Inliners International Forums General Discussion Hi Performance Howard 12 port

Stumbled across this on the hamb

https://www.jalopyjournal.com/forum/thre...mc-302.1104041/

Would have thought it would be snapped up and put to use? I have a 302 and a single seater project this would be an amazing addition. Problem being I have no engine knowledge what so ever, let alone anything this in depth.

What’s holding people back buying such a piece? The funding it would need to build a good short block?

As shown, it's a "plank" head, with no chamber. It has vertical valves like the original, but here the chamber must be created in the piston dome to have quench and turbulence - about $700-800, but you get a wide range of compression ratios.
Since the GMC and stovebolt have swapped intake rocker arms, and both valves are vertical, the stovebolt intake rocker may work for the GMC exhaust (the stovebolt exhaust rocker is definitely wrong, has a steep angle). Stovebolt and GMC rocker shafts same OD but GMC is longer. I don't like the single rocker stand holes, GMC has 2 bolts per stand? Stands may be special. Can't tell if the rockers are left and right offset.
The valve sequence looks stock: X I I X X I I X X I I X, so any GMC cam will work (some heads have different sequence and require custom cam).
Intake will be a problem could begin with some aftermarket manifold for a big 12 port L6 like AMC and slice it into sections.

I can think of several reasons it does not generate interest.

He is asking A LOT for it.
It is not the more desirable crossflow Wayne head.
It has had repairs done to it.
It is not a "bolt-on-and-go" proposition.
It requires additional fabricating, special parts, and knowledge to complete the set-up.

For a similar example go to the topic on the Spalding Bros replica build:


https://www.jalopyjournal.com/forum/threads/spalding-bros-repro-for-too-tall-ganahl.983332/

The short stud appears to be for the other hole in the gmc rocker stand so it might actually use a gmc rocker stand.

Afterthought: we don't know the relative position of the valve stems vs. tappets (across the engine) - both the stovebolt and GMC use very long rockers. It may need a completely different rocker assembly.

This head is one of 5 or 6 produced in the 1950s by Howard Johansen. I currently have one in my shop (however mine has a combustion chamber). It is an improvement to the Wayne GMC head since it has a 45 degree intake shelf vs the Wayne 90 degree shelf. The head was designed to take the original GMC rocker arm assy.

Howards design was used by Nick Arias in the 1990s when he reproduced this head. The head was marketed as the Howard/Arias GMC 12 port. At the time Nick was selling intake and exhaust assys along with roller rockers.


This particular head has a been raced at Bonneville and has set multiple records. I feel the reason the head has not sold is because there are better designed heads available today (Skinner, and the Ferguson Wayne). Also early GMC 12 port heads were known to have porosity issues....todays alloys are significantly better.

Thanks!
Were the roller rockers unique, or an adaptation of something commercial?

It hasn’t sold because of price. It’s more of a museum piece than a functional one. It would hard to have $3500 worth of 1950s aluminum on a shelf for viewing. Just like everyone has said, metallurgy was bad back then and the part may fail if used. I’ve been told the combustion chamber is no big deal. The new castings from the 90s look identical and are built well. The intake and exhaust all need to be fabricated... but that’s better anyway. Make him an offer and put it to use.

The chamber must be created in the piston dome to have quench and turbulence.
It's not a big problem, but it requires a fairly tall compression distance and a heavy piston. The stock 302 height is probably OK but any stroker or long rod will have to be done carefully.
The minimum depth of the cup (negative dome) is close to the lift near TDC for both valves + safety margin (look at the cam data), the area roughly a triangle circumscribing the seats and spark plug, and both made larger until you have the volume you need for the static CR you want. In a 302, 9:1 is 6.3" or 103cc, 12:1 is 4.6" or 75cc. If you have the room (low CR) the exhaust side of the cup should be deeper.
The chamber outline should tend to extend out more on the side facing away from the port.