'69 427/390HP Heads vs '70 454/390HP Heads; any difference?
I have '70 454/390HP cast iron heads on my late '69 427/390HP coupe. Any difference in the heads? (part number GM8T; J 25 9 (= Oct 25, 1969); 3964290; PASS)
Thanks...Don
Thanks...Don
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
I think 70 went to the tapered seat style spark plug -
Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
For all Chevrolet models except Corvette & Camaro the 1970 model year began with August 1969. So the choice for the production managers was either all those other models got 1969MY parts or Corvette/Camaro late 1969 got 1970MY parts. We know the latter happened.
In reality it is not completely accurate to call the second design heads 1970 heads -- but most of the reference material continues to do that.TerryComment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Don------
The late 1969 3964290 heads MAY be machined for tapered seat spark plugs rather than gasketed plugs. However, I think there are some of these heads out there that are machined for the gasketed plugs especially those used for 1969 model year applications. What type of plugs do your heads use?In Appreciation of John HinckleyComment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Both the 69 3931063 and 3964290 have the same 100.9 cc combustion chamber volume. I have a 290 head dated F-20-9 so they were in use during the regular as well as extended 69 model year. I will check it to see if the early heads had gasketed or taperd plug seats.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Don
I agree with Joe that there are most likely 3964290 heads that were produced and machined for the 1969 model year that use a spark plug that requires a gasket. I think that is what you will probably find.
Ray
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Patrick-----
Are you sure? Many of the heads machined for gasketed plugs APPEAR like they are machined for the tapered seat plugs because they have a relatively large chamfer at the lead-in to the threads. The best way to tell is from the COUNTERBORE diameter. If a gasketed plug fits into the counterbore, then the head is machined for gasketed plugs. If it does not fit into the counterbore, then the head is machined for tapered seat plugs. The tapered seat counterbore is 0.91" OD; the gasketed type plug counterbore is larger.In Appreciation of John HinckleyComment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Joe- The head was dirty so I didn't trust just a visual inspection. I had a peanut plug and a long reach gasketed plug and also a clean 1968 3917215 head for comparison. The 3917215 had a prominent flat shoulder for the plug gasket to seat on. The same spot on the 290 head appeared to be tapered. I tried to put the peanut plug in the 215 head but the gasket shoulder kept the peanut plug from going in far enough to engage the threads. The peanut plug would easily screw into the 290 head. The long reach gasketed plug would also screw into the 290 head but I think the gasket would rest on a tapered rather than flat surface. I might actually work in a half-assed way. I think the test you suggest would work for small block heads with short reach gasketed plugs, but since the long reach plugs have the same thread as the peanut plugs and are smaller in diameter above the threads they will always manage to screw into the threads meant for a peanut plug.
Since the peanut plug would not even engage the threads of a 68 427-390 head but would screw into the proper depth on the 290 head, I conclude that the 290 head was machined for peanut plugs. This conclusion is in agreement with the "Chevrolet by the Numbers" book which lists the 290 head as in use in the 69 model year (for more than just Corvettes and Camaros) and describes it as identical to the 063 head except that it is machined for peanut plugs. I think there may be people using gasketed long reach plugs in these heads because they will screw in and maybe seal against a tapered shoulder.
If my conclusions are not convincing to the group, I will try to bead blast and photograph the spark plug holes on this head.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
This is a issue I know very well. I wrote a story for the SCC Chapter newsletter about it.
After much research and investigation I can tell you that a set of 290 heads for a '69 Corvette will definitely have flat plug seats for a gasket style plug. The same set of heads cast on the same day for a Chevelle, Impala or whatever will have tapered seats for a peanut plug, no question about it.
Remember the casting number is just that, the part number was different for a '69 Corvette versus a '70 Chevelle. Tonawanda machined the seats for the application and specific part number.
if you have a correct set be thankful. A very late 290 head for a Corvette are extremely difficult to find, trust me.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Don,
I forgot to ask, what is the built date of your motor?
Trim tag date of your car?
My motor is 11/04, trim tag date 11/20. My 290 heads are machined for '69 gasket plugs. One head is J22, the other is J29.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Patrick,
Though I've never tried I don't see why not?
Both type heads use the standard 14mm thread, it was the seats that were different.
The early style used the flat seat for the 13/16" gasket plugs, and the later heads had the tapered seat for the 5/8" peanut plugs. The threads were the same.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Jamie -- Although the threads were the same, the counterbore between the threads and the gasket mating shoulder of the 1968 big block heads designed gasketed long reach plugs is too small for the peanut plug to fit in far enough to engage the threads. The body of the peanut plug (which is not long reach) touchs the gasket mating shoulder of the 68 heads before the threads of the plug reach the threads of the head. You push the peanut plug in and turn and turn but it won't screw in.
However, the long reach gasketed plugs will screw into the peanut plug hole and tighten up in a way that feels normal. They will probably even function normally. The test for a big block head machined for peanut plugs is whether the peanut plug will screw in. The long reach gasketed plugs for a big block will screw into either type of head.
This is the opposite of the case of small blocks in which the short reach gasketed plug would not fit a peanut plug hole but the peanut plug would probably screw into a small block hole for a gasketed plug. I think Joe Lucia's comment was describing the situation of small blocks whose gasketed plugs do not have a long reach and therefore would not fit deeply enough in a head machined for tapered plugs to engage the threads.Comment
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Re: '69 427/390HP Heads vs '70 454/390HP Heads; any difference?
Patrick,
I understand. Thanks for the explanation.
i do have to say that with a visual inspection it is very clear to tell if the hole is machined for tapered plugs. There is a definite 40* bevel that matches up to the same bevel on the tapered plugs. The gasketed hole is much more a 90 degree affair. I looked at many heads and could easily see the difference between the two.Comment
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