I don't know what tranny I should go for. I should have around 300hp with my new 350 setup. I bought a TH350c with less than 1k miles and with a shift kit but someone urged me not to use it because "the torque converter clutches would blow up into the tranny and ruin the tranny if I didnt flip the toggle switch at the right time", don't know if thats true. And I dont know how exactly to wire the switch. Anyhow he has a good condition th400 sitting around he would sell me for $300 but I read somewhere that the Th400can rob anywhere from 30-40HP. Is there any proof that the TH400 will rob that much HP?

 

All automatic transmissions rob anywhere from 18-20% of engine horsepower. Manual Transmission rob 13-15%. So, either way you go, you will lose power. That's just the way it goes. If you're running 300 at the crank now, you should expect a 50-60hp loss through the drivetrain.

As for your transmission choice, if it has to be an automatic, i would go with a th400, or a 700r.

Have you considered doing a manual swap?

 

I swapped in a built-up TH350 last weekend. It was a straight forward swap from the TH200 with no modifications.