The International Cessna^® 170 Association

bagarre wrote:.......Higher compression requires higher octane.

Exactly! Or to say it another way, higher octane fuel needs higher compression to work properly. 100LL is the only option for most of us and I can't see a downside unless the engine just couldn't take it. The crankshaft and rod bearings are the same as the IO-360. Unless the cylinders are too weak, it ought to work. And according to Blueldr it does work, very well.

How hard could it be to get an STC?, he said while rolling his eyes.

Claims of higher horsepower, better gas mileage, better whatever are so anecdotal and without documentation ...that it's difficult to believe. The same claims are made about super exhaust systems and snake oils.

Higher compression pistons would also reduce piston-to-valve clearances. What if a valve sticks in flight?
HIgher compression pistons would also increase connecting rod stress. What about reduced reliability due to failed connecting rods? What about increased main bearing wear? What about reduced TBO? What about the mogas STCs?

The reason the experts at TCM never approved C-85 pistons in O-300 engines probably is good. It's not like they didn't have access to parts, or a reason to improve their engines. It must be because it's NOT an improvement!
And/Or it's mod that adversely affects reliability. And/Or there was no money in it. (The last is unlikely, as an improvement would increase sales for them.)

gahorn wrote:Claims of higher horsepower, better gas mileage, better whatever are so anecdotal and without documentation ...that it's difficult to believe. The same claims are made about super exhaust systems and snake oils.

Higher compression pistons would also reduce piston-to-valve clearances. What if a valve sticks in flight?
HIgher compression pistons would also increase connecting rod stress. What about reduced reliability due to failed connecting rods? What about increased main bearing wear? What about reduced TBO? What about the mogas STCs?

The reason the experts at TCM never approved C-85 pistons in O-300 engines probably is good. It's not like they didn't have access to parts, or a reason to improve their engines. It must be because it's NOT an improvement!
And/Or it's mod that adversely affects reliability. And/Or there was no money in it. (The last is unlikely, as an improvement would increase sales for them.)

Anecdotal data isn't necessarily wrong. If it didn't do anything but reduce valve sticking, it would be an improvement. Would a stuck valve actually hit a piston?

The crank, rod bearings, and main bearings are already identical to the IO-360 of 210hp.

What about hitting the trees at the end of the runway because of lack of power?

I'm sure Cessna had its reasons, heck they built all sorts of aircraft that never made it to the production line, and some that did make it and were flops. Whatever the reason Cessna did not do it then might not be valid today with no 80/87 and alcohol in the mogas.

I gave up the mogas STC in my 180 when I went with the O-520 and never looked back. We wouldn't be giving up much today by not using mogas STCs since very few can even use the mogas STCs they have.

hilltop170 wrote:...Anecdotal data isn't necessarily wrong. If it didn't do anything but reduce valve sticking, it would be an improvement. Would a stuck valve actually hit a piston?

The crank, rod bearings, and main bearings are already identical to the IO-360 of 210hp.

What about hitting the tree at the end of the runway because of lack of power?

Huh? Since when did anyone claim C85 pistons would reduece valve-sticking?

The IO 360 doesn't make it's horsepower due to C85 pistons. It uses different cylinders, different valves, and different pistons, and different piston pins, rods, and rod bushings. It also uses different props.

HItting a tree at the end of the runway is not likely due to lack of power, It's likely due to lack of preflight planning!

OK, so you wouldn't do it, fine, but that doesn't mean it might not be a good conversion

We just cannot let bluEldr toss out here that all anyone has to do is install illegal pistons in our engines and everything will be hunky-dory. 'Taint so.

An properly functioning engine of any horsepower rating is capable of hitting a tree at the end of the runway. It isn't a lack of horsepower that is the cause, it is a lack of planning.

FredMa wrote:An properly functioning engine of any horsepower rating is capable of hitting a tree at the end of the runway. It isn't a lack of horsepower that is the cause, it is a lack of planning.

I was just playing "what if?" with George.

was everyone typing at once or what? I see george beat me to the punch.

There are OTHER issues as well.
What about harmonics with the propeller when the engine has been modified to higher compressions.?
What about engine mounts? What if higher compressions DID result in changed performance? (Remember the Lockheed Electras?)
There are valid reasons such homespun modifications need professional engineering scrutiny. Just because one's brother in law races hot-rods doesn't mean his logic works well with airplanes.

gahorn wrote: Higher compression pistons would also reduce piston-to-valve clearances. What if a valve sticks in flight?
HIgher compression pistons would also increase connecting rod stress. What about reduced reliability due to failed connecting rods? What about increased main bearing wear? What about reduced TBO? What about the mogas STCs?

There are OTHER issues as well.
What about harmonics with the propeller when the engine has been modified to higher compressions.?
What about engine mounts? What if higher compressions DID result in changed performance? (Remember the Lockheed Electras?)

That was the question George, could the engine take it? Who knows, I sure don't but it would be good if someone did, like the guys that designed the O-300 if they are still alive.

FredMa wrote:was everyone typing at once or what? I see george beat me to the punch.

Yeah...I think we're all on the same subjecgt simultaneously. Richard even edited his post and it made my response seem misdirected until I also edited it.

Aryana wrote:Just give me a viable TCM IO-360 STC and I'll be happy. Oh, and while I'm dreaming I'd like it for the same cost as a O-300 please.

I agree, if there was one out there, I would have done it instead of overhauling the old O-300. But, if just changing the pistons was indeed a good mod, I would do it now (but only if it was legal, George).

We haven't had a discussion this spirited in a long time!

The guy that I am, or was, acquainted with that had the bootlegged pistons in his O-300 seemed to be very well versed in the business and claimed to a lot of experience with that modification in the O-200 engines used in racing. When we met the first time, It was during the annual Swift fly in at my airport. At that time I had posted a for sale notice for a Continental IO-360D engine that I had in my hangar. That's a popular modification for the Swift too and he came down to look at the engine I had for sale. We spent quite a visit together. as I said, he seemed to be very well versed in what he had done. Unfortunately, he was unable to buy my engine at that time, The following year, during their annual fly in, he looked me up, but I had sold the engine by that time. I never thought to ask him if there was a possibility of interference if a valve stuck. I think maybe that was because I have never had a stuck valve and as a result I don't often think about them.

The O200 engines for Formula One are supposed to be stock. They way they get more HPs is to use a short prop and wind the engine up to 4000+ rpm.