I've transplanted a 18,000 mile Lq9 into a 70' Chevelle... Headers, 3'' exhaust, unrestricted 4'' intake, mail-order tune... Gm says it makes 345 horsepower and 380 ft lbs of torque, but with the slight modifications I have made, what kind of flywheel horsepower/torque should I expect... Thanks!

 

400HP!
CarCraft dynoed one a few years back.
Jarhead

 

Yeah, with an aggressive tune, 400+ hp

 

If the motor is out of a Escalade then I think they said 400HP and 380 from a Denali

 

400 easy