Milling 67cc heads to 62cc
Milling 67cc heads to 62cc I tried searching, but didn't come up with anything.
I have Patriot stage 2 67cc heads coming, and I was wondering if its possible to mill them down to around 62cc. I'm looking to get the compression up in the higher 10s for the cam I'm putting in. I should have researched more before I bought the heads, and bought different ones to start with. But, these were pretty reasonably priced, so I picked them up.
What should I expect to pay a local machine/engine shop to do this so I don't get ripped off big time?
Thanks for any help.
I have Patriot stage 2 67cc heads coming, and I was wondering if its possible to mill them down to around 62cc. I'm looking to get the compression up in the higher 10s for the cam I'm putting in. I should have researched more before I bought the heads, and bought different ones to start with. But, these were pretty reasonably priced, so I picked them up.
What should I expect to pay a local machine/engine shop to do this so I don't get ripped off big time?
Thanks for any help.
They are LS1 heads with the stock sized 67 cc chambers, no welding. Stock deck height and everything. So I can take off .060" and be fine? And yes, I know I will have to flycut so don't worry about mentioning that.
Ok, after trying some new searching terms, I came up with some more info but I'm still unsure how many thousandths equals 1cc. Ive read all the way from .003-.006. I'm thinking of getting around .035-.040" milled. Would that be about right?
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Teching In
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On my engine, 00 ls1 and stock composition gasket, .040 flat mill made intake fit
borderline ugly. It seals-but just barely and I had to relieve the plastic "posts"
around the intake bolts so they wouldn't interfere with the reliefs in the heads.
Now that I think about it, I also had grind the vertical walls of those reliefs back a bit as well.
If I were to do it again I would: (1) use a thinner head gasket which I think you
can get from Cometic or others because you get a better "bang for your buck" as it were for cc reduction, because your reducing volume more per every thousandth because the gasket area is larger than the chamber and get the added benefit of reducing the squish clearance. (2) I would angle mill because it
helps intake fit and piston to valve clearance issues. Angle milling also raises the
port angle slightly-never a bad thing IMO.
I hope someone with more experience chimes in on this question.
borderline ugly. It seals-but just barely and I had to relieve the plastic "posts"
around the intake bolts so they wouldn't interfere with the reliefs in the heads.
Now that I think about it, I also had grind the vertical walls of those reliefs back a bit as well.
If I were to do it again I would: (1) use a thinner head gasket which I think you
can get from Cometic or others because you get a better "bang for your buck" as it were for cc reduction, because your reducing volume more per every thousandth because the gasket area is larger than the chamber and get the added benefit of reducing the squish clearance. (2) I would angle mill because it
helps intake fit and piston to valve clearance issues. Angle milling also raises the
port angle slightly-never a bad thing IMO.
I hope someone with more experience chimes in on this question.
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When I researched this I came up with .035"-.040"
Keep in mind the difference between a 5.3 (62cc) head and a 5.7 (67cc) is the combustion chamber is .035" lower on the 5.3. So theroetically milling a 5.7 head .035" gives you almost the same head as a 5.3 head (5.3's also have smaller inake valves, but that is easily fixed). Doing it this way changes the valvetrain geometry and intake relationship by the milled amount also.
Felpro also makes a .041" gasket know as the Felpro 1041.
Keep in mind the difference between a 5.3 (62cc) head and a 5.7 (67cc) is the combustion chamber is .035" lower on the 5.3. So theroetically milling a 5.7 head .035" gives you almost the same head as a 5.3 head (5.3's also have smaller inake valves, but that is easily fixed). Doing it this way changes the valvetrain geometry and intake relationship by the milled amount also.
Felpro also makes a .041" gasket know as the Felpro 1041.
Teching In
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Thanks ssheets for brining up the pushrod length point. You will definitely end up with a shorter pushrod-the dimensions of which you will have to measure. The best way is to get an adjustable pushrod from whomever your going to get your pushrods, in my case it was Smith Bros.
I don't remember my deck clearance but .033 would be too close for comfort for me, but if your trying to wring every ounce of performance out of your engine... you may go where others fear to tread.
I don't remember my deck clearance but .033 would be too close for comfort for me, but if your trying to wring every ounce of performance out of your engine... you may go where others fear to tread.
TECH Senior Member
Joined: Mar 2004
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From: BFE
Call Gunnar at patriot he will help you out.
Seing you have a 98 are those perimeter bolt heads as well?
.030 mill should get you there. Milling is between $60>$100 depending on shop.
But be careful, what cam are you putting in? make sure it will fit with milling.
If you mill more than .020>.025 you'll need shorter p-rods (XE-R size lobe)
Seing you have a 98 are those perimeter bolt heads as well?
.030 mill should get you there. Milling is between $60>$100 depending on shop.
But be careful, what cam are you putting in? make sure it will fit with milling.
If you mill more than .020>.025 you'll need shorter p-rods (XE-R size lobe)
FWIW, my AFR 205's are milled @ 60cc with GM MLS gaskets and the formula for determing compression put the car at 11:2-11:3. at least that's how it came out for me ... still left room for less quench, so, 3-5 is still left on the table, I believe.
I haven't bought pushrods yet, and I plan on getting an adjustable to measure it. The cam is 235/240 .647"/.608" 112lsa. So if I mill the heads .035-.040", get either cometic .040's or felpro .041s, flycut the pistons 2cc, I should be good to go. I will definitely talk to Gunnar and research more on it, but that sounds like the plan so far.
On a set of 243s, milling them .025 is worth about 4-5 CCs. I would expect other castings to be similar, but I dont use much besides 243s, so I cant say for sure. But I know for fact, on 243s, .025 is worth about 4-5 CCs.
Teching In
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I know that I got my intake to fit with .040 flat milled off, I don't see any reason yours wont fit, order them milled .040. What you end up w/for compression? Who knows? My guess would be in the 10.9 to 11.2 range, about .5 a point better than non milled heads. Not a huge difference in power but hey, its "free" power at every point in the powerband.
