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Anybody know how to regain a bit of back-pressure on straight pipe exhaust?

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Old 12-09-2014, 05:54 PM   #1
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Anybody know how to regain a bit of back-pressure on straight pipe exhaust?

Its a considerable straight pipe, still have the cats on just no muffler.

About 2.25 inch pipe used to replace the stock "Y-Pipe" basically comes in the same format as the stock do, they meet under the front dash part of the passenger seat but do not connect as a "Y" and they both face down just under the passenger seat.
Obvious that much of the back pressure is lost, how would we be able to regain that pressure without adding a Muffler. Still want it to be a considerable "Straight Pipe".
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Old 12-09-2014, 05:59 PM   #3
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Not a great idea for motor longevity. Just my .02
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Old 12-09-2014, 06:07 PM   #4
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You could put the stock exhaust back on to increase back pressure.
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Old 12-09-2014, 06:39 PM   #5
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Back pressure isn't the issue. I'm probably wrong but the exhaust gasses are running out of pipe before they can scavenge the exhaust gasses behind them. No way that I know of to fix it in that short of run. You could add mufflers but that's not what you want to do.

Supercharger will fix the power issue.
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Old 12-10-2014, 06:41 PM   #6
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Think this effect the engine in the long run?
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Old 12-10-2014, 08:11 PM   #7
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not sure if back-pressure is beneficial in any sort of way on a 4 stroke.

the guys that made the engine in the picture are lots smarter than me and it doesn't look like they gave two shits about having back-pressure. looks like they were trying to keep it minimal to me. . . . .

on 2 strokes, backpressure was a side affect of acoustical tuning; not acoustical as in sound quality to the ears, but using sound waves to "pulse" wasted fuel back towards combustion
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Old 12-10-2014, 08:29 PM   #8
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Quote:
Originally Posted by 92dlxman View Post


not sure if back-pressure is beneficial in any sort of way on a 4 stroke.

the guys that made the engine in the picture are lots smarter than me and it doesn't look like they gave two shits about having back-pressure. looks like they were trying to keep it minimal to me. . . . .

on 2 strokes, backpressure was a side affect of acoustical tuning; not acoustical as in sound quality to the ears, but using sound waves to "pulse" wasted fuel back towards combustion
Yes, the F1 guys are smarter than all of us but they rebuild those engines after every race. I'm not sure who wants to do that to their Tacoma.
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Old 12-10-2014, 08:31 PM   #9
With sufficient thrust, pigs fly just fine.
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Quote:
Originally Posted by Rock Lobster View Post
Back pressure isn't the issue. I'm probably wrong but the exhaust gasses are running out of pipe before they can scavenge the exhaust gasses behind them. No way that I know of to fix it in that short of run. You could add mufflers but that's not what you want to do.

Supercharger will fix the power issue.
Quote:
Originally Posted by 92dlxman View Post


not sure if back-pressure is beneficial in any sort of way on a 4 stroke.

the guys that made the engine in the picture are lots smarter than me and it doesn't look like they gave two shits about having back-pressure. looks like they were trying to keep it minimal to me. . . . .

on 2 strokes, backpressure was a side affect of acoustical tuning; not acoustical as in sound quality to the ears, but using sound waves to "pulse" wasted fuel back towards combustion
This ^^^^

Back pressure is bad, all around. Scavenging is where its at.
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Old 12-10-2014, 08:39 PM   #10
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Quote:
Originally Posted by 92dlxman View Post


not sure if back-pressure is beneficial in any sort of way on a 4 stroke.

the guys that made the engine in the picture are lots smarter than me and it doesn't look like they gave two shits about having back-pressure. looks like they were trying to keep it minimal to me. . . . .

on 2 strokes, backpressure was a side affect of acoustical tuning; not acoustical as in sound quality to the ears, but using sound waves to "pulse" wasted fuel back towards combustion
Race cars are at high RPM 99% of the time. Exhaust scavenging is only beneficial in the low to mid RPM range.
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Old 12-10-2014, 08:42 PM   #11
With sufficient thrust, pigs fly just fine.
chris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shedchris4x4 is one of the sharper tools in the shed
 
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Quote:
Originally Posted by Rock Lobster View Post
Your right about them not caring about backpressure but at high RPM where race cars run at 99% of the time, backpressure doesn't matter. Backpressure is only beneficial in the low to mid RPM range.
"Back pressure" at any RPM is bad.
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Old 12-10-2014, 08:43 PM   #12
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Quote:
Originally Posted by chris4x4 View Post
"Back pressure" at any RPM is bad.
Change back pressure to scavenging and that's what I mean.
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Old 12-10-2014, 08:49 PM   #13
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The cats create all the back pressure needed for whatever you think backpressure is needed for.

Scavenging is a function of tube length. It's why headers are often built to be equal length tubes, and why the collectors on open headers are various diameters and lengths.

In my drag racing days (well before computer modeling) we'd install collector extensions on a car and make passes. Cut off some extension and make more, repeat till we figured out the optimum length for that particular engine build and car set up.

Sometimes you had more low RPM end results, sometimes in the high RPMs. For us, the overall ET was what mattered. For anything else, the use of the vehicle is what matters.

Grunt or top end?

Problem is, most folks with streetable vehicles want it all. And reality says every choice you make is a compromise of something else. So, know what you want to accomplish (and why) then pursue that.

As Rock says, boost fixes more than dinking with I/H/E bolt ons, particularly on modern, fairly efficient engines.
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