TH350 vs TH400

Formula1973

Formula1973

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OK, I want to throw this out to everyone. I am sure this has been debated before on this site.
I am going to be installing a transmission and rear end gears. I current have a 1975 400 motor. It is a good one, rebuilt and very strong runner. And a TH250lock up tranny behind it (don't ask).
Should I spend the $$ and go with TH400 and it's conversion? or just go with a TH350, which will be direct bolt up in my case. Both would be fresh transmissions.
I do plan on building the motor at some point to about 400HP, maybe even go with a 455. Not sure though.
I also plan on 3.55 gears and the car is a 1973 Formula.

Thanks !
 
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neither one. You should be looking at 700R4 or 200R4
 
then the 400 would be my choice. You need one with the BOP bolt pattern not the Chevy bolt pattern.
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If the T-350 is a new build with the modern upgrades for handling a 400+ Pontiac it will be fine, you can now build a T-350 to live behind 500 Ftlbs of torque. They are lighter and take less HP to turn so they can be a win/win. But if your car weighs over 4000 lbs you could be pushing the upper limit with a high torque engine.
But if you upgrade to a T-400 it will require a new driveshaft (shorter) and a new Slip Yoke (bigger) to make the T-400 work.
It may not be that much more to go to a 2004R that will basicly bolt up
 
Hi Everyone-

So my TH400 is finally in, with 3.73 gears in the back.
This is a great combination and I recommend it to anyone in the position I was in. I appreciate all the feedback.
So...here is my next question. What is the best radiator for my 73 Firebird? Any suggestions?
When I was moving lines around I noticed mine is quite old.
Thanks
 
If by best you mean the most efficient go for an aluminum radiator. I believe the firebird catalog from www.amesperf.com has some as well as other Pontiac vendors.
 
Any modification needed for an aluminum radiator? mounts?
I do not know much about them.
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You need to read the fine print of whatever radiator you buy. They make aluminum radiators that just drop in which is why I recommended a Pontiac vendor who one would expect would have already determined the ease of installation. If you look at the Ames catalog you will see they use Desert Cooler units that require no mods.
 
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