Cal Club Autocross Forums

As some know my 1990 C4 Corvette is having it's engine rebuilt. Because of my impending job situation the engine is just getting a straight rebuild, stock configuration, no mods. My mechanic is trying to convince me to swap out my Monza style muffler (really a glass pack) for standard mufflers. The logic is that the little bit of back pressure they will provide will improve drivability.
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Given that I have always thought of backpressure more as an enemy of performance than a benefit, my question is should I go the muffler route. Money is tight, so I want to understand the concept better. I figure this is the most knowledgeable group I know.

Thanks
Art

IIRC, the theory is cam timing involves an overlap period when both intake and exhaust valves are both partially open. With bigger cams and lower rpms, enough fuel sneaks out to the exhaust without being compressed and burned to make it worthwhile to add a little backpressure to thwart that. But at high rpm there isn't time for that fuel to escape so the back pressure hurts performance instead of helps.

So a little back pressure can mellow out a bigger cam. I would think stock cams would not benefit much from this. And I wouldn't believe a word of it anyway unless I saw it on a dyno with my own eyes.

Keep the glasspacks, chambered mufflers are quite a bit more restrictive.

Seeing as you still have cats on your car I can't see a more restrictive muffler helping anything.

Generally back pressure helps low torque, hurts high HP. I don't think a corvette really needs more low torque for 'drivability'.

Regardless, if you wanted a 'stock type muffler', I'm sure you could find a used one DIRT cheap somewhere from those who've upgraded.

Jay W

Bobby is right... if you have stock catalysts, mufflers are just for sound quality.

Thanks guys appreciate it.