[DeTomaso] 351C (ignition) timing

[Will Kooiman]

True, with some additions.

Hook the vacuum advance to ported vacuum (zero at idle, only vacuum once you
give it a little bit of gas).  If you hook it to manifold vacuum, the idle
hunts up and down.

Vacuum advance give 3-4 more mpg, plus it's quieter at cruise speeds, so
there's less droning.  It doesn't generate near as much heat, either - at
cruising speeds.

At WOT, it's exactly the same as no-vac advance.

Throw the factory vacuum advance in the trash can - the one with two lines.
Better yet, sell it on ebay for $500.

If you're setting the total advance by revving it up to 3500 rpm and shining
the timing light, unhook the vac advance line first, otherwise, it'll show
50+ degrees.

If you're setting it like I do, it doesn't matter. I set it so it's hard to
crank, then I back it off just a tad.  If it pings, I back it off a little
more.  That's where my car runs the best.  Who cares what the total advance
# is?

By the way, at our dyno day years ago, my car made slightly less HP at 12
initial, 36 total (mech advance on a Mallory is 24 - if I recall correctly).
I left it there since it should have been less ping-prone.  I stopped on the
side of the road on the way home and advanced it back where it was.  It ran
like crap at 12 initial.  It runs great at 16-18 initial.


-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of MikeLDrew at aol.com
Sent: Monday, April 13, 2009 12:21 AM
To: artstephens at verizon.net; detomaso at realbig.com
Subject: Re: [DeTomaso] 351C (ignition) timing


In a message dated 4/12/09 21 53 33, artstephens at verizon.net writes:


>      It sounds like we sacrifice performance by running vacuum advance?  
> I
> would imagine we have no vacuum advance at WOT?  If that is the case,  
> let's
> say we subtract 8 degrees of vacuum advance from the 36 total,  leaving us
> with 28 at WOT. 
> 

I don't think that's the way it works.   There are many other people who 
know far more about such things.   But I think you set a vacuum advance 
distributor with the vacuum disconnected, so that the mechanical advance is 
(whatever).   Then, with the vacuum hooked up, it goes even further
advanced.   

So under part-throttle cruising, you might have what on the surface would 
seem to be ridiculous amounts of advance, i.e. 50+ degrees.   But as soon as

you boot the throttle, the vacuum drops to zero, the vacuum advance goes 
away, and you're left with your full 35 degrees or whatever of mechanical 
advance.

True?   Or not true?

Mike


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