Cat delete with LM1 sucks

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Apr 11, 2007 | 11:52 PM

#16

LiENUS

Registered User

Joined: Jul 2005

Posts: 747

From: Baton Rouge, LA

Quote:

Originally Posted by JP95ZM6

Thanks for the explanation. I think there must still be increased backpressure as an unwanted side effect when the valve is closed, which must be more than offset by the resonance benefit, then.

So, that means it the Exup valve must close at higher RPMs, since the resonant frequency is higher with the shorter effective length to the valve? I can't see mine when I'm driving around, but I always thought it was closed at idle. Hmmm.

It seems to reduce noise a bit when closed, too.

I can't find any definitive information on the EXUP valve. I know its there partially for emissions. Most sites claim its to increase velocity by altering the effective diameter of the pipe, which seems plausible. Other sites are claiming its only closed during the overlap period on the camshaft, which seems less plausible as the valve would have to be moving hella fast to accomplish that feat. Looking at the design of the valve I would have to guess that its altering the effective diameter of the pipe through some strange resonance effect, similar to how two-stroke engines will have a resonance chamber, this one is just a resonance chamber that changes with the engines rpm.

Apr 12, 2007 | 04:27 AM

#17

95ttoplt1

Registered User

Joined: Jun 2004

Posts: 411

They use those exhaust valve on alot of snowmobiles as well, they are closed at idle/low rpm and open as the RPMs go up. I had them on a SKi-doo 800 open mod and they work great. They really increase the bottom end. It dyno'd 186hp, not to shabby for a 800cc 2 cylider engine.