REFLECTOR: Running LOP

Chuck Harbert c.harbert at comcast.net
Wed Jan 3 17:18:53 CST 2007


Guys, I'm not sure I agree that the EGT's aren't that important, especially 
for our air cooled engines. I ran mechanically injected drag boats for 20+ 
years and one of the key factors was EGT's which is almost a direct reading 
of cylinder temp. Initially, we could only "read" cylinder heat by the 
threads on the spark plugs. We actually worked on a fast acting EGT that 
would control the fuel to each cylinder (NDBA outlawed any electronic 
control). Modern EGT's are pretty accurate and can tell you a lot about 
what's happening in the cylinders.

For race engines, you try to build it so that each cylinder puts out the 
same high hp which means ideally you try to have each cylinder get the same 
amount of air and fuel. That's the tough part because air flow is hard to 
control. We'd play with the individual cylinder jets until the plug "heat" 
was close to the others, so they're all working equally. Too much heat will 
destroy an engine because it can't reject it fast enough to avoid detonation 
and overheating of the piston crown and cylinder heads, particularly for air 
cooled engines. I've got a box of collapsed pistons if you want some.

Carburated engines are very tough to equalize the cylinders because air and 
gas don't flow the same way due to different densities. You can compare at a 
180 hp Lyco vs. a 200 hp and see the efforts they went to for equalizing and 
improving the air flow with the intake tubes and valve arrangement. Also, 
the airflow distribution changes with engine speed. The lead (timing 
advance) also significantly affect power and EGT's. Ideally, for max power 
you want to make as much cyl temperature and pressure as the engine can 
safely handle with all cylinders at the same output. This is very hard to 
accomplish which is why our computer controlled engines have all those 
sensors.

GAMI injectors are just fuel jets that are the right size for the individual 
cylinder based upon cylinder airflow determined by actual testing. Don 
Rivera at Airflow Perf. can get you close for a lot less money. I think with 
properly sized jets, your cylinders should all peak at nearly the same time, 
but at slightly different EGT's.  Then running 50F LOP is a safe position 
provided your CHT's are reasonable (below 375-400F).

Okay, tell me why I'm wrong.

Chuck H




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