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Excellent article Dusty and nice job on the heads. One thing I'd like to comment on is the valve seat widths. You say those are 60 thou. That's very narrow for valves as big as these and what the flowbench tells you isn't always the full story as far as power output goes.
The valve seats not only have to flow well but they have to seal well, last a reasonable time and perform the vital job of removing heat from the valve heads. Any heat that doesn't get dissipated through the seat or guide ends up heating up the incoming charge and reducing VE. Now you might at first think that this is mainly going to be an exhaust valve issue but the inlet valves, albeit running at lower temperatures, have perhaps 50% to 2/3 more surface area than the exhausts and in terms of total heat capacity can be the main problem in the chamber.
Wide seats might not give you the best high lift flow figures (although if you get the seat geometry right they can flow pretty darn well) but they do a much better job of removing that heat and preserving engine efficiency.
I've done back to back tests over the years on a number of occasions and increasing the seat width can literally transform how an engine runs. More torque at low/mid rpm, better emissions and a big hp boost at the top end.
Many years ago I had a customer come to me with a short (1/4 mile) oval track Ford Pinto 2L motor that had to stay in one gear throughout the race. Corner speed was about 50% of the speed at the end of the straight which meant a good spread of torque was needed over about 50% of the engine's rpm band. His problem was the cam they were using to get good top end power and straightline speed wasn't pulling out of the corners. They asked me for advice on a milder cam choice.
I said first thing is let me look at the head and see what's been done for you. They couldn't understand what the head had to do with anything but sent it to me anyway. As expected it had very narrow seat widths as per most race engine builders over here who think narrow seats are the real deal. There was enough material left to recut them from 1mm wide to 2mm wide (42mm inlet valve) and a minor bit of tidying up in the throat area.
Next race day I got a very excited call from their mobile phone. The engine now had not only more top end bhp but so much low rpm grunt it wasn't just pulling out of the corners it was spinning the wheels out of them. They eventually ended up going to an even higher diff ratio to get more speed at the end of the straight. The cam choice they had didn't even need looking at.
Valve seats are about the most critical part of the cylinder head as far as power goes. Flowbenches are part of the story but sometimes you have to go past what they tell you to get engines to work at their best. With valves of this size you want seats at least 2mm wide and maybe wider. Have a look at Bill Jenkins Chevy book and talk to DV about it. I think he'll back me up.
Dave
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