Kahuna said:
OK now Im scratching my head and getting side tracked (the main reason I pay attention to these boards:D). So if I run 50 LOP, and the CHT's are always 45 degrees colder than running 50ROP, then would you expect it to be cleaner in the cylinder with LOP or ROP? Perhaps if I could measure top of piston temperature that would answer my question. I guess lower cht's do not translate into lower combustion temps. Nor do lower EGT's for that matter since the EGT probe is down stream from the comustion.
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There's no question running lean (LOP or ROP) will leave the combustion chamber clean..when I was charging around in my LEZ with an 0235, it was aggressively leaned and had none of the problems the 152 or Tomahawk had with lead fowling. The plugs were always clean as a whistle. I did the same with the 0360 in a Cozy and when it was torn down for OH at 2000 hours the guy said this engine could have gone another 300 hours easy, it was clean.

I predict you will find your engine clean as a whistle also. Hopefully, you won't find any little aluminum balls anywhere.

Whether running LOP is a good idea, I have no opinion except I don't think Lycoming recommends it. However, lots of guys have done it for years. I never did because I never had a fancy engine monitor. It was lean until it rumbled a bit and a little rich to get it smooth. It was right on the edge cause flying into colder air made it rumble and a little more rich cured that. How you guys run LOP and don't have a rumble beats me. Maybe I was in that area and did not know it.

Good luck, Kahuna, I sincerely hope the motor is OK. This is a very interesting thread.
 
<<If you look at your data from the engine monitor, detonation will show as a sharp increase in egt and then a plateau at that much higher level>>

Maybe you meant CHT? With all due respect, I think detonation EGT would plateau lower than the usual peak EGT. The EGT graph might look something like this with a smooth mixture pull toward lean (red w/detonation, blue without):



ROP is more detonation prone, thus the largest part of the plateau is on the rich side of the graph. When the mixture gets lean enough detonation would stop and EGT would assume it's normal trend. Remember, the whole problem with detonation is that is dumps energy into metal parts rather than sending it out with the end gas.

<<If an engine has lots of heat from detonation or from very lean mixture, advanced timing or any other reason, you can get a self cleaning effect in the combustion chamber that will burn off normal combustion deposits.>>

With detonation, the "cleaning" effect is from the ringing shock wave cutting through the boundary layer and blasting deposits off the parts; heat and shock. A LOP mixture results in lower EGT and CHT; no self-cleaning, just less unburned excess fuel turning to deposits. Advanced timing certainly raises CHT and cylinder pressure, but lacking detonation to blow away the boundary layer, an extra 50-100 degrees isn't gonna remove much carbon from a flat surface. Self-cleaning ovens operate at 900-1000F.
 
Hi Dan,
Yes, I would agree your graph depicts what I was trying to say...just didn't say it very well. Sorry if I confused anybody! The wording was poor and very misleading.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
mag check

Dang Mike

You have got everybody pulling cowls and checking mag and EI timing.

I did mine yesterday afternoon.

I was hot on CHT's also. On a long shot, I thought this might be the answer.


Cary rhodes
 
Im sorry for creating additional work load.

I pulled the plugs and looked closely at them with magnafying glass. Also bscope and compression check. Everything looks, well actually great. Darn clean in there. The link to the Skyranch http://www.sacskyranch.com/deton.htm article was very helpful JR thank you.

Im not even gonna say case closed again for fear of someone asking me to pull my wings off or something. So lets just call this a cold case file that will remain in the drawer.:rolleyes:

Thanks for all the smart guys here. I have learned a lot as usual!
Off to Texas today to prepare for the Temple Air Show this weekend. You all ARE coming to watch us aren't you???? Falcon Flight is letting me stand in on their very cool routine with "The Beast". No not my plane, in fact not an RV. Its a "beast" of a plane that gets intercepted by RV's during the air show and forced to land as part of the routine. Its a hoot. You will just have to come and see the show to see what it is.
Best,
 
<<your graph depicts what I was trying to say>>

Aww, heck Mahlon...even a blind hog like me roots up an acorn from time to time.

<<Everything looks, well actually great.>>

Mike, that's excellent. And your own safety aside, it wasn't wasted effort....you've provided a really good datapoint. Experienced pilot, known engine, specific operating conditions, including a known value for the abnormal timing. No guarantees, but it looks like a 15 degree timing advance isn't enough to create a detonation condition in a normally aspirated (MP <30) Lycoming like yours. Compare that with James Freeman's recently-reported IO-550N experience (advanced timing, exactly how much unknown, runaway detonation, engine destroyed). I appreciate the knowledge and I'll bet others do too.

"Like yours" needs two little details to complete the picture. You have a parallel valve? And what is the compression ratio?
 
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Another interesting tidbit. I went LOP at 17.5k' and got a miss. Leaving it LOP I ran the mag only. Yikes. Imediate loss of power and airspeed went from 180TAS to 140 before I threw the EI back on.
Click to expand...

When I had the Lasar system, I was able to directly compare mags to EI in the same flight. I found that with just the mags, it was difficult to get LOP without roughness at low MP's, like 22" or so. I suspect it is mostly the timing advance, but the spark intensity is probably also important at low MP's. Now, with the dual Lightspeed ignitions, I'm able to go ridiculously LOP, to where the airspeed has dropped 30 knots, yet the engine is still reasonably smooth. Not a practical point to run, just interesting.
 
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Basically speaking...

I know this is elementary at this point, but did you measure the inlet vs outlet area on your cowling? I dropped my RV4 temps 40 degrees across the board by trimming 2 inches off the bottom cowling lip when I had high CHT/Oil temps...
My Dos Centavos

Rob Ray
Old School RV4 builder
HR2
 
Hey Smokey,
Yes I did. I did that early on in my flight testing. Id guess round 2" trimmed off the exit area, whcih is a "scoop" cowl. And it did the trick.
 
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