Thorp Air Command - T18.net

O.K. all you engine gurus. I have a set of custom O-290 10:1 pistons made by Jahns for John Thorp back in the day. Question, as these are cast but with no hard anodize in the ring lands which is the better option. Sell them as John Thorp antique ashtrays or have the crowns thermal coated and use them? My thought being that pushing the heat back into the combustion chamber would reduce the micro welding if you will or am I going somewhere that is of no real concern? If you are inclined to tell me to send them to have the ring lands anodized, only do so if you can include good contact info for the person you know that will do it.

Thanks,
Dana

I have no insight on that but wanted to comment on the 10:1 CR. That would make this 290 sing! I wouldn't mind having some of those high compression in mine.

Well now, I have had the thought in the past, could I sell pistons like these if I commissioned a small production run? Of course I would have them forged, offered in std. or .015. I had Deeves make rings for these as the lands are straight cut and say, how about NEW wrist pins as long as we are thinking about it, titanium of course. How many old O-290's could have a new life?

I'm thinking about two o-290 projects that i have that need these pistons. However I believe Speed pro makes a ring that fits. Also there is a So Cal racing piston maker that is rumored to have o-290 'air boat piston forgings on the shelf. haven't gotten to sorting all this out yet... YET.

so depending on availability and price i might be in for a couple of sets.

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http://www.dixiefriedfabrication.com/

How much does a wrist pin weigh?

Another issue that needs to be dealt with is finding a shop that is willing to do cylinder work. They are getting harder to find as most just want to buy new cylinders.

this all brings up a question. As you say these were made for John Thorp. Were these intended for a G or D? John is pretty well known for saying the G crank is fine for flight as long as the engine doesn't exceed ratted HP.
does anybody have anything to add to that?

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http://www.dixiefriedfabrication.com/

I have a O290G with the original crank with 7.5:1 pistons (140 HP), what would 10:1 pistons do for me and would I still be able to burn 92 mogas?

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

I installed 10:1 pistons in my 0-360 and would estimate another 10 HP. When you "cob" the throttle you had better be hanging on.
Just remember the more horse power the shorter TBO and more fuel burn,
I would be concerned about the crankshaft. I know a race car driver that has a lot of squish 15:1 and he breaks crankshafts.

Total seal has the rings but a bit salty @$64 per bore. That's why I went to Deeves, had nothing but good from them years ago when I was doing Porsche engines that had to hold 20lbs of boost. Wrist pins, I can get Ti pins made in modest quantity for about $100/per. If I were to get some pistons made I would limit compression to 9:1 and anyone that is concerned about TBO should not be in an experimental. Count how many people build a airplane, hang a factory new engine and fly it to TBO without work. I'll bet a burger and beer it's a short list.
Fuel burn should not be affected as it is a result of displacement and volumetric efficiency. More compression allows tuning for more efficient combustion and about 4% more hp. per point of compression, the real bonus is increased torque. 9:1 would be my choice for the upper limit on Mogas.

At 7:1 comp min rec. octane is 80-87. at 8.5:1 min octane rating is 91-96.

jumping from 135 HP/2600 rpm at 7.5:1 compression too 9.5:1 should be worth 155 HP in theory. would need to run premium or 100LL

I personally don't care much about shorter TBO, fuel mileage or type. speed cost money.

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http://www.dixiefriedfabrication.com/

Funny, My 180 horse Lyc. burns around 91/2 to 10 gallons an hour and Les' 160 Lyc burned around 7 1/2 to 8 gallons, Wondering if horse power resulted in more fuel burn?

I'll call my buddy at Arias in the next few days to see what a run of pistons will cost me. I already have a design on my computer machine here. Pretty much a stock design piston with the wrist pin bore lowered .125 gave 8.75:1 if I remember right. Thermal coat the piston crown to keep all that nasty heat in the combustion chamber and you would be surprised at how much compression you can run without destroying your engine. Even better would be to raise the pin bore and go to a longer connecting rod. Piston dwell at TDC has the wonderful side effect of suppressing detonation and fattening the torque curve. Aircraft engines for all the claims of improvement are still 60 years behind the times. Their answer to make more power is to increase displacement. My process has always used better technology to make power more efficiently on less fuel.

Lou
you may want to talk to Corona aircraft engines in Corona, Ca. last I new they were still doing cylinder work.

Phil
118BC

Zephyr Engines in Zephyr Hills, FL Has a cylinder shop.

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Bob Highley
N711SH
SN 835
KLAL

Zephyr Engines in Zephyr Hills, FL has a cylinder shop.

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Bob Highley
N711SH
SN 835
KLAL

Talked to my buddy today and I'm coming up with about $900 for 4 pistons, 4 pins matched to pistons, thrust buttons for the pins and rings for either steel or chrome cylinders. Standard or plus .010. Let me know what you all think, I may be able to do a bit better on volume.

Dana LaBounty
Project Director and line cook
The Possum Works