Exhaust System

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Jul 26, 2013 | 01:06 PM

6brau

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Joined: Apr 2013

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Exhaust System

Hey guys I want to get a new exhaust pipe for my 91 f150. Does the size of my engine matter when getting a new exhaust? Also does the exhaust come in pieces that have to be welded together?

Jul 26, 2013 | 07:37 PM

RIKIL

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Joined: Sep 2008

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Size Does matter, don't listen to what women say.

For a gas motor you can't go too large, back pressure is needed to create velocity to move exhaust gases.

Jul 26, 2013 | 08:03 PM

86LariatXLT

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Joined: Jul 2012

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From: Los Molinos, CA

Dont get anything over 3". Id recommend 3" if its a 351 and 2.5" for a 302. Ive got 3" on mytruck and i like it, but 2.5" may be just as good. Larger pipes allow exhaust gases to linger instead of working like a siphon and pulling all of the exhaust out of the engine.

Jul 26, 2013 | 08:23 PM

RIKIL

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Joined: Sep 2008

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Quote:

Originally Posted by 86LariatXLT

Larger pipes allow exhaust gases to linger instead of working like a siphon and pulling all of the exhaust out of the engine.

That's what I said, just more words.

Maybe this will help..

http://www.allfordmustangs.com/forums/attachments/5-0l-tech/90293d1265774832-exhaust-diameter-tuning-exhaust-size-tuning-guide.jpg

Jul 26, 2013 | 09:28 PM

f100beatertruck

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Joined: Apr 2003

Posts: 2,408

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From: Parkesburg PA

Quote:

Originally Posted by RIKIL

Size Does matter, don't listen to what women say.

For a gas motor you can't go too large, back pressure is needed to create velocity to move exhaust gases.

It's not back pressure. There's a reversion pulse that helps scavenge the exhaust and large pipes can cause that pulse to be weak or non existent. Also, different mufflers, cats, pipes, etc can make the engine see different things. For example, given a constant diameter front to back, flowmaster mufflers need a tail pipe. I forget the exact amount but I think it's something like 18". In other cases a large increase in area 'looks' like the end of the exhaust and now you've changed the tuned length of the system.

With that said 2 to 2.5" single for <350, 2.5 to 3" single >350. The 460 can handle a 4" but since it's such a low rpm motor a 3" is usually good. For true duals 2" on the 5.0, 2.25 on the 5.8 and 2.5 on the 7.5... That's just a ball park, I know people running the Magnaflow 15003 tailpipe on 5.0 trucks with 2.25" pipes between the Y pipe and the muffler.

If you post what size engine and what you're looking to do it would help. Duals, single, performance, stock replacement, etc.