RPM higher when cold?
03-25-2012 | 08:37 AM
#1
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From: Salinas,
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RPM higher when cold?
It is not the needle settings.
I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?
I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?
03-25-2012 | 09:11 AM
#2
My Feedback: (6)
RE: RPM higher when cold?
Yes, I have frequently seen this; a sort of a "flash" reading of a couple of hundred rpms higher when an engine is cooler. It could be due to the viscosity of the oil helping ring seal, but I always attributed it to the crankcase being cool, and the engine getting a denser fuel/air charge than it does when the crankcase is warming the mix before it gets to the combustion chamber.
AV8TOR
AV8TOR
03-25-2012 | 09:13 AM
#3
Senior Member
RE: RPM higher when cold?
ORIGINAL: Scota4570
It is not the needle settings.
I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?
It is not the needle settings.
I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?
ORIGINAL: av8tor1977
Yes, I have frequently seen this; a sort of a ''flash'' reading of a couple of hundred rpms higher when an engine is cooler. It could be due to the viscosity of the oil helping ring seal, but I always attributed it to the crankcase being cool, and the engine getting a denser fuel/air charge than it does when the crankcase is warming the mix before it gets to the combustion chamber.
AV8TOR
Yes, I have frequently seen this; a sort of a ''flash'' reading of a couple of hundred rpms higher when an engine is cooler. It could be due to the viscosity of the oil helping ring seal, but I always attributed it to the crankcase being cool, and the engine getting a denser fuel/air charge than it does when the crankcase is warming the mix before it gets to the combustion chamber.
AV8TOR
I've seen similar results on all of my Saito 4 strokes even when running glow fuel.
I think the assumpsions regarding ring seal & denser charge are correct.
