We had a chance to use LS2edit and tune a 2005 C5 with a MN6 manual transmission
Car owner used the Ease PCM scanner to record testruns and then emailed me the recordings and the flash file from the PCM so I could custom tune while the only mod it has was a 3rd party aircleaner and airbridge.
After PCM tune then longtube headers and high flow CATS were installed and tested to see what those mods did for performance.

We see in the results the HP and Torque was before the tune, after the tune and then with the exhaust mods


Viewpoints :

Halltech aircleaner/airbridge gave no real gains and the intake airtemps were higher then outside temps were

Dynatech headers and highflow CATs without a retune had a loss of performance
With a tweak of the tune we then could get 20 flywheel HP gains but no torque gains

Stock exhaust then was designed very well by GM and spending $1,500 plus for headers are not needed for even the new Z06 using stock exhaust manifold handles 500 plus HP just fine.

Very cool!

Seems like modern cars get better and better every year, seems like at some point performance mods will be just for the heck of it and not for much more

I agree that most so called mods people hype to buy are really useless and in fact can hurt performance.

Much different then cars in the 1980s that were real smog losers so almost any mod helped but todays car powertrains do just fine stock and adding more performance only makes traction even worse and chance of breaking something due to higher torque much easier to happen