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Onan JB/JC High Compression Pistons


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  #1  
Old 05-17-2016, 11:24:26 AM
nothingbutdarts nothingbutdarts is offline
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Default Onan JB/JC High Compression Pistons

Well, I'm thinking about seeing if anyone has a set of 4 high compression pistons that they want to sell. Since I can't get full A/C output on my JB I would imagine it will be the same for a JC I have torn apart and think I might go with the high compression pistons because of living @ 8,700'.

Pistons for sale or comments anyone????
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Old 05-17-2016, 11:33:33 AM
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Default Re: JB/JC high compression pistons

What's the parts number , we can search too.
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Old 05-17-2016, 12:16:32 PM
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Default Re: JB/JC high compression pistons

I think Jim McIntyre milled the head on a JB to raise the compression. What fuel are you running?
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Old 05-17-2016, 12:36:58 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: JB/JC high compression pistons

Nope. I would if I had an extra JB head to tinker with. I have done this on several CCKs with success...
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Old 05-17-2016, 01:02:22 PM
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Default Re: JB/JC high compression pistons

Piston # 112-0174 Std. bore
112-0174-10 .010
112-0174-20 .020
112-0174-30 .030

I will be using either gasoline or propane, mostly propane but, if I needed too I would run gasoline.
Really looking for STD. bore pistons.
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Old 05-17-2016, 01:06:17 PM
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Default Re: JB/JC high compression pistons

Someone tried it here on the site. Can't remember who.
The only other way I would think of gaining power for altitude loss would be turbocharging with a small amount of boost. Use a small turbocharger like the ones used on the Kubota diesels.
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Old 05-17-2016, 01:10:51 PM
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Default Re: JB/JC high compression pistons

Can't get full AC power?

What happens? What is the indication you are not getting full power? Frequency drop off, voltage drop off?
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Old 05-17-2016, 01:26:14 PM
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Default Re: JB/JC high compression pistons

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Originally Posted by Motorhead View Post
The only other way I would think of gaining power for altitude loss would be turbocharging with a small amount of boost. Use a small turbocharger like the ones used on the Kubota diesels.
Or get creative and use a supercharger, I know there is a small Mazda supercharger on ebay right now
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Old 05-17-2016, 02:02:33 PM
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Default Re: JB/JC high compression pistons

Here you go....
http://www.theboombopshop.com/Garret...ett-gt1241.htm
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Old 05-17-2016, 02:34:31 PM
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Default Re: JB/JC high compression pistons

I have run 2-6.5NH's, a DKD and a JB, none will get full A/C output. On all, the throttle is wide open and the HZ/RPM just starts dropping.

If you refer to the charts on here you will see Onan's derating figures:

http://www.twinslan.net/~n0nas/manua...%20GenSets.pdf

I figure I would not put a turbo on it, lots of money and modifications so I figured if the compression was raised that would help gain back some lost horse power because of the altitude.
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