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Old 05-25-2010, 03:13 PM   #1
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Default Tuned pipe performance vs. engine displacement

I'm assuming most tuned pipes are designed for .21 displacement engines.

What is the effect of using them on larger displacement engines?

Using the Jammin' pipes as an example, if a JP-2 gives more high end, a JP-3 more low- and mid-range and a JP-4 gives more mid- and high-range for a .21 engine, what performance effect would those same pipes theoretically have on a .30 engine?

Would the RPM range of the expected performance boost be moved up or down from what would be expected for the .21? Anyone know the real deal?

Thanks for any info,
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Old 05-25-2010, 06:14 PM   #2
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Well it really isn't so much to do with displacement as it is the port timing of the motor.

The timing of a .21 vs. that of a .28 are very similar, and the design of the pipes are "tuned" to the exhaust pulses of the engine. The timing of the pulses are more tuned to the exhaust.

Most of the exhaust is sent back into the engine, that it how a expansion chamber works.

Beleive it or not, that small hole in the end of the stinger is big enough to flow a .28 engine
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Old 05-26-2010, 07:05 AM   #3
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Originally Posted by FLHX1550 View Post
Well it really isn't so much to do with displacement as it is the port timing of the motor.

The timing of a .21 vs. that of a .28 are very similar, and the design of the pipes are "tuned" to the exhaust pulses of the engine. The timing of the pulses are more tuned to the exhaust.

Most of the exhaust is sent back into the engine, that it how a expansion chamber works.

Beleive it or not, that small hole in the end of the stinger is big enough to flow a .28 engine
+1

The "pulses" of the exhaust work to scavenge the flow. A longer pipe means it takes longer for the pulse to travel the length of the pipe, therefore the pulse is reflected back at the port at lower RPM... that's why longer pipes are for lower RPM use. Shorter pipes are "tuned" to higher RPM.

Tuned in this case literally means what it sounds like... tuned to a particular frequency, like a musical instrument... and the tuning is done by length.
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Old 05-26-2010, 05:15 PM   #4
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Quote:
Originally Posted by FLHX1550 View Post
Most of the exhaust is sent back into the engine, that it how a expansion chamber works.
Really?



Quote:
Originally Posted by DOMIT View Post
+1

The "pulses" of the exhaust work to scavenge the flow. A longer pipe means it takes longer for the pulse to travel the length of the pipe, therefore the pulse is reflected back at the port at lower RPM... that's why longer pipes are for lower RPM use. Shorter pipes are "tuned" to higher RPM.

Tuned in this case literally means what it sounds like... tuned to a particular frequency, like a musical instrument... and the tuning is done by length.

I'm familiar with the way an expansion chamber/tuned pipe works. Length is critical for sure, but I'm thinking a larger displacement engine needs a longer pipe, so a pipe designed for a smaller displacement engine would have an effective wave at a higher RPM range if fitted to a larger displacement engine.


What I'm asking is if anyone knows, from experience or education, how a pipe designed for a .21 will perform on a .30. I'm guessing the RPM range of the "boost" will be higher with the pipe on a .30. How much higher is what I'm wondering... ...negligibly higher? ...significantly higher?



Take it easy,
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Old 05-26-2010, 07:17 PM   #5
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Originally Posted by desmobob View Post
I'm familiar with the way an expansion chamber/tuned pipe works. Length is critical for sure, but I'm thinking a larger displacement engine needs a longer pipe, so a pipe designed for a smaller displacement engine would have an effective wave at a higher RPM range if fitted to a larger displacement engine.
The length decides how long it takes for the pulse to return, and punch a small amount of exhaust back in to the exhaust port making sure you got as much air/fuel mixture in to the cylinder as possible. The small amount of exhaust supposedly is needed since the glowplug isn't actively feed, but I'm not sure about this. The wave travel time is identical regardless of the displacement of the engine.

Quote:
Originally Posted by desmobob View Post
What I'm asking is if anyone knows, from experience or education, how a pipe designed for a .21 will perform on a .30. I'm guessing the RPM range of the "boost" will be higher with the pipe on a .30. How much higher is what I'm wondering... ...negligibly higher? ...significantly higher?
No difference what so ever. Boost will likely be less in %, but in the same RPM range. Reason? Flow. The pipe is designed for a engine a fair bit smaller, with a lower flow through it. At peak RPM a pipe designed for a .21 on a .30 could very well be limiting. At lower revs your never going to notice it. (Flow is why the Buku pipes have 2 exhausts.)
Pipes are always a compromise. To get good idling, and reasonable low rpm fuel economy you have to have enough resistance not to flood the pipe with unburnt fuel/air mix, and that makes it run with a tad to much resistance at the high end rpm's making you not fill the cylinder to the same extent. With less resistance at full speed you could run slightly leaner and still have the same amount of fuel in the cylinder, getting a bit more power, and revs...

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