means that it would be quicker in the first three gears and the same as 2.7 in 4th and 5th. Perfect on track! (if the reduction in ratio can be felt) I am not skilled enough to judge what the difference can be translated to in acceleration times.

3rd gear 2.5 total red=5,56:1
vs
3rd gear 2.7 total red=5,09:1
10% differance, but will this give a noticable improvement?
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Old 11-09-2010, 06:58 PM   #5
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My 3.6 is mated to a 2.5 tranny. I'll trade anyone for a working 2.7 5 speed tranny even up.

The biggest problem I have with the setup is that first gear is almost worthless since redline comes in a second or so.
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Old 11-09-2010, 11:33 PM   #6
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I have an old friend that bought a "S" with a blown tranny and put in a 5 speed because he wanted the better ratios for autocross. Not sure if it was a 2.5 or a 2.7 though. Until I looked it up in the Bentley, I didn't know there was a difference in them.
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Old 11-26-2010, 08:21 AM   #7
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Wouldn't it be easier/cheaper to just change the final drive ratio?
Maybe you could get a limited slip at the same time?
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Old 11-26-2010, 09:29 AM   #8
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Yes it would work but... it would be even easier and cheaper to simply run lower profile tires for AX days It's the best of both worlds. Short gears for AX and tall gears for driving around town. Your own adjustable final drive ratio.
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Old 11-27-2010, 04:36 AM   #9
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I have a cayman 5 speed mated to my 3.4. I don't know the ratios but I like it.
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