I found a noticeable difference on a 136 cubic inch four cylinder toyota engine back in the day.

Lately it seems there's a dyno on every street corner and the wealth of information they produce has been illuminating, for those of us who care to find out, at least. Torque increases below the torque peak are what I notice, and that's where a set of headers shines on the street. I really don't care about max rpm horsepower. What do I feel when the light turns green is more important, and headers improve that. Also, any increase in mileage helps me be able to drive my car more, so that's a good thing too.

R.