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Gear Selection twin turbo big cubes

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Old Dec 2, 2008 | 06:54 PM
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Default Gear Selection twin turbo big cubes

Got a friend with 427 twin turbo trying to decide what gear to run in the rear end. Car will be used for drags quite often. Tranny is also M12 vette. Any insite would be nice. I am a blower guy dont know much about the spooling affects of a low or high gear in a turbo app esp with the m12 tranny. Thanks for any info you coul help with...

Car put down around 750 last dyno 3:42 gear
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Old Dec 2, 2008 | 07:19 PM
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tire size will come into play but somewhere between 3.08 and 3.73
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Old Dec 2, 2008 | 07:20 PM
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tire 28" MT ET street... Thanks
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Old Dec 2, 2008 | 07:27 PM
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I'd use a 3.45
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Old Dec 2, 2008 | 07:37 PM
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3.25-3.50 depending on rear.
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Old Dec 2, 2008 | 07:43 PM
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I was thinking he should stay with the 3:42 but to be honest the gearing of the m12 transmission kind of scares me going any bigger.

Maybe possible to gear rear for 3rd gear 1/4 traps? Maybe go something real low in the 2 somethings? Or is that a bigtime stretch?
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Old Dec 2, 2008 | 07:49 PM
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As most have said 3.25 to 3.50 is perfect. The lower the gear, the more load it puts on the motor and will help the turbo spool. To low, its hard to get the car going, but get a 2 step to launch and you should be good.

On a 28 inch tire, in 4th, which should be 1 with a 3.50 gear in the rear @ 6600 rpm you could trap around 157 according to the calculation.

Chris
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Old Dec 2, 2008 | 07:54 PM
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2 step launches on vettes kind of scarry... The rear ends dont like the hard launch...
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Old Dec 2, 2008 | 07:55 PM
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Originally Posted by mikep2002
I was thinking he should stay with the 3:42 but to be honest the gearing of the m12 transmission kind of scares me going any bigger.

Maybe possible to gear rear for 3rd gear 1/4 traps? Maybe go something real low in the 2 somethings? Or is that a bigtime stretch?
How high does he spin his motor?

3rd gear in the m12 is 1.43 so if you stuck with the 28 tire, and did a 2.90 in the rear you could hit about 133 in 3rd...

use the lpe 2 step, pull some timing, get 5-8 psi out of the hole, and the car should do very well.

Zombie has a th400, and has 2.xx gear and used 1-2 for drag, and 3rd like a overdrive. Didn't affect to much on the slip.

Chris
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Old Dec 2, 2008 | 07:58 PM
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Originally Posted by mikep2002
2 step launches on vettes kind of scarry... The rear ends dont like the hard launch...
Time for a solid rear end??

Ive never looked at the vette stuff to much, but i know there are cars out there making big numbers.

Chris
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Old Dec 2, 2008 | 08:18 PM
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Thanks for all the help gonna recomend to him to stay with the 3:42 and hope for the best. I am sure he plays on the streets so the 2:90 gear I dont think is an option.
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