11-07-2010, 11:30 AM
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#1
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Registered User
Join Date: Aug 2006
Location: Sweden
Posts: 116
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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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11-07-2010, 11:46 AM
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#2
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Registered User
Join Date: Oct 2008
Location: San Diego
Posts: 434
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Not sure what the gear ratio differences are. I have been SERIOUSLY thinking about this, though...
http://www.gboxweb.com/
__________________
1999 Carrera 4 • Aero kit • 4" UD Pulley
My Corvette doesn't leak oil... it sweats horsepower.
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11-08-2010, 02:36 AM
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#3
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Registered User
Join Date: Dec 2007
Location: Seattle
Posts: 735
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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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11-09-2010, 10:59 AM
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#4
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Registered User
Join Date: Aug 2006
Location: Sweden
Posts: 116
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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.
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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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11-09-2010, 06:58 PM
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#5
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Porsche "Purist"
Join Date: Aug 2003
Location: Wisconsin
Posts: 2,123
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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.
__________________
1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster original owner. I installed used motor at 89k.
1987 924S. 2002 996TT. PST-2
Owned and repaired Porsches since 1974. Porsche: It's not driving, it's therapy.
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11-09-2010, 11:33 PM
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#6
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Registered User
Join Date: Dec 2007
Location: Seattle
Posts: 735
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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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11-26-2010, 08:21 AM
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#7
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Registered User
Join Date: Apr 2007
Location: San Francisco
Posts: 40
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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?
__________________
Jason
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11-26-2010, 09:29 AM
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#8
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Track rat
Join Date: Nov 2006
Location: Southern ID
Posts: 3,701
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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.
__________________
2009 Cayman 2.9L PDK (with a few tweaks)
PCA-GPX Chief Driving Instructor-Ret.
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11-27-2010, 04:36 AM
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#9
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Registered User
Join Date: Dec 2006
Location: shoreham, ny
Posts: 1,619
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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.
__________________
996 3.4 engine with 2.7 986 5speed transmission
Ebay Headers, Fabspeed high flow cats, JIC Cross, IPD Plenum, H&R Coilovers, B&M Short Shifter, AEM Uego Gauge Type Analog, Apexi S-AFC Select, 987 air box, Litronics, 2000 Tails and side markers, painted center console, 18" 987 S-Wheels, GT3 Front bumper with splitter.
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