We did a flow test on the GM '54 Corvette Split exhaust manifold. the flows were about 22% greater than a stock single outlet exhaust system. The comparison with the headers showed they were allowing the movement of about 28% less flow than the headers would allow. Flows do mean something and I interpret that as being useful to make horse power. The best flows we did obtain came from the Fenton and Shop manufactured tubes.
Normbc9
