I'm about to do some porting on a spare head for my zook, and I've just flowed my totally stock g13 head on our flowbench at work. Here is the graph.
The interesting thing is that the exhaust flow is way up on the intake flow, especially at low lift. Typical heads have a the exhaust port flow 70-75% of the intake port right through the range. Some go as low as 60%, and over 80% is generally only used in turbo applications.
The zook is running at 100% up to 0.150" lift! It stays at around 80-85% at large lifts. I almost don't believe this, so I might just have to re-flow it to check!
I read with interest that everyone is putting 2.5mm larger diameter 1.6 exhaust valves in their head and claiming to get better performance. I've seen a pic of a head with them installed, and it made me wonder... It looks like there hasn't been much chamber work done, and the valve could actually be shrouded worse than the stock valves? Maybe they actually flow worse? This could even out the flow ratio and possibly improve performance.
Its not uncommon for an over exhausted head to run poorly, and go much better when the flow is reduced in the port, sometimes by cutting poor valve seats or otherwise impeding exhaust flow.
Anybody else actually done any flowbench work, or have an opinion? Sarge? DaveAZ?
Also, does anyone know what the stock valve lift is? My spare cam is in storage so I can't measure it at the moment.