back pressure and size
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Junior User
Joined: Sep 2010
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back pressure and size
My 79 has 2 1/14 inch pipe after the initial 2" comes down about 2 feet offthe manifold. Is it fine having the bigger pipe? And there is no catalytic converter. Will there be a loss of power or anything like that? Or damage to the engine?
Post Fiend
Joined: Dec 2007
Posts: 8,521
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From: Lost
The pipe should be fine. My 80 came with 2.25 from the manifold back thru the cat, muffler, and tailpipe, so 2.25 certainly isn't too big for a 300. I recently had it all replaced (except the first couple feet), and went 2.25 full length and flowmaster muffler. Works fine, and sounds even finer.....
Postmaster
Joined: Mar 2005
Posts: 2,949
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From: Earth
FYI, the idea that an engine needs some sort of "back pressure" is a huge bunch of hooey. The exhaust should be big enough to not offer any restriction, but not so big you lose exhaust velocity and the associated scavenging effect.
Moderator
Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
Too small and the exhaust bunches up on itself and plugs up. Kinda like an interstate full of cars bunching down to two lanes.
Too big, and the speed slows down inside the pipe, and the exhaust behind it bunches up. Kinda like an 8 lane highway but everyone in front keeps slowing down and no one can get around them.
On mine, I have a 2.5" all the way back, and it works great.
Post Fiend
Joined: Dec 2007
Posts: 8,521
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From: Lost
On the other hand, too large pipe, and the velocity is lost, which is key to helping to pull the spent air/fuel out of the combustion chamber. You don't want to rely solely on the push of the piston to get rid of the old gasses, making way for the new......
Senior User
Joined: Mar 2010
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I run 2.5 all the way from the EFI manifolds... from past threads here that is about max you want to go tho. some even do duals at 2.5 with great results from what I read but need a ton of intake mods to do so.
The 300 has plenty of exhaust stock if no head work is done to it as thats the bigest issue with it is, the intake side IMO
stock for mine was 1 7/8 inch iirc? out the back. pre EFI
The 300 has plenty of exhaust stock if no head work is done to it as thats the bigest issue with it is, the intake side IMO
stock for mine was 1 7/8 inch iirc? out the back. pre EFI
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Postmaster
Joined: Dec 2006
Posts: 3,603
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From: Spokane, WA
High-flow, 3-way Cats are available at a reasonable price and only necessary if you like a bit cleaner air to breath...and to meet Federal regulations if it was originally equipped with a Cat. Other than that, there is not enough difference to make a difference in back pressure.
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