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Gear selection for turbo car
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Posted: 10/15/09
12:53 PM
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Can anybody give me advice on rear end gears for a turbo car? This is the first time I've run a turbo. I was planning on 3.73s but I've been told by some people that they may be too steep and I may be better off with something around 3.42. The car is a 3600 lb. 72 Camaro with a 355 with a Comp NX274H cam (2400-6500 powerband), twin T3/T4 turbos running 10psi boost, 200-R4 with 3000 stall and I plan on running 28 inch tall slicks. Any suggestions on the gear ratio?
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Posted: 10/15/09
01:41 PM
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in the 1/8 mile or 1/4 or just around town?
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68scott385
Enthusiast
| Posts: 314
| Joined: 05/09
Posted: 10/15/09
02:10 PM
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the gear sets are too close together too make much of a difference...
at 6500rpm in first gear the difference is 5mph
at 6500rpm in fourth gear (not likely that any motor will pull to its max rpm under full load at speed) the difference is only 20 mph
at 70mph there is only 200 rpm difference
all calculations done with no provisions for slippage
the 3.73 will be less likely to spin off the line at the track
with the overdrive either gear set will give decent mileage on the highway
-
the red-headed step-child of the mailing list
fuzzy dice, air shocks & N50's rule
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Posted: 10/15/09
03:31 PM
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The car is a street car but I'll be running it at a 1/4 mi track.
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Posted: 10/15/09
03:34 PM
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thanks for the feedback. i've already purchased a set of 3.73's so i'll go ahead and have them installed instead of exchanging them for 3.42's.
thanks again
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Posted: 10/15/09
06:59 PM
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good luck
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TurboTed
Enthusiast
| Posts: 503
| Joined: 04/05
Posted: 10/16/09
10:29 AM
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Gear for trap speed.
Assuming peak power is ~6,200 rpm, 3.73:1 gears with 28" tires ought to be good for a trap speed of 138-140 mph. 3.42:1 will bump it up to 150 (assuming you've got the power to pull them).
Some suggest that if you overgear a turbo, you'll have "boost lag." But that shouldn't be a problem here (smallish turbos, modest gearing,automatic transmission).
The 3.42s should be 1-2 mpg better than the 3.73s The engine in OD will be turning around 9% faster with the 3.73s. The engine will also probably wear out about 9% quicker . . . .
*****
TURBO TED --Internationally known as the "John Force of the Yugo Racing Association."
Sergeant-at-Arms and immediate Past President of the SoAL Yugo Owners Group.
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