[DeTomaso] Initial Timming

Wed Apr 29 12:38:42 EDT 2009

Goran,

15 years ago, when the engine was new, we searched on the engine dyno for
max power which was actually achieved at anywhere from 41 to 43 degrees of
advance.  Both 40 and 44 gave noticeably lower HP.  Since we were running
115 race gas, we weren't worried about detonation.

Later, when I started using 92 pump premium and octane boost in the car, I
tried 38 vs 41 degrees and could notice a power difference so I stayed with
41 total even on the pump gas since I heard no detonation.  To pick the
amount of advance, I picked the smallest amount that would still let the
engine start well when hot.  This turned out to be 22 degrees which is set
via the size of the centrifugal weight bushings.   At only 20 degrees
advance, I had hot start problems.  This is with a CR of 10.2:1 and iron
closed chamber heads.

10,000 or so miles later I had to remove one head due to the loss of a lash
cap and found no evidence of detonation so the 104+ octane boost is really
earning its keep.  Once, I had to run for a few miles without the 104+ and
it would ping easily.  I also tried the standard 104+ and it would still
ping slightly.  With only 1/2 bottle per tank of the 104+ "Super" I get no
ping.

I don't set timing at idle, I set it to get 41 degrees at 3500 RPM.  Then I
check that it drops back to 19 at idle to prove that the advance weights are
working properly.  For those of you running MSD ignitions and MSD
distributors you should periodically check the condition of your centrifugal
advance systems.  These ignitions generate a lot of ozone especially when
you run .045 to .050 gaps on your plugs like I do.  In MSD distributors,
where the weights are mounted high, just under the rotor, I find that about
every 3 years, the ozone in the distributor cap has corroded the advance
weights to the point where they won't move freely so I R&R them every 3
years to keep the advance system working well.  All it takes is a little
wire brushing and some grease.

Doug Braun
blue 73L #5505

-----Original Message-----
From: Göran Malmberg [mailto:hemipanter at hemipanter.se]
Sent: Wednesday, April 29, 2009 2:54 AM
To: doug at silicondesigns.com; JDeRyke at aol.com; rimov at charter.net;
deTomaso at realbig.com
Subject: Re: [DeTomaso] Initial Timming

19 and 41 dgr, thats is some unusual but very okay numbers. What I see
as unusual is the odd numbers, moost of the time there are only 34-36-38
steps for some strange reason. I have been wondering why?
Goran

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

-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of JDeRyke at aol.com
Sent: Sunday, April 26, 2009 9:58 PM
To: rimov at charter.net; deTomaso at realbig.com
Subject: Re: [DeTomaso] Initial Timming

In a message dated 4/26/09 7:36:46 PM, rimov at charter.net writes:
snip....
> .... Chevy or Ford have their timing around 18 degrees BTC and run around
> 42 degrees total advance by 4200 rpm. Does this sound about right for a
> mildly build 351c......
>
IMHO, way too much total OR initial timing, especially on todays gasoline,
for a normal pushrod V-8 except during light-load cruise. I run 10-12
degrees initial and 22 degrees centrifugal in our 351C for a total of 34,
with no
vaccum advance at all. Makes starting the engine easier, too. The Cleveland
closed-combustion chamber is very efficient and only needs about 34-36
degrees of total ignition lead. Very late Chev LS-2, -3 and -6 engines also
only
need about the same. F-1 engines with extremely efficient combustion
chambers currently run around 18 degrees TOTAL ignition lead.   Only old
open
chamber heads such as early '60s Hemis and flathead Fords actually run very
well
under load with that much lead. And many of those are set for drag racing.
Are you referring to a DOHC Ford? I'd expect those to not need such timing
either. Last engine I worked on that needed that much initial lead was a
turbo
Corvair, and it had centrifugal RETARD to keep the pistons in the
block..... My 2¢- J Deryke

_______________________________________________

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