Originally Posted by gary c

It's not the HFCs that cause rasp! There's major restriction in those OE cats and the factory exhaust is designed to handle it. Once that restriction is released the OE exhaust can't handle the increased volume, resulting in rasp! HFCs or ART pipes using the factory exhaust won't sound good unless you're deaf!
Gary

Originally Posted by gary c

It would be interesting to get a tune before adding all our boltons and then get a tune with each addition. That way everyone could see where the most gains are without listening to manufactures b.s.! Motordyne gave us a good idea of what his gains were by adding spacers then the MREV manifold, I don't doubt his word! Having seen up close what OE cats look like I don't doubt replacing them with ART pipes or HFCs doesn't offer major gains in WHP and torque there too! I've been thru 5 different exhaust systems (two sponsored) starting with OE and my final choice HKS, due to quality (except the crossover issue) and sound! You can't believe what manufactures tell you so you end up stacking WHP gains they claim! A tune is the only true way to see gains, it only costs 1/3rd of what a ARK exhaust costs.
Gary