wow, excellent explanation...thats what i was looking for!
thanks
-adam
----- Original Message -----
From: "Canucker Trucker" <mal5@ualberta.ca>
To: <dakota-truck-moderator@bent.twistedbits.net>
Sent: Thursday, May 30, 2002 9:59 AM
Subject: Re: DML: Exhaust bottleneck? ATTN CRM
>
> Hey CRM, I'm not sure if someone answered this question for you yet, but I
> couldn't find a reply to it. So here goes nothing:
>
> Scavenging 101
> When your exhaust leaves your manifold (or header) it comes out in a
> 'pulse'. This is due to the piston moving up and forcing the exhaust out,
> then the exhaust valve slamming shut. Basically what this pulse is, is a
> high pressure node in your exhaust 'wave'. If you remember back to high
> school physics (and I know, its tough) recall the experiment with the
> slinky. If you held the slinky tight, and gave it a flick at one end,
you'd
> see a pulse travel down the end and back. Now suppose this slinky is your
> exhaust piping. As the pulse travels down, there is a low pressure area
> just behind it. The whole concept of scavenging is for the 'pulse' from
the
> OTHER header to be 'sucked' along by the low pressure pocket just behind
the
> first pulse. The only way to do this is to connect the two headers (via
an
> 'h' or 'x' pipe). This allows pressure communication between the two
> systems. The 'x' pipe is preffered over the 'h' pipe because it has less
> flow impedence. Scavenging is only effective at low RPMs when the exhaust
> is still being sent in pulses ... at high RPMs the exhaust flow is
> essentially uniform and not affected by the pulsing affect (i.e. the
pulses
> are so close together they might as well be a continuous flow).
>
> I hope that explains it a bit better ... now Tuned Length exhaust is a
> different story ... let me know if you want to know about that. :)
>
> --
> Canuck
> --------------------------------------------
> Y2K 4.7L 2wd 5spd
>
>
> > > If you are planning for modded truck then go with the 3-inch to the
rear
> > for
> > > a single exhaust and 2.25inch sounds good but add a 'X' pipe (Gibson
> > design)
> > > for a cross-over between the exhaust for back scavenging and a balance
> > > exhaust flow.
> >
> > Okay, pardon the ignorance, but what exactly is "back scavenging"? I've
> seen
> > that term tossed around but dont really understand what it is. Also,
since
> > this is just a dual exit, not a true dual from the headers, would I
really
> > need an X or H pipe?
> >
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