Quote:
Originally Posted by Bruce Lancaster
We have at least two schools of thought to look over:
Ron's book (MANDATORY READING) details his efforts to straighten that last bit of exhaust tunnel by shifting the end ports toward the ends of the block.
Flatdog ended up going with the stock routing, and drastically slanted the front and rear of each port to match the tunnel, slanted toward center of block, with headers made to follow that path before turning.
Both obviously require fully custom headers built for the individual engine.
Vergel posted excellent cutaway pictures of the exhaust system on the HAMB recently, showing the path to be more smoothly curved than seems possible from external observation.
It seems to me that the high level of power increase flatheads can show with a big blower exonerate the design of the exhaust passages...if they are the engine's choke point, big increases driven by the intake side would not be possible. The engine would simply choke on its own exhaust.
Ever see the heads from a highly developed high-pressure turbocharged SBC??
Exhaust valves are offset and increased in size to the absolute limit and X ports are hogged out almost beyond belief to allow the engine to accept really radical increases on the intake side.
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Bruce:
I am currently doing it like Flatdog minus custom built headers. Maybe later on down the road.
I've ground a heck of a lot out of material out of those end ports to the point I'm worried how thin it got after taking out the "hump" casting flash & wire and what ever other crud was lurking around in there. I had to also open up the exhaust flanges on the my headers to extreme as well.
When I run my fingers in there it seems like it is certainly a much better path.
I am concerned that I may have increased the possible volume too much and therefore reduce the amount of back pressure. Not sure if this is even a problem, but I'm sticking with top of line 1.5 SBC hi-flow valves for both I & E and a Potvin 3/8ths cam (well- Potvin for know- On deck are also Clay Smith 272-2 & 284-2 cams, Crane 352-2 and/or Melling A-400 short track full race if the 3/8ths doesn't work out.)
I'm hoping the duration/overlap of all these cams (except the Crane which has more duration and lift on the exhaust side) will also help get some of that bad stuff out of those ports when needed.