Quote:
Originally Posted by Model A Ron
Funny you say that. On my first drive to a car show last Saturday with the 5.5 Head I used less spark and the car started to boil over a little. I went back to half spark advance and the problem went away. When going around 45/50mph I drop it a little more to maybe 60/70% spark and the car runs fine without any knocking or boiling over. This is the exact way I drove it with the stock head. In my opinion full spark advance is just to much for any Model A.....I think that's almost 40 deg. of Spark 
Ron |
Quote:
Originally Posted by jayvee34
I did two things to my A. 5.5 heads and the NuRex centrifugal advance kit.
My spark advance is still hooked up, and looks stock, but you do not have to
move it. The lever stays in the 0 degree' position all the time, and my temp
moto meter gauge runs at a quarter up from the bottom.
|
It has been my experience that controlling ignition timing is VERY over-rated on a Model-A engine. Most people do not understand the fundamentals of a Model-A engine yet tend to use characteristics and practices of a modern V8 engine tuning to dictate how the ignition timing on a Model-A engine should be done. This leads to WAY more problems than it corrects IMO!!
To begin with, most 'modern era' engines built in the last 5-6 decades have much greater (higher) compression ratios than what most Model-A engines will ever see. Additionally, the feet per second of piston travel in a typical Model-A engine are almost always one-half the speed, -and sometimes as much as one-third of the speed of a 'modern era' engine. Additional ignition timing is needed for higher compressions due to the mixture being harder to ignite and completely spread. Also, the speed of flame travel is slower when there are obstacles such as domed pistons. And, at higher RPMs the flame travel can be slower than the piston motion where a "head start" of the air/fuel ignition is needed to ensure complete ignition just as the piston has reached TDC. None of the above applies to a Model-A engine since it has lower compression (-under 7:1) where the mixture is easier to ignite, the piston does not have an obstacles to overcome which would require additional ignition time, and it is a slow-spinning engine which does not "outrun" the mixture's flame travel. This is why distributers with centrifugal and vacuum controlled advancing is required on 'modern era' engines using a much wider RPM and Power band of operation. None of these reasons for needing this apply to a Model-A engine!
There really only needs to be two to three ignition timing settings throughout the entire RPM of a Model-A engine being driven normally on streets & highways. The first one is a setting to make the electric starter easier to rotate the engine during the starting process. Many drivers omit the need for this timing location. Generally speaking, a Model-A engine will start with 15° of total timing which is the primary setting for low-speed driving (spark lever around the 9 o'clock position). At RPMs over 2,000 of operation, the driver can advance the spark lever for a total advance of around 28°-30°. THAT is all that is needed to have a perfectly healthy engine, ...and this even includes using a high-compression head on a Model-A engine. Any type of special distributer that advances or decreases the timing on its own is just not necessary any more than requiring an automatically shifted transmission or power-assisted braking to make a Model-A safe to drive.
One other thought to prove my point. These vehicles and their engines were designed for Ladies to operate them. As a general rule, these Lady drivers did not understand the fundamentals of spark timing location, nor how to fine-tune the Carburetor's GAV, or other facets of operation. A Lady could operate her Model-A by leaving the spark lever in one location from starting to driving without a single issue nor any harm to the engine. Today, if someone is concerned after adding a higher compression ratio cylinder head, then follow the same timing as original and just increase the octane of the fuel which will curb any detonation. Many hobbyists today try to over-think what is necessary for reliable performance and operation by trying to add all of these modifications under the mindset that they are required to be able to drive it in today's environment.