Scott at Hillside recommends milling down my heads to get the 9.5 - 1 compression which I am looking for.
I'm not sure I like that as it takes meat away from the heads I might need later incase they do warp.

So my question is this
Which is better milling the heads or getting higher compression pistons?

 

Cant answer your question directly, but the info I've read states that the MoCo cut the heads .050" on the Police bikes back in the early 90's.. So, it doesnt appear to be much of an issue.. I actually didnt think you get that much compression by milling. Obviously, they are a well respected shop and know what they are talking about, but I'm kind of supprised.. Now, the other side of it is, once you cut them, there's no turning back.. Another thing, how would it affect your intake?

 

Since you're pulling it all down, you could have them mill the bottom of the cylinders instead of the heads. Same effect, just check piston clearance on the skirts.

I've notched shovel pitons to pass each other on the down stroke using longer skirted pistons and milling the cylinder bottoms.

Griz

 

I had my heads milled quite some time back. The only issue I've had is that the bike has more power now.

 

Scott knows his stuff and offers EXCELLENT advice.

 

In my day dreams I often thought about riding out to Hillsides and have them perform an engine power upgrade -just as they recommend. How sweet it would be!

 

I milled .050" off my heads about 90,000 miles ago. No negative issues.
A friend did his engine shortly after I did mine, the only difference was mine was milled, and his was HC pistons. The thing I noticed was that my bike always started quicker with less turns of the starter.

 

THC,
Like the guy said, there is no going back.
Because of that I am inclined to use pistons to get the compression since you probably will be pulling the cylinders anyway. Didn't you say somewhere that your base gaskets are leaking?

 

Most of our performance engines got the heads milled for two reasons. First and most obvious more compression. Secondly to balance the combustion chambers. Harley heads can and do vary from head to head more than we like to see. This can make for more vibrations than there should be. So in closing if you are going to have the heads CC'ed then go ahead.
John

 

I think it depends on the individual's preference. Some, like myself, don't like taking material from the heads for reasons stated. Can't put it back on if you ever want to go back to stock compression. On the other hand, some people will argue that using domed pistons interfere with flame propagation. I tend to go along the later, reason being I come from a background of riding panheads & shovelheads that use dome pistons & know that dual-plugs are a fix for the flame propagation issue. You can dual-plug evo heads, but that costs more money. I went with S&S replacement heads, that are 8.8:1 out of the box & installed with a .030 head gasket gave me a cr of 9.25:1. Not a upgrade for everyone, but worked for me, & I still have my stock heads ,stored away. If I had to choose between milling the heads or domed pistons, I would go with milling the heads, because it would be cheaper, ( unless you needed a re-bore) & I think the performance would be a little better. And I do know that bumping the compression up put a BIG smile on my face! And this is just my opinion.
hth

Ride Safe,
Harold