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Old 11-13-2017, 01:28 AM   #21
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that backpressure comment always gets me. you dont need any. it contributes to pumping losses. you can always tell who hangs out in old hot rod shops and who is an engineer by those kinds of comments.
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Old 11-13-2017, 04:05 AM   #22
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u saying that engineers think all that about back pressure because its a 'technical' thing rather than realistic?
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Old 11-13-2017, 03:58 PM   #23
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i didnt really follow that but the frank fact is you dont need "back pressure"

if you watch a simple video from Dave Coleman, R&D Engineer at mazda, he talks about how a header or down under, an extractor works. how the pulse wave of pressure travels at the speed of sound and the objective is to keep it from traveling from one cylinder to the other before the second cylinders valves open to push out exhaust gasses.

The idea of needing back pressure is ridiculous. think about what a pressurized system does and how it affects a pump. really all piston engines boil down to big pumps.

if you think of an electric pump pushing water down a pipe some restrictive forces would cause a current spike theoretically increasing the output momentarily to dislodge whatever was causing the restriction. relating it back to a piston engine, that blockage is back pressure but we dont have an electrical current in those that produces propulsion.

blah blah blah science.

you dont "need" back pressure for anything.
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Old 11-13-2017, 04:33 PM   #24
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Correct. Back pressure is not anything that's really needed. I think muffler companies make that up to sell their product.
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Old 11-13-2017, 05:03 PM   #25
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Yep. I drove my truck around for a while with open manifolds. It idled just find and drove normally. The noise was horrible but it worked fine. If back pressure was really an issue I'd think it would have shown its face in an engine with 250k on it.
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Old 11-13-2017, 05:09 PM   #26
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JP: i do wonder how that train of thought came to be. I dont know if its from the old muscle cars having a 1.25ID exhaust or what but its amazing how wide spread that opinion is.
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Old 11-13-2017, 05:14 PM   #27
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There's a motorcycle forum I used to be a prominent member of along with another guy who works at the place that bought Hooker Headers.

We used to have discussions about backpressure. He would say it was necessary and use his years of header design as his proof.

I built an exhaust for my motorcycle that had 0 backpressure, and it dynoed with gobs more power than his exhaust system did.

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Old 11-13-2017, 05:21 PM   #28
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Most things about exhaust systems seem to be loads of garbage. Frieburger (one of the Roadkill/Motor Trend guys) did a bunch of videos on the "Engine Masters" series testing exhausts. They bashed the crap out of some headers with a hammer, tested different pipe diameters, all sorts of things to separate the wheat from the chaff on exhaust. It's a really good series.
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Old 11-13-2017, 05:38 PM   #29
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i think if i had to use two words to describe my assumptions of that bike they would be "FUCKING LOUD" with my hands over my ears and screaming.
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Old 11-13-2017, 09:15 PM   #30
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Quote:
Originally Posted by street_rulerr View Post
i didnt really follow that but the frank fact is you dont need "back pressure"

if you watch a simple video from Dave Coleman, R&D Engineer at mazda, he talks about how a header or down under, an extractor works. how the pulse wave of pressure travels at the speed of sound and the objective is to keep it from traveling from one cylinder to the other before the second cylinders valves open to push out exhaust gasses.

The idea of needing back pressure is ridiculous. think about what a pressurized system does and how it affects a pump. really all piston engines boil down to big pumps.

if you think of an electric pump pushing water down a pipe some restrictive forces would cause a current spike theoretically increasing the output momentarily to dislodge whatever was causing the restriction. relating it back to a piston engine, that blockage is back pressure but we dont have an electrical current in those that produces propulsion.

blah blah blah science.

you dont "need" back pressure for anything.
yea dude i agree, its what i said on page 2.
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