Thread: Milling heads

I am taking my heads into a local machine shop to have them ported and reconditioned. Should I also have them mill the head down. ZZP says that you can safely mill .030" off and raise the compression by .5. I just want to here your guys' input before I trust ZZP.

Good question. If you mill that much off you can run into problems on your manifold lining up with your ports, so you would have to have the intake flange corrected as well if you want to do it right and have them line up nice. I would not mill that much off I would keep the half of point of compression and play it safe, it would not be worth the power gains for all the trouble. Have them make a clean up pass and youll be in good shape. You have a decent blower you are going to make power regardless.

If you mill them .030 you will in fact gain .5 in compression but you'll probalyo want to run shorter pushrods at that point. I'm also going to say i've seen others do it but i've also heard that it can weaken the head. I had mine surfaced .005 and then i dropped a valve and had to replace a head so i went .010 on the old head and the new head. I'm also running .052 HG so I'm running about .020 shorter than stock. That is probably on the edge of the range of preload on the stock lifters. I think having an XP cam with base lobes smaller than stock might be working in my favor.

Also don't let the machine shop hog out your exhaust ports. The D-shape is important. Tell them to clean up the bowls, runners, and casting imperfections. I've seen some shops turn heads into paperweights by drastically changing the shape of the exhaust port and porting too much.

Originally Posted by Preotic

I've seen some shops turn heads into paperweights by drastically changing the shape of the exhaust port and porting too much.

More good info...I was planning on just cleaning them up myself here soon when I put my L26 in...just to get rid of the imperfections...do you, in your honest opinion think I will notice it anymore over my higher compression? I know running high comp. and boost is a lethal combo

I just want to know some solid info before I go doing it. Aaaaaaaaaand...maybe some tips on how I can make it better than just taking out the imperfections in the stock casting...

Supposedly these heads flex a lot in stock form, milling them will just make that worse. Thinner head gaskets would probably be a better way to go.

As for porting, check these threads:
ClubGP Message Forum troubleshooting
ClubGP Message Forum troubleshooting

If you don’t have a lot of porting experience your better off with just a fluff and buff and send it down the road, there are some spots that can get thin in the ports if you’re not familiar with them.

High compression and eaton blowers are good for each other. These blowers get worse the faster you spin them. If you put it on a high compression setup you just spin it slower and keep it in it's efficiency range. Just run bigger pulleys and you'll be fine but you won't be slower.

I ran a 3.4 with .052 HG, .005 flatness on the heads w/ xp and gen v. When i dropped a valve i picked up a l26 and I just went up to a 3.6. I'm sure i could run the 3.4 but last time i tried I saw like 6 degrees of knock and took it off in the nearest parking lot. I see 0KR on my 3.6 with no tuning yet(I'm lazy).