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I put myself thru college porting cylinder heads and consigning them at Speed Center & Super Shops, so while I'm waiting for a new job to come my way, I decided to build a Mass Air Flow Bench, and start experimenting with a "core" I got for a future build-up on my Z. After seeing a sectioned head, I decided that there are a few peculularities inherit to the design of this head.
If you draw a triangle from the spark plug to the exhaust valves, there is not allot of area (above the combustion chamber) there for coolant flow.
After verifying this with an Engineer at JWT (who also confirmed), the spark plug boss is critical to prevent detonation, and in extreme circumstances thermal runaway.
Unfortunately, the spark plug boss shrouds the valves! So the inclination is to remove it... BAD move! IF you study the pictures of the heads sold by Z1, you'll see what I mean. They (Z1) removes this boss (again, BAD move).
After reading and researching everything that I could find about the VG30DETT heads, I discovered that installing O/S valves is not the way to go with these heads! In this case, bigger is NOT better. Here's why:
Unless you have a stash of blocks, and plan on going to at least a 89mm bore, O/S valves cannot buy anything. The valves are already so close to the cylinder bore, installing larger valves just causes additional area to be shrouded.
I remained very conservative when I ported my set of heads, blending / matching the port bowl to the seats, port matching, and re-profiling the valves.
I install the head on the bare block, and scribe around the bore. This allows you to very slightly open the combustion chamber and remove the "depression" in the chamber which un-shrouds the valve.
Again, the material removal is very slight, which is basicly just in the corners of the combustion chamber (near the valves).
All of the combustion chambers were matched to 50cc, the intake ports all came in at 150cc, and the exhaust ports came in at 86.0 cc except for #2 which came in at 85.6 cc.Testing at 28"wc, all of the intake ports flowed 246 cfm, while the exhaust ports flowed 220 cfm.
All of the ports seem to have a "sweet spot" between 6mm - 10mm, going past that seems to be a waste of motion (and energy).
Some quick math reveals that doing these simple mods will give you the capabilty of producing 984HP! Finally, any lift past 10mm the lifter will "un-mask" the lifter oil gallery, dump the oil pressure, and eventually (if not sooner) starve the cam bearings of oil. There were some additional changes that I made to get to 246 cfm, however, I'll keep them in my back-pocket for now...
S2Z
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