REFLECTOR: Running LOP

[Bernard Despins]

Chuck,

No problems with your statements, until the last line.  "Then running 
50F LOP is a safe position provided your CHT's are reasonable (below 
375-400F)."  I don't disagree with that line either, but I would expand 
on it to say that you should always have reasonable CHT's, whether LOP 
or ROP.  There is nothing inherently more dangerous about being LOP that 
makes monitoring CHT's more important than when ROP.

What we are all in need of is a system capable of monitoring peak 
cylinder pressure.  By monitoring CHT's and EGT's we are all beating 
around the bush of what we truly need... An instantaneous reading of how 
much pressure is in each cylinder during the power stroke.  The PRISM 
system from GAMI promises this. I'm setting up a cheap version on a test 
stand for my engine (www.tfxengine.com). 

Bernard Despins

Chuck Harbert wrote:
> 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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