da747

I read on the net that the 3782461 heads used 64-67 have 62 or 64cc chambers and 160/62cc ports. i read in a few places that the 461X heads have the same port configuration, 62 or 64cc, and 170/64cc. I read in several other places that the X heads have 57.5cc chambers. is either info wrong, or were all these sizes produced? also are the 462 heads better than standard 461's? thanks

aquaroscoe

can't help you on the port sizes. But I thought the only difference between the 461 and 462's was a casting change for the temp sensor to be moved from the intake to the head. The late 67 462's have the casting change, but it was not tapped. 68 had the 462's tapped.

SWCDuke

Port volumes are about as you say. Figure 461s with 1.94"/1.50" valves are about 61cc and 62cc with 2.02"/1.50" valves due to the radius cut on the chamber centered on the inlet guide axis.

The 462 castings have slighly larger chambers since the quench area on the spark plug side was beveled in the coring, so they work out to about 63 and 64 cc. I think the spark plug is also slilghtly higher.

IMO the 461X castings are the best vintage heads for a high performance engine because of their larger port volume (all of which is in the bowl above the valve) and slightly smaller chambers to yield the highest possible compression without a dome or with a small dome.

NHRA head chamber volume specs may be a little less than nominal because they usually take the minimum volume from the OE tolerance range and allow a slight cut to level the surface.

Duke

da747

Im actually planning which heads to look for for a race application that requires either 461, 462 or 492 heads. The rules are quite specific about requiring at least a 60cc chamber. i was thinking of looking for a set of X heads for their higher flow potential, but if theres a good chance the chambers are at or less than 60cc before any machining, then ill choose another. any comment on the 492 iron heads still available through GMPP? ive heard some of the modern crate engine blocks are made in mexico and arent produced to the same quality as the 60's and 70's small blocks. im wondering if thats true and if same is true for the modern 492 heads, or are they still made the same way in the same exact molds as 1970? thanks

SWCDuke

I don't think you'll find a set of production machined 461X heads with OE valves that are less than 60cc unless they've been signficantly milled.

As far as I know the 462 and later big port castings all have essentially the same port cores. The casting changes were primarily to enable other features such as the front accessory mounting pads, etc, and the post '70 versions have larger chambers for lower compression.

If you're looking for a set of 461X, I know of a guy who has a stash of old SB heads, and may have some 461X laying around. I've heard, but have never been able to independently confirm that the early SB big port heads like 461X have a higher nickel content in the iron alloy, which yields a harder and more crack resistance material.

Duke

wesmigletz

Duke, if you have access to a way to test the nickel content of the heads, I have a pair of 1962 and 1963 461X heads that I could volunteer for testing, I also have a set of 186 heads for comparison, but don't have any other earlier heads.

I've also heard that the X heads had larger ports and potentially made a better performance piece due to the larger port volume. If that is the case, does anyone know why the 461X castings would have been discontinued in favor of the 461 casting? Wes

SWCDuke

I don't know of any metalurgical labs that can test iron alloys.

The 461X heads have about 172 cc port volume and the extra is in the bowl above the valve.

IMO they are the best vintage head to rework for higher performance both because of the larger port volume and the slightly higher compression ratio that can be achieved because of the small quench zone on the plug side.

Don't know why the design was changed in later heads.

Duke

JohnZ

Nope - 462's never got the temp sender boss, and weren't used in 1968; the boss appeared on 291 heads in late '67 production (April) when they replaced the 462 heads, but it wasn't drilled or tapped for the sender until the 1968 model year.