[DeTomaso] Initial Timming

Wed Apr 29 21:52:25 EDT 2009

Doug

I concur with your advance findings.  When we initially dynoed my 408 
stroker with quench heads on an engine dyno, it continued to make more power 
as we advanced the timing to @41 degrees total.

I run a more conservative 36 -38 on the street for a margin of safety.  I 
recall at our last chassis dyno day.  David Bell was just a bit shy of the 
power number he sought to achieve.  He advanced his timing to about 38 from 
some lower number and hit the power number on the next pull.

I'm my admittedly limited experience, I have never seen a Cleveland make 
more power with less advance than 38. Of course, it would be foolhardy to 
run this much advance if your engine is suffering detonation or preignition.

JT
----- Original Message ----- 
From: "Doug Braun" <doug at silicondesigns.com>
To: "Göran Malmberg" <hemipanter at hemipanter.se>; "DeTomaso Forum" 
<detomaso at realbig.com>
Sent: Wednesday, April 29, 2009 11:38 AM
Subject: Re: [DeTomaso] Initial Timming

> 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
>
>
>
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