I run 2 Garret turbos (GTP-38, A/R 1.00 on the compressor side and .68 on the turbine side) on a 515 ci big block Chevrolet. Makes 11 psi boost with waste gates open and 19 psi with them closed. I plan on using the same turbo on the 302 GMC I am now building, it will be EFI using Mega Squirt controller. I also put a GMC 4-71 supercharger on the straight 8 Buick in the #1950 Buick, it makes 8 psi boost, that really helped the performance. Cya