Flathead mechanical advance only timing questions.

M

Myke

Junior Member
I am setting up a new ignition that is using a magneto. I will only have a mechanical advance.

My engine is a 59a, 276 ci, 9 to 1 compression, with a literio L100 cam. It has a steel flywhell that has been lightened some.

I am looking for some advice on setting the timing and advance curve.

I do know 4 degrees initial.

What would be the best total advance? At what rpm should it be in total advance?

The car has an overdrive so I spend a lot of time around 2000 rpm cruising and I drive pretty mellow for the most part.

Right now I am running a Harmon Collins Dual Coil with 6 volt coils. It has 4 degrees initial, 24 to 26 total advance (not exactly sure). I am not sure of the advance curve. It still has the vacuum advance hooked up.

Car does run great. It will detonate on long up hills in overdrive (when at 1800 rpm-ish) so I have to down shift. I think this is a combination of vacuum brake adjustment and my gearing being too tall (3.78 combined with a Columbia and 31” tall tires hence the low rpm) but no problems otherwise.

Maybe this is too much information but I figured I would add it.

Thanks for any comments.
 
I would bump the initial up to about 6 - 8 deg. I think 26 - 28 overall is not a bad place to be and I would have it all in by 2000. The total is probably more than you need for max power, but with most of your driving at part throttle, it will help economy. If you have to down shift, so be it. 1800 is probably below your torque peak anyway. With my car, at 73 mph, I'm turning 2500 rpm, get over 20 mpg.
 
flatjack9 said:
I would bump the initial up to about 6 - 8 deg. I think 26 - 28 overall is not a bad place to be and I would have it all in by 2000. The total is probably more than you need for max power, but with most of your driving at part throttle, it will help economy. If you have to down shift, so be it. 1800 is probably below your torque peak anyway. With my car, at 73 mph, I'm turning 2500 rpm, get over 20 mpg.
Click to expand...

Different engines will vary with what they like for maximum but most of them like 24-26 all in by 2000. The initial will vary also but is not critical.
THE MAIN THING is do not let it ping at any rpm..This is a quick way to create scrap iron.
 
We spent a couple days with a flathead ( our Bonneville engine) on the dyno and 4 intial, with a advance of 24 degrees ( Makes a total of 28 ) makes the most Horse power .
Also a .025 plug gap made the most power as well.

Info on our testing at www.gasolinealleyshops.org
 
I have found the total advance for maximum hp is dependent on engine size and of course fuel type.
At Bonneville in 1956 I had a 315 ci engine with a manual cable advance on an H&C mag. After reaching maximum rpm playing with the cable usually produced a few more rpm. The optimum with that engine was 36 degrees using 145 av gas. Av gas almost always requires more advance than race gas or alcohol.
Nitro is whole other ball game. I ran 43 degrees with 50%.
I realize all this hasn't much to do with street use.
Forgot to mention, on my last 323 ci engine with the H&C mag with the hot coil mod, .035 seemed to be best on the plug gap.
 
WOW;

A 3.78 R&P with a Columbia will give you aboout 2.58:1 when you are in Over Drive. That is a tall gear to be pulling with 31in. tires. It probably runs right along on the flat but I can understand you may want to put it into direct when going up a hill. Just be very careful with detonation. I think 25 deg @ 2000 is a good number for your total mechanical timing.

Chris
 
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