[Amc-list] Detonation -static vs. dynamic calculator

["Bruce Hevner" <scramblr@xxxxxxxxxxx>]

While the Silvolite calculator is helpful it won't help you determine if
what you have NOW is close to right.
DO A COMPRESSION TEST. MOST stock (8.5-1) motors with stock type cams should
be in the 120-140 psi area. Mildly modified engines (10-1) should be in the
140-160 area and "hot" street motors (10.5) should be in the 160-180 area.
Competition engines (11-1) should be 180-210. 
This gives you an idea of where you are with cam timing to static
compression relationship.

In other words,, if you have a stock 8.5 motor with a stock cam that cranks
140, but after a cam change cranks 110,,, you need more STATIC compression
ratio (say 10-1) to get the running compression back up. Running the engine
with low "running" compression results in a "lazy" motor that does not make
full power and will run on less than expected octane.
Running an engine with excessive "running" compression results in a motor
with an appetite for higher than expected octane that is on the ragged edge
of detonation (and heat).

If you're close in you're running compression you can adjust the cam timing
to get best power for the combination you have. 

On our Toyota's (22R OHC) we ran cams with about 240'@.050 to 260'@.050
(depending on the track). Static compression was 10-1 to 11-1 depending on
which cam we chose initially. Our running compression was always 170-200
although we would shoot for 180-190 (less heat). We would start with the cam
"straight up" and then advance it 2' at a time watching the compression.
Once the compression stopped rising we ran the cam there (or 2' less). We
found this ALWAYS resulted in the maximum performance for that particular
combination.

I know this might not be a real exact way to tune your engine but over the
years I have found it to be a valuable trouble shooting tool. 

But HEY,,, that's just ME!!!
Bruce Hevner
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