For you guys, i had this talk with someone whos building their 300 i6 up, and an idea came to my head, back in the 90s volvo shaved a their inline 5 850s cylinder head at an angle witch gave them a net 65 total hp, has anyone done anything like this on our 300 i6 heads, if not i have a spare head i can test with my 83 f150 thats carbed, im looking to make more power if possible, even if its not a 300 i6, if you have done this, have you gained anything out of this

 

Angle milling really works great on heads that have a large quench area and a deep chamber. Rolling the head over allows you to take off a whole bunch of material where the chamber is big and deep and very little off of the quench area where it doesn't help at all. As an example a set of Chevy V8 heads with 64cc nominal chambers can be dropped down to 50-55cc pretty easily by going .120-0. The limitation really becomes the edge of the intake valve seat. The angle cut can be done where it doesn't go all the way across the head and stops just above the top row of head bolts too.

After cutting the deck the head bolt holes have to be spot faced so that they are parallel to the deck again and the intake face needs to be cut back to the original angle. Sometimes the sides of the holes have to be ground a little for bolt clearance. Depending on the head design certain other things can cause limitations. When angle milling the water ports where a bunch is being cut away tend to move. On an older style Chevy head the drilled spark plug cooling holes usually have to be plugged because they will move over under the gasket fire ring and cause a leak.

The first time I ever did this to a set of heads I was amazed at what didn't change. I had a 350 Chevy on the dyno and it was built for a class that required the use of flat top pistons and the smog open chamber heads. I had cut a set of 441's 120-0 (from 76 down to about a 64cc chamber) and swapped them onto the engine. I assumed that the pushrod length requirement would change after all that milling but it didn't at all. Nothing much was removed from that side of the head. The valve to piston clearance also didn't change very much when I checked it either. While the valve angle is changed about 1 degree or so the bottom edge of the valve isn't moved all that much closer to the top of the piston. I did have to use a double thick intake gasket set but the bolts all screwed right in using my fingers!

Rolling over the head helps the compression but it also does tend to improve air flow slightly because it stands the valves more upright very slightly all of which helps performance. In my example engine I think it was making around 250 horsepower before and about 315 after. I can't remember exactly but it helped a lot. The engine was run for several seasons after that and never had any problems.

I'd look around and see if the smaller chamber 240 and EFI 300 6 heads sacrifice any flow to the more open version too.