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Tech'ish question. Inquiring minds want to know.



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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