GX390 Head milling to raise compression

BrandonF260Rem

New member
Hey guys,
Unfortunately I can't search this topic any more. But has anyone milled a head down to raise the compression on a Honda GX390?
How much did you mill off?
In the process of overhauling a GX390 and putting some performance parts back in. Was wanting to raise the compression some and get some extra power out of it.

Thank you
 

mikelavite#72

Premium User
hey guys,
unfortunately i can't search this topic any more. But has anyone milled a head down to raise the compression on a honda gx390?
How much did you mill off?
In the process of overhauling a gx390 and putting some performance parts back in. Was wanting to raise the compression some and get some extra power out of it.

Thank you
i started with .080 and stayed with it some guys have gone .100+ but then you have more things to change after taking off that much
 

fredjones

New member
nah...and I actually milled the block so the piston was right at the top on the block.....so....thats kind of .300 .....
 

cubcadet70

New member
I've had a head that I've built and it was only milled .110" and the combustion chamber was 19cc and I was running 17:1 compression ratio without any welding. I built this motor for my local pulling class. Must use all stock parts and decking the block and milling the head and porting and Polish was allowed. Had to run stock cam and carb. So I decided to take it to the max! Needles to say it was the best motor I've built for that class. Won two pulls in a row and was on my way to point champion but the motor blew and there went my season.
 

2kdime

New member
I just checked mine today with some clay

1.3 rockers

40mm intake, 35mm exhaust

.360 lift cam

And Ive got no room to mill/deck anything
 
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