head gasket question

[steve340]

Above post is quite right. If the pistons stick out of the block or are zero deck you will have a major collision with a 27 thou head gasket.
You need a safe minimum of 40 thou between the cylinder head and the piston top.

 

[dvw]

Before swapping anything use should remove the head. Then measure the bore, deck height, chamber volume, and piston to valve. Also how far the rocker adjuster can be backed out of the rocker and still have running clearance. Then knowing the actual current compression and safe piston to head you can make an informed desicision. The heads may be able to be milled. If you also have the intake side of the head milled as well, everything will bolt back together. Depending on the amount of milling and gasket thickness the pushrods may end up being to long. Isn't all this fun.
Doug

 

[ksurfer2]

Looks like I will put this on hold. I am just trying to squeeze as much as I can out of this engine without doing the bottom end. From what I have been able to find out, the pistons are 17cc dished and .015 in the hole. My cranking compression is 150psi. I was hoping to bump that up some and a thinner head gasket seemed like a easy way to accomplish that.

 

[PRHeads]

“Assuming” the bore is .030 over, and that the .049 measurement is correct for the gasket thickness, and that the heads are 75cc...... with the pistons down the hole .015, combined with the 17cc dish....... would put the CR at right about 10.5:1.
Changing the gaskets to .027 would bump it up to 11:1.
Taking another 5cc out of the heads would put it at about 11.5:1........ for a total increase in CR of one point.

Personally, I’d just leave it as is and wait until you’re willing to really get into the bottom end and swap out the pistons for flat tops.

Then with the thinner gaskets along with some head milling you could be up to 12.7:1.
At which point you could go up to a more suitable sized cam for additional power if you wanted it.

 

[padam]

“Assuming” the bore is .030 over, and that the .049 measurement is correct for the gasket thickness, and that the heads are 75cc...... with the pistons down the hole .015, combined with the 17cc dish....... would put the CR at right about 10.5:1.
Changing the gaskets to .027 would bump it up to 11:1.
Taking another 5cc out of the heads would put it at about 11.5:1........ for a total increase in CR of one point.

Personally, I’d just leave it as is and wait until you’re willing to really get into the bottom end and swap out the pistons for flat tops.

Then with the thinner gaskets along with some head milling you could be up to 12.7:1.
At which point you could go up to a more suitable sized cam for additional power if you wanted it.

Plus racing fuel.

 

[PRHeads]

Another option is get it to 11-11.5:1 and have the heads ported during the “off season”.

In particular, if those heads are the 2nd generation version, and have zero porting, there is def some flow/horsepower there for the taking.
The lower/mid-lift flow on the 2nd gens is pretty weak ootb.

 

[RemCharger]

Plus racing fuel.

That's the best part!

 

[Budnicks]

if it's a truly a 512cid
it should be a
4.380" bore x 4.380" x 4.25" stroke x 8 cyl. x .7854 = 512.295 cid
depending on how much deck the deck has been removed
checking compression height 'of the pistons',
how much below the (block) deck surface
will dictate quench area

 

[Budnicks]

What cylinder heads are you using. Make sure the fire ring does not overhang the combustion chamber. I heard the early Edlebrocks had this problem.

IIRC it was more the early Stealths were an issue
I had it happen, & 440source made (edited spelling, damn) it good
I didn't notice any on the Edelbrock 84cc RPM heads
I used to replace the early Stealths
that broke/dropped a cheap *** org. as supplied 'Chinese valves'

 

[RemCharger]

IIRC it was more the early Stealths were an issue
I had it happen, & 440sorurce mad it good
I didn't notice any on the Edelbrocl 84cc RPM heads
I used to replace the early Stealths
that broke/dropped a cheap *** org. as supplied 'chinese valves'

Yeah it's all fun and games until a valvehead takes out your motor

 

[451Mopar]

You will have to check the cylinder head chamber diameter, it could be larger/wider than the engine bore size.
I would use a gasket that is a bit larger than the chamber/bore size it won't change the compression much and having the gasket seal all the way around is more important than a tenth of a compression point.

What dish pistons are in the engine? With flat tops you should be around 12:1+

 

[ksurfer2]

You will have to check the cylinder head chamber diameter, it could be larger/wider than the engine bore size.
I would use a gasket that is a bit larger than the chamber/bore size it won't change the compression much and having the gasket seal all the way around is more important than a tenth of a compression point.

What dish pistons are in the engine? With flat tops you should be around 12:1+

17cc dished

 

[451Mopar]

I was thinking it might just be easier to replace the pistons with the flat tops?