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Bruce Lancaster · 06-24-2011, 10:59 AM

I was privy to a limited range of selected bits of secrets from the late great Flatdog, builder of probably the most powerful (12.9 in 3,000 pound '34) street driven flathead on the planet. Remember, canted valves and closer chamber, so not necessarily transferable to bangers...
One thing was that flow at back of valves was minimal...best approach was minor clearance behind valve, at least .030 above valve to allow the slight flow. Almost all serious flow was right out the cylinder side, across the back of the valve, and shape of the BOTTOM of the pocket was critical to encouraging this.
He also said that flow bench showed that most flow was on the intake side of chamber because...startling observation, confirmed by other flowbench wizards...the EXHAUST flow mostly followed that side!! I suspect this was a big factor in his work on chamber roof. And I have seen elderly circle track engines with a block relief only on that side...
Flatdog was a major presence in the flathead world, and regularly conversed by phone with various Bonneville types, all people with some sort of flow bench, some with dynos.
They would very guardedly mention tiny fragments of theri secrets to each other, and try to gauge if the other guy had observed anything similar. High tech spy world...I think if I had ever walked into the garage at the wrong time and caught a glimpse of his total chamber design, he would have had to kill me.
Low tech secrets: He started his flow work with a humungous shop vac, tossing kitty litter into the airstream! As things got more sophisticated, he learned from Elmo Rodge how to forn clear plastic shell copies of his chambers so he could put a transparent roof over the flow.

06-24-2011, 10:59 AM	#24
Bruce Lancaster Member Emeritus Join Date: May 2010 Location: Madison, NJ Posts: 5,230	Re: Cylinder head design I was privy to a limited range of selected bits of secrets from the late great Flatdog, builder of probably the most powerful (12.9 in 3,000 pound '34) street driven flathead on the planet. Remember, canted valves and closer chamber, so not necessarily transferable to bangers... One thing was that flow at back of valves was minimal...best approach was minor clearance behind valve, at least .030 above valve to allow the slight flow. Almost all serious flow was right out the cylinder side, across the back of the valve, and shape of the BOTTOM of the pocket was critical to encouraging this. He also said that flow bench showed that most flow was on the intake side of chamber because...startling observation, confirmed by other flowbench wizards...the EXHAUST flow mostly followed that side!! I suspect this was a big factor in his work on chamber roof. And I have seen elderly circle track engines with a block relief only on that side... Flatdog was a major presence in the flathead world, and regularly conversed by phone with various Bonneville types, all people with some sort of flow bench, some with dynos. They would very guardedly mention tiny fragments of theri secrets to each other, and try to gauge if the other guy had observed anything similar. High tech spy world...I think if I had ever walked into the garage at the wrong time and caught a glimpse of his total chamber design, he would have had to kill me. Low tech secrets: He started his flow work with a humungous shop vac, tossing kitty litter into the airstream! As things got more sophisticated, he learned from Elmo Rodge how to forn clear plastic shell copies of his chambers so he could put a transparent roof over the flow.