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20mm end cap too small? (pics)

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I have an 06 YZ450 and need it to be quiet on a private track we're building. I have a spare exhaust and installed this piece I had in the garage from my karting days. It seems to keep it really quiet and still runs well in the 5 minutes I rode around the yard. My question is, am I going to have excessive engine heat buildup due to such a small opening or is this not an issue?

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If you jet correctly for it you'll be alright. The stock WR muffler is significantly more restrictive than that and people run those week in and week out with no issues

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If anything you have richened up the air/fuel mixture (assuming you have the same jetting from before the add-on). The motor should run cooler.

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it should be fine as long as the jetting is the same, you could probably lean it out if you want some more power and crisper throttle responce, the way the AMA is going that will be standard in like 2 years :applause: and how quiet is it?

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If anything you have richened up the air/fuel mixture (assuming you have the same jetting from before the add-on). The motor should run cooler.

The engine will run cooler for sure but the exhaust temps will acutally be hotter because of the pressue of all that air trying to exit the muffler from that little hole. I experienced that when I put the quiet tip on my pro circuit T-4. Its no biggie.

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The engine will run cooler for sure but the exhaust temps will acutally be hotter because of the pressue of all that air trying to exit the muffler from that little hole. I experienced that when I put the quiet tip on my pro circuit T-4. Its no biggie.

A little baked-leg is always good for you:busted:

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If anything you have richened up the air/fuel mixture (assuming you have the same jetting from before the add-on). The motor should run cooler.
That's not necessarily true. That statement makes the assumption that the net throughput of air through the engine will be reduced by this exhaust. It might, of course, but that doesn't mean the AF ratio will change. Fuel is metered by the jets according to the air flowing through the carb, which is a function of the intake stroke, and is, to a large degree, independent of the exhaust system.

If the mass air flow through the carb were in fact slowed down significantly by whatever cause, the strength of the vacuum signal at the jets would also be reduced, so a smaller amount of fuel is delivered, in proportion to the smaller amount of air.

The effect of an exhaust system on jetting is far more complicated than that which appears to make sense on the surface, and is not always intuitive or predictable. An example is what happened when we put a WB R4 on our 250F. The pipe had a muffler core half again as large as the stock pipe and was much more open. The bike ran rich all the way up to the main jet, and we went down from a 42 to a 38 pilot.

You'll just have to run the bike and see what it does.

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That's not necessarily true. That statement makes the assumption that the net throughput of air through the engine will be reduced by this exhaust. It might, of course, but that doesn't mean the AF ratio will change. Fuel is metered by the jets according to the air flowing through the carb, which is a function of the intake stroke, and is, to a large degree, independent of the exhaust system.

If the mass air flow through the carb were in fact slowed down significantly by whatever cause, the strength of the vacuum signal at the jets would also be reduced, so a smaller amount of fuel is delivered, in proportion to the smaller amount of air.

The effect of an exhaust system on jetting is far more complicated than that which appears to make sense on the surface, and is not always intuitive or predictable. An example is what happened when we put a WB R4 on our 250F. The pipe had a muffler core half again as large as the stock pipe and was much more open. The bike ran rich all the way up to the main jet, and we went down from a 42 to a 38 pilot.

You'll just have to run the bike and see what it does.

Good info. Thanks.

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Thanks for the replies. I will run it and see.

Kurt, I don't have a dB meter but it's gotta be close to the dB level of a WR with a bit more bark.

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