[62 bv]

hi just got a set of 716s heads can some one tell me what the x over the frees plug means and the xo over the casting number in the head thank you brody

[johnta1]

I think you mistyped - should be 76?

The 'XO' are stamped?

The 'O' if it is stamped usually meant stiffer valve springs.
The 'X' if it is stamped was for higher compression ratio.
(smaller chamber)

Have a picture of them?

[62 bv]

no the heads are 716s with a date f14 64 thanks thou for getting back to me

[Dick Boneske]

Never heard of added coding on the '64 716 heads. Maybe we'll learn something new on this thread!

There must have been a way to ID the 421 heads from 389 heads used on GTO's. The chambers were quite different in volume. Maybe that's what the X's and O's mean.

[tom s]

They were used on 389 and 421 so maybe chamber size?

[johnta1]

In the previous years, what I wrote is how they differentiate the heads.

The 'O' if it is stamped usually meant stiffer valve springs.
The 'X' if it is stamped was for higher compression ratio.
(smaller chamber)

I did not think they did it after 63, but they could have.
I tried looking through the tech bulletins but haven't found any for 64.
(doesn't mean it didn't happen)

Seems I remember them doing it for the higher performance heads in a later year (1966?)?

The 'X' on the front of the head, is it a stamped 'X' or a casting?

[62 bv]

the casting x on the front of the head is on a pad and inverted so its cast in the pad thanks for all the in put

[johnta1]

That is just part of the casting/process.
Doesn't mean anything.

[remy30006]

Does anybody have a pair of these heads or know where to find some. If so please message me Thank you!

[Dick Boneske]

Does anyone know how Pontiac identified heads used on two different-sized engines---like these '64 716 heads, '65 77 heads, '66 093 heads, and '67 670 heads, and others? There had to be a code since cc's would be different for the two engine displacements.

[tom s]

Dick,also 69 48 heads for a 350HO and a 400.Tom

[johnta1]

I've always wondered about the 48 heads as Tom said.
The others, I wonder if the pistons had more of a chamfer on them to make the CR come out right?

[tom s]

I do know the factory did use diff thickness head gaskets for some builds!Tom

[b-man]

The 421 used pistons with deeper valve reliefs to keep the compression ratio on par with the 389s, much in the same way that 428s used dished pistons to match the same compression ratio as the smaller 400 engines that shared the same heads.

Definitely a big difference in valve relief volume between the 421 and 389 pistons, very likely a 6cc difference between the two.

Pictured below are factory pistons that came from 1964 421 and 389 engines.

[MescaBug]

63 389GTO/421HO 9770716 9770716 9770981 Press 1.92 1.66 68 (72)

[johnta1]

His are dated f14, which is for a late 1964 car.
(June1, 1964)

I still haven't found my info on the head stamps.


I believe McCarthy wrote of it in his book, also.

[MescaBug]

"The '64 9770716 GTO (and '63 -'64 421 HO) head has a 17 degree valve angle and uses 1.92"/1.66" valves, these were the big-valve Pontiac performance street heads of their time (standard 389 heads up through '64 used 1.88"/1.60" valves). The early offset chamber placement doesn't allow the practical use of valves any larger than the 2.02"/1.76" valve sizes used in the race-oriented '62 -'63 421 Super-Duty heads."

[johnta1]

Mescabug, is that your head?
If so, what engine did it come off of?

[Dick Boneske]

Yes, these 9770716 casting numbers were used in '63 and '64. Was this the only instance of Pontiac using the same head casting for more than one year?

Did any Tripower '63 421's use the 9775088 intake casting? Or, did they use the casting number 9770275 intake like the '63 389's used?

From my experience, Tripower intakes had different casting numbers for each year from '57 through '66, even though some were very similar--notably '61 and '62.

[johnta1]

As far as I know the 63 421 used the '275 intake.
(389 and 421 both)