Below is info on the Johansen head copied from "The 12 Port Story Pt. 6" written
by Herbert Hall (originally printed in Vol. 2, Issue 1 of the 12 Port News)
By the late Fall of 1951, about 3 to 4 months after that day Art was down to see
Howard about the Bonneville car, Howard Johansen had gone ahead and produced
just such a cylinder head; like the one they had talked about that afternoon. In
producing his first 12 Port head for the GMC, Howard Johansen chose 356
aluminum. He not only patterned his combustion chamber after Harry Warner's GMC
head, but also after the earlier, flat chamber of the 1928 Chevy four. Howard also
decided he was right concerning the intake ports. On his 12 port head, he inclined the
intakes to about 45 degrees for better flow, straight down to the valves. In doing this,
he was looking back to the intake design of the Riley 4, and engine Howard has
successfully campaigned around the country with Jim Rathman at the wheel in a car
owned by Andy Linden.
The new Howard 12 port head for the GMC had 1 7/8" intake valves and 1 3/4"
exhausts. The intake ports were 1 7/8" x 1 11/16" and the exhaust ports were 1 19/32"
x 1 28/32". The head had bronze valve inserts and bronze valve guides. A stock
GMC rocker arm assembly was used and Howard reground a stock steel cam for the
head. With a Howard F series cam, these Jimmies revved into the 5,000 to 5.500
r.p.m. range and up to 6,500 r.p.m with a Howard M series cam. Howard also had
special tubular pushrods available for the GMC. In April of 1952, "Hot Rod"
magazine ran Howard's first ad for the new 12 port head for GMC. Art Benjamin,
who was often over to Howard's shop and who was a distributor of Howard cams and
speed equipment, recalls that there were from 10-12 of these heads produced, all in
aluminum. This conflicts somewhat with other estimates of around half dozen heads
produced, but Art is very confident in his estimate.
The dyno tests proved out Howard Johansen's thinking on the design changes he
envisioned after looking over the Wayne 12 port that summer afternoon. In an
advertisement for "Howard's Racing Cams," h.p. levels of 303 h.p. from a 297 cu. in.
GMC with the Howard 12 port head and using straight methanol were
obtained. When the fuel was beefed up with the addition of 25% nitro, the h.p.
jumped to 351, that's right, over 350 h.p. form a 297 cu. in engine. I have in my files
copy of a Howard GMC engine testing report, in which a 298 cu.in GMC fitted with a
Howard 5 carb manifold, Howard F-7 cam, 12:1 compression and Howard pistons,
running methanol and of course the Howard 12 port head, turned out a top h.p. rating
of 355 h.p. at 5,200 r.p.m., and amazing figure. These 12 port cylinder heads were
first offered at $270, and later were raised to $290. What deal, that was a very low
price even in 1952.
