pop23235

What exactly is the difference in the 461 and 461X heads. I've seen both with 2.02 intakes and both without. Are the runners (molds) the same?

65tripleblack

461x heads never came from the factory with 2.02/1.6 valves.

461 heads have approx. 160cc intake runners while 461x heads have approx.170cc intake runners.

DZAUTO

The 461X heads are 61-63 ONLY. They ONLY came with 1.94/1.5 valves, and as mentioned, they had about 170cc intakes. PERIOD.
The 461 heads were 64-66 ONLY. They could have EITHER 1.94/1.5, or, 2.02/1.6 valves, depending on engine application (350, 365, 375hp/327). Also, as mentioned, they had about 160cc intakes. If the 461 heads were machined for the larger 2.02/1.6 valves, then the wall of the combustion chamber next to the intake valve was relieved by machining to reduce flow restriction. If they got the 1.94 valves, this extra machining was not done.
Below is one of my 461X heads which I had machined to accept 2.02/1.6 valves and the added machining for relief around the intake valve. The other head is an untouched head with 1.94/1.5 valves. Back in the day, and to some extent, still today, heads (either 461X or 461) which got the smaller valves are machined for the larger 2.02/1.6 valves and also have the extra machining done to improve flow around the intake valve. Of course, porting and polishing is also still done to these early heads. On mine, I only had the intake runners smoothed up to relieve the rough casting.

SWCDuke

I recall that Bill Clupper who has a lot of experience with 461X heads back in the day recommends against increasing the valve sizes and relieving the chamber on the inlet valve side as was done on OE 461 heads for SHP/FI engines.

...could be that they might not have enough material thickness in those areas since they were not designed with the larger valves in mind, but it can probably be done on a case by case basis by sonic testing to determine if wall thickness is sufficient.

I expect the 461s were cast with slightly different internal cores to provide sufficient wall thickness for those that were machined for the larger valve sizes.

Duke

jccvette

With the extra machining done, did the compression ratio change much?

C2Racer

The X heads have a larger intake runner is about the only difference I remember, maybe 10cc's? I have run big valves in both type heads on my 63 327 with no problems. Currently I have a set of ported/polished 461's on it and a set of X heads sitting on the shelf. X heads were on it when I bought it but I cracked one of them overheating at Indy last year so changed them out. Good luck.

Steve

63 340HP

My late 63' 461X heads have slightly larger intake ports than my late 66' 462 heads. Both are 1.97/1.5 valve heads. The pockets above the valves have been cleaned up on both sets of heads. Without a caliper you cannot tell a difference. With a caliper you need to know where to measure (the porting Technician at the machine shop did a quick comparison).

The 462 chamber is slightly different, with a beveled or angled edge above the valves near the spark plug. The machine shop cylinder head Technician says the chambers are about 2 c's different, with casting and mating surface machining errors fudging the numbers a cc on some of the uncut factory heads.

Since I have both sets, the Technician said there is no good reason to not use the 461X heads. He said they do flow better, but pocket porting cleanup equalizes much of the difference unless you plan over 6500 rpm or a long stroke engine.

He did comment the 462 heads have more meat around the seats to machine for larger valves, but the flow gains of larger valves are minimal with under .500 lift cams compared to pocket porting and the original valves (he says the 1.97 valves are big valves compared to earlier and later heads). His opinion is larger 2.02 valves work with larger ported 172+ cc ports, not so well with stock 160 cc ports (not enough to cut heads unless full porting and chamber machine work is included).

I don't think there is much difference between 461 and 462 heads (maybe only thickness for larger valve seats).

My 461X heads are going back on my original 340hp 327. The modifications were pocket porting, surface straightening, screw in rocker studs, and larger valve spring seat relies. Not much else to do or to gain with the planned modern ~.520 lift solid lifter cam.

SWCDuke

461X heads with the OE 1.94/1.50" valve set have a nominal combustion chamber volume of about 60-61 cc, and the '62-'63 advertised CR for SHP/FI engines is 11.25:1 and 10.5 for 250/300 HP engines.

AFAIK the 461X/461 as cast chamber volume is the same, but the inlet valve unshrouding machining operation for the 2.02/1.6" valve set used on SHP/FI engine increased chamber size to about 64cc, and the advertised CR was reduced to 11:1.

The 461X/461 heads have a small quench zone on the spark plug side of the head, but the 462 head that went into production for '67 eliminated this with a different mold that beveled it away in the finished casting. These heads with the standard valve size have a nominal chamber volume of about 62 cc and 65-66 cc with the big valves. The advertised base 300HP engine CR was reduced to 10:1, which is a lot more realistic, but L-79 remained at 11. Go figure!

As a general rule, advertised CRs like advertised horsepower in that era was highly optimistic. Production engines of the era actual CRs are a few tenths to as much as half a point lower than advertised. The primary variable is deck machining, and it's typical to find them .005-.015" higher than the nominal small block 9.025" deck height dimension.

Since CR is calculated by dividing a relatively large number by a relatively small number, small changes in the denominator can make a significant difference.

The best way to get a feel for this is to play with any online CR calculator. Changing chamber volume by 1-2 cc and deck clearance or head gasket thickness by 5-10 thou can make a difference of up to half a point.

Duke

66jack

Where do they "HIDE/STAMP THE X" at on the head?

pop23235

It's cast in on the spring side and the inside of the engine on the runner.

vettsplit 63

Steve, PM sent

66jack

You have any pics....?

DZAUTO

Here ya go.

SWCDuke

You can't see the "X" with the head installed. You might be able to see it with a mirror if the inlet manifold is off.

Beyond this the date code cast in the rocker box usually tells the story. Any "461" head cast before the June/July '63 time frame is a 461X.

Duke

PAmotorman

the X is inside that rusty looking D shaped hole on the port runner.

pop23235

My mistake guys. Thought the X was also on top near the 461 and date code.

R66

I have one 461X head dated F12 (June 1, 1962). Unfortunately, some of the bolt hole bosses on the edge have been machined down (probably to remove cracks). I never felt comfortable using it on anything.
Did only the 461X have a problem with this cracking or was it all double humps??
Great thread. I learn something every day.

C2Racer

Now days they all crack, they are old In vintage racing its not if, just when.......

Steve

GOSFAST

Just a tip, but don't toss heads that have the bosses cracked/broken, we've been repairing them for years now.

After the repair you can't notice it on the finished unit.

Thanks, Gary in N.Y.

P.S. Here's a shot of one broken, after the repair/build it's been out for years now and running fine!

C2Racer

My last one cracked from the valve seat up the runner. At 7,800+ rpm this is where the heat is!

Steve