Date: Sun, 29 Apr 2001 22:15:21 -0400
Reply-To: jhlauterbach <jhlauterbach@msn.com>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: jhlauterbach <jhlauterbach@msn.com>
Organization: Microsoft Corporation
Subject: Re: Digijet timing ATDC or BTDC? compare air cooled AFM
I advanced the timing on my '84 more by the sound of the engine than
anything else as I did not want to mess with pulling off and blocking both
the vacuum advance and vacuum retard hoses and fool with bypassing the
digital idle stabilizer. In any case, performance much improved. I am not
sure where I will finally set the timing when I have things ready to go, but
5 deg BTDC seems a good start. Apparently my distributor must have slipped
in its mounting as performance suddenly fell off the last Monday in
February, and I have been taking care of the more obvious problems since
then.
John Lauterbach
Macon, GA
----- Original Message -----
From: "Jean-Guy Savoie" <jgsavoie@nbnet.nb.ca>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Sunday, April 29, 2001 9:45 PM
Subject: Digijet timing ATDC or BTDC? compare air cooled AFM
> Hi ya
>
> Recent discussion of the timing of the Digijet 1.9L led me to look into
the
> Good Book, you know, the other Good Book, officially sanctioned by VW.
>
> I noticed in Bently section 28 that the two Air cooled AFM models are
> strikingly different in regards to timing: The Calif. model sets timing
at
> 7.5 ATDC and the USA/Canada model way far the other way, 5 BTDC. So what
> gives?
>
> Is this a smog thing? Or is it a
>
California-cool-dude-I'm-not-in-any-rush-waiting-for-the-wave-so-I-don't-wan
> t/need-the-extra-power type of thing? ;~)
>
> It seems to me that, by retarding the ignition so much, either the
> combustion wouldn't complete as there is less time in the cycle for all
the
> fuel to burn, or else the power is lost because the explosion is happening
> after the piston has already started it's down stroke. Assuming I am right
> (many factors I didn't consider, no doubt), then this would only increase
> consumption, no?
>
> Any comments would be appreciated.
>
> I set mine (84 1.9L) to specs last year, 5 ATDC, and noticed a distinct
lack
> of power, I then reajusted to TDC, much better. Now I read that some of
you
> set it even further back to 5 BTDC. I'm confused, but I think I'll try it.
>
> BTW, there was discussion about the pulley not having a TDC mark. SEE
Bently
> 28.33. The TDC mark id not a sharp V cut, but a rounded depression.
>
> BTW (2), a poor man's tach for setting idle speed: I downloaded a "tone
> generator" www.nch.com.au . With this you can generate a tone of 28.333
hz
> which is what your engine should sound like at 850 rpm as per digijet
specs,
> if my math is correct: 850 rpm * 4 cylinders / 2 (only fires once every
> two revs) /60 seconds = 28.333333333333333333333333333333333etc. You can
> record this on a MD or CD (a cassette tape's speed may vary depending on
> conditions and on the machine) and set idle speed it by ear, of course the
> deaf and tone deaf need not apply. Besides the big tach dashboard
> conversion or expensive equipment, any other suggestions?
>
> JGS
>
> 84 Wesfalia
> Bleu Schtroumpf
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