asnxps2

Just changed my transmission from an M6 to a TH400. Im trying to make the car streetable for the highway. Right now I have 3.90 gears at at 70 mph Im spinning the car at close to 5000 RPMs in third gear. Do you think switching to a 3.42 or may be something like a 3.02 would get me to spin at like 3500RPM?

DanZ28

iTrader: (5)

You would be 3100 rpm at 70 with 3.42 gears and 78 mph with 3.08's. This of course will have negative effects at the track.

BTW, at 5000 rpm you should be closer to 100 mph. With 3.90 gears, you should be around 3500-3600 rpm at 70 mph.

Dan

lethal93ta

put your car in forth thats 1-1 in your car that would be the same as 3rd in a th400.

SMOKKINU

iTrader: (4)

3.73 with taller tire.

mzoomora

iTrader: (36)

You wont like a TH400 with less gear. The taller first gear will make it slower out of the hole, then give it a taller gear/tire combo will really make it show. For high HP or nitrous cars its a great transmission choice, but for a street driven car there are too many compromises. I would guess that since you did go with a TH400 it isnt a daily driver, so I would say either suck it up or just try a smaller gear change. Also, the RPM's you are giving almost sound like 2nd gear RPM's not 3rd. If that were the case and you had a 6500 rpm redline you would only trap 91 mph. Either you have a really loose converter or something else is going on.

asnxps2

I have a 4200 stall converter. The car is a 408 stroker with a supercharger. I have to double check the RPM it could be around 4000 RPM at 70 mph but I take the insurance off of the car during the winter months. At 6800 RPM which is my redline it is around 135-140. This was just a highway blast test though. Probably go with a 3.42 just like I had when my car was stock with a 6 speed.

Photochop

iTrader: (74)

With the power that thing should be making you could probably get away with a 3.23 or even a 3.08...you shouldnt need much gear to get that car moving in a hurry

gator's 99TA

iTrader: (2)

3.73 and a 28" tire on my car is VERY streetable. 3200 rpms @ 70mph

less gear and the car wont perform very well.

revtime

iTrader: (1)

I second that. You need at least a 3.73 gear with TH350/400.
Unless you have monster HP, then you can get away with a 3.08 or 2.73 even.
With only 350 to 450 horse the car just won't leave the way it should.

In my car with the 3.73s the car would leave hard, but with the 2.73s that are in it now (temporarily) its a slug off the line.

asnxps2

Have not dynoed the car with the TH400 but with the 6 speed it was at 600 rwhp and around 580 lbs torque to the wheels . With the high stall I should have no problem leaving on boost with my t-brake. Looking maybe at 3.08 gear.

asnxps2

Anybody have a gear calculator for a TH400 and how gear ratios would translate?

DanZ28

iTrader: (5)

On a turbo car, I think a 3.42 or 3.23 gear would be nice.

TH400: First gear is 2.48:1, Second gear is 1.48:1, and Third gear is 1:1

calcultor: http://www.angelfire.com/fl/procrastination/rear.html

Dan

mzoomora

iTrader: (36)

Think about it like this- With a 700r4 first gear would be 3.06 x 3.42 = 10.47
Divide that by 2.48 and you get 4.21. That would be the gear you would need to have an equivalent first gear ratio. Its obviously not that simple, and every car is different, but it gives you an idea. The TH400 really shines on the shifts since there is less RPM drop.