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For these original 461 head specs, what does it mean to have no accessory holes? I've heard of some people drilling them, why would they and what would they be used for? Looking to rebuild my original block. Thanks.
62cc
2.02/1.94
1.60/1.50
Double hump heads, no accessory holes 160 cc runners
302/327/350
These holes on the front of the head came about with the advent of the "long" water pump in 1969. They allow for mounting of the alternator in front of the head (and smog pump on some applications) for sbc engines. I would not try to drill them as the casting is different and not enough "beef" there to drill and tap. Run a short pump and don't worry about them.
There actually was a 57 head that had the accessory pad on one end of the head. The holes weren't drilled but the flat machined area is there. There's a reason I know this. I built an engine for a customer with a beautifully restored 57 convertible. Several years after I closed my shop he calls one day and asks if I remember him, which I did. He goes on to say when I rebuilt his engine I had swapped heads and it cost him a few points in judging. One head had the accessory pad while the other had the power pack casting mark. I explained to him there was no way I swapped or miss matched his heads because they had staggered valve cover bolts. He finds another pair has them rebuilt and asks if I would come install them. I took the heads off and showed him they each had the same markings but when installed one of each of the ends was facing forward. He says Hmmmm I've never seen that, I said me neither but they are definitely the heads you brought me originally. This isn't a good pic but you can see what I'm talking about.
For these original 461 head specs, what does it mean to have no accessory holes? I've heard of some people drilling them, why would they and what would they be used for? Looking to rebuild my original block. Thanks.
62cc
2.02/1.94
1.60/1.50
Double hump heads, no accessory holes 160 cc runners
302/327/350
If these heads are '64-'66 vintage (no X in the casting under the water transfer ports) then nominal cc with the standard valve size is 60-61 cc, same as the '62-'63 461X heads, and about 64 cc with the large valve set due to the unshrouding cut centered on the inlet guide.
The 462 heads ('67 and maybe late '66) eliminated the small quench zone on the spark plug side of the head, which yielded about a 62 cc chamber with the standard valves and 66 with the large valves.
There actually was a 57 head that had the accessory pad on one end of the head. The holes weren't drilled but the flat machined area is there. There's a reason I know this. I built an engine for a customer with a beautifully restored 57 convertible. Several years after I closed my shop he calls one day and asks if I remember him, which I did. He goes on to say when I rebuilt his engine I had swapped heads and it cost him a few points in judging. One head had the accessory pad while the other had the power pack pyramid. I explained to him there was no way I swapped or miss matched his heads because they had staggered valve cover bolts. He finds another pair has them rebuilt and asks if I would come install them. I took the heads off and showed him they each had the same markings but when installed one of each of the ends was facing forward. He says Hmmmm I've never seen that, I said me neither but they are definitely the heads you brought me originally. This isn't a good pic but you can see what I'm talking about.
The 1958 Chevrolets had air suspension as an option. I believe that engine had special cast heads to mount the pump there. No double humps but I believe it had the holes to mount the pump. One year only option.
I drilled a set of heads for an alternator mounted on a long pump engine with a hand drill. Spaced the bracket out square with washers. Ran them about 60K miles on my truck with no issues.
There actually was a 57 head that had the accessory pad on one end of the head. The holes weren't drilled but the flat machined area is there. There's a reason I know this. I built an engine for a customer with a beautifully restored 57 convertible. Several years after I closed my shop he calls one day and asks if I remember him, which I did. He goes on to say when I rebuilt his engine I had swapped heads and it cost him a few points in judging. One head had the accessory pad while the other had the rectangle. I explained to him there was no way I swapped or miss matched his heads because they had staggered valve cover bolts. He finds another pair has them rebuilt and asks if I would come install them. I took the heads off and showed him they each had the same markings but when installed one of each of the ends was facing forward. He says Hmmmm I've never seen that, I said me neither but they are definitely the heads you brought me originally. This isn't a good pic but you can see what I'm talking about.
That's really interesting that he went through all that just for a few points.
The 1958 Chevrolets had air suspension as an option. I believe that engine had special cast heads to mount the pump there. No double humps but I believe it had the holes to mount the pump. One year only option.
I drilled a set of heads for an alternator mounted on a long pump engine with a hand drill. Spaced the bracket out square with washers. Ran them about 60K miles on my truck with no issues.
I hung a Vortec blower and A/C compressor on a set with no issues either.
"The 462 heads ('67 and maybe late '66) eliminated the small quench zone on the spark plug side of the head, which yielded about a 62 cc chamber with the standard valves and 66 with the large valves."
Is this change also responsible for the drop in the manufacturer's stated compression ratio on the on the 300 HP engine from 10.5:1 for '66 to 10:00:1 for '67? If so, Why wasn't the L79 similarly affected?
That's really interesting that he went through all that just for a few points.
ive seen your car. If something even less important than the wrong heads was amiss you'd take care of it. This wouldn't be able to let it go knowing he had incorrect heads on this car.
"The 462 heads ('67 and maybe late '66) eliminated the small quench zone on the spark plug side of the head, which yielded about a 62 cc chamber with the standard valves and 66 with the large valves."
Is this change also responsible for the drop in the manufacturer's stated compression ratio on the on the 300 HP engine from 10.5:1 for '66 to 10:00:1 for '67? If so, Why wasn't the L79 similarly affected?
That's pretty close to my analysis. The '62 to '66 300 HP CR was 10.5:1, advertised. I believe it dropped to 10.25 in '67 and that would be logically due to the slightly larger 462 head chambers. It was dropped further to 10.0 in '68, but I'm not aware that the '68 head chamber was any different. Perhaps they decided to use a more realistic number.
'62 to '63 340/360 HP engines were 11.25:1, advertised and had 461X heads with the standard valve size; '64 to '66 350/365/375 HP engines' advertised value was 11:1, logically due the slightly larger chamber because of the unshrouding cut with the larger inlet valves that all these engine have.
The '67 L-79 advertised CR remained at 11:1 despite the larger chamber 462 heads with the unshrouding cut. I can't account for that, so it was probably a marketing decision not to reduce it slightly.
Due to the larger chamber volume of the big valve heads beginning in '64 the double gasketing from mid '62 through '63 of 340/360 HP engines was discontinued for the '64 365/375 HP engines.
The 1958 Chevrolets had air suspension as an option. I believe that engine had special cast heads to mount the pump there. No double humps but I believe it had the holes to mount the pump. One year only option.
That's right Mike. But there was more than one. '58 & '59 2bl left head casting number 3755537 and '58-'59 w/4bbl left head casting number 3760116 or 3755550. The Level-Air was also optional in '59.
That's right Mike. But there was more than one. '58 & '59 2bl left head casting number 3755537 and '58-'59 w/4bbl left head casting number 3760116 or 3755550. The Level-Air was also optional in '59.
Verne
Thanks for the refresher course Verne. What about the 348 engine? Special head casting there?
I just happened to have a '64 printing of the P&A book behind me today. Looks like if your air bags managed to last until '64 and you needed a head, you were out of luck. No listing in the parts book for air suspension head.
Thanks for the refresher course Verne. What about the 348 engine? Special head casting there?
I just happened to have a '64 printing of the P&A book behind me today. Looks like if your air bags managed to last until '64 and you needed a head, you were out of luck. No listing in the parts book for air suspension head.
The W heads already had the holes in them.
The recommended SB head after that was the '60 (& up head) with a note that different valve covers had to be used.
That was probably designed into the head from day 1 since the 348 was initially going in to medium/heavy truck to replace the Buick engine they were using.
02-04-2019, 11:51 PM
Double-Hump Head Specs – 3782461
