Need MPH and RPM info for 3.70 and 3.90 gears, for M6 LS1

[Billiumss]

I'm in the market to get a new rear end since my stock 10 bolt is shot, I'm going to get a 9" but I'm not sure what rear gear to get, let me explain.

 

With my stock tire size and stock rear 3.42 gear, I hit 140-142 MPH on a dyno at redline (6,700 RPMs) in 4th gear.

 

If things go the way I hope in the next 2-3 years, I will have a LSX 454 under my hood with a 100-150 shot of N20. Should make at least 580 RWHP N/A & 680-725 RWHP on the N20.

 

I'm not sure what gear I should go with, 3.70 or 3.90.

 

If I make that much power the car should be mid 10's in N/A form and low 10's when I spray. With that much power and ET's my MPH will be up there.

 

My concern is, will I run out of gear and have to shift into 5th when I'm on the N20? I'm going to guess that I might hit 135 MPH in the 1/4 on the N20.

 

I know that if I run MT ET slicks at the track it won't be much of an issue since they are taller than stock tires but I will be running a stock tire size on the street so I don't want to go to high of a gear.

 

1st gear will be a joke anyways with that much power but the higher the gear, it will be that much harder to lay into it when in 1st and 2nd gear on the street with stock tire size.

 

Since I know my goals, I only want to buy one set of gears and be done with it.

 

Thoughts/Opinions?

 

Bill

[Ramsey]

http://www.csgnetwork.com/gearratcalc.html

 

http://www.csgnetwork.com/automotiveconverters.html

 

These may help

[Tshensley]

need a tire height

[gillbot]

stock tire height is 25.66

[koolrayz]

http://www.f-body.org/gears/

with stock height tires 3.7 gear is 144mph at 7000 rpm

3.9 is 137 at 7000

4.1 is 130 at 7000

28" tire 4.1 gear 142mph at 7000

get the 410gear and 28x10.50 slicks on the gas

run stock height tires on motor

60# injectors, dual pump, keep the dry shot.

[koolrayz]

P.S. dont bore the lsx out to 4.25 there isnt enough between the cylinders