Tech'ish question. Inquiring minds want to know.

[roccit_53 at scirocco.cs.uoguelph.ca (C Boyko)]

Klaus did it a lot before this functional fuel distributor, so that means
three holes were likely rich, one likely lean, nobody burning all the
gazzzzz....pop pop pop... (so perhaps Blackie's just not misfiring like
previous incarnations?)


The popping's not so bad now (he's lean) So I'll report back when I start
turning that screw righty richy....the exhaust is free flowing I'd say (2",
no cat), and is obviously capable of sounding like it'd been into the bean
burritos...

Cathy

On 11:27:05 pm 05/23/06 "Scourge" <scourge@cogeco.ca> wrote:
> Hmm..... odd. Blacky doesn't do it at all ..... at least not that I
> can hear. I think I'm even running a touch on the rich side right now
> too.
> About the low backpressure response. I'm currently running the Dual
> Out mani, TT long DP, and TT 2" w/ no cat ..... where as my old golf
> that went nuts with it was stock save the muffler(N/A diesel muffler,
> haha, sounded like a dirtbike) it was definately not free flowing,
> lol.
> I agree that rich during low vacuum would be a fair assesment ....
> but i'm not sure why some cars do it and others don't.
>
> -George -Oh, and my car didn't even do it much with an open DP(the
> whole "exhaust giving me the finger" fiasco on the dragstrip last
> year)
>
> ----- Original Message -----
> From: "Ron Pieper" <rapieper@yahoo.com>
> To: "Scourge" <scourge@cogeco.ca>; "Scirocco List"
> <scirocco-l@scirocco.org> Sent: Tuesday, May 23, 2006 9:45 PM
> Subject: Re: Tech'ish question. Inquiring minds want to know.
>
>
> > I can only answer by telling you my experiences with this via
> > Megasquirt, where I learned from
> >  someone on their forums that you can eliminate the backfiring you
> >  are desiring by leaning out the
> >  mixture at VERY low vacuum levels - seen only with the situation
> >  of zero or negative load with the
> >  engine typically decelerating.  With MS, that's really easy to do.
> >  I leaned out that range, and
> >  presto, no more pop-pop-pop.
> >
> >  This was only evident with my free-flowing exhaust (straight
> >  through) because a normal exhaust
> >  muffles it greatly.
> >
> >  Sooo...we can extract from that that your engine is getting more
> >  fuel in those conditions than it
> >  needs, and some 'explosion' is likely happening in the exhaust
> >  system. With CIS, I reckon you're
> >  stuck with it.
> >
> >  I guess the little holes you write of could cause or amplify this,
> >  but it happens anyway under the
> >  right conditions.
> >
> >  Dan Bubb, please shed your light here.
> >
> >  HTH
> >
> >  Ron
> >
> >  --- Scourge <scourge@cogeco.ca> wrote:
> >
> >>  So I've been wondering.
> >>
> >>  What makes a car backfire? Not regular loud single shot
> >>  backfires, but the awsome little pop pop
> >>  pop some cars have on heavy downshifting.
> >>   My golf used to do it like mad, I loved it. Made it sound so raw
> >>  and hardcore, lol. Non of my
> >>  rocco's have ever done it.
> >>
> >>  One guy I know once told me it was cause by small holes farther
> >>  up the exhaust(I guess he meant
> >>  near the DP) that while leaking a bit would also create a sort of
> >>  scavenging effect and pull
> >>  some air back into the exhaust system. That air had oxygen in it
> >>  and could then act as an
> >>  accelerant with the bit of unburnt fuel and it would ignite in
> >>  the exhaust, thus creating the
> >>  "pop pop pop" when downshifting. I have no idea how accurate this
> >> is.
> >>  Any thoughts/input??
> >>
> >>  -George -missing crazy things my golf could do(like shoot flames
> >>  out the tailpipe!)
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> >
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