Power-pac heads. .570 guide bosses(std.I think?). .3415(11/32")valve stems. Problem; the previous owner installed beehive springs(tapered)on the heads during the rebuild and didnt have the guide bosses turned down so as to allow the spring loaded nylon style stem seals to fit over the guide bosses. They tried to just drop in the umbrella type. They rode so high on the valve stem because of the tapered spring that the plugs were getting oil fouled. I ordered the correct standard style spring/retainer kit matched to the Crane "blueprint series" 327/350hp cam (according to crane). Now the umbrellas fit down onto the boss as they should, though tight on the stem. Is it supposed to be tight? Is the seal supposed to ride up/down with the valve or be stationary. Mine ride with the valve. Big concern is will this allow enough oil to get to the valve guides by splash? Do not want to gull stems and guides. Thanks. Dave.
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Re: C3 68,327 w/power-pac heads
umbrella type seals ride up and down with the valve. if the guides are not worn these seals will work fine. positive type seal allow even less oil to the guide and valve stem. -
PS do NOT use the "O" ring seal on the stem
with the umbrella type seals as this will cut down too much on the oil.Comment
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Re: C3 68,327 w/power-pac heads
Dave-----
I agree with clem. However, one additional note: I hope that you don't have a set of "Power Pack" heads on a 1968 with 327. The heads you should have, regardless of 300 hp or 350 hp, should be "double hump on top of rectangle" heads. "Power Pack" is a term usually applied to 283 heads with a "single pyramid on top of rectangle".In Appreciation of John HinckleyComment
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Re: C3 68,327 w/power-pac heads
Yes Joe, they are power-pack heads with the pyramid on the rectangle. Why the negitive response? Please respond. This dose not make any since to us either other than achieving sky high comp ratio. The previous owner did some crazy things that my son and I are correcting. This thing is supposed to have 11:1 compression & 400ish hp! Haven't put a gauge on it yet. The heads supposedly have been messaged; milled!,larger valves,ported,port matched etc...My son has been trying to research all this to find any info such as original parts and paper work from past owners. The heads,carb,POP etc. would be nice too. The tank sticker should still be there also. Thats this week-ends "project". We've contacted the owners son but understandingly the old man is bitter and reluctant to talk because he had to sell due to financial distress. This thing runs like a scalded cat though suprisingly with street manners? That is before my son did any of his magic. Only things left to do before cruising are the springs/seals and trying to get an air cleaner to fit with the hi-rise,edlebrock and BB hood set-up. Thanks for your response. DaveComment
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Re: PS do NOT use the "O" ring seal on the stem
Thanks Clem. Do you favor 7 or 10 degree locks?Comment
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Re: PS do NOT use the "O" ring seal on the stem
stick with the stock stuff just make sure the locks are hardenedComment
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Re: C3 68,327 w/power-pac heads
Dave------
"Power Pack" heads were, basically, 283 heads although they were also used on some low performance 327s in the 62-65 period. These heads were popular once-upon-a-time, but they are quite "obsolete" by today's standards. These heads have small intake valves and, by today's standards, pretty inefficient combustion chambers.
Just about any Chevrolet head can be modified to improve its performance. I suppose if enough work and money are spent, these heads could be made to be ok. I don't know why anyone would do it, though. In today's world, "Power Pack" heads have value to restorers looking for correct heads for their restoration. That's pretty much it.In Appreciation of John HinckleyComment
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Re: C3 68,327 w/power-pac heads
The real "issue" is the small inlet port. All SB engines, even medium performance with 461s like the 300 HP are limited by head flow, which is why I always recommend massaging the heads using the time proven methods that have been in print for over 30 years.
I doubt if a set of reworked Power Pack heads will be any better than any OE machined big port head like 461s and their decendents, and when these later big port heads are mildly reworked they will be better than any heavily reworked small port 283 head.
What you have might be worth something for someone looking for a set of "pyramid" casting symbol heads. Then you can get a set of later "double hump" big port heads and have a much better engine.
DukeComment
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Re: C3 68,327 w/power-pac heads
Great info all, thanks. Anybody want to purchase a set of power-pack heads? If this thing will run even stronger it'll get me in trouble! Were gonna pull the heads after this cruse season just to measure things. I'm leaning towards getting it back to stock. Anyone have a set of 391729 or 461 double humps for sale for a C48 build block?Comment
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Re: C3 68,327 w/power-pac heads
"Anyone have a set of 391729 or 461 double humps for sale for a C48 build block?"
They come on eBay regularly either as cores or as fully rebuilt. Personally, I'd rather buy a good core offered with a money-back 'make' guarantee (no cracks) and let my local machinest build 'em up so I've got control of the process and end result...Comment
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