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Which Pistons?

D.A.

D.A.

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Free America
There are a few great threads on here from the past about putting high compression pistons in a Continental and now that more time has gone by I'd like to revisit the subject and ask a few questions.
  1. From what I can see there are 3 primary high compression Continental piston providers, NFS, LSE and Ly-Con. Has anyone had issues running any of these pistons?
  2. The NFS pistons are 9-1 and others probably have that compression as well, can you run Mogas reliably at this compression?
  3. Do the high compression pistons make enough of a performance increase at NORMAL operating ranges to warrant the time and expense of installing them? One of the posters seems to exceed redline regularly, that's not what I'm talking about. I'm referring to a C-90 or O-200 operated within the normal RPM range with high compression.
  4. Are there any pistons that we should stay away from?
  5. Are there any piston providers that I didn't list that are recommended?
Thanks in advance.
 
Maybe ask Bob Barrows, the Bearhawk guy, his LSA that he built the engine for has 9.5 to 1 pistons in it. C-85
 
I used the O-200-D pistons for 8.5:1 compression. Had to turn the top ring groove to square it up to use the O-200-A ring set rather than the overpirced and unavailable O-200-D ring set. I run it on a diet of Alcohol free premium Mogas.

-Cub Builder
 
I ran the LY-Con for a while in 300 hour cylinders on a c-90, Loved the power hated the smoke after 10 or so hours reringed same thing after break in, oil consumption was about a quart every two hours, ran them for a couple hundred hours the re-cylindered again (stock) still have the good cylinders and 9 or 9.5 to 1 pistons for another try down the road. have finally got most of the black off the bottom of the plane. Some guys have had great luck with them, they are a three ring piston but I think the problem was oil through the exhaust valve but never dug into it to find out for sure.
 
I'm running the NFS pistons in the O-200. We run it on ethanol free 91. Yes it's worth the time and effort. Your oil consumption will go up a bit going from the 4 ring piston to a 3 ring piston.


Matt
 
supercubc37 said:
I'm running the NFS pistons in the O-200...
Click to expand...
Is there any machining required with the NFS pistons or are they just plug and play? I thought I read on one of the threads that one of the high compression pistons required that you ream the wrist pin bushing to accept a different size wrist pin, but I can't find that thread again and I can't remember the piston manufacturer. Are most of the high compression pistons 3 ring?
 
tempdoug said:
Would the 85 pistons be an option?
Click to expand...
I originally thought of the 85 pistons and I know that used to be the trick set up, but it doesn't raise the compression as much as you'd think, maybe only 8.5 or so if I remember correctly. I read one thread where a guy said he ran 85 pistons and the top ring was actually traveling past the top of 2 of his cylinder barrels.
 
D.A. said:
I originally thought of the 85 pistons and I know that used to be the trick set up, but it doesn't raise the compression as much as you'd think, maybe only 8.5 or so if I remember correctly. I read one thread where a guy said he ran 85 pistons and the top ring was actually traveling past the top of 2 of his cylinder barrels.
Click to expand...

That was my engine that had that issue on a set of older cylinders. I must have been a bit unlucky as I haven't heard of anyone else seeing that issue. but with so many different pistons available, why mess with the C-85 pistons?

BTW, the O-200-D piston is also only a 3 ring piston (2 compression rings). I turned the top ring land square to accept the top ring from the O-200-A ring set and installed in new Superior cylinders. (The O-200-D piston has a tapered top ring) Only have ~ 100 hrs on the engine since installing pistons and cylinders, but my oil consumption runs at roughly 1 qt/15 hrs. Also changed over to Pmags at the same time.

-Cub Builder
pistons.jpg
O-200-D piston next to O-200-A piston.
 

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Just install and go. It's already got a chamfer cut into the top of the piston to fit the cylinders. The O-200-D uses the same crank, rods and cylinder as the O-200-A. As a point of disclosure, I don't know how well the straight cut top ring ring will hold up vs the tapered ring. I've only run one compression check last year at 50 hrs since installation. All was well at that time and I have indication of it to be otherwise now. I'll be checking it again in a couple of months when my annual comes due. Currently have ~100 hrs on it now.

-Cub Builder
 
C85 pistons have a lower pin hole for the shorter stroke of the 85. The edge of the dome has to be chamfered to not hit the head of the cylinder. The rings don't travel out of the cylinder. The 85 pistons give noticeable more power. They were much cheaper when I put them in my clipped wing tcart. Also removed lunch be your pipes and put 4 pipe exhaust on it at the same time. Had to open I p the main jet 2 drill sizes.
 
Just thought I'd give an update. I'm running the 9 to 1 NFS pistons in an O-200 swinging a McCauley 1B90CM7443 prop, gutted muffler and the timing set to 28 degrees. It'll turn that combo 2500 RPM static verified using a MicrovibII today during the dynamic balance.


Matt
 
85 pistons in a 90 or O-200 give 8.67:1 compression ratio. On some cylinders (but not all), the top ring will overtop and hang on the top of the cylinder. Makes for a bad day when they do. I've had good luck running 9.5 NFS pistons in an O-200 on premium car gas with ethanol. I like both the 7440 and the 7142. The 7440 pulls a liitle better and has a nice sounding sonic bark at high rpm.
 
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