[DeTomaso] Initial Timming

[Barry Seib]

Hi Doug

I wonder if even a small difference in the quench area clearance at TDC
doesn't have a pretty marked effect on ignition timing. It's all good to
relate flat top pistons and closed chamber heads to octane and ignition
timing, but when I measred the quench clearance in my 351C with flat top
pistons in it and closed chamber heads, the pistons were 0.036" down the
hole at TDC. Adding a 0.045 thick head gasket meant there was no favorable
quench effect to speak of (at 0.081"), so the flat top pistons and iron
closed chamber 4V heads would have been largely a waste. I set about
correcting the quench to 0.040 and I found that all the flat top pistons
available off the shelf had a similar compresion height, so just as bad on
quench at the deck !  The only pistons I found that had the compression
height correct for CC heads were KB from silvolite. (Keith Black). I
chickened out on the 11:1 and went with the KB148 "D cup" style and 9.8:1

And a lot of head gaskets are 0.060 thick and even worse lack of quench.

Ignition timing will be a guess to start with for me too. I'm trying to get
all I can get without adding octane booster to 92 octane pump gas.

Barry






DeTomaso] Initial Timming
Doug Braun doug at silicondesigns.com wrote:
Tue Apr 28 15:57:16 CDT 2009


Paul,

	I have another data point for you.  I'm running 22 degrees of advance with
19 initial and 41 total on closed chamber iron 351C heads with 353 cu-in
displacement.  It starts fine when hot and doesn't ping on 92 pump premium
as long as I run a half bottle of 104+ "Super" octane boost (not the
standard cheaper 104+) plus 4oz of Bardahl Instead-O-Lead to keep those
valve seats happy.  This amount of advance was arrived at on the dyno where
it made 444 HP through long tube (70 Mustang) headers.  A change to Mind
Train headers dropped the dyno HP to 415.  I'm using an Edelbrock F351-4V
dual plane intake, large Holley Carb, MSD-6AL, and Autolite #25 plugs.

Hey Jack, aren't your heads aluminum?  Maybe the iron heads need far more
advance than aluminum heads or maybe it's just the difference between our
cams

Doug Braun