How much can I mill my 318 heads before...

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MrJLR

MrJLR

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How much can I mill my 318 heads before I run into problems like intake bolt holes not lining up etc....
And how much compression will I gain?
Is it even worth it?

They are stock 318 heads from about '74.....I've already done a home porting job on them.
I plan a Whiplash cam & springs...I'll be running my Doug's D453 headers

Thanks!

Jeff
 
From what I've read, .020" off the heads is doable without needing to mill the intake. As for compression... You might be better off just running a thinner head gasket. It's hard to say exactly how much compression would be gained without knowing the cylinder head CC's, pistons, etc.

You'll need to double check your valvetrain geometry if you mill the heads or run a thin head gasket, in addition to making sure the intake will still bolt up.

I wouldn't bother milling the heads, I'd run a thinner gasket if I needed a little more compression. The Whiplash cam is designed for lower compression engines anyways, right?

You should measure everything and do some math before making any decisions.
 
You should gain about 0.9 point of SCR for milling .050". So, yeah, it is worth it, IMHO, especially if you are using stockish pistons that are .070-.100" down in the hole. (BTW, you reduce the combustion chamber volume by approximately 2 cc for every .010" milling on the open chamber heads.)

Going more than about .090" milling will make it go up even faster as it removes the open area of the chamber and you end up with a closed chamber; but .090" inch milling is getting pretty serious so I would not go there for a simple build.

If you are going to the .050" level of head milling, then milling the intake to match the heads holes is pretty much mandatory. IIRC, .009" intake mill per every .010" of head milling is the correct number. Otherwise, it is asking for intake sealing difficulties.
 
I will tell you what I've experienced, and I will also tell you that very few here will agree with me.
I have shaved 360 heads .045 and bolted them on a 318, zero issues. I did not use the end cork gaskets on the intake. I have done this more than once. Zero issues. I've never milled the intake, EVER! However, I've always used the Felpro head gaskets and they are about .025 thicker than the factory metal gaskets, so I have back some of my milling.
I will also say that using 318 heads on a 318, I wouldn't mill any more than .030 to gain back the gasket thickness +. If you end up around a true 8.5 compression, that will be more than sufficient for a healthy 318 to run on todays gas.
 
MrJLR said:
Well.....I don't!
They sure "look" stock.....LOL!
Click to expand...

I would buy new pistons to get the desired compression as I don't think adjusting large compression "bumps" should be done with milling. This makes your engine an "orphan" and cannot interchange parts with other similar engines. :violent1: They now are a custom matched set.... :twisted:


I found that if you put a 10.5 piston into a 318, then add a set of 340/360 heads, the larger combustion chambers for the larger port heads brings the compression down to a nice 9.2.

I know you want to use your newly modified heads after putting all the time in them. You can check the compression for the parts combo that you have by following this thread and work from there:

http://www.forabodiesonly.com/mopar/showthread.php?t=278215

You can also use a thinner head gasket. Fel pro makes a sb head gasket in .062" and .039" thickness. All the kits have the thicker one, you have to dig deep in your pockets to get the .039" one for $40 each.... Sold separately... 4 cc difference....

Or see if there are any others out there that are thinner...

Just a few suggestions...
 
I have seen small block milled .200" before. They were so light I think if they had been dropped, they would have busted in half but that engine ran like gangbusters.

As long as you mill the intake side accordingly, you can mill a lot. I wouldn't recommend .200", but you can go a good bit. lol

Course, my disclaimer is that aint the "correct" way to gain compression, but it'll work.
 
get some 302 heads with smaller CC's off the bat. Even with no porting, they offer better performance than the "cleaned up" open 273/318 castings. They are pretty cheap off any '91+ LA 318 and no intake milling.
 
RustyRatRod said:
I have seen small block milled .200" before. They were so light I think if they had been dropped, they would have busted in half but that engine ran like gangbusters.

As long as you mill the intake side accordingly, you can mill a lot. I wouldn't recommend .200", but you can go a good bit. lol

Course, my disclaimer is that aint the "correct" way to gain compression, but it'll work.
Click to expand...

Holy CRAP! 1/5 of an inch!
I would never try that! I'm talking one tenth that much - .020"

That's pretty crazy...!
 
It was crazy. It was for a dirt track class that allowed only stock type heads, but nothing in the rules about milling. If the guy couldda drove worth a snot he wouldda won cause he had the fastest car. lol
 
RustyRatRod said:
It was crazy. It was for a dirt track class that allowed only stock type heads, but nothing in the rules about milling. If the guy couldda drove worth a snot he wouldda won cause he had the fastest car. lol
Click to expand...

Oh....well that "kinda" makes sense now....
Bet it didn't last long though!
 
pishta said:
get some 302 heads with smaller CC's off the bat. Even with no porting, they offer better performance than the "cleaned up" open 273/318 castings. They are pretty cheap off any '91+ LA 318 and no intake milling.
Click to expand...

Around here, FINDING those is no go
 
krazykuda said:
I would buy new pistons to get the desired compression as I don't think adjusting large compression "bumps" should be done with milling. This makes your engine an "orphan" and cannot interchange parts with other similar engines. :violent1: They now are a custom matched set.... :twisted:
Click to expand...
Besides the non-standard parts, I am trying to think up some good reasons to prefer bumping up CR with pistons versus head shaving. The only thing I can come up with is the thinking/experience that getting rid of the exposed cylinder walls below the head gasket by zero decking the pistons at TDC may lower detonation tendencies. Not sure why this thinking is true.... Any other thoughts to share on why to do one versus the other?

And OP, any reason to shave just .020" versus .040" or .050"?
 
nm9stheham said:
Besides the non-standard parts, I am trying to think up some good reasons to prefer bumping up CR with pistons versus head shaving. The only thing I can come up with is the thinking/experience that getting rid of the exposed cylinder walls below the head gasket by zero decking the pistons at TDC may lower detonation tendencies. Not sure why this thinking is true.... Any other thoughts to share on why to do one versus the other?

And OP, any reason to shave just .020" versus .040" or .050"?
Click to expand...

Just don't want to run into bolt holes not lining up.....I may go as far as .030"
 
My buddy running a 318 has 360 heads on it milled 60 thousands..no problems with any bolt holes lining up..
 
Why don't you just buy my original low mileage 1969 318 heads. They are 69CCs ( I checked them myself) which is one of the smallest CC head made for the 318. I think yours are 63/64CCs. If you use a thin gasket you should be able to get your compression up there???

Treblig
 
Treblig said:
Why don't you just buy my original low mileage 1969 318 heads. They are 69CCs ( I checked them myself) which is one of the smallest CC head made for the 318. I think yours are 63/64CCs. If you use a thin gasket you should be able to get your compression up there???

Treblig
Click to expand...

I have a set of 920's that measure 63 cc's...
 
I went .025" on the heads on my 331 Hemi. Since the chambers are round, it takes MUCH less to remove a LOT of chamber volume. JUST that small amount added about 1 full point of static compression. But guess what? I had to have the intake milled .060" to get it to line up. The intake angle on the heads is so drastic, that it multiplies the angle much more than standard heads. I got it done, though. It pays to always check to see what the intake should be milled.
 

Flat valves can help with CR also. .020" should give you similar chambers size as 302 heads. I believe in building cr with pistons but if your not gonna cracked into the bottom end I'd mill the heads .040"-.050" there only 318 heads. And if you ever do a rebuild with better pistons you'll probably want to step up to better heads anyways.
 
MrJLR said:
Oh....well that "kinda" makes sense now....
Bet it didn't last long though!
Click to expand...

The engine did, the CAR did not. He couldn't drive and went over the wall. The engine actually went into a street car. I lost track of it after that.
 
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