Re: Exhaust backpressure

["Dan Bubb" <jdbubb@ix.netcom.com>]

Isn't this the exception that proves the rule???
I'll think about it some more, but right now I have no explanation.
Dan

----- Original Message -----
From: Brad Sterling <bgsterling@earthlink.net>
To: Scirocco List <scirocco-l@scirocco.org>
Sent: Wednesday, August 08, 2001 12:08 AM
Subject: RE: Exhaust backpressure


> <snip Dan>
> So, my summary is that backpressure is not beneficial in any way, but
> the presence of pressure pulses, and how they are tuned and interact
> with other cylinders, can make a huge difference in engine performance
> or the shape of its power curve.
> <end snip>
>
> Okay, I've got to ask.  Up front, I'll say I've been enjoying this thread
> and learning a lot.  For that matter, I'm still not sure what side of the
> argument I'm on.  One of the things that keeps bugging me is the stock
> exhaust on my (ex) Yamaha FZR600.  I know we're supposed to be talking
cars
> here, but this may be relevant.  The California model of this bike (mine)
> came with an EXUP valve.  The EXUP was a servo-controlled valve that was
> located in the collector beyond the headers (4-into-1).  In essence, the
> valve was a half of a cylinder.  At lower RPMs, the solid part of the half
> cylinder would be turned into the path of the exhaust.  I assume this is
> limiting flow and creating backpressure.  As RPMs would increase, the
servo
> motor would turn the half cylinder so the solid part would rotate out of
the
> way.  This valve was put in place for smog reasons initially, but Yamaha
> found that the same motors coupled with this exhaust produced more power
in
> the low and mid rev range compared to the same engines with a more
> traditional 4-into-1.  So, if my assumption is correct that the valve is
> creating backpressure, doesn't this add credence to the some backpressure
is
> good theory?
>
> - Brad
> '86.5 Volkswagen Scirocco 16v
> '76 International Scout II
>
>
>
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