AMC 360 heads

[chrisnsarah]

I just took my heads to the machine shop to have them inspect a bad valve seat and possibly redo the guides and valves. The machinist told me I had the "Dogleg" heads, which are rare and desirable. He said I would be money ahead if these were built right. I've never heard of these type of heads, so could someone fill me in please, or know a good source for more info.

[RustyJeep]

All the Jeep 360's and 401's used the dogleg heads. They are rarer and desirable on a AMC muscle car, such as the Javelin, but all our engines had them. They flow really well out of the box, and with some work, they flow extremely well.

[Bob Barry]

Well, if by rare he means "installed on every AMC 360 and 401 built from '71-'91", then yeah, they're rare. I wonder which heads he was thinking about; maybe the '70-early '71 versions with the smaller chambers for higher compression.

[Michael]

Well how small are the chambers for the 360 heads??? 70 something cc's???

[chrisnsarah]

Thanks, I'm almost positive my heads are original ('75) and my 401 has the same heads. I guess this shop sees more early AMC muscle cars than jeeps.
I've also heard of early and later heads where the bolt holes are different and I uses rocker arm bolts with a bridge like my '75 and the pre-jeep motors used studs. Do you know if there were any compression ratio differences that varied by year and how do you determine what year the heads were built? I want to make sure someone didn't put early heads on because I could tell this motor was messed with quite a bit before I bought the jeep.

[Cliff]

AMC Cylinder Head History

When the AMC V-8 first appeared in 1966, it had square port heads. The AMC techs realized in 1970 that they could open up the runners a little and greatly increase flow. This placed a "notch" in the exhaust port, and they were called "dogleg" heads.

In 1970 and early 1971, the 390 and 401 heads had 52cc combustion chambers and a compression ratio of 10.25:1. In mid 71, the c/r was dropped to 8.5 by enlarging the chambers to 58cc. It is rumored that some of the 360 engines also had these heads, but most had the open chambers (58cc) like the 304. Hooker even makes a dogleg header, as did most other brands at one time.

The 52cc closed chamber heads are rare, but ordinary dogleg heads are a dime a dozen. The earlier square port heads are somewhat rare, and few people want to use them due to the reduced flow characteristics. The AMX crowd, for purity, will stick with them.

For Jeepers, I have heard of using the smaller valve 304 heads on 360's for better low end torque. Never tried it myself.
:rolleyes:

[Cliff]

Cylinder Head History Part 2

The bridged rockers first appeared in 1974, so these are most likely your original parts.

If you go for the head buildup, DO NOT buy Crane roller rockers. The ordinary Cranes are a poor fit, and cause problems. If you want to spring for the Crane Gold Race, they work, but check out Harland Sharp. Less expensive and a good reputation with AMC racers.

All the heads with bridged rockers are 8.5 compression ratio. In 1970, they also enlarged the size of the head bolts, increasing them by 1/16" diameter. That is the only change you have to make to bolt late heads on the early engines (290-343-390).

[Bob Barry]

AMC Head History, Part III: On the possibility of variations in accessory bolt holes (or why all-thread is your friend).

One other change: in '79 Jeep reduced the size of some accessory bolt-holes, specifically the hole for the alternator pivot bolt (from 7/16" to 3/8") and four outer exhaust-manifold bolts (from 3/8" to 5/16").

[Michael]

That is great info...thanks guys...

Little off topic....with such high flow heads....compared to sbc stuff anyway that come stock. Why did amc not use a larger cam???? Seems really small to me.... That would be another topic huh?

[chrisnsarah]

Thanks for the info guys, you pretty much answered all my questions. So it seems the major differences are found in pre-'71 heads. Just wanted to know in case I ever went scrounging for heads.
Now one of the 401's I have has the studs instead of the rocker bridge. The code date on the valve cover dates it a '72 and it did come from an AMC car. Is it still an 8.5:1 ratio? Will later heads fit without any problems? Is the studs a better setup, or does it matter?
Michael, I don't know any reason why they didn't put a big cam in other than emissions. Maybe they did in the late 60's. A buddy in high school had an AMX with a 390 that was a neck-snapper.