head milling

[benjpi]

Has anyone tried milling the stock cyl head for additional compression?

 

[LordWorm]

Has anyone tried milling the stock cyl head for additional compression?

plenty of people machine the head when it comes off, but this is more about getting a good flat surface for remounting than raising the compression.

To get an appreciable increase in compression you should look at replacing your pistons for high compression units - milling a few thou off the head won't give you much gain.

 

[benjpi]

On the bike in my signature, I raised the compression to 11.5:1 (about a point) from milling 0.030 from the head, and running a 0.020 head gasket (half stock), and re-used the stock pistons.

I know there are places that will cut custom head gaskets, so I was just tossing around the idea of milling a junkyard head & installing it with a thinner gasket. That allows for a driveway upgrade, rather than assembling a new engine.

My plan, should it come to pass, includes a home-porting job (bowl blend & polish, port matching, maybe some meat from the valve stem bosses), a ported/VCTS removed intake manifold, and the J-spec intake cam. I'm not looking to make massive power, but 140whp would help to peg the fun meter.

 

[njaremka]

you'll want to make sure you get adjustable cam gears, too - milling a head on an overhead cam engine messes with cam timing

 

[LordWorm]

you'll want to make sure you get adjustable cam gears, too - milling a head on an overhead cam engine messes with cam timing

maybe its because its 2am and i'm not quite thinking straight - but i some how don't think this is right.

The timing relative to the crank position would remain exactly the same. Yes you are physically moving the valve train closer to the pistons BUT the valves will open at the same time as they would otherwise.

 

[njaremka]

cam phase timing is controlled by a toothed belt, and is dependent on the distance from the crank to the cams. mill the head, and you change that distance, which in turn changes the cam phase timing. the miata guys had figured this out back in the early 90's when trying to find ways to bump compression. in order to regain the exact cam phase timing, you'll need adjustable cam gears.

 

[benjpi]

the miata guys had figured this out back in the early 90's when trying to find ways to bump compression.

Do you know how much they were milling? If I remember right, the service limit is somewhere around 0.020". How much more will the head take?

 

[njaremka]

not much, but it was enough to raise the compression, and mess with the cam timing