Thread: SDS CPI2
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Old 09-27-2019, 06:05 AM
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M McGraw M McGraw is offline
Join Date: Dec 2012
Location: Greenback, TN
Posts: 530
Default Angle valve engine timing

I have been testing my angle valve engine timing as a function of mixture, RPM, and MAP for about two years. I am very close to what I consider my best curves. I say curves because the most fundamental thing I have learned is that you need a minimum of two curves, one for ROP and another for LOP. My ROP curve covers everything from starting to climb and high power cruise. My LOP curve covers only 2350 to 2700RPM and below 25MAP. Mostly I use it between 18 and 22MAP because of my typical cruise altitudes. I plan to distribute those curves to a friend with a similar engine soon. If he confirms my data we hope to distribute that data to the community.

If you use only one curve you will be too advanced for ROP or not advanced enough for LOP. Both conditions can be acceptable if you set limits on the advance curve, but it is important to understand that too much advance is merely adding heat to the combustion without increased power. A quick summary of my results would be that an angle valve engine and a parallel valve engine respond very differently to advance changes.

All my testing has been done with the SDS EM5 computer which uses the CPI/CPI-2 ignition software, but adds electronic fuel injection.
Marvin McGraw, 5TN4
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