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Expert
Posts: 2478
  
Location: Dalveen, Queensland, Australia | With no fewer than four available unusable heads for his Poly project, Ben has cut one up to see how thick the walls are on the ports and that sort of thing... he's done a nice job too, colour coding everything:
Black = combustion chamber (with valve rusted in place!)
Silver = head gasket face
Blue = water jacket
Red = exhaust port and exhaust crossover tract
Yellow = inlet port
Note the head bolt (which had to be broken to remove the head!) in the middle of the exhaust crossover...
 (cutheadlayout.jpg)
 (cutheadchamberandexport.jpg)
 (cutheadinletandcrossoverspreadandinletspkplg.jpg)
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 cutheadlayout.jpg (29KB - 267 downloads)
cutheadchamberandexport.jpg (23KB - 169 downloads)
cutheadinletandcrossoverspreadandinletspkplg.jpg (38KB - 179 downloads)
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Board Moderator
Posts: 3186
Location: The not-so-great, dirty-white North ( Michigan) | Ray....Looks like you have quite a bit of cross section you can use to contour the inlet port.
Also, if the rules allow it, I would go with a modern valve and reduce the stem diameter as well (go maybe with 8mm stems?) This will allow you to really work over the port, and then use a bronze valve guide pressed into the old guide hole. You have the meat to ream that cast in guide bore for this.
The result will be a lighter valve, and you can run more aggressive lobe ramps and yet keep the spring pressures reasonable. Speak with your local cam grinder on this. Also, the "beehive" spring units like the ones Comp Cams sells can be made to fit.
Of course, the most exotic would be to get those valves as light as possible (Titanium intakes, and Stainless exhausts), use titanium retainers and 10 degree valve locks to suppliment weight reduction. Since you are running a rocker SHAFT, you already have a pretty stabilized platform for rocker arms. Then you might be able to really run some wild lift profiles. The cast iron of the head should be soft enough on the intakes to be compatible with a Titanium valve.
Regarding head porting per se, I would match those ports at entrance, and try and get the cross -section of the sidewalls straighter. Also, you could lower the bump in the floor slightly to closer match the entrance. If you go with the bronze valve guide idea, I would take that intake guide area up to match the rest of the collector bowl, as the new bronze guide will stand proud in this area, but with reduced cross section profile.
The exhaust port roof can be raised, and the sidewalls straightened. Your headers would have to be flanged for this custom "raised exit" port, but I expect you guys will fab your own anyway. BTW - If you know somone who can plug up that exhaust crossover, do it. Keep the heat off your intake floor. You might even want to make the option to run coolant in the manifold exhaust crossover under the carb. I have seen guys get someone to cast-in an aluminum plug into the head cross-over passages in the heads. Then they just pipe water to the manifold side of the crossover. |
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Expert
Posts: 2478
Location: Dalveen, Queensland, Australia | Actually that section across the inlet port is right at the side of it... the valve stem is only drawn in there, IIRC...
All that you suggest is actually in the pipeline, the valves and stems, the porting, the beehive springs, with the exception of the crossover being blocked off. Maybe we can do something, but under the rules it's not legal to add metal to the head. And even epoxy fill would be considered 'adding metal'.
But we could choke it up, I guess, fill it with something that simply sits in there and prevents the exhaust gas from flowing into it. The manifold won't have provision for the crossover anyway. |
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Board Moderator
Posts: 3186
Location: The not-so-great, dirty-white North ( Michigan) | "with the exception of the crossover being blocked off. Maybe we can do something, but under the rules it's not legal to add metal to the head. And even epoxy fill would be considered 'adding metal'."
Hmmm....OK. I think the reason for that rule is so you cannot actually move a port by welding one side and grinding the other. So be it, since they have to enforce it without regard to thought of actually what you are doing it for.
How about this? Make up about a 3/4" thick aluminium plate that can fit snugly into the crossover in the head on ech side, and RTV it into place behind the intake manifold gasket. It would just be a real thick blanking plate, and I think those may be legal in competition rules.
Of course, if you do your AirGap manifold, you just blank it off both sides that way.
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Expert
Posts: 2478
Location: Dalveen, Queensland, Australia | Oh, sure, the manifold flange will blank it off, but to seal it off at the port end might be harder.
I'll work on it and let you know... but I think short of some kind of permanent fill it's impossible to do anything with it to smooth the port flow... though it might not work out too badly in that department. Ben will be gas-flowing a head or two so there's the opportunity to try things there. |
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318 Poly head section cuts
