Thorp Air Command - T18.net

Hey all,
I'm about to order a run of pistons but would like opinions of what would be most popular size to begin with. One prospective customer suggest .010 or .020 as he will be able to make use of a bunch of cylinders without having them chromed. Also what compression would be most popular. I can do anything from 7.5:1 to 10:1 without a dome. Higher than 10:1 requires fuel that is not generally available on airfield ramps except maybe at Reno during the races and at other performance events. That's right, those fancy race planes are not flying on 100LL. Your input is highly valued and thanks in advance.

Dana

I might be wrong (has happened) but I think .010 over is max on nitrided cylinders as the nitride only goes .015 deep.

_________________
Bob Highley
N711SH
SN 835
KLAL

Disregard previous. Rookie error! Basic machinist math.

_________________
Bob Highley
N711SH
SN 835
KLAL

Bob, You are no rookie. A rookie would not have caught the error and I value input from any of you. I don't care for .020 oversize myself but the guy that suggested that has dozens of O-290 cylinders that would be of value to his airboat customers again. I'll start with one set of each and see what is in highest demand. There has to be more than a couple of these engines out there in the experimental community that would be candidates.

from my point of view, anything less than 10:1 isn't worth doing.
I have four O-290 cores myself.
Before I pull the trigger there is a lot of research that I need to do and i'm not at that point of any project yet.
will the "G" crank take it?
how much will reworking the cylinders cost Vs boring the case and bolting on narrow deck O-320 cylinders, etc.?

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http://www.dixiefriedfabrication.com/

My lowest compression cylinder just dropped down to 58psi when checked this week after sitting the last 6 months for updates. It's not alarming but the AP would like to pull the cylinders, hone and put new rings in. We can't find rings though. What sources do you have for rings on these pistons? I would possibly be interested in a new set of pistons as well if we find more than acceptable wear on the current ones.

I would want stock or not much over stock compression ratio as I sometimes use 90 octane no ethanol petrol. I would like to continue to use some of the 90 octane petrol since it's half the price of avgas. Normally I do cut it 25/75 avgas petrol in order to keep a little bit of lead in the system.

Put some Marvel Mystery Oil in the oil and gas and run forten hours and check it again. Then make your decision.

_________________
Bob Highley
N711SH
SN 835
KLAL

We ran it for about 30 minutes on the ground and did some full throttle run ups without much change. I'd like to get it in the air and run it to free up the rings although the plane is down for other maintenance at this time. We bore scoped the engine and since there is some wear he said it would be best to just hone the cylinders and put new rings in while it was down since it hasn't had good compression for quite some time. The other cylinders came up after the run and this one didn't. The ap is also going to inspect the valve train as well while it's open.

I'm sure I could get away with just running it but while it's down I might as well fix some things.

I'll pm Binder on this and try to expedite a solution for at least getting him rings. As to boring the cases and building a O-320 from O-290, get O-320 sump and intake runners also or your intake track volume will be lacking. It will have a choking effect at higher power settings.