High Compression Head Numbers

segajeep

OK, according to my 1952 Hudson Mechanical Procedures Manual, all three I6 motors came in high and low compression variants. What do I need to look for to identify one the next time one comes up for sale or in the off chance my motor has one?

[Deleted User]

Aluminum is high compression, and cast iron is regular compression. Walt.

oldhudsons

If you look in the parts book under section Z, special parts, the 7X or high performance parts are listed inc. heads,cams, radiators, rear axles, etc. The head #s, such as 232, 262, & 308 are all cast into the heads.
I beg to differ with Walt but all the high performance 7X heads were steel, the original ones had "232" on them but drilled out for the 1/2" studs used on the 7X blocks.
One has to be careful when purchasing any Hudson heads! Take a micrometer along as many may have been "planed", "milled", or "decked" so many times that they are no longer usable. Also bring a straight edge to see how "flat" they still are as altho a lot of "meat" left (ascertained by measuring the thickness with the micrometer), it is so warped that milling it flat will make it unusable.

Marconi

Also because of the Korean war Hudson made up some cast iron hi-comp heads. These mhad a metal tag put on with escutcheon nails(?) on the left side about 1/2 way back with the comp ratio and I think the part number. Jay, at Vintage Coach has 1 or 2 of these heads.

Geoff

My 53 Hornet has a cast iron head which is inscribed "H145, Super Power Dome,305854, Use premium gas". So what does that make it???

oldhudsons

Hi Geoff - as I recall that was a high comp. head offered in '51 (& I believe the "H-145" was only used in '51 on the emblem placed on the inside of the doors, beginning in '52 the emblem said "HORNET"). I don't ever recall, either in parts books or in all the numerous Parts Bulletins which the factory put out, them giving the actual ratio.
As most of you know you could not order any Z section parts installed on the car at the factory (when ordering a new Hudson) - if you ordered a new car with any of those items, the factory put them in the trunk so were to be dealer installed.
Twin-H did not fall in that category.
So Geoff I'd assume someone got their hands on one of those rare '51 high comp. heads & put it on your '53.

dougson

I suspect that heads got switched around like crazy on these engines as gaskets wore out or heads warped or who knows. The highest production compression ratio head that came on a 308 was 7.5:1. Any aluminum head with "308" cast on the front is a 7.5. By '54 both iron and aluminum were 7.5. Regarding heads, "cavaet emptor" big time, and check casting numbers. Based on my experience, head casting numbers will vary from the parts book by a digit or two typically at the end of the number, but the parts book is still a good indicator of the year the head was cast.

Marconi

Geoff, I think that's one of those 'Korean War' hi-comp heads!

Park_W

Geoff,

A Dixie Chapter friend of mine has one of those heads on his '51 Hornet sedan ... he was told it's original on that car. A little side note ... those who recall Special Interest Autos magazine (forerunner of Hemmings Classic Cars) will remember editor Michael Lamm occasionally mentioning that his "daily driver" was a '51 Hornet sedan. That's the car my Dixie friend has now.

Geoff

Well, of course anything goes as far as my Hornet is concerned, as it was built in South Africa. It is a '53 but still has the single lever transmission, and is of course r.h.d. It has the Dana rear end with 4.55 ratio, so I am going to change that to 4.1 as the original is too slow, and the 308 will handle that o.k. even with overdrive. I found in my stuff a pair of diagonal grille bars as in earlier version, so have fitted them to my car. I always reckoned the '53's looked a bit toothless without them and the bars complete the inverted triangle. Not original I know, but then I can always claim "special export status"! Thanks to Dave Sollon, I now have the little metal piece that goes between the medallion housing and the front shield.
Geoff

bob ward

Geoff C., N.Z. wrote:

It is a '53 but still has the single lever transmission, and is of course r.h.d. It has the Dana rear end with 4.55 ratio, so I am going to change that to 4.1 as the original is too slow, and the 308 will handle that o.k. even with overdrive.
Geoff

Locally assembled Australian stepdowns, up to and including 53 had the single lever box. Like many manufacturers, Hudson sent their superseded stock to the far corners of the earth. Dana diff arrived here in '54 models.
4.11 and overdrive will give you a 2.9ish? rear end, an ideal combination for todays roads with a 308.

Geoff

Marconi wrote:

Geoff, I think that's one of those 'Korean War' hi-comp heads!

Further inspection of the head reveals a little oblong section with 4 24 51 cast in, so you you guys are right! I'm happy with this head as I have the best of both worlds, high compression, and no troublesome alloy. I wonder what octane the "Premium" fuel was in 1951?