Mark30

What would be your choice between the two behind a stock lq4 in a GM A-body.

Game ova

400, because it would be future proof.

MaroonMonsterLS1

TH350 because around me cores are way cheaper and I can build a 500hp unit for about $150

bbond105

TH350 because it is lighter.

Tuskyz28

350 is lighter but the 400 guts are beefier. Hard choice..... but I say 400 as well. A body cars are pretty heavy.

Game ova

Seriously doubt that the extra 15 pounds of the 400 will degrade performance. I'd rather have the durability, put it in and forget about it.

MaroonMonsterLS1

a 400 is about 10-15 lbs heavier overall and 90% of that is rotating mass. But I agree...unless you are a class racer looking for every hundredth...it's not going to matter. For a stock LQ4, I would honestly go with whichever one you can find more cheaply. Around me, th350 cores are cheap and th400 cars are getting expensive.

Dual feed the directs
LEAVE the 1-2 accumulator alone
Block the 2-3 accumulator
Hardened Int. Roller clutch race
Shim PR Spring
Block the Low Control Valve Inboard
Drill the Separator Plate
You can block and loop the governer too, very easy, but that's only if you want full manual control

Do these things and you have a unit that will survive a long time at 500hp so long as you don't do a stupid burnout and explode the sprag.
These are super easy and very cheap to build.

RockinWs6

TH400 is a no brainer, to make that 350 hold up @500hp good luck. Stock the 400 will take a hell of a beating, the 350 forget it. I've built 100s of both trust me on this.

MaroonMonsterLS1

Then you must not do a very good job building them then?
500 is pretty easy for a th350, so long as you can avoid blowing up the intermediate sprag

RPM WS6

iTrader: (3)

I agree with @MaroonMonsterLS1 above. 500hp isn't beyond the limits of a proper TH350. Old/stock or poorly built ones could certainly be a different story.