Hey everyone, I have a base C6 corvette ls2 block. So far I have dome longtube headers with a cat-less mid pipe, Cold air intake and a dyne tune. Im experiencing a loss in low end torque which I don't like. Is this related to back pressure from having no cats at all? Or what could be a reason for this. The headers I'm running are 1 7/8 to 2.5" axle back again no cats. I also have a Vitesse throttle controller could this have anything to do with it?

Furthermore looking into the next perforce upgrades for my car, how much benefit would I receive from a intake manifold such as an MSD ported manifold and a re-tune. Im shying away from a cam as of now because of reliability. What other performance upgrades would benefit the ls2. Thanks guys!!!!

 

Question. How do you pass smog in California with Long Tubes and no Cats ?

 

Back pressure is an urban myth. Back pressure does not help low end torque. The last thing an engine wants is something restricting the ability of spent gases to exit the cylinder. Emptying the cylinder so it can be reloaded with fresh air involves a few variables. Changing the exhuast manifold impacts exhaust gas velocity and scavenging. 1 7/8" headers at very low rpms (e.g., under 2,000) might result in the exhaust gas velocity being slower than smaller diameter headers, but not worse than the LS2 stock manifolds. The bottom line is headers did not kill your low end torque, but they will change the exhaust flow. As a result, the tune needs to be changed at low rpms to reflect this. Without seeing your tune, I suspect the dyno tune focused on WOT and ignored part throttle and low end drivability. After adding my CAI and headers, my car was more responsive at low rpm and mpg went up 1 mpg (when not being beat upon. ) When I tuned the low end I spent a fair amount of time driving around at part throttle and below 3,000 rpms to log data to get my fuel trims and spark optimized for change in air flow caused by the mods.

A ported FAST intake and a re-tune would be excellent next steps. The FAST intake will provide solid midrange and top end gains over the stock LS2 intake manifold.