There will deff be different oponions about these two but here is my experence..... 400 is deff a heavier built trans for working BUT it kills horsepower and IN MY EXPERENCES does not hold up to the abuse like a 350 does. If I was going to beat on it at all I would (and currently running) with the 350 turbo...... Now If you really want a good transmission build you a powerglide (my next buggy will have) and free up horsepower and out last both turbo's.