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Old 04-16-2013, 09:29 AM
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3 inch exhaust looking for back pressure?

I currently have 3 inch straight pipes on my truck, has a small block 350 with mild cam. I love the sound but i feel like it needs some back pressure. Seems as if since i have installed the straight pipes it has taking away some horsepower from the truck. Just wanted to see if anyone had any ideas of what i could do without affecting the sound that it has now to much because a muffler will quiet it down more than i would like. One of my buddys mentioned high flow cats??? Thanks I appreciate any feedback, open to all ideas

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Old 04-16-2013, 11:52 AM
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I'm struggling with the concept that you need backpressure to increase HP. If that were true, Top Fuel cars would have mufflers.

Now, if the increased flow of your exhaust system is causing the carb to run lean, that WILL cause a power loss. Rejet the carb.
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Old 04-16-2013, 12:11 PM
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I have seen where a large exhaust negatively affects the performance. It was on a stock s10 4.3L v6. They were hot rodding it, and went exhaust manifold back. There was a lot going on, but performance was worse.

A good way to determine if you have excessive backpressure, is to take a reading from in front of the mufflers. A Boost gauge stuck in the o2 bung will work fine. Any reading above 2 1/2 psi is excessive and could be costing some power. You might have to put a bung in. It can be used for o2 sensor tuning later.
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Old 04-16-2013, 04:24 PM
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back pressure is NOT a good thing. Sometimes having too large of a pipe will cause problems from inadequate velocity though, adding back pressure will make the problem worse- not fix it. It could also be that your tuning needs to be tweaked a little after the exhaust change too.

For a stock 350 with just a mild cam a single 3" is about right.
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Old 04-16-2013, 08:27 PM
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Quote:
Originally Posted by ap72 View Post
back pressure is NOT a good thing. Sometimes having too large of a pipe will cause problems from inadequate velocity though, adding back pressure will make the problem worse- not fix it. It could also be that your tuning needs to be tweaked a little after the exhaust change too.

For a stock 350 with just a mild cam a single 3" is about right.
sounds like he has 3" duals, as he says pipe(s)
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Old 04-16-2013, 08:34 PM
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Quote:
Originally Posted by joe_padavano View Post
Now, if the increased flow of your exhaust system is causing the carb to run lean, that WILL cause a power loss. Rejet the carb.
Common sense to the fore Joe, thanks for that.
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Old 04-16-2013, 09:49 PM
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headers and sometimes collector extensions,any more back pressure will not add power.
use a x or H pipe and you can buy super short mufflers,just enough to take a little off the top.
check my tread for a moderate 3 inch system,and many other members also posted their cars making noise
land shark,painted jester and a few you tube postings,quite a few actually
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