Randy:
I’m trying to do some research on the Brazilian head but in the mean time I’ve done some thinking on the subject of an aftermarket Chevy L6 aluminum head. I’m certainly no expert on such things but I can see where the technical issues and marketing realities makes this a very difficult proposition.
Classic Inlines apparently got a lot of grief for not developing a cross-flow design for their small Ford (144/200/250) aluminum head. But I think they actually got everything just about right in the sense that the head could utilize nearly all of the OEM parts and pieces, or at least readily available off-the-shelf aftermarket items. This keeps the true cost of ownership down to a level that makes the head viable from a marketing standpoint since existing intake and exhaust manifolds work, as do valve covers and rocker arm assemblies. I believe CI did raise and reshape the intake and exhaust ports to significantly improve overall flow and velocity, and to get the exhaust flow into a much more optimal relationship to the intake. Of course, there is the obvious benefit of casting in aluminum that reduces weight and that allows for higher compression without detonation problems due to better cooling.
As I understand it, CI is following the same path with their big Ford (240/300) aluminum head and I’m sure hoping for similar results and another exceptional product. It’s my understanding that they have a prototype head nearly (?) ready for testing but that the overall project is apparently on the “back burner” mainly due to the economy (which is understandable). But I have no doubt that the big Ford head priced around $1,600 in street trim when it finally comes to market will be another great success, particularly for those interested in racing applications since the restricted flow of even a fully reworked stock head really can’t support larger displacements (300+ cubic inches) at high RPM levels.
So when I think about a Chevy aluminum head, I would take the CI model into account and would work towards a head that is a straight bolt-on replacement, that improves and balances port flow, that increases combustion efficiency, and that allows the buyer to use most (if not all) of his existing parts (i.e. intake, exhaust, valve cover, rocker arms, and such) or at least those aftermarket parts that are already available.
The first obvious problem has to do with the stock head bolt placement relative to the siamesed intake ports. The bolt location needs to stay in its stock location – I think that’s a given. So splitting the three siamesed intake ports into six individual ports would seem to require enough room between the adjacent pairs of ports to clear the head bolt such that any original or aftermarket intake manifold will no longer work. If you now require the use of a new cast or custom fabricated intake manifold, the cost of ownership might become prohibitive and so far fewer heads would be sold. Not a good outcome when you’re trying to recoup your R&D, production, and marketing costs, much less make a reasonable profit.
So what if you could find another make of inline six that has a good offering of aftermarket intake manifolds and adjust the new Chevy head intake port configuration to align? While that would not allow the buyer to use his existing manifold, there would at least be substitute manifolds already in production from which to choose. But the problem with this approach is that I know of no other inline six with the same order of intake and exhaust ports that would match the Chevy, and that also has a workable selection of aftermarket intake manifolds. Re-positioning the new Chevy head intake ports to use manifolds designed for (say) the 258 AMC/Jeep or the 240/300 Ford would, at a minimum, require a custom ground cam to deal with the changed intake and exhaust valve order. I’m guessing such a cam would cost as much, if not more than a new dedicated intake manifold. Hardly a bolt-on proposition.
One other thought would be some kind of an intake adapter that would merge the new head’s six individual intake ports (that are split to clear the head bolt?) back into the original three siamesed ports so the buyer’s original intake could be bolted up. That solution might work but it also might create a number of linkage, alignment and clearance problems – particularly in tight engine compartments. Then there’s the wisdom of using an intake manifold that doesn’t take advantage of the individual ports to consider.
So this sure isn’t an easy puzzle to solve effectively. My guess (which aligns with CNC-Dude’s comments above) is that, if you produced an aluminum head that takes into account all the best practices of the highly modified original Siamese port iron heads and price the street version at the $1,500 to $1,600 range (as CI has done with the small Ford head), I suspect there would be considerable interest. It won't have the potential of Mike Kirby's 12-port head, not to mention a true cross-flow design. But both of those options come at a significantly higher price due to the need for specialized intake and exhaust manifolds, and in the case of the cross-flow head, some solution to the ignition issue.
Such a head could incorporate the added lump port inserts and altered head bolt treatment as an integral part of new aluminum casting. Possibly the ports could be slightly raised (but kept in there original orientation so existing intake and exhaust manifolds would not be adversely affected) to improve flow and velocity even a bit more. Of course larger valves and hardened seats would be part of the package, as would the provisions for springs that would support much more radical cam choices. As I mentioned earlier, I’d also raise the valve cover mating surface to accommodate roller rockers and a rocker support without needing a spacer or custom fabricated valve cover. I’d also expand the openings to allow for larger diameter push rods and it might be worth looking at the combustion chamber size and shape for possible improvements.
Much more than just 2 cents worth . . .
Russ
PS: I assume the photos above are of one of Kirby's 12-Port heads? They are a thing of beauty and I sure wish one would show up under my Christmas tree this year. Fat chance!
By the way, the design does seem to be very similar to the Fontana 4-banger head (or vice versa since I don't know which came first). I think there may be a difference in the valve angles and the combustion chambers are not the same as I recall.
