I am taking a hard look at a -4 which has the O-320 D2G in her, however, it has new pistons/cylinder assemblies which utilized 10:1 high compression pistons. Should I be concerned at all about any negative impact from this, such as reduced TBO, higher incidence of some kind of failure from the higher engine output (estimated to be 175-180hp), more difficult to start, etc. ? Being an old conservative 170B driver flying over extremely nasty terrain, I do tend to wonder about such things. But otherwise the plane sounds fantastic. Thanks!
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High comp pistons?
- Thread starter RVMike
- Start date
Sid Lambert
Well Known Member
From what one of the better known engine builders told me... You can subtract 500 hours from TBO for every .5 increase you do over 'standard'. 10:1 falls in to their time bomb category. Good for a racer or aerobatic performer but not as good for an XC cruiser. I'm sure someone has a 10:1 that made 2000 hours but it's not the norm.
10:1 is high for me in MY RV-4 the way I fly but I wouldn't run from the airplane. If the engine is a low time SMOH you can drop back down to 9:1 or 8.5:1 for not much money.
The prop will effect starting more than the compression ratio. I lightweight prop can kickback easier.
BTW. I have 9:1 in my O-320 D.
10:1 is high for me in MY RV-4 the way I fly but I wouldn't run from the airplane. If the engine is a low time SMOH you can drop back down to 9:1 or 8.5:1 for not much money.
The prop will effect starting more than the compression ratio. I lightweight prop can kickback easier.
BTW. I have 9:1 in my O-320 D.
1,900 hour 10:1 O-320
I ran 10:1 pistons for 1,900 hours without issue. CHT can be higher if you run hard. Pull the prop back to a reasonable RPM and CHTs drop but you get great fuel efficiency. Valve guides were worn out at 1,900 hours but compression was 68/80 or higher. Cylinder bore was still new spec including taper / choke. I did not reinstall 10:1 but did use 9:1 with new cylinders.
There is no substitute for cubic inches when it comes to horsepower in our Lycoming (or clone) aircraft engines. If you want more horsepower, get the largest engine recommend by Van's Aircraft for your RV.
I ran 10:1 pistons for 1,900 hours without issue. CHT can be higher if you run hard. Pull the prop back to a reasonable RPM and CHTs drop but you get great fuel efficiency. Valve guides were worn out at 1,900 hours but compression was 68/80 or higher. Cylinder bore was still new spec including taper / choke. I did not reinstall 10:1 but did use 9:1 with new cylinders.
There is no substitute for cubic inches when it comes to horsepower in our Lycoming (or clone) aircraft engines. If you want more horsepower, get the largest engine recommend by Van's Aircraft for your RV.
FORANE
Well Known Member
I have about 800 hours on my O-320A with 10:1 pistons.
We have experienced one cylinder stud shear off which my mechanic advised was likely due to the increased stress from the 10:1 pistons. My "a" model O-320 is a narrow deck which as I understand is a weaker design than the later wide deck. If that O-320 D2G is a wide deck it may tolerate the 10:1 better than mine.
Starting in winter has not been a problem for me so long as I preheat. Mine does bog the starter sometimes though which I believe is due to the 10:1.
We have experienced one cylinder stud shear off which my mechanic advised was likely due to the increased stress from the 10:1 pistons. My "a" model O-320 is a narrow deck which as I understand is a weaker design than the later wide deck. If that O-320 D2G is a wide deck it may tolerate the 10:1 better than mine.
Starting in winter has not been a problem for me so long as I preheat. Mine does bog the starter sometimes though which I believe is due to the 10:1.
Cylinder problem
A friend with a Midget Mustang had high compression pistons installed on his Lyc during a professional overhaul. He was doing a low pass at a fly in and one of his cylinders broke loose. The engine kept running enough for him to get down. He stayed with the high compression pistons but is more careful about his RPMs.
A friend with a Midget Mustang had high compression pistons installed on his Lyc during a professional overhaul. He was doing a low pass at a fly in and one of his cylinders broke loose. The engine kept running enough for him to get down. He stayed with the high compression pistons but is more careful about his RPMs.
