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Master Fabricator
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Discussion Starter #1
I have a set of JE Blower Pistons (#257950) going into a tall deck Dart Big M. The CI is 598.

The paper work with the pistons recommends .004 - .005 wall clearance and .001 - .003 additional clearance for power adders.

I called JE they recommend .005 - .006 clearance. I wanted to get a second opinion from the members here.

This is a gas blown application running 10 -15 lbs of boost.

Let me know if you need any additional information.

Thank you.
 

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I called JE they recommend .005 - .006 clearance. I wanted to get a second opinion from the members here.

This is a gas blown application running 10 -15 lbs of boost.
Thank you.
If you keep it in that boost range the .006 will be just fine.

Blessings.........Ron.
 

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Master Fabricator
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Discussion Starter #4
Would there be any disadvantage to adding an additional .001 to make it .007 in case I decide to up the boost a little more?

I am just trying to think ahead for the future.
 

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aside from a more pronounced amount of piston noise. Not really.


Would there be any disadvantage to adding an additional .001 to make it .007 in case I decide to up the boost a little more?

I am just trying to think ahead for the future.
 

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If you keep it in that boost range the .006 will be just fine.

Blessings.........Ron.
Ron, what have you been doing when boost is well over 30.
 

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It's dangerous giving piston to cylinder wall clearances to someone over the internet without know the specific piston that's being used.
That's why you really need to work with the piston manufacturer. They need to know exactly how you are using the piston. Expansion rate is specific to the piston design, piston material and how much heat it's going to see.

But to answer your question about bumping it up to .007. Probably won't make much difference in the overall of things. If it's not seeing the extra heat it will have a little more piston rock. Which if your class racing will give up a little power from ring seal. But if your just racing in general you'd be hard pressed to detect a power difference.

To answer the last question, I'm currently running a specific designed Diamond piston for a high boost (38+psi) non-intercooled gas application. It takes .009 clearance and the pistons happy.

Blessings.........Ron.
 

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I was watching a couple of kids rebuilding a blown nitro engine in a low budjet fuel altered and I don't know what the clearence was but if you could have probably put a penny between the skirt thrust surface (coated, teflon?) and the wall...cold at least ;) it was really amazing the thing would seal enough compression to run cold.

Richard Gavle
 

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I was watching a couple of kids rebuilding a blown nitro engine in a low budjet fuel altered and I don't know what the clearence was but if you could have probably put a penny between the skirt thrust surface (coated, teflon?) and the wall...cold at least ;) it was really amazing the thing would seal enough compression to run cold.
Richard Gavle
It dosen't stay cold very long:rolleyes:.

Blessings.........Ron.
 
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