[GMCnet] Oldsmobile 455 heads G vs J

[Matt Colie]

I may have a chance to collect a nearly complete (short carburetor and distributor) 455 with no attached history. It has G heads. My research so far
has found that it should have the same combustion volume, but may or may not have hardened seats. The valve sizes are listed as the same.

Does anybody in our community have experience enough to tell me if these are even worth saving? I know that if one needs hard seats they can be
installed, but I do not know the current cost of this.

Thanks

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

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[Carl Stouffer]

Matt Colie wrote on Sat, 23 September 2017 18:39

> I may have a chance to collect a nearly complete (short carburetor and distributor) 455 with no attached history. It has G heads. My research so
> far has found that it should have the same combustion volume, but may or may not have hardened seats. The valve sizes are listed as the same.
>
> Does anybody in our community have experience enough to tell me if these are even worth saving? I know that if one needs hard seats they can be
> installed, but I do not know the current cost of this.
>
> Thanks
>
> Matt

Matt,

I would certainly save them. They might not be worth much as cores, but in my recent search for heads, I found that ANY 455 head is kind of hard to
come by.

I think most, if not all 'G' heads are 'big valve' (2.071) heads from about '71 or '72 ('Ga'). Ga heads are 'W-30 heads and are worth a lot of $$$ in
the hot rod crowd. One source I found said the G heads DO have hardened valve seats.

If you look for a flow chart, there isn't much difference between the best flowing and the worst flowing Olds BB heads. I ended up with a pair of K
heads and the coach runs great with them on (of course one of the old heads had a leaky valve, so it should run better with new heads).


--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

[Andy]

Carl S. wrote on Sat, 23 September 2017 23:15

> If you look for a flow chart, there isn't much difference between the best flowing and the worst flowing Olds BB heads.

I've been debating on which head to use for my 4.5" stroked engine build. Have a set of Cs that came off the donor engine, the slightly larger intake
runner hit might be positively offset by the Cs much better exhaust.

Still pondering, no luck finding either J or G locally.
--
77 Kingsley

[Bill Wevers]

I rebuilt a 455 out of a Revcon with G heads and put it in my 75 Glenbrook.
They do have bigger valves and rotaters with induction hardened exhaust seats.
But I would imagine after 40 years they probably need exhaust valve seats.
--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose

[roy keen]

I had Ga heads that were small valve with hardened seats and rotaters. Not all Ga's are large valve.
--
Roy Keen
Minden,NV
76 X Glenbrook

[James Hupy]

You guys are confused. The K a heads have the large valves and ports
combined with a smaller combustion chambers. They are NOT induction
hardened, nor are the valves anything exotic. They are not the ideal head
for heavy duty use. More suited for light weight high performance use. W-30
option and 4-4-2, Hurst Olds, etc.
The J and G heads are what you want for motorhomes.
Jim Hupy

[Emery Stora]

I fist posted this to the list back in 2004.

Many of the GMC motorhomes use J heads.

According to information that Dick Paterson published a few years back here is the head information.

Those with “soft” seal areas that require hardened exhaust seat inserts:

455 1966 B
455 67-69 C
455 68-69 D
455 68-70 E
455 1970 F
all of the above were for leaded fuels

Those with hardened seal areas that don’t require inserts:

455 1971 H
455 71-72 G
455 1972 Ga
455 71-72 J
455 73-76 (Cutlass) K
455 73-76 (Marine / Irrigation) K

403 77-79 4A

These all were for unleaded fuels.

Note that this information was for all applications of the 455, not just the GMC motorhome.

I have just created a gmcphotos.com <http://gmcphotos.com/> album which has a more comprehensive listing.
See it at:
http://www.gmcmhphotos.com/photos/g7088-olds-big-block-heads.html <http://www.gmcmhphotos.com/photos/g7088-olds-big-block-heads.html>

Emery Stora
77 Kingsley
Frederick, CO

[Matt Colie]

Thanks to all

Special thanks to Dick and Emory.

Dick has passed me a listing that gave combustion volumes.
This listed answers my worry as someone said that G might not have hard valve seats.
If thing go right, we pick up the G head engine tomorrow.

Things have been a little crazy here and I will fill that in more tomorrow.

[Emery Stora]

James there is still confusion.

I agree that the G and J are what you want for a motorhome.
The G and J heads have a 2.000 intake and a 1.625 exhaust, except the marine G had a 2.070 intake.

However the 1973 and 1976 Ka had a 2.070 intake but the 74, 75 has the same as the J and G heads, 2.000.
And the Ka DOES HAVE hardened seats. The Ka has a 79cc combustion chamber which is the same as the J while the G has a 80cc chamber.

[Carl Stouffer]

Apparently Toro and 442 G heads have the big valves. Also it seems like the G heads have slightly less restrictive exhaust ports than the J heads.

--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

[James Hupy]

Emery, just a bit of what I know about Olds cylinder heads.

1. During the production run of our GMC coaches there were only 2 heads
listed as being produced (manufactured) in the 1973 - 1976 time period and
that I know for sure are induction hardened. They were as follows:

A. 1973 - 1976 "J" heads made for 455 cubic inch engines, 82 cc
combustion chambers. Known as "Smogger Heads". Racers don't like them
particularly because of the big combustion chambers and smaller valves. We
like them for the motor homes because they make good torque at the RPMs
that we run our coaches, plus they are regular fuel, and have hardened
valve seats.

B. 1973 - 1976 "K A" heads. 455 cubic inch, Marine, Irrigation,
Industrial, Some motor homes, W/30, Toronado, 442 4 speed cars, Big Valves
and ports. 80cc chambers. Most were induction hardened, and the H/O
versions had strong valve springs and used a bit different rocker arms and
camshafts that were not suitable for motorhome use.

Other heads that can be used with modifications like hardened valve seats
and different exhaust valves, springs and keepers that were manufactured
before 1973 were the the "G" heads, manufactured in 1971, and "E" heads
made 1968 - 1970. These are getting scarce, and frequently are in poor
shape, due to cracks, stripped bolt holes, etc.

There are still a couple of aluminum heads manufactured. Mondello and
Edelbrock both show them in their catalog. I don't know much about them.

There is a whole lot more info out there, and much of it centers upon
"numbers matching" stuff for collector car guys that want the right date
codes for when their cars were produced. That stuff means nothing to us,
and clogs up my memory cells, so I try to not remember it.

Just what I know. Dick Paterson's sources may differ a bit from this. He is
an encyclopedia of Olds data.
Jim Hupy
Salem, Or
78 GMC Royale 403