Pistons - High compression Vs Low compression

Not cub related - sorry

In my Glastar Sportsman is a hotted up 200hp I0-360 built by Performance Aero Engines. 200 hours only. There have been a lot of problems with these engines where they fitted forged 10:1 pistons without the appropriate bore clearances. I found stuck exhaust valves, scored barrels and gudgeion bushes honed not bored. Hence I am up for a tear down and at least new pistons, rings, valves, guides, gudgeion bushes, and big ends just for the hell of it. Nothing indicates that we need to split the case but I don't trust the PAE so I am going the whole hog.

My question is, should I put High comp pistons back in?

The motor has been ballanced and polished and is reported as being 200hp and it is my cross country speed machine that was supposed to replace my RV6 which I am regretting I ever sold.

If I go for the standard comp cast pistons (I think that is 8.5:1) I will loose that Hp but might get a more reliable engine?

And are there any recommendations of piston suppliers?

Col Goldy

Lycon NFS pistons.

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Combustion Technologies http://combustech.com/contact/default.html

I seem to hear about a lot of 10:1 piston hot rods that don't make it very far before a new top is required. I am sure it can be done but lots of factors have to be considered. Proper engine monitoring would be key in figuring out issues before the become big problems. Sounds like yours was doomed from the start.
DENNY

DENNY said:

I seem to hear about a lot of 10:1 piston hot rods that don't make it very far before a new top is required. I am sure it can be done but lots of factors have to be considered. Proper engine monitoring would be key in figuring out issues before the become big problems. Sounds like yours was doomed from the start.
DENNY

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More compression = more horsepower=more heat . That said I know many engines with 10:1 that go full life without issue, I have also seen stock engines require a top very early , probably within a few hundred hours.

If you control the cooling, service the engine well and don't run it hard it should last as long as any .

I just redid my cylinders, I did have the port and polish including flow matching done. I opted to go with stock pistons mainly because the majority of the benefits are there from that process, I also run a powerflow exhaust . Adding the
10:1 will not add the additional HP over what I have done, probably more like another 5HP. Bonus I can still run auto fuel with the STC I have, though I will still run a 50/50mix for the most part .

Bottom line, 10:1 seems to work very well if getting work done anyway, control the cooling and service the engine you will have no more problems that with any other engine .

Thanks everyone. I also posted this question on the Lancair, Glastar, Beech and Vans forums. After all the wonderfully incitfull comments I have decided to go for either 8.5 or 9:1.

It seems that that's the best chance of achieving 2000 hour TBO and a little less critical when it comes to engine management. And roxiedog summed it up pretty well I think re port and polish balance and machflowing.

Other comments that stuck in my mind were.

"Building with HC pistons and your building a hand grenade"

"10:1 and your TBO will be 1000 hours.

"If you want more HP get more cubic inches"

Have had 4 recommendations for combustion technologies.


Thanks again.

Col Goldy

roxiedog13 said:

More compression = more horsepower=more heat . That said I know many engines with 10:1 that go full life without issue, I have also seen stock engines require a top very early , probably within a few hundred hours.

If you control the cooling, service the engine well and don't run it hard it should last as long as any .

I just redid my cylinders, I did have the port and polish including flow matching done. I opted to go with stock pistons mainly because the majority of the benefits are there from that process, I also run a powerflow exhaust . Adding the
10:1 will not add the additional HP over what I have done, probably more like another 5HP. Bonus I can still run auto fuel with the STC I have, though I will still run a 50/50mix for the most part .

Bottom line, 10:1 seems to work very well if getting work done anyway, control the cooling and service the engine you will have no more problems that with any other engine .

Click to expand...

I looked at it on my RV8 a few years ago, and a local engine builder also made the 1000 TBO comment with 10:1 pistons.

lancef53 said:

I looked at it on my RV8 a few years ago, and a local engine builder also made the 1000 TBO comment with 10:1 pistons.

Click to expand...

One would think the engine should have made more than 200hrs unless there were other mitigating issues causing the short life.
Were there overheating issues involved?

cgoldy said:

Thanks everyone. I also posted this question on the Lancair, Glastar, Beech and Vans forums. After all the wonderfully incitfull comments I have decided to go for either 8.5 or 9:1.

It seems that that's the best chance of achieving 2000 hour TBO and a little less critical when it comes to engine management. And roxiedog summed it up pretty well I think re port and polish balance and machflowing.

Other comments that stuck in my mind were.

"Building with HC pistons and your building a hand grenade"

"10:1 and your TBO will be 1000 hours.

"If you want more HP get more cubic inches"

Have had 4 recommendations for combustion technologies.


Thanks again.

Col Goldy

Click to expand...

I agree, there is no replacement for displacement. Provided the weight penalty, installation fitment and cost are acceptable, it will always yield the best solution . When I built up my O-320 , actually still a work in progress, I chose the stock 8.5:1 pistons
simply because the 10:1 alternative realistically only yields 5HP more combined with the other improvements but has the potential to raise heat levels, potential for detonation, can lower longevity and also requires AVgas only to be used.

If my engine was due for full overhaul the O-360 would have been on the menu but for the improvements I have made I get 95% of the benefits at a fraction of the price.