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6 bolt head height question....

EagleTalonTim

Proven Member
834
13
Jan 10, 2007
Brighton, Tennessee
Good evening all! I am in the middle of a build and am checking what the last machine shop did on the head of my car and found something interesting... The milled surface is not even and I think it is out of the service range :( Here are the readings I got :

Transmission side (#4 piston side) : 131.69 mm
Timing belt side (#1 piston side) : 131.63 mm

About 2 years ago, I had the head and block milled for MLS use. After it was milled, the MLS sealed just fine. I drove it for about a year until I pulled the head back off to do what I should have done before milling the head....the oil port mod.... Since the MLS was pretty much missing all the Viton coating, I decided to go back to a Felpro composite head gasket and did not mill the surface again. Another year and I am now back in the same boat and needing to make the decision of milling the head for MLS once again, or throw an MLS on it and hope for the best? The machine shop I just took my head to scratched the surface with something when pulling the valves out for me. The scratches are not that bad, but are noticeable and go between one cylinder and the water port right next to that cylinder. I can take pictures if needed.

Having said all that... What should I do? Mill the head again? Find a thicker MLS? Anything else? I want to eventually run over 30 psi once I get my tune right and have heard that composite gaskets don't do well over 30 psi. Also, since the head has been milled several times and the block has been milled, I am worried I will now need adjustable cam gears to get the cams dialed in again. Any help is appreciated!
 

EagleTalonTim

Proven Member
834
13
Jan 10, 2007
Brighton, Tennessee
I honestly don't know how much was taken off the block since the machine shop who milled everything first messed up and had to redo the surfaces due to the RA tolerance of an MLS. Where can I get a thicker head gasket? I was told by another machine shop that I could be experiencing "cross flow" where the intake gases are not being fully burned before they exit the exhaust since the intake opens later and the exhaust opens sooner due to the difference in height. Getting the head milled again and getting a thicker head gasket seems to be the way I need to go, but where do I get a thicker head gasket?
 

EagleTalonTim

Proven Member
834
13
Jan 10, 2007
Brighton, Tennessee
I just remeasured everything on the head I was just using and another head I had from the previous build. The old head has all exhaust valve guides cracked so I bought another head from an individual for cheaper than the machine shop quoted me to do all the work to the other head.

Here are my findings with the "last ran" head :

IF = 5.186 IR = 5.187
EF = 5.180 ER = 5.182

And the "old" head with cracked guides :

IF = 5.188 IR = 5.190
EF = 5.1875 ER = 5.1875

The "old" head seems to have more "meat" but will require more work. If the surface did not have to be milled for MLS, that would be even better!
 

My1GLaser

Proven Member
1,565
30
Dec 4, 2006
Bartow, Florida
Mine measures at 5.175 and I run it with a .039" Felpro composite HG. I degreed the cams and clayed the pistons and have tons of clearance on HKS 272s.

I would get adj cam gears and run the good head with a composite HG!

What I don't like about thicker HG is that you end up with too much piston to deck clearance and mess up the quench. Your motor will be more prone to knocking if the quench area is too large.
 
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