GO parts are non-existent. The 2700 RPM is dependent upon prop length. Short props aren't as efficient for most of our planes.

McCauley and Hartzell frequently obsolete their props, so, w/o new STC, etc., for a new prop($), no suitable or legal prop. Use of higher compression pistons, slight RPM increase, most bang for $. Still lots of FP props out there.

I don't think that just different pistons will be enough. For the kind of flying and the loads I want to haul I think 180hp with a CS prop is required.

Legalities aside... this is an ESTIMATE based on my limited experience running O-200's at Reno:

The O-200 / O-300 piston and cylinder ass'y is good for about 4200 RPM before you start to have immediate catastrophic problems. This means having it break on this flight, instead of wearing it out sooner than normal but later. (Please note that at 4200 RPM, we estimated that our engines would hold together for an hour, which was more than what we would put on the airplane. The airplane went to the race on a trailer because it was not prudent to ferry it)

At 3500 RPM you are going to accelerate wear significantly, but if balanced and assembled right... and cooled right... the piston and cylinder assembly will hold together for a couple or three hundred hours without making too much metal.

Steve Wittman was noted for routinely running small Continentals at 3000 RPM in his Tailwind sport planes Numerous Vari-Eze, Cassutt, and Midget Mustang pilots turn their motors at these speeds with only a moderate amount of accelerated wear. But these owners have their engines balanced well and cooled well.

Look at the difference between the TBO of the O-300 and the GO-300. The difference was due to RPM and heat. A large part of the "problems" that the GO-300 was known for were due to heating and cooling.

IMHO back country flying is not the proper scenario for turning an engine faster, with or without a gearbox. In back country flying you are looking to make the max power at the slowest speeds. This means that your cylinders are going to be generating the most heat when there is the least amount of airflow to cool them.

One of the big "gurus" pf the small Continental engine world is a guy named Harry Fenton, from Unison (Slick Mags).

I think that you can get away with MILDLY bumping up the compression and ignition much more than you can get away with turning it 25% faster.

Also REMEMBER, the HP and torque curves fall off with RPM at an exponential rate. At 4200 RPM, the O-200 was estimated to be putting out only 118 or so HP. Not a big benefit for the cost in reliability. Drag and weight are straight-line benefits, they do not fall off exponentially.

I wouldn't plan on running it at a constant high rpm but more like 2900rpm for 5 min on take off and 2700 all other times.

I suppose one could leave the low compression pistons and install an aerocharger and fuel injection but then why not just go with an conti TIO-360. I really like the idea of an experimental O-300 but after further review and looking into finding an E case I figure it would just be wiser to go with a IO-360. The compression is low enough on them you could run pump gas and to overcome the vapor lock concern you could either install a boost pump in each wing or find a way to install a carburetor.

C-85 pistons in an O-300 will give a compression ratio of 8.68:1, and will increase the power and torque by almost exactly 7% for 155 hp at 2750 rpm. Note that the periphery of the piston top has to be champhered. If you don't, about half the pistons will strike the top of the heads. On some cylinders, the bottom side of the top rings will clear the top of the steel cylinders and hang the pistons into the heads by the top rings so that the pistons can't be pulled. Not fun, but doesn't happen on all cylinders either. You might get lucky.

9.5:1 pistons will give a 9.76% increase in power and torque without the interference issues for 159 hp at 2750 rpm.

EZFlap wrote:[u]Legalities aside[/u
Steve Wittman was noted for routinely running small Continentals at 3000 RPM in his Tailwind sport planes Numerous Vari-Eze, Cassutt, and Midget Mustang pilots turn their motors at these speeds with only a moderate amount of accelerated wear. But these owners have their engines balanced well and cooled well.

I'd read the same about Steve Wittman. One article in EAA's magazine said he used to tell people the average sport pilot's engine would rust out before it wore out, so the extra wear from running at 3,000 rpm didn't matter. But as people have commented previously, the higher rpm does limit prop length, which isn't good for take-off performance.

I thought about running an O-300 in my Patrol. I've ridden in C-170's and 172's with them, and was impressed with how smooth and quiet they were compared to the 4 cylinder Lycomings. But when I talked with Bob he said it was too heavy and would upset the balance too much. Oh well, I found a good deal on an O-320 instead.

Phil

I've run a Mac 7535 on an O-200 J3, climbing out at 55 mph and 2850 rpm for an ROC of about 1100 to 1200 fpm, which seemed to me like a decent rate of climb for a J3. I didn't find the diameter to be a problem, and that prop is approved for an O-200.

J3 top speed in level flight with the 7535 is a little over 110 mph at slightly over 3100 rpm.

Top speed level flight with a 7142 is 118 mph.

As long as the tips don't go super sonic your fine. But sonic speed varies with air density, so you can get away with a longer prop at lower altitudes.

Doesn't engine speed govern the redline for most common aviation engines.... not the prop speed? Genuinely asking.

Something to do with stress on the cams or possibly crank?

And then there's the power question. Bob told me I could have 300hp from my engine if I liked, no added weight, but he said he didn't think the thrust case was strong enough and that it would have a lower TBO.

Even with a 7142, the high velocity air across the front side of the outer blades will go supersonic at max static rpm and low altitude (the aft sides will still be subsonic). It gives the prop a slight 'barking' sound at high static rpm, but doesn't noticeably reduce performance. Best static thrust that I'm aware of is produced by a Mac 7440 up to 2750 rpm. Above 2750 static, the Mac 7535 seaplane prop produces more thrust and has a far more pronounced bark. Continental power curves for both the C-85 and the O-200 go up to 3100 rpm (well above rated power), but the TBO is reduced for the higher rpm. Results would be similar for the O-300.

JimC wrote:
J3

Top speed level flight with a 7142 is 118 mph.

Take the tape off the static port...

Got a chuckle out of that. Run your O-200 J3 up to 3100 rpm level with that prop and see what you get on a 4-way GPS run


You can get 110 mph level with the 7535. Also at about 3100 to 3200 rpm. Since max allowable continuous speed is only 90 mph, you don't want to do it for very long at a time though.

In a 55 mph climb, the 7535 will turn 2800 to 2850 rpm. Climb performance is almost perky.

Only gauge worth watching on a J3 is oil pressure.

Coyote Ugly wrote:Doesn't the 175 geared engine turn a way higher rpm? Its an O300 too isn't it?

Yes it does!
I think the tbo is 1000 hours though.
I have also heard that airboat guys would run about 3000 rpm with o-300's

C-85 pistons in an O-300 give 8.68:1 compression ratio. If the circumference is left unchamphered, about half of them will strike the heads.