[DeTomaso] Initial Timming

Tue Apr 28 23:49:20 EDT 2009

When I was putting my engine together, I decided to measure the CC's of the
chambers and the tops of the pistons to get an accurate compression ratio.

I was surprised at how much variance there was.  The CC's of the tops of the
pistons varied so much, I decided to measure how far the pistons were in the
hole.  Going from memory, so I may be off a bit - #1 was 0.004", #4 was
0.008", #5 was 0.010", and #8 was 0.010".  You could catch your finger nail
pretty easily in #5 or #8, but #1 appeared to be almost zero decked already.

What's even worse - the driver's side head had more CC's.  The shop that did
my valves, shaved the head (passenger's side).  It's the one that dropped a
valve, so maybe they wanted to make sure it was straight.  At any rate, when
I added it all up, the driver's side had 0.5 to 1 less CR.

I had the original shop deck the block.  I sent the heads to a race shop.  I
rechecked the block, and it was on the money - zero decked.  The heads are
within 2/10ths of a CC.

I can't tell you how it runs.  I've been working too many hours to spend any
time on my car.  The CR is 11.08 to 1, though.

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of Barry Seib
Sent: Tuesday, April 28, 2009 10:24 PM
To: Doug Braun; DetomasoList
Subject: [DeTomaso] Initial Timming

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

_______________________________________________

Detomaso Forum Managed by POCA

Archive Search Engine Now Available at http://www.realbig.com/detomaso/

DeTomaso mailing list
DeTomaso at list.realbig.com
http://list.realbig.com/mailman/listinfo/detomaso
No virus found in this incoming message.
Checked by AVG - www.avg.com 
Version: 8.5.287 / Virus Database: 270.12.4/2081 - Release Date: 04/28/09
18:02:00