Advance is unique to each different engine. In this case, two intake
valves eliminates swirl, and a broad combustion chamber with essentially no
squish area further hampers good combustion. When new, this engine ran 47
deg advance. I've raised the compression from 10.5:1 (in the day, it ran
on 100 octane gas) to 12.7:1, which had the expected effect of reducing
required advance. When we first ran the engine, I expected about 36 deg
advance and the engine literally wouldn't run there. You might be
interested to learn that the Ford double overhead cam 4 valve Indy car
engine of 1964 ran 52 deg advance over 2000 rpm, and when Coventry Climax
first built a 4 valve engine they found that the timing had to be 10 deg
advance beyond what a two valve engine would have run. The biggest issue
is apparently poor combustion due to the lack of swirl in the intake charge.
This isn't to say that I wasn't nervous when finding the point of minimum
advance for best torque, which is apparently how the best advance figure is
found. I did a lot of research on the things that impact ignition advance,
and consulted with the technical staff at Superflow on dyno technique to
find advance requirements, before doing this test.
Cheers, Brian
At 09:22 PM 12/30/99 -0500, you wrote:
>I would bet that If you run 44 degrees total timing, you will be building
>a new engine soon. Try 36 degrees max total and you engine will be a lot
>happier.Bob C. "unsolicited advice is worth what you pay for it" happy
>new year!
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