Anyone have any experience runing bigger valves on the GEN II heads? Like an 1.50 for the exhaust side?  anyone use "undercut valves"?

You'd want to talk to Jeff Middaugh about that.

Where did you see 1.50 valves used on theise heads. Under cut valves might be great.

Stock valves are 1.72 intake & 1.48 exhaust,  Just wanted to see if anyone had gone to 1.50 for the exhaust.

Could be possible... I should use my 2.8 heads for some R&D. hrm.....

2.8 heads have smaller valves than the 3.1's


I lived in Sparta...many many many years ago (late 70's)

Quote from: GPChief


I lived in Sparta...many many many years ago (late 70's)

I'm sorry..... :D

The heads, other than valve size, are the same correct? I have a complete engine sitting on my shop floor that had a rod knock. I was thinking of building it for the TGP, as an experimental enigne. I thought the 2.8 and 3.1 were nearly identical, other than minor things like bore and valve size.

this is what I was told when asking about larger valves................... "You aren't going to find many people using bigger valves in these engines, because there just isn't that much room available in the combustion chamber to do so. If you look at how close the intake and exhaust valve are to each other, and also how close they are to the edges of the combustion chamber, there isn't much room for growth.

I have used slightly bigger valves from a 3.8 Buick engine in my iron-head 3.4 engine. The intake was only about 0.7-1.0 mm bigger than the original, and the exhaust valve was the same size. The main reason I used them was that they had a flat face instead of the concave face of the stock valves. This bumps up compresion slightly. These valves could not be used with the aluminum heads due to the smaller valve stem diameters.

The extra mm of valve diameter has very little effect on airflow. You would gain more by prting and polishing the intake ports and combustion chamber. Even if yu could fit larger valves, you would need to have machine work done to accept the valves."

I have a 4g63 Mitsu with dohc and 4 valves per cyl, that can run oversize valves. We have pleanty of room.