I've had 243 heads milled .075" before, anyone gone farther?, if so, how much and where did your chamber c.c. end up at?

 

I have not seen 243 heads milled that far personally but I know the general rule for milling and chamber size is .006" per cc.

 

what was the end result of that motor? 243's shouldn't be milled any more than .035"

 

I was advised not to go more than .035" due to possible fitment issues.

 

milled mine .040 and cut flycuts into the piston

 

Why do you say that?, did you have issues milling farther than .035"?

The only issue for me was manifold fitment, I cut off the plastic nubs and just used the brass ones to locate the manifold.

The 243 heads were ported by AI, went 10.60's N/A on my flycut but unassembled LS1 short GTO.

I am asking because if everything works out, I want to try to run NMCA Mean Street with the car next year. I must use unported LS6 heads, but can valve job any way I want, and can mill as much as I want.

 

.075 is a **** ton. I've never been past .045 on any GM casting.

 

I think anything beyond .045", I would be concerned with quench area being too tight, among other things.

 

Not sure what you are getting at, but the distance between the piston and the head deck surface doesn't change with milling. Only milling the deck on the block, changing head gaskets, or changing compression height on the piston will change the quench.

To the OP - if you need to mill the heads that far to get your compression where you want it, you need different pistons. What are you trying to build?

 

I think I was having a brain fart. I forgot that the quench area of the head is milled right along with the rest of the head. Sorry lol

 

If I do the engine it will be 365 c.i., and per Mean Street rules a flat top piston must be used, need as much compression as possible, and can't just throw a dome on it. Sounds like I've already milled farther than anyone else.

 

I've got .050 (on 5.3 heads) done with no ill effects, however we did compensate the intake face to make up for the millling. At that point, the only issue you might run into is the intake bolt holes either need to be shifted, or oval the intake holes in the manifold. We took off .006 intake for every .010 deck. Intake manifold/port alignment was perfect with a victor jr where we could see the floor. Bolt holes were a little pushed up, but on the victor jr, the holes are big.

If the deck surface looks thick, and you're not taking off part of the valve seat, I can't see a problem with your .075, or more.

Using Johns rate of .006 per cc, you're down to 51 - 52cc's. How much smaller you want to go? This puts you at approx 13:1

Down to 47 ccs should take approx .030 more, and leave you with around 14:1, but I would definitely cc at stages before you do a full .100 mill, since the .006 per cc isn't completely accurate. the shallower the chamber, the more cc's you cut for the same amount removed. So a 317 head will lose more cc's for a .030 mill than a 243 head will.

You could try and work on your quench distance as well, since ally blocks expand more, even with the sleeves (although not as much as a all ally block) and tighten it up a little at a time. Just don't run it hard/high when cold!

Have you considered angle milling as well? its a good way to get more cc's milled away if you get close to the intake valve seats.

 

I ended up at about 57 c.c.'s because the chambers were opened up.

Seats weren't close, might try .100" if I end up doing the motor.

 

Ive gone .080

 

Ahh, makes sense why you'd want to go more then.

You could always try lots with a junk head, see where things get iffy...

 

So what was the decision.

 

Which part?, guess I can answer both - will be running Mean Street in 2011, and will be milling the heads more than .075"

 

very nice the setup will rip...compression is where it is at...let us know what the setup runs and puts down...

 

yes, please do comeback with the end results.