[GRX]

Would like to discuss 670 heads and why the notches are located where they are. Valve placement in relation to cylinder? Chamber shape? Are people getting full potential from their 670 heads with the later style notches?

For comparison, below we have a 1967 400 HO block that came from the factory with 670 heads and 1969 350 HO block.

[54nomore]

I wonder if all '67 blocks got notched for the early 20 degree heads only, as if the new style heads were an afterthought. ???

[77 TRASHCAN]

Somebody here, knows...

[Old Man Taylor]

Pontiac changed the valve angle in 1968.

[54nomore]

The 670 head is a '67 head with the "new" 14 degree valve angle. Lo-po engines for '67 used the old style heads.

[lust4speed]

My December '66 cast 400 GTO WV block still had the early notches.

[GRX]

The block pictured is my October 1966 cast 400. Hopefully someone else with 1967 blocks will respond.

[steve25]

Even up to about mid 67 all the 2 bbl 400 motors where still using the early 143 casting and its 20 degree valve inclination angle!

I have no idea if, or how many of the 3 per side freeze out plug 400 blocks got the early type head notch in the cylinders even though the motor may have came fitted with one of the newer ( casting 061, 670, 97) 14 degree angle heads?

In term of intake air flow the later heads ( 14 degree ) used on a block with the early ( 20 degree ) cylinder notch will start to shave off air flow at about 350" lift and up dependant if the head is ported or not!

This should be investigated more because I tend to think that many, if not all of the 1967 400 blocks got the early notch cut in as I can not see Pontiac going through the cost of doing a seperate change over maching step at mid year when it's every likely that to do so would not provide enough time to age the blocks before maching that would have been intended to be used with the 14 degree only heads!

[Pontiac Derek]

Weird! I have seen a Lot of 67 400 blocks but i have never seen the notches that are in your picture on the right aka 2 picture.
I don't know if they make them yet but Cometic didn't make Head Gaskets for the 67 block, Even Though the 67-400 is the strongest 400 block pontiac made for mass production.

[54nomore]

That is a 350 only thing because of the extra small bore

[Skip Fix]

So is the notch more adjacent to the earlier "closed chamber" on those heads.

[Old Man Taylor]

To my knowledge all Pontiac blocks got the notches in the same place through the 1967 production year. I originally thought that the valve angle had changed on the 670 heads, so when I put them on an early block I added the later notches (3 O'Clock and 9 O'Clock). I was later told by someone that the 670 heads had the old valve angle, not the new one. I am not sure which is correct, but I was covered by adding the later notches. All the later Pontiac blocks were notched, but as the bore size got bigger the notches got smaller. On big bores they go away (with stock valve sizes).

[steve25]

The 670 heads and in turn the restamped # 97 heads have the later 14 degree angle .

[Old Man Taylor]

Originally Posted by steve25

The 670 heads and in turn the restamped # 97 heads have the later 14 degree angle .

That was always my understanding, but someone told me that was not correct. The only logic behind the 670's being the old valve angle is that the factory did not change the reliefs for them. Pontiac was usually pretty good about matching parts correctly.

[54nomore]

Because of the closed chamber, I can see how someone might assume they had the early valve angle. If you had a 670 head and an 093 (for example) side by side, you'd see that the 670 chamber was much more centered over the bore. Paul (gtofreek) has some good pics of the 670 heads in his 413 build thread.

[steve25]

At the stock valve lifts and durations the piston to valve clearence between the early pistons notched for the 20 degree heads and the and the later heads 14 is not a issue.

[Blued and Painted]

I thought the block relief's are for improved conical air flow around the larger valve heads.

[b-man]

The 20-degree '62-'63 Super Duty #127 and #980 heads used 2.02"/1.76" valves, but the valves were spread further part in the chambers on these rare factory race heads. The valves probably ended up very close to the chamber walls with a bit of shrouding.

The 2.11"/1.77" valve sizes simply can't fit in a 20-degree head, there's not enough room with the offset chamber.

Only after changing to the 14-degree head with the centered valve valve placement in the chamber was it possible to go larger than the 1.92"/1.66" valves on Pontiac's regular passenger car heads.

You can bet that the bean counters at Pontiac simply said to use the same machining procedure for all of the blocks in 1967. Since the majority were still using early design 20-degree closed-chamber heads (at least at the beginning of the production for 1967 models) the blocks were machined to match them. The larger valves on the new design 14-degree heads weren't going to hit the bores, so it didn't really matter where the bore chamfers were placed from that perspective.

While rebuilding my '64 421 heads (20-degree) we ended up using larger valves cut down to fit, because the factory sizes weren't readily available in stainless steel. We used readily available 1.96" and 1.66" stainless valves with .100" longer stems, with the heads cut down to 1.93" and 1.645" respectively to eliminate any possible valve head to valve head interference. The original valve sizes were 1.923" and 1.663" according to factory specs. There's simply no room to enlarge the valve sizes, they're just too close together.

1964 9770716 421 HO head. Chambers have been opened up slightly to match the head gasket on the spark plug side.

[GRX]

"Only after changing to the 14-degree head with the centered valve valve placement in the chamber was it possible to go larger than the 1.92"/1.66" valves on Pontiac's regular passenger car heads."

Precisely. Imagine a pivot somewhere near the valve tips with the valve heads swinging inward.

[steve25]

Actually the pivot point is more like at the top of the rocker stud boss when viewing the end of a 20 degree head.