Tranny humpin' query - TH350 to TH400

[SafetyHelmet]

Made you look!

Quick question as I'm redoing the front floors. I eventually will upgrade the TH350 to a TH400, unless there is some way to keep a modified 454 (shooting for 600hp on pump gas) from blowing a TH350 apart. Will a TH400 need a larger transmission hump in the cab? I only want to redo the cab floors once, so if a TH400 does need more space, I'd like to figure out how much more it's gonna want, and cut some flooring for it.

Thanks!

 

[max 02]

You should be good to go.

 

[diesel4me]

I have not had to modify the floor tunnel on any vehicle when I swapped a TH400 in place of a TH350,though some might need to be,I dont think GM trucks do though,they only made one style floor for all the factory optioned transmissions...about the only mods I did to a few trucks was to cut out the shifter hole for a manual tranny, in place of an automatic...

GM used some TH350's behind big blocks factory in cars,they might not like 600+ HP,but I bet if built up right,one would hold up OK..
TH350's have less parasitic drag than a TH400 and weigh a bit less too...

I've had good luck with TH400's,but a friend who had a '71 Buick GS 455 went thru 4 of them in a few months,and he put a TH350 in it instead,and it lasted 4+ years till he sold the car...I've had a few TH350's lose reverse,or not want to shift into forward gears right away...never "blew one up" though..

 

[SafetyHelmet]

Awesome! Thanks for the info, guys.

 

[Upstate]

I have not had to modify the floor tunnel on any vehicle when I swapped a TH400 in place of a TH350,though some might need to be,I dont think GM trucks do though,they only made one style floor for all the factory optioned transmissions...about the only mods I did to a few trucks was to cut out the shifter hole for a manual tranny, in place of an automatic...

GM used some TH350's behind big blocks factory in cars,they might not like 600+ HP,but I bet if built up right,one would hold up OK..
TH350's have less parasitic drag than a TH400 and weigh a bit less too...

I've had good luck with TH400's,but a friend who had a '71 Buick GS 455 went thru 4 of them in a few months,and he put a TH350 in it instead,and it lasted 4+ years till he sold the car...I've had a few TH350's lose reverse,or not want to shift into forward gears right away...never "blew one up" though..

Usually not enough gear combined with heavy car and plenty of torque kill 400. The lower gear in the 350 does make up for some of the issues of lack of gear.

See it more in trucks but that car is plenty heavy like a truck.

 

[Hogback Fabrication]

Usually not enough gear combined with heavy car and plenty of torque kill 400. The lower gear in the 350 does make up for some of the issues of lack of gear.

See it more in trucks but that car is plenty heavy like a truck.

Stock TH350 is 2.52 and stock TH400 is 2.48, they're practically identical first gears.

TH400's are built MUCH stouter than 700R4/TH350's.

 

[Upstate]

My wife noticed the .04" difference.

All seriousness, I am sure you know this but the TH350 has less parasitic loss than the 400, combine that with a lower first and second gear and I have seen it hold up.

Back in the early 90s I hung around with Scott Gliden who was all about efficiency and pushing the envelope on drivetrain. He ran 8.5 rear on 8 second car with a th350, super consistent and almost never broke.

This part I may be talking out of rear on butt, from what I remember the 350 was not as picky with fluid pressure either.