High compression timing ?

G

Greg out west

Senior Member


Hey Guy's



I remember talk about setting the timming back when running a H/C head...I'am getting about 100 Lbs. running a compression check...


Is 30 degrees total advance about right ?


Thank's,

Greg out West

 
Your ears are better than any tool . Drive your car at different speeds , loads and play with your timing . Feel and sound will find the sweet spot .
 
I set the timing the same with all of my model A engines with original distributors. The ones that I run with Mallory dual point distributors are tuned by ear just the way that they came out of the box. I think that maximum advance on these distributors is 28 degrees
 
Combustion chamber shape/aerodynamics affect the mixture burn. Adding compression will cause the mixture to ignite sooner which the engine reads as advanced timing. More squeeze more heat. Different engine-cyl. head-piston-distributor/ignition combinations-altitude-temperature-humidity-fuel-overall engine condition are factors.
Any deviation from stock usually results in some road test trials. One example is the setup instructions with some Mallory dual point distributors. Final timing is done with road tests which requires a patience and experience.

Chet
 
When my grandpa was alive and I was just a kid, I'd sit and talk with him by the hour. Its amazing what I still remember 30 years + later. He told me "set the timing advanced enough so you just get a little knock when the lever is all the way down, then run it just a click up so it doesn't." Simple is usually the best.
 
When the timing pin drops in place, I set the trailing edge of the rotor tip aimed at the number one contact in the distributor cap body. It is very important that when the points cam is locked down that all of the backlash in the distributor shaft is in the counter clockwise direction. Points gap has an advance-retard effect. Less gap, more retard. More points gap advances. Factory specs for points gap is anywhere from .018 to .022. I set my points at .022. The wider gap gives better throttle response and more time before the gap closes and needs readjustment.

If the engine is lugged in the higher gears it will be necessary to slightly retard the spark lever untill the pings or timing knocks dissappear. Heads with compression ratios over about 6.2 will need more attention to spark use to avoid knocks, same for cars running higher gear ratios . There is more risk of lugging with higher ratios. I run BF 5.9 heads on three of my engines. As long as momentum is maintained, My 5.9 heads handle full advance at speed as well as originjal heads. I see no need in running any engine so retarded that it actually loses power and runs hotter. Knowing how to drive the model A has more to do with spark adjustment than anything else. As long as proper speed and gear is maintained, I have no problem running with full advance at speed.. A lot has changed since the owners manual was written. We nave much better roads, traffic moves much faster and fuels have higher octane that are not as likely to cause timing knock as the fuel that was available when the model A was produced.

Over the years i've read a lot of what I consider to be myth and just pure bull **** about spark plug and spark lever use with higher compression heads . My lifetime experience with model A's tell me that it is more about how the model A is driven and how much over 6 to 1 the compression ratio actually is.
 
Purdy's post #10 is about as good as it gets as a primer for driving an HC head with the stock ignition. It all depends on the engine, the car and the conditions, and what works for one guy may not for another. There is not hard and fast rule.
I drove a 7/1 Weiand with a stock ignition and started to really learn about the engine and driving conditions. I soon got into the habit of driving with my fingers on the lever all the time and adjusting to changing conditions--such as coming off a turn, descending a grade, accelerating level, and up a hill, without worrying about specific degrees of advance because you cannot tell anyway with any precision with a stock ignition. It was fun and made me a better driver.
I drove hillclimbs with the stock ignition, but changed to FSI for the mechanical advance (and changed the curve) because in competition conditions change too fast to play with the advance lever. When you start tuning for high performance operation it is a different ballgame. Then you should worry about 1 or 2 degrees of advance, because the guy who beat you did worry about those things.
For regular driving with an HC head, or any head for that matter, even a stock head, and stock distributor, learn to listen to and feel your car without worrying about specific advance figures. It will make you a better driver and you will have more fun driving the thing, which is the point anyway.
 
Almost all engines combinations will need different ignition timing to suit the different rpm and loads
the best way to find the correct timing is on a dynamometer
2nd best is by reading the spark plug there 2 different timing marks or colour change idle and full timing
just reading your plugs will tell most of what you need to know about what is going on with an engine
 


Hi guy's


Learned a lot reading all the comment's,,, Way, way back I used to advance the spark lever & leave it there !!..no wounder it would ping starting from a stop !!!



Take care, Greg out west
 
I advance or retard the advance lever at highway speeds and see if the engine speeds up. I think I run my HC Antique Engine Rebuilder about 30 degrees retarded, or as I have it, the spark advance lever sits at "line of sight" in front of the pin striping on my dash at highway speeds of around 60 MPH. I retard it SLIGHTLY for around town, and retard it for steep hills if I do not care to downshift and it is not lugging particularly. I really fell the ENGINE should dictate where it feels best advanced or retarded when driving.
 
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