[steve25]

In the last few weeks I have posted inaccurate info on some cylinder heads as I was just reaching back into my mind about it from info jammed up over the years.

I have two used sets of heads in my stable , one set is a 1972 D port big valve 7K3 casting, and the other a 1978 6X-8 casting.

The as stock Intake valve lenght in the 7k3 is 4.962".
The Intake valve installed height is 1.575"
As is the case in all Pontiac heads the Exh valves are a few thousands longer so the installed height will be taller also.

The 6X head uses the same lenght valves as the 7K3 head but has a Intake installed height of 1.588" .
Retainer to guide clearance is .564".
Once again the Exh valve is a tad longer.

I will go out on what may be a thin a limb and assume that a 1971 casting number 96 head would be set up the same as the 7K3, and the 1975 5 series heads would be the same as the 6X series.
Until I get these castings to full confirm such if anyone has a bone stock one to check please correct me here if I am wrong.

[Skip Fix]

Most of the later larder deeper D port chambers used that length valve. I assume to keep the IH and vale tip to rocker stud geometry about the same as the shallower smaller chamber D port heads. They do give you that much more valve to piston clearance sine the valve heads are further away from the pistons with the deep chambers.

The 6X-4 head has a slightly smaller diameter chamber than the 6X-8 head is why it specs smaller CC chamber. Easy to see when they are side by side, and it also means an equivalent milling will reduce chamber size a hair less than the larger OD 6X-8 chambers.

[shaker455]

Originally Posted by steve25

In the last few weeks I have posted inaccurate info on some cylinder heads as I was just reaching back into my mind about it from info jammed up over the years.
.

Your forgiven Steve relax

[steve25]

Thank you!��

Skip that milling detail is something indeed we never talk about , but very right you are as Yoda would say!

It's been generally accepted that on 68 and up open chamber heads that a mill of .006" will shave off 1 CC of volume , so that would be in regards most of the D port, round port HO heads RA4 heads , SD 455 and to the late 4 series, 5 series and 6 series heads that where not machined for usage on 350 cid motors , or the last of the 400 / 220 hp motors used in the TA cars.

On the 91 CC heads there spec for milling off 1 CC of volume would fall in between what's needed to do such on all the first mentioned castings here and the 67 and earlier closed chamber heads.

In other words every .008" milled off the 91 CC heads would shave off 1 CC of volume.

At the other end of things we have the late 1967 first open chamber 061 casting ( Pontiac really went off the rails on this one! ) with its very wide chamber that in my best guess would only need a mill of .0045" to take off 1 CC of volume.

You can clearly see why in this photo.

[Skip Fix]

Steve with the even larger OD of the more open chamber round port heads the same mill might take a different CC off. I know the valves in the RAIV head are even closer to the piston than other 72cc chamber D port heads because the chamber is shallower. Maybe another reason Pontiac used a longer valve in them.

[steve25]

Seems the bigger the area of the chamber opening in the head deck the more CCs get removed for any given mill amount regardless of the depth of the chamber.

When I reworked a set of 6H heads 9 years ago with there massively deep 124 .8 CC chamber a .050" mill took off the same CC amount as seen 4 months latter on a set of 6X-8 heads with the same .050" mill.

[footjoy]

Steve

Is there a difference between the #16 heads and the #13 heads?

Thanks

[steve25]

The answer is no, and your welcome.

['ol Pinion head]

Originally Posted by steve25

The answer is no, and your welcome.

Chambers are slightly larger on 13's, than '68 16's. Many years ago cc'ed chambers on several low mile 13's & all came in with between 78-80 cc chambers.

[steve25]

Yes they are larger, but not in a way that effects how many CCs get removed if my notes I am looking at from 1982 are correct when I owned both of those casting numbers ( 13s and early 68 number 16s ) in my parts stack.

Also we need to keep in mind that the 16 casting number was used in 68 with heads that have a air injection boss and late 68 version heads with no air injection.

Footjoy did not post his casting date and in regards to my statement about milling it was in regards to a Chamber shape with a 68 head with the air injection boss .

I don't have a 16 casting without the air injection to determine if there is indeed a chamber shape difference that would account for a 4 to 6 CC gain, but I may be able to borrow a casting to do such.

[Kenth]

Also, 1970 #13 heads uses shorter valves than 1968 #16 heads due to higher roof in chamber for larger volume.

[footjoy]

[QUOTE=steve25;6103807]Yes they are larger, but not in a way that effects how many CCs get removed if my notes I am looking at from 1982 are correct when I owned both of those casting numbers ( 13s and early 68 number 16s ) in my parts stack.

Also we need to keep in mind that the 16 casting number was used in 68 with heads that have a air injection boss and late 68 version heads with no air injection.

Footjoy did not post his casting date and in regards to my statement about milling it was in regards to a Chamber shape with a 68 head with the air injection boss .

#16 DATES
A 15 8
A 08 8

['ol Pinion head]

Have at least one K of 67 dated '16's & have access to a K dated pair. have to ck to see if AIR galley is present. Also have a pair of F228 dated 16's off a late WQ block

If I was going to pair up big valve high compression D-port heads by similarity, it would be 62's & 13's.

Pete's book & many websites that have copied it show big valve 16's as also being used on some '69 models, but in over 35 years pulling parts, buying core parts, & cking out original cars, have never ran across a pair of big valve 16's dated for a '69 engine.