The International Cessna^® 170 Association

Rebuilding my 0-300 and have heard from several sorces an increase in compression is possible and advantageous.
Performance engines has a 9 to 1 piston -- anyone know anything about this ?
Have been told by several that the C-85 piston is also a little taller and works well to raise compression (legal in experimental is my understanding ). One shop owner said the piston had to be relieved for plug or valve clearence ?
Positives for the compression increase -- horsepower -- cleaner burn=less carbon -- using the 100LL more efficiently
Negatives ??
Seems to me the same application as the 0-320 increase from 150hp to 160hp.

Negatives might be is it legal? Anyone can improve the performance of any engine if they aren't restricted by regulation.

Can't recall hearing of a legal way to improve the HP* of our engines and I'd think we the forum collective would know of these things. 0-300s have been around for a long time. If performance enhancements for the 0-300 existed you'd see them all the time. We don't because they don't exist.


*Discounting that fancy power exhaust George likes so much of course.

You can raise the compression with pistons,but the engine then no longer meets the manufacturers spec and is out of certification specs. OK on an experimental but not on a certified aircraft.

If it was possible to change my airplane registration to experimental, and be able to use it for normal operational type flying as is done on a homebuilt, I'd do it in a heartbeat. Think of the possibilities! No more worrying about "one time" approvals, and I could install that turboprop engine!

It would not necessarily result in "cleaner" burn of 100LL. (Which isn't the problem anyway.) Leaning your engine will result in a clean burn.

The reasons it isn't approved are numerous. You know, this engine holds several world records for longevity and reliability. What will the life of your well-used crankshaft be if you increased the hp? And how much would it really increase without a prop that allowed the rpm to turn up? How would it affect the dynamic balancers on your crank? How would you utilize the increased hp with the same prop? Or are you willing to spend $2500-$5000 additional or so on a different prop? What would the effect be on the valves? Would the carburetor still be optimum or would it need to be changed? Would you need a new superduperexhaust?

(Having invested additional money into it, would your new superduperplane still be insureable? Or would you be willing to take the risk upon yourself for you and your passengers?)

One of the really interesting aspects of motorized hobbies such as hot-rod cars, is the fun of "hopping" them up. One of the fun things about airplanes can be the restoration to a legal status, with legal documentation, using genuine, legal parts. It's a pride-of-ownership accomplishment thing. IMHO.

Oh George,

Have you no sense of adventure?