Russm
Member
I recently put a new 330 hp GM crate engine in my '69 and was all set to put a set of plated headers and probably Flowmasters on it when I ran into a guy that told me something that really set me back. I would have ignored the guy, because what he told me is inconsistent with everthing else I've heard. But I'm hesitant to dismiss what he said because he seems to know more about Holley carbs than the techs at Holly. He tore mine down in about five minutes, diagnosed the problem, made a couple of modifications to stock design features, totally cleaned it out, set all the adjustments (all on the bench). I took it home, put it back on my truck and it ran perfectly from the minute I put it on. I figure a guy like that deserves a good measure of credibility.
So now that you have some background this is what the guy told me: He said that a high flow exhaust actually hurts horsepower at lower rpm's. He said this is not an issue with a manual transmission, because you can build 3 to 4 thousand rpm's before releasing the clutch, but with an auto transm, you actually lose power from zero to 3000 or 4000 rpm's by putting headers, dual exhaust and high flow mufflers on. He confirms that once you get above 4000 to 5000 rpms that the high flow exhaust gives you more horse power, but that for low end power, which is what most of us want for rodding around town with an automatic transm, you get more power (as much as 40 or 50 horse power) with a stock exhaust manifold, a crossover pipe, and normal mufflers. He even had a technical explanation for why this is true, although I didn't understand a word of it. By the way, part of his opinion on this was that anyone in the business of selling exhaust systems doesn't want you to know this, because they obviously make money selling headers and expensive mufflers.
I think most of us novices believe the more flow, the more power, but does anyone out there have the true expertise and/or experience to dispute what he told me?
So now that you have some background this is what the guy told me: He said that a high flow exhaust actually hurts horsepower at lower rpm's. He said this is not an issue with a manual transmission, because you can build 3 to 4 thousand rpm's before releasing the clutch, but with an auto transm, you actually lose power from zero to 3000 or 4000 rpm's by putting headers, dual exhaust and high flow mufflers on. He confirms that once you get above 4000 to 5000 rpms that the high flow exhaust gives you more horse power, but that for low end power, which is what most of us want for rodding around town with an automatic transm, you get more power (as much as 40 or 50 horse power) with a stock exhaust manifold, a crossover pipe, and normal mufflers. He even had a technical explanation for why this is true, although I didn't understand a word of it. By the way, part of his opinion on this was that anyone in the business of selling exhaust systems doesn't want you to know this, because they obviously make money selling headers and expensive mufflers.
I think most of us novices believe the more flow, the more power, but does anyone out there have the true expertise and/or experience to dispute what he told me?
