[shermanator2]

Do all #48 heads have the same combustion chamber volume? If so, what is it?

I notice that these came on 350, 400 and 428 engines in '69, The advertised compression ratio was 10.5 on the 350 and 10.75 on the 400 and 428. Did the 428 use dished pistons, lower compression height, or a larger chamber in the head to get the same CR as the 400?

The reason I ask is that I have one #48 head that came to me with a '69 400 HO (code WT) engine in pieces 40 years ago and I am sort of watching for a mate for it. I want to know that I am getting one with the same size chamber. If they are different, is there any easy way to tell which is which without actually cc'ing them?

[wbnapier]

Mine were 70cc.

[Formulas]

My #48s came from a 1969 judge stick 67cc with a valve job and 2 very slight head gasket surface cleanups

They are on a 350 now

[Jay S]

I dug the 48 out and cc’d it. Been in storage awhile, a little different than I remember it. It wasn’t beed blasted like I remember and I thought it was a bare head. Lol. So I am not batting 100% on what I remember. But I cc’d it again at 71-72.

The date code is f179. Very late 69 head. I also notice a X stamped on the head above the 4 on a head boss. Probably means something, just not to me. . Could be a machining or set up designation. I.E. similar to what Steve25 mentioned.

[JKrull66]

Originally Posted by Jay S

I dug the 48 out and cc’d it. Been in storage awhile, a little different than I remember it. It wasn’t beed blasted like I remember and I thought it was a bare head. Lol. So I am not batting 100% on what I remember. But I cc’d it again at 71-72.

The date code is f179. Very late 69 head. I also notice a X stamped on the head above the 4 on a head boss. Probably means something, just not to me. . Could be a machining or set up designation. I.E. similar to what Steve25 mentioned.

Interesting I have F189 just down the road from you from Shenandoah. Too bad Im late to the party.
John

[johnta1]

Does it have an 'X' stamped on it?

[JKrull66]

[QUOTE=johnta1;6205689]Does it have an 'X' stamped on it

Yes it does, It is a little higher. But in same spot above the 4.
John

[Dragncar]

The ones that came on 350 HOs had 65cc chambers.

[Kenth]

I have found factory 1969 #48 heads has the same size chambers as the 66-67 cc 1970 #12 heads.
After 50+ years of usage, valve jobs and decking these figures may differ.

FWIW

[Will]

I have heard that there are two different versions of the 48s. The ones used on 350 HOs had smaller chambers, according to this information. See Dragncar's post above about 65cc chambers. The ones that came on the 400s and 428s were spec'd at 72cc. I don't know how much supporting evidence there is for that - how many 350 HO heads have been CC'd and documented vs. heads from the larger engines? We all know Pontiac was fudging the compression numbers a little and certain heads had slightly bigger or smaller chambers than others.

428s used the same heads as 400s and came from the factory with dished pistons to keep the CR the same.

[steve25]

Your WT motor being a manual trans code motor should have the 66 CC chamber as the auto trans XU coded cars never did.

Up to engine stamping code 709185 the 744 Cam should be in your motor, after that they all came with the smaller 068 auto trans cam.

The original Carb for the WT motor should be 7029263.

None the less since you only have one head I would still CC one chamber it as its the only way to confirm its chamber size.

[Kenth]

1969 XU is a 350 H.O. engine and used #48 heads as all 1969 350 H.O. engines did.

All 1969 400 "RAIII" engines used #48 heads, except Firebird YW code wich also was the only "RAIII"using the 067 camshaft and #62 heads.

Comparing #48/#12 heads with any #16/#31/#62/#13 head it is easy to see the difference of chamber size.

[Jay S]

Rocky I will clean it up later today and send you photos.

I will put some better photos on the forum too.

John we only have the one 48 head. I never knew any history from the head, we bought close to 20 years ago from a local guy when we went to look at his 76 Black 455 T/A. Looking at the head it was ran very little. There is no electrolysis on the head surface and the valve seats and valve guide seem new. I am curious what the head has for stock valve springs, and whether the springs were for a 744 cam or a 068, the spring coils looked a little bigger than a typical poncho head. I will clean the head up an check for more identifications.

[Kenth]

#744 cam got #9794934 and #9794939 springs. 124lb@1,586".
#068 cam got #9781476 and #9779009 springs. 115lb@1,586".
#067 and milder cams got #9779008 and #9779009 springs. 100lb@1,586".

Bying new springs for all #48 equipped heads thru eng.-#709185 you´ve got the #9794934 and #9794939 #744 Ram Air springs.

[Jay S]

Rocky would there be a way to tell if that combustion chamber on the head I have matched the 12 ? 69.2 cc is darn close to what I measured.

[PontiacJim1959]

The AMA specs for 1969 show the 350HO having a compression of 10.5. The 400 RA has a compression of 10.75. That would indicate the same chamber size?

The 350HO and RA heads used different spring pressures depending on auto or manual and cam used.

In the 1969 Super Stock magazine, the article on the 350HO Firebird build states that Milt was sure to get the head chambers to exactly 61.2 CC's. How much of a mill would that take?

The "X" on the head that was provided may have indicated something as simple as an oversized valve - ie a fix or repair of some sort. Minor blemishes or some other fixable repair would be done before they tossed out a part that could be salvaged. I think we have all heard, and or seen, the stories where an engine had 1 piston oversized or 1 bearing undersized. I myself have seen a 70's era Ford head that the rocker arm pedestal was not fully formed from casting it and the factory built it up with weld and machined it for use as a production head.

Pontiac used the same 400CI cast piston from 1967-1974. The RAIV used a forged piston said to have been 50 grams lighter than the cast piston.

[steve25]

Yes, I slipped up!

Yes, it appear that accomplished the chamber reduction with the same machine work change they did in later years with the dash 4 and dash 8 stampings.

[gtospieg]

So...how can you tell the difference between the 350HO 48 heads and the RAIII 400 48 heads? ...other than ccing them.

[Formulas]

You cant because there isnt a 350 or a 400 head
There is just a #48 head

[Dragncar]

Originally Posted by Formulas

You cant because there isnt a 350 or a 400 head
There is just a #48 head

Dan Whitmore told me otherwise.
He took heads right off Pontiacs in the 60s and cc,ed them. 350 HO #48 actually had 64.5 ccs.
He gave me a list of all the actual head cc when by the book they were 72 ccs.