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 Guide to the Hudson 7X engine
Engine Rebuilding Many of us Hudson owners are preparing to rebuild our engines, or are in the process of rebuilding our engines. Most of us know of the Hudson racing heritage and the engine project designated 7X. In an ongoing project I am trying to document the actual specifications for the 7X build and list suppliers where you can get the components to complete the build.

308 Engine factory Stock

The standard factory 308 for 1951-52 has a 3 13/16" bore and a 4 1/2" stroke and with the Cast Iron head has a compression ratio of 6.7-to-1 and with the Aluminum head 7.2-to-1. The inlet valves are 1 13/16" and the Exhaust is 1 9/16" This combo delivered 145 hp with the standard single WGD Carter 2 barrel carb.

For 53-54 the cast iron head was 7.0-to-1 and the aluminium was 7.5-to-1 engine specs were the same but the Twin H dual carb manifold was introduced which raised the horsepower to 170 for the Twin H and 160 for single 2 barrel.

The true 7X factory to dealer option had the same specs except the engine block was machined around the valves to create a relief to produce the venturi effect. The port area was hand finished by the factory race team. The valves were bigger, the inlet was 2" and the exhaust were 1 11/16" the head options were a reworked 232 head in either iron 8.7-to-1 or aluminum 9.2-to-1. This engine was only offered with Twin H and delivered 210 hp. The pistons were a special knurled type and had a chrome compression and oil ring. The head bolts were 1/2" studs with special thick washers to hold the head gaskets. The exhaust was a tuned dual outlet manifold.

Here's where some of the confusion about the 7X engine comes into play. The factory 7X engine was a racing engine and was designed to run fast on the track the use of the 232 head gave it a higher compression and both the head and the block were hand finished to produce the most horse power. The cam offered in 53 was the 311040 which was designated "super 7X" this was not a street engine unless you liked a rough idle but if you liked to race this was the engine for you, it was produced as part of what might be called a factory skunk works to support the Hudson racing efforts, which were by no means a formal effort. You can tell a factory 7X as the engine number will be prefaced with a State so for example the California dealers used CALXXXXX to designate the engine serial number. These engines were hot and they liked to eat timing chains but as evidenced by the track record they performed nicely on the track. Most engines were pulled down after 500 miles and new timing chains installed. This is the true 7X, the factory hand finished, dealer installed bear of an engine.

Most of the 7X engines you see out there are a little different, mostly to produce a street driveable powertrain. I guess a purest might say its not a true 7X but its close enough to be really nice. This 7X was built by the industrious owner who got his hands on the 7X spec and had a talk to Jack Clifford who pioneered the aftermarket Hudson performance market. Jack spent a lot of time working out the rough spots and produced parts that could give you a lot of the horsepower of the 7X without the rough idle or tuning problems. He realised most owners wanted more horsepower but also wanted to drive there cars daily. He produced a variety of cams and parts that could help you build anything from a mild street 7X to a screaming race track 7X.

Cams and the difference they make

A brief discussion of the cams offered and what effect they have will be helpful in deciding which build of 7X to aim for.

Standard factory cam for Hudson engines 232,262 and 308 is 306344 lift is 356

Designated Super 7X cam introduced in fall of 53 was 311040 lift 390 duration 268 rough idle lobey exhaust note.

Designated 7X FlatTop introduced in april of 54 309742 lots of customer complaints about this cam. Trouble setting up and ate timing chains. Was replaced later in 54 with the 306344A series cam. I do not have lift and duration for these cams yet.

Clifford designated 1956 mechanical grind cam which has a lift of 376 and a duration of 254 and is considered the best cam choice as its super smooth and has power, nice to setup and none of the roughness at idle of the other cams. With Twin H and 262 head will give you 176 hp with 7X engine relief and 7X valves around 185-200.

Where To Get Your Cam

Clifford still offers 3 Hudson cams. They used to offer 6 with 3 being Isky full racing cams. Randy Maas offers cams and I have listed them below for comparison.

Clifford HK 115 is Hudson model # 309742 $199 with $100 refundable core charge added

Clifford HK 116 is Hudson model # 311040 $199 with core charge above

Clifford HK 117 is 1956 mechanical grind cam $199 with core charge above

Randy Maas Cam sizes available are as follows:

1955-1956 Mechanical Cam: 372 lift, 254 duration equivalent to Clifford HK 117

Super 7X Cam: 391 lift, 268 duration this is Hudson model # 311040

Super Street Cam: 402 lift, 276 duration Randy's race grind

All of Randy's cams are $165 with $50 core charge.

Uncommon Engineering offers a variety of cams as well. Links to all of the dealers mentioned are available in our links section.

Building a street 7X Engine

I am in the process of building two 7X engines. A street 7X as I call it and a hotter 7X that will go into a 54 Hudson as soon as I find the right project car. I am taking pictures and building a guide to the build that I will make available to members. I have a lot more to add here and will do so later so keep coming back to see whats happening.
Posted by 51hornet Saturday, July 23, 2005 (02:27:02)
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Guide to the Hudson 7X engine | Login/Create an Account | 1 comment

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Re: Guide to the Hudson 7X engine (Score: 1 )
by Toby_Peters on Sunday, August 14, 2005 (01:04:28)
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This is gold. I have found just sketchy items on 7X on the Internet, to get the specs and part numbers is excellent. My heartfelt thanks for the effort.

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