PBMGoatM6

Im considering picking up a used TH400 and swapping it into my M6 GTO, and wanted to know how many people are using the 3 speeds as DDs? My setup will probally be a front mount single turbo, or maybe a KB or TVS blower on the stock motor.

What RPM will I be looking at at say 70mph on the highway? Also could I lower the rear gear ratio to something around a 3.31 to help with traction/spooling turbo/better highway MPG?

I know there are only a hand full of GTOs with TH400s (I think 4 or 5) but it can be done for relitavly cheap, and the FBody guys seem to have more experience with these trannys. Thanks for the help!

Strahley

iTrader: (4)

Mine (th350) isn't a daily driver, but I drive it about half the time to work during the nicer months. Around town it's no worse on gas than it was when I had he M6 in it. Cruising at ~70mph it sits around 3k rpm with 3.42s. Once I switch to 3.73s/3.90s (dunno which yet) I'll probably just slow down to 65 or so, to keep it around 3k rpm

I like it much more than the M6 though

TurboAv

iTrader: (6)

Mine is. GTO here as well. 65mph is 3050rpm with 3.46's and 26" tall tires(255/45r17). The only other gear ratio available to us is 3.07, so you better have crazy power to run that in the 1/4. Hopefully I will soon enough. I told my wife I need the nitrous so I could swap to 3.07's and get better RPM on the streets, lol. Working so far.

I used my stock 6 speed crossmember and the stock 6 speed tranny mount. You don't need to cut the ears off the trans either. It will bolt right in so you can mount the dust cover shield on it.

My MPH in the 1/4 with the new TH400 is the same as I was able to get with my old 6-speed setup on street tires. 12.28@113.3 1.81 60ft