u/CraftyPotato8348

I have a VF Gen F Ls3 Senator (340kw) and I have had a full 3 inch exhaust system with a otr put on. It made around 260kw at the rear wheels, I’m not too fussed with power but a mate had a 2017 redline with the exact same exhaust and no otr and made more power, around mid 280kw (same tuner aswell) just wanted to see if anyone knows why this might be the case? Something to do with the factory hsv tune? Bigger rims being 20s over his 19s? Cheers :)