Mark, You can correct me if I am wrong but back in my auto racing days and auto racing engine building ( its been a while) as I recall ram air in a standard carbureted engine will drastically change the air fuel ratio to the point of potentially over leaning and engine. That is an engine that is not re jetted to compensate for this or an engine that has an ECU that could change the AF via either program changes or the ability to regulate the AF when ram air is added . My guess is the engine went into an over lean condition causing the motor to quit.
Can you remind me why we seek to keep our engines below 8.5 to 1 compression ratio ? I have been doing some calculations and if I go from 7.8 to 1 compression to 9 to 1 compression I will increase my torque by 4%. I know 4 % doesn't sound like much but it all counts/helps. Is it a higher pressure causing higher temperatures issue ? What started my thoughts on this was doing calculations on a set of EMPI 56 CC heads versus Revmaster 58CC heads. The EMPI 56 cc heads come out to 8.1 to 1 compression and the Revmaster 58cc heads come out to 7.8 to 1 compression ratio. Not enough difference to matter in this case but, got my mind going about compression ratio. Now all that said, I imagine pre detonation is probably an issue in a carbureted engine. I understand that but, if you are not running car gas with a lower octane this is very important but if you are running 100 LL then you could run a higher compression ratio because 100 LL obviously has a higher anti knock index than 87 octane auto gas. Jeff On Sat, Nov 5, 2022 at 9:49 AM Mark Langford <m...@n56ml.com> wrote: > Jeff York via KRnet wrote: > > > I think I am also going to buy the RevFlow floatless carb in 34 mm size. > > I recall Jim Hill flying behind what I remember was a RevFlow, but it > could have been something else. It worked fine, but Jim decided to feed > it ram air to improve performance a bit, so he redid the cowling a bit > and provide ram air down the carb throat (as one would naturally do). > He took off, went into a climbing turn to down wind to circle the > airport, and the engine suddenly quit! He was able to complete the loop > and come back to the same runway he departed on, but there were some > very tall trees right at the end of the runway. > > The adjacent landowner refused to cut the trees due to some feud with > the airport board, so the airport was a "one-way" runway....you had to > take off to the west, and land from the west, with only 2500' of 40' > wide runway. Jim had to land over the tall trees, and burned 90% of the > runway trying to get it on the ground, then ran off the end and about > 200 yards into a plowed field before hitting a drainage ditch, which > resulted in a nose-over that broke the whole tail of the plane off, just > ahead of the empennage. > > The best explanation we could come up with for that was that apparently > the ram air pressure over-powered the head pressure of the fuel tank (or > reduced it considerably) and reduced fuel flow to the carb, and it > quit. It ran fine on the ground...after another prop was installed. > Ram air was removed, and no more problem. I'm not saying there's a > problem with the RevFlo, or that the carb I'm talking about even a > RevFlo....that was a long time ago, but whatever carb you use, read the > directions and pay particular attention to air inlet and intake > parts.....it really matters! > > As for the Ellison, the installation manual goes into lots of detail > regarding the air inlet path, as well as ensuring that the carburetor is > not subjected to high temperatures or exhaust radiation. I'll dig that > up and post it later today. > > If you want to see what Jim Hill's plane looked like after the repairs, > see http://www.n56ml.com/jhill.html . Since the tail was broken he > turned it into a KR2S, using the NACA tail surfaces that are included in > the "new airfoil" drawings, and it looked pretty good. He sold it to > somebody in Pine Bluff, OK, if I remember correctly, to fund the engine > for the Sportsman he was buying. Note that his engine is a single port VW. > > The photos at the website above were taken in Jim's hangar, which I now > own (after his sudden death), but it's a LOT more cluttered now than > when Jim owned it! > > Mark Langford > m...@n56ml.com > http://www.n56ml.com > Huntsville, AL > > -- > KRnet mailing list > KRnet@list.krnet.org > https://list.krnet.org/mailman/listinfo/krnet >
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