IO-375

[miyu1975]

Is anyone flying yet with the 375?...would love to hear the performance numbers...

[Noah]

Sorry for my ignorance. I was under the impression that the conventional wisdom (Bob's comments notwithstanding) allowed use of mogas with a compression ration of 8.5 or less. Given this, why would you want an engine with lower compression than 8.5? Additional longevity?

[breister]

Originally Posted by Noah

Sorry for my ignorance. I was under the impression that the conventional wisdom (Bob's comments notwithstanding) allowed use of mogas with a compression ration of 8.5 or less. Given this, why would you want an engine with lower compression than 8.5? Additional longevity?

Still waiting back for a response a few posts back, but my non-scientific understanding was that with 8:1 or 8.5:1 you could run Premium, and with 7:1 you could run Regular, without fear of detonation. My assumption is that this means with a modern electronic ignition (which advances more than 25 degrees BTDC). But that is all assumption and based on heresay.

I'm hoping one or more of the engineering-types will chime in with a factual and scientific answer.

[frankh]

That detonation is primarily dependant on temperature..The higher the temperature the faster the flame front travels. So if the engine is running at high temp (Arizona in Summer) and then you add more advance then the flame front is so fast that it is in effect detonation..I.e the whole charge goes bang at once..i,e the flame does not travel across the cylinder.

Having said that it is clear now that the engine supplies have large margins for error..They have to cus most pilots look at the mixture control as a direct link to Satan himself and rarely touch the thing!

So you have to allow for the pilot that absolutely has no clue how to lean properly and will more often than not run the motor in the worst possible position (now thought to be about 50F ROP).

if you run the motor the right way (probably 100F ROP or even better 25 to 50F LOP) then the 8.5:1 CR number is probably very conservative.

i currently run 91 octane and am considering a swap to 87..Maybe running 91 in the Summer,..I have two Pmags and run almost exclusively lean of peak.

Frank

[nomocom]

RocketBob said
"I have never seen a shred of empirical evidence that shows a Lycoming can't be operated with a higher compression ratio and lower octane fuel."

True enough, but it can be complicated and there are safety implications to the fuel we choose to run. These Lycoming engines years ago were going in the spam cans with very little engine instrumentation. If you were a lucky enough pilot to have instrumentation, you probably knew what 1 of the 4 or 6 cylinders were doing. Lacking information, the detonation safety net was the high octane fuel. Thanks to the instrumentation folks, we have engine computers available that let us know what each cylinder is doing. That multi-probe monitor without too much work, should be able to keep us out of dangerous detonation, and help us as operators decide on what makes sense as a fuel. Somewhere I read significant detonation makes itself clearly known with CHT's going up 2 degrees a second or more. (help, reference) I suppose it would be nice to have a "rate of change" alarm for just that situation, but with a CHT high alarm set for say 380, still should give you time to adjust operations to interrupt runaway detonation.

No multi-probe monitor, 100LL, and high compression, you still have some margin for error. All the same, think I'd feel just as safe, maybe safer with mogas in the tank, high compression, plus the engine monitor. Something as simple as a intake vacuum leak or a plugged injector can put one cylinder 50 ROP on climb out, when the others cylinders are nice and cool at 250 ROP. That is a good recipe for an overheated cylinder, runaway detonation, scouring of the protective boundary layer, more heat transfer, more detonation, a very, very, bad feedback loop. if you run that way long enough, that hot cylinder will destroy a piston, whether you've got MOGAS or 100LL. Rather, a better situation, you've got the monitor set up and you are paying attention, that scenario doesn't play out to engine self destruction. (Thank John D. for your great Pelican Perch description of detonation).

In addition to avoiding engine loss, the monitor will give you feedback on fuel quality. Once you know your engine doesn't have chronic high CHT's or runaway CHT's on say 92 octane, an operator may as well try lower, though to me if running a high compression lycoming, the small price advantage of 87 octane wouldn't be that attractive, I'd rather rather pay for a bit more octane.

IO375? Ok, my wish list just got longer.

[jrvssgl]

They must not be all that.. How come no one has given us a report yet on how well these engines perform. I have been hoping to read something from someone here who has experience running these engines first hand and would love to see some performance numbers from these people. Also some operational numbers as far as temperatures and fuel flow would be nice too, carbed or injected. Come on and give us a report!!! If I missed a thread somewhere here on VAF someone please redirect me. Thanks.

[Bevan]

for some names that are currently running these engines. I bet there are some.

Bevan

[Dan Langhout]

There are several of us here on the forum who have bought IO-375's but aren't yet flying. If you can wait about a year, I'll be glad to post some numbers!

[CZ75shooter]

I'm flying now with a 0-375 high compression 205 HP engine from Aero-Sport with a 3 blade Catto on my 7A. I asked Bart and Craig about turning it 2800 RPMs. Both seemed to think it would be OK. I not going to do that much, mostly 2500 RPM. but I asked Craig to pitch the prop for 2800 at 1000' MSL.
It's dead on the money. I will post some speeds, climb rates and more details soon.
Just from the little bit that I've flown it, I'm disapointed with the speed.
Looks like 205 MPH everything forward at 1500' MSL. It may be off as I still have some other issues with left roll and ball not centered.
CHTs and EGTs are good, oil temp a little high. Drinks gas like there is no tomorrow.
I'll post more details in a week or two.
Larry

[Romeo Victor]

hi Jake,
I've found a comment regarding the IO375 in the Vansairforce forum. I am here in Germany and building my second RV8. This time I'd like to install the IO375 as well. Presently, the control items for the engines must be ordered and installed. Can you remember the lengths of your control cables (throttle,mixture,prop) in combination with the CT83 levers?

Thank you
Best Regards
Stephan Servatius
Bockhorn
Germany