angle milling the head

[6bangerwanab]

i was reading through my new car craft and they were talking about how some roundy rounders that had pretty strict class rules would angle gring the head to help flow a little bit and to gain a bit of valve clearance, and that the biggest problem was that you had to regrind intake and exaust, plus something abouut milling the bolt head seats, which really confuses me because my common sense tell me that the bolt holes would need to be completely redrilled, if not, would it possibly be worth doing to our six's since we wouldnt have to gring on the intake or exaust?

 

[Lazy JW]

This is an old trick used on the small block Chebbie. It allows an increase in compression with flatter top pistons and still keeping the valves from hitting aluminum. The SBC really objects to having big domed pistons in the way of the flame front, and straight milling brings the valves too close to the pistons. Angle milling solves this quite nicely. I don't think it would do much for our 300 Fords because there is ample room for valve clearance. IIRC, The Frenchtown Flyer said that the valves can lift something like .700" before getting too close.
Joe

 

[Asa]

"in excess of .600" actually

just to nitpick

 

[Lazy JW]

I stand most humbly corrected
Joe

 

[CZLN6]

Howdy Back 6bangerwannabe and All:

There is nothing to be gained by angle milling the head of a small six either. You can safely mill OEM head .090" if needed, with no piston to valve interference with most street cams. There are no rules limiting you with an inline Six. The reasons on a V8 have been explored and have limited application.

The reason for angle milling the bolt seats is to keep the seats square with the bolt angle. A degree or two does not require the bolt hole to be redrilled, but the bolt face-to-seat surface must be square.

Angle milling a small block head would also compromise the level of the intake and carb mounting surface.

I've explored the idea of angle milling the exhaust flange surface to straighten the hook the port makes before exiting. Again, a few degrees does not make a big difference to performance and it would compormise sealing integrity of the exhasut mounting bolts.

Adios, David

 

[6bangerwanab]

wow, i guess i didn't realize that these motors had so much clearance in them, or does the design naturally allow for more cam? and is it the same on the smaller engines as well? if there is that much room in there then doesn't that leave alot more elbow room to get quench and combustion chamber shape just right?

 

[CZLN6]

Howdy Back All:

The extra clearance on our Sixes is due to the unnecessaryly large deck height- at least .025" on most 200, a dished piston top and a .025 OEM thick steel shim head gasket. Aftermarket composite type gaskets are even thicker= more clearance. And relatively low lift cams specs. When building a performance engine with tight clearances it is always best to check piston to valve clearances before start up.

To improve quench, clearances have to be tightened, or reduced- specifically deck height and gasket thickness. Deck clearance- the distance from the highest part of the piston, not the dish, to the mating surface of the head, not the combustion chamber. This is determined by the deck height- top of piston to the top of the block plus the compressed thickness of the head gasket. Milling the head does not reduce deck clearance. Ideally our Sixes benefit from zero deck height, or possibly a positive dimension, and/or a thinner head gasket to gain a quench of .035" to .040" deck clearance for quench to have a positive effect on combustion efficiency.

To maintain quench you need to maintain as high a quench area to bore ratio. Reshaping the chamber almost always reduces quench to bore ratio. Ideally our Sixes would benefit from a "D" shaped dished piston where the dish mirrors the shape of the combustion chamber.

About the only chamber reshaping that makes sense is to unshroad the intake valves and/or, when necessary, removing material to reduce CR.

Adios, David

 

[ASMART]

David,
Wouldn't angle milling the head so as to make the plug side of the head "taller" help by having more of the combustion chamber closer to the plug? That might be a good thing. I don't have a head to look at but it seems that an angle milling cold also change the angle created with the bore center and the valve. I wonder what effect that would have on flow

 

[6bangerwanab]

i think that that is why they did it in the first place, rotating the valve up and away from the piston (or actually not making it any closer while increasing compression)

i guess that there isn't much gain in it though,

at least i think that thats what im trying to say.

 

[6bangerbill]

I think your right on the use of angle milling for street use. But for the extreem hp guy, rotating the head by angle milling will also raise the intake and exhaust port angles for straighter mixture flow. Just be sure to mill more off the spark plug side not the port side.
Most of the resulting improvement I suspect would be from the c-ratio increase. Most 300 inliners could use much more compression anyway. Be sure to re-level the carburator unless you habitually drive in circles.