Most hp gains are from adding Turbo's or superchargers, a good dual down or header will give you modest hp gains. Plugs and coil paks are ok, but do not really increase the HP more than they decrease the capital in your wallet. I would say that the dual down to cat back will give you 10hp, but the thrill of the difference gives you 100hp by the SOP (seat of the pants).Right now I have a 2008 Rabbit straight piped. PSA: Do NOT straight pipe your rabbit if you drive on the highway. It sounds great around town with lots of backfires when you downshift but the drone on the highway is unbearable. I just ordered an ECS tuning short ram intake, spark plugs, Audi R8 coil-packs, and a cat-back exhaust. Once these parts come in I will install them and run a custom stage one tune, thanks to a friend who tunes Volkswagens. With these upgrades how much horsepower and torque will I have?
I have been running with Straight pipes on older 4 bangers, ie: MG's and AH Sprites MK1 where the muffler on them were more of a resonator on a newer car.
yep, the droning on highway runs could be deaf dealing to your ears, but always added to the thrill that a 948, 0r 1100CC engine could muster.