piston to head clearance

[moparpoor]

Good Grief boys, this is a quench dome piston. It is designed to stick up inside the open chamber of the 88cc RPM or the factory large chambered head like the 906. The piston dome should be milled down to at least zero deck if he is using the .040 thick gasket with the 81cc Stealth head. Milling even further would be appropiate if required to obtain the desired compression ratio. Whatever that unannounced ratio may be.

So you really think they need to be milled down!He has already said the dome sticks up .033 past deck,head gasket is 0.039 plus,chamber is well beyond .100 deep. :eusa_think: Compression will still be low enough to run 93 octane with no problems.You have to remember all KB pistons are way down in the hole at least .010.Do as KB suggest and clay to check for clearance.I don't see it being a problem on paper at all.Check it with clay and find out exactly were he is.

 

[Cranky]

Isn't a Stealth head closed chamber?

 

[IQ52]

I'm with you Cranky.

Boys, this piston was designed for the open chamber head, there is NO OPEN CHAMBER on the STEALTH head like there is on the 1968 and later big block heads! If the dome sticks up .033" past the deck and he uses a .039 gasket he has .006 piston to head clearance. You dont need clay to measure that!

 

[IQ52]

IQ52..I gotta say, thats playin it TO safe ... granted your right !!!!!!!!!! BUT wouldn't it be a little better to know EXACTLY how much to cut by claying...then Guessing ??? I'm sorry I'm from the OLD SKOOL of engine building the measure twice ...cut once...law does apply here.... JUST MY Opinion

I'm not guessing.

I'm using the measurements he gave me. I only used the 88cc RPM head for illustration as it has an .060" chamber cut that gives it another .060" quench area. The OP, IF he was using the 88cc RPM head and the 8519PT1 head gasket, would have .066" piston to head clearance.

Because, .039" gasket +.060 head chamber minus the +.033 deck height on the piston = .066"

He is not using the RPM 88cc head, he is using the Stealth which has NO chamber like the RPM head. So again, he has .006" clearance if he is using a .039" thick gasket and has .033" above the deck.

 

[arizona satellite]

ok guys I checked with clay this morning and after milling the quench dome to zero deck with the .040 gasket and head torqued it yeilded a 0.039 clearance. thank you all for the input. oh and by the way I am shooting for comp in the 10.5-11.0 range. I think this should be close. you all had me second guessing about the piston orientation with the "dome" being above the valve pocket.

 

[moparpoor]

Are the domes rising into the chambers or the flat quench area????Take a pic and post please!The domes should rise into the chambers at the valves and spark plug,not at the flat quench area

 

[67 B-body]

Are the domes rising into the chambers or the flat quench area????Take a pic and post please!The domes should rise into the chambers at the valves and spark plug,not at the flat quench area

I'm with you,,, I don't get the dilema. The domes should prutrude in the "D" chamber area of the head, not the flat portion. Why have a domed piston just to cut it down flat again?

 

[67 B-body]

I'm with you Cranky.

Boys, this piston was designed for the open chamber head, there is NO OPEN CHAMBER on the STEALTH head like there is on the 1968 and later big block heads! If the dome sticks up .033" past the deck and he uses a .039 gasket he has .006 piston to head clearance. You dont need clay to measure that!

You dont need an "open chamber" head to have domed pistons....... Mine are 75CC certainly not "open chamber" with .140" domes on the pistons!
Not to mention the chamber design being D shape not heart shape gives you even more space to fill up with a dome piston. Unles your building a flat head "no combustion chamber" you have a void that a dome would be able to fill "ABOVE DECK HEIGHT". I'm at a loss on this one.... Am I missing something here?
Is the non domed section what the OP was suggesting was .030" above the deck? Or was it the "dome" as stated?

 

[67 B-body]

Here's a look.

 

[67 B-body]

75cc Victor Head with Domes underneath.

 

[moparpoor]

I am thinking it's a simple booboo that all of us have made at one time or another!!It could be a very costly mistake if not caught early.

 

[Cranky]

The KB236 piston is a quench dome or reverse dome piston, right?

 

[67 B-body]

The KB236 piston is a quench dome or reverse dome piston, right?

????? Perhaps that would explain everything...

 

[Cranky]

That's where I first got cornfused early on......

 

[67 B-body]

Ahha... That is the case! the damn thing has a step on the "what would be flat" portion of the piston! Otherwise, it's a flat top... I still dont get it though.... Whay would you get it, then mill it flat? Whats the point in buying these?

 

[67 B-body]

Here's a picture of that thing...

 

[383man]

Good Grief boys, this is a quench dome piston. It is designed to stick up inside the open chamber of the 88cc RPM or the factory large chambered head like the 906. The piston dome should be milled down to at least zero deck if he is using the .040 thick gasket with the 81cc Stealth head. Milling even further would be appropiate if required to obtain the desired compression ratio. Whatever that unannounced ratio may be.

This is correct. The question I have is he using open or closed chamber heads ??.. The quench pad piston is to be used in an open chamber head so you can try to get quench. Yes you can use it on closed chamber heads but you have to cut the quench pad off. At .033 above the deck if it is a closed chamber head and a .040 gasket you would only have .007 head to piston clearence. If they are open chamber its alot of work to get the .045 quench (head to piston clearence) that you want.
I used the KB quench pistons you see in this pic in my old 440 with open chamber 906 heads. This is just a mock up here as the rings are not on the pistons. You will need to install all the pistons and take all the measurements of how far the quench pad is above the deck and how far the piston flat is below the deck so you can also determine comp ratio. Then you have to measure the depth of all the open chambers on the heads and do the math including the head gasket thickness. Thats with open chamber heads. If they are closed chamber heads either get new pistons or mill the quench pad off.

Here is how my 440 came out that I used to run. My heads had been cut .060 so my chambers were not as deep as a stock chamber.

Piston quench pad above the deck - .054
Piston flat below the deck - .023
Head chamber depth - .026
Head gasket thickness - .074

So it came out at .046 quench which is what I ran it at and the comp was 10.0.
It had .020 below the head gasket (.020 + .026 = .046) and the chambers were .026 deep which gave me .046 quench piston to head clearence ( .020 piston flat below the head gasket and the .026 depth of the chambers). It was alot of work to try to get all the chambers equal as you have to check them all and check all the piston pad heights.
If it was me I would use a closed chamber head and a flat top piston at zero deck with a .040 head gasket. The only reason I used the quench pistons in my old 440 was I had all of these laying around. My new eng the 493 is closed chamber heads with a dished piston to get 10.6 comp and it has a flat on the chamber side for .046 quench in my new eng as my pistons came out .006 below the deck. Ron

 

[arizona satellite]

Ahha... That is the case! the damn thing has a step on the "what would be flat" portion of the piston! Otherwise, it's a flat top... I still dont get it though.... Whay would you get it, then mill it flat? Whats the point in buying these?

the reason for the purchase was the fact that the original plan called for open chamber heads and then the wallet opened and stealth heads fell out:headbang: so now with the small step in the quench area I pick up a little more comp.by milling the step down from 0.060 to .027 i will pick up small amount of comp.:blob1:

 

[67 B-body]

yep, I figured that after seeing everything.... I have never used a piston like that in the past, so it took a bit of time before I figured out what was going on.

 

[arizona satellite]

no problem guys, I have never used one either so I had to sit back and rethink it all. I was like why do I need to mill the dome down??? I was used to the "dome" being in the chamber area NOT the quench, but it is all good now and with what I hope to be a 10.5-1 motor it should work out fine, again thanks for ALL the input, the members on this site are by far some of the best!!!