Date:         Sun, 29 Apr 2001 22:45:03 -0300
Reply-To:     Jean-Guy Savoie <jgsavoie@nbnet.nb.ca>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jean-Guy Savoie <jgsavoie@nbnet.nb.ca>
Subject:      Digijet timing ATDC or BTDC? compare air cooled AFM
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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