performance exhaust (eisenmann) decrease power?
so i went to a pretty well reputated tuning company in the east coast last weekend to look around and ask about my future mods, and particularly, i asked how much power an eisenmann race would produce on my car.
the owner said it in fact is going to decrease power due to lowered backpressure compared to the stock system. is this true? seems hard to believe, because isn't the second most sought after effect of an aftermarket exhaust the power? (after sound obviously)
nonetheless, he said a tune would fix it and bump (he assumes) 40hp overall. he provides cobb tuning.
what do you guys think?