340 with KB243 pistons

[75dartsport]

I have a question? I'm looking to purchase a 340 .040 with KB243 pistons. They should come above deck .018. Would I be able to use a closed chamber head if I go with a .045 to .060 head gasket. Or is there something i'm missing?

 

[75dartsport]

Anyone?

 

[75dartsport]

I know someone out there knows the answer i'm looking for?

 

[1wild&crazyguy]

You can use q closed chamber head...but with .050 thick gasket ull only have .032 clearence.
I would like to see .035-.039 but u could get by.

 

[moper]

Yes - assuming the deck height is at blueprint, and with that piston and a factory rod you can get the quench down to .030 with no wories.

 

[75dartsport]

Thanks.

 

[ValiantRacing]

I have one that is .023 out and run a .066 gasket and works just fine

 

[mopar410]

I have that same set up with open heads at roughly 66cc.Calculated with .039 compressed gasket with 4.1 opening it get 10.34:1 ratio so if you are planning to run pump gas you may want to rethink all the components for your build.Just saying

 

[72bluNblu]

I've got a 340 I built up with KB243's. They ended up exactly .018" over the deck with my '68 340. I decided to run open chamber 308's on mine. Not saying you can't run closed chamber heads, but you're going to have to run them with a pretty fat head gasket to make it work and get your compression down to pump gas levels (if that's what you're looking for).

Just some info also, I actually got some additional info from KB on calculating the compression ratio.

This is my email to KB tech

The KB 243 specs state that it should be .018" over the top of the deck.
However, the small pop up on the top of the piston is .030" tall (from the
shoulder to the top of the piston). So, in order for the top of the piston
to be .018" over the deck, the shoulder of the piston is .012" below the
deck. My pistons do measure at .018" over the deck (to the tops) as
specified, so the piston shoulder sits .012' below the deck surface.

My question then is what to put into the compression calculator? Is the
.012" to the shoulder of the piston taken into account in the 6cc piston
head volume, or do I need to enter that separately?

The specs on my 340 are:
bore: 4.1"
stroke: 3.31"
cylinder head volume: 64cc
head gasket thickness: .040"
gasket bore: 4.125"

with KB 243's measuring .018" above the deck at the top of the piston.

And this was the response...

Hi,
The protrusion has to be treated like it is a dome so the piston is down in
the hole .012 and it has a .030 thousands high dome of 2.08cc's.This all
equates to positive 7.3cc's.Use this to calculate your compression ratio.
The 6cc's figure is incorrect and the 7.3cc is the one to use. Your ratio at
4.100 bore is 9.95 to 1.
Tech

So if you really do end up .018" over the deck, you can use the +7.3cc for the piston volumes, and run the piston above/below the deck number at .018.