[unruhjonny]

After getting ALOT more activity than I could have forseen from my last question here, I figured I'd try again;

I'm curious if there has ever been any testing on the 1968 RA I heads (casting #31 iirc);
I know that there have been many cc & cfm tests on 67 RA I, as well as #16, #48, #62, #12, #13 heads;

I have understood (if I recall correctly) that for all insensive purposes the #16, #62, #13 heads are about the same, and the #48 & #12 heads are about the same...

But am wondering if there is anythign that makes the #31 heads unique.

[b-man]

Doubt there's much difference between 1968 #31 & #16 heads other than deeper spring pockets to accept taller valve spring installed height.

Much like the difference between 1967 #670 & #997 RA heads, 1.71" RA vs 1.58" standard height.

[Old Man Taylor]

Taller springs and swirl polished valves (when new).

[69goatboy]

Forgive my stupid question, but is there an advantage to the taller springs?

(I also have a set of #31's)

[unruhjonny]

Originally Posted by b-man

Doubt there's much difference between 1968 #31 & #16 heads other than deeper spring pockets to accept taller valve spring installed height.

Much like the difference between 1967 #670 & #997 RA heads, 1.71" RA vs 1.58" standard height.

oh really?

I don't think I've read this, but then again, I haven't spent too much time pouring over pre-1970 info...

Originally Posted by Old Man Taylor

Taller springs and swirl polished valves (when new).

Hmm, thanks for confirming b-man's post

[unruhjonny]

Originally Posted by 69goatboy

Forgive my stupid question, but is there an advantage to the taller springs?

(I also have a set of #31's)

I'm guessing to reduce the chance of coil bind on an engine which would likely see higher lift cams ~ or be rev'd higher(?)

IIRC this also plays into selecting a spring which is less prone to valve float, if the engine is going to be rev'd...

[The Boss]

Confirming what B-man & OMT said, chamber & passages are the same as the 16's.

[67GTO4SPEED]

Originally Posted by The Boss

Confirming what B-man & OMT said, chamber & passages are the same as the 16's.

In Pete McCarthy's Ultimate head testing years ago, he ranked the #16, #48, and #12 as the best the D port heads in the test. He did not test the #31, #62, or the #13, but the general consensus is the 72 - 75cc '68 - '70 D ports are about the best flowing D ports in stock form. These heads tend to flow better mainly because of a better short turn radius than later heads with large combustion chambers, especially on the exhaust side. The intake to exhaust ratio is typically around 80% and flow in the neighborhood of 208/165 range, give or take a few cfm depending on the quality of the casting, condition of the head, etc.

In comparison to the Ram Air II heads you were asking about in the other thread, these heads flow basically the same on the intake side as the RAII heads did. The exhaust is what was the major difference. You could in theory have the exhaust side of the #31's ported to flow what factory RAII heads did on the exhaust side, and you would pretty much match the factory performance of the RAII.

[steve25]

You will ifnd a wealth of Pontiac cylinder head flow facts on the Stan Weiss enterprizes web site.
I do not know that they have the #31 s flow numbers on the site, but the last time I had one on my flow bench and testing 2 Intake and exh ports in each head, I did not keep the flow sheets in my files do to flowing so close to the numbers I had for a #12 head.

[unruhjonny]

Do you have a web page for me?

EDIT: Never mind!
I found it;
http://users.erols.com/srweiss/tablehdc.htm#Pontiac

[screamingchief]

The RAI and #16 chambers are indeed very similar,but not exactly the same.

My guess,the slight difference is most likely due the RAI being closer to the "nominal" 72cc spec vs. the #16 heads that usually check in with looser adherence to the 72cc spec,that or just chalk it up to minor refinements to the machining used for either casting.

Anyhow,pics of both vvvv:





Pics courtesy of HPP article.

HTH

Bret P.

[Half-Inch Stud]

good photos. does seem like the #16 chamber would promote a wet plug from an accelerator pump shot?

[67GTO4SPEED]

Originally Posted by screamingchief

The RAI and #16 chambers are indeed very similar,but not exactly the same.

My guess,the slight difference is most likely due the RAI being closer to the "nominal" 72cc spec vs. the #16 heads that usually check in with looser adherence to the 72cc spec,that or just chalk it up to minor refinements to the machining used for either casting.

Anyhow,pics of both vvvv:





Pics courtesy of HPP article.

HTH

Bret P.

The RAI head you have above seems to have been deshrouded on the intake and the ridges have been smoothed. Steve did this on my #16's. You can tell the distance between chamber to chamber on the RAI head that there is less meat in between them than the untouched #16 chambers. That chamber looks very much like my modified #16 and the 2nd looked like my #16's did when stock. That head also appears to have had the valve guide boss worked as well, so I'd guess it has been modified.

[Old Man Taylor]

Originally Posted by 69goatboy

Forgive my stupid question, but is there an advantage to the taller springs?

(I also have a set of #31's)

There were two cams used with the #31 heads: the 068 ("S"); and the 744 ("H"). The 744 had a flat nose due to the constant lift profile used by Pontiac. The 744 had enough additional duration that the nose had to be flattened to keep the lift at .404" (+/-). They found out in late '66 that the standard height springs were not adequate for keeping the lifter on the lobe. This caused camshaft and valve spring damage problems that were resolved by using stronger springs. That's why people recommend a new profile cam with similar specs rather than using the original 744.

[steve25]

If you look close at the non RA1 chamber you will see how the big cut back in the chamber that leads up to the deck surface goes deeper down towards the chamber floor. This is where the extra chamber CCs come in over the RA1 chamber.
This is the same mod done to get the lesser CCs between the low comp 5 and 6 series heads and the corresponding stampings of -4 or -8 with all the -4 heads being for the 350 CID motors until they used up the last of those -4 machined castings on the 220 HP 79 TA motors.

[The Boss]

In the pictures shown above, I believe it's just a difference in lighting that's giving the illusion of a deeper cut.

[Ed Fitzgerald]

I bought a set of 48 HO heads from (HO428) Gord Slingerland that came on a 366 clone engine he had done and sold to me. The 48 HO heads look like the pair shown in the above HPP post. They are 65 and 66 cc respectively and are going on a 60 over zero decked 350 with flat top pistons. I'm thinking of a mild roller cam with 224/230 @50. Hoping that with a good tune and 93 gas it will survive on the street. Ed

[steve25]

With the added fast Intake opening rate of a roller be sure to check the Intake valve to bore clearance in the 350 as you may need to add the factory like chamfer to the top of the bore, in fact the added Intake flow gain from having that chamfer there will more than offset the compression loss of 3 CCs.

[steve25]

In the top photo take note of how close the OD of the intake valve seat is to the point where the flat of the chamber meets the verticle wall on the plug side of the chamber, and do the same for the non RA chamber.
See the added width / distance for the greater chamber volume?