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Tech'ish question. Inquiring minds want to know.
My first 85 Scirocco use to do it alot on both downshifting & hard
acceleration up until 2500 rpm. My exhaust wasn't anything special, just an
Autotech 2.25 CatBack system and a header.
It definitely turned heads when I was in high school. I would roll into the
parking lot and downshift into second with waaaaaaam pop, pop, pop, pop,
ummm pop, pop, pop, pop.
The car was running alittle richer than stock but I didn't think much about
it at the time, or for that matter much about CIS or cars. I did my own oil
changes and brakes and that was about all. It wasn't until my Senior Year
that I started learning more.
Brian
85 Scirocco 8vT 01 Jetta 20vT 84
Rabbit GTI
----- Original Message -----
From: "C Boyko" <roccit_53@scirocco.cs.uoguelph.ca>
To: "Scourge" <scourge@cogeco.ca>
Cc: <scirocco-l@scirocco.org>
Sent: Wednesday, May 24, 2006 6:35 AM
Subject: Re: Tech'ish question. Inquiring minds want to know.
> 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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