exhuast/back pressure

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Jul 8, 2008 | 05:21 PM

83maverickf-100

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exhuast/back pressure

i have recently eliminated my cat and it is a huge gain in mpg i am geting around 20 know istead of 13 (small power gain) - stock muffler stll on it though i am wondering if i get rid of it i woudn't have enought back pressure? or will it run like crap? still got a log maifold i have heard it with no exhaust period with stock log on it not very loud so i am not worried about noise untill i get headers(anyone tryed something other than clifford or headman sound diffrence?)

Jul 9, 2008 | 12:47 AM

dan91ford150

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How did you go about the cat work? I'd like to do the same thing to mine...
As long as you don't go with a really big pipe, or too short I don't think it will affect the "backpressure"...

Jul 9, 2008 | 05:13 AM

Motorhead351

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Seems a single 3" pipe would be as far as youd wanna go with a single, also seems your cat was seriously clogged.

Quote:

How did you go about the cat work?

Not suggesting you should or shouldnt remove the catalytic converter but on your 91 efi, the O2 sensor is before the catalytic converters. If the catalytic converters were to disappear, it wouldnt affect the engines ability to operate, as the engine has no idea if the catalytic converter is there or not. Youll be left with a tube from the air pump that you can let hang or weld into the exhaust.

Just be aware, if your vehicle requires inspection/ emissions testing, you will fail. Its also illegal to remove a catalytic converter unless its faulty.

Jul 9, 2008 | 08:49 AM

5.0Torx

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Quote:

Originally Posted by 83maverickf-100

going from 13 to 20 with a single cat removal is impressive. that was one seriously messed up cat.

anyways, how much backpressure are you looking for? have you, or anyone else on this board, acutally measured backpressure and compared different exhaust setups / backpressures to performance and fuel economy?

when i cut my exhaust out i fired it up with the open log manifold and it wasnt that loud. why? its not a very powerful motor. and i doubt putting a header on an otherwise stock 300 is going to take it from "not that loud" to waking the dead. I dont really know how you could make an engine louder than open manifold/header anyway.

i would highly recommend you rip everything after your manifold and downpipe out and replace it with 2.5" tubing with a muffler of your choice. I ntoiced a pretty significant difference when i did that to mine, stock log crap and all.

lastly, i highly doubt anyone here has spent $300 on a header twice to compare the infintessimal sound differences between the two. just pick one

Jul 9, 2008 | 05:25 PM

Harte3

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From: Spokane, WA

That an engine "needs" back pressure is a myth that was debunked by David Vizard and others way back in the last century. An O2 sensor bung can be welded in to the exhaust pipe ahead of the muffler, plumb in a pressure guage...like a dual vac/pressure guage... and one will know what the back pressure is. IIRC under 5# is acceptable.

With the 300's poor breathing head scavenging is what helps. Too large of an exhaust pipe can reduce scavenging. The 2.5" that 5.0Torx mentioned is probably as good as it gets on an otherwise stock set up or even a mildly modified build.

Jul 10, 2008 | 05:44 PM

83maverickf-100

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its a samefull looking red neck butch job lookin exhaust stock log head and down pipe to asorted pipe i found at my dads shop, with cherry bomb glass pack lol all welded in the pipe isnt to bad lookin underneath and comes out ahead of the tire it's just i cheaped out hanging it NO not chicken wire, angle iron wrapped around and dilled into old hanger slots

*** far a cat and muffler removal i gust cut it off peroid and replaced with staight random pipes of what fit

lol i tipped the cat ofter it was out and hit it with a hammer the biggest pice left of it when all the garbage came out was about 1 inch if it was lucky!!