#48 head combustion chamber volume
 

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?

Mine were 70cc.

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 :)

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

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

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.

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.

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.

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.

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

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.

Nope ... show me the engineering tech data from Pontiac

He said she said is bravo sierra

My dog just said your wrong

I agree... My dog has never seen a stock 70 cc 48 head. It makes no sense Pontiac would use two versions of the 48 head. History repeated itself with the 6X-4 head.

All you have to do is work in a massive production environment to realise that the smallest minute change in any part drives a part number change an identifier so that part ends up where its supposed to be later in the production process

Each step starting at the foundry a person has to know what is in front of them and what they are doing with it and that is based on identification and engineering directives show me the money or there is none

I've had my #48s since 1982 the gent advertised them as Ram Air heads in the Los Angeles recycler I was still wet behind the ears I was looking at them and said how do I know they are ram air heads he got a bit touchy and said sternly they are #48s and I pulled them off a judge ok ok and handed him the money

I've listened to this wives tale along time without any evidence

.

Remember when the 197 heads used to be 191 heads... I wonder which one is better.

We have a untouched 48, no valve job, factory machining, other than bead blasting, no post factory surfacing.. It cc’d at 72 cc. I believe I had it on the flow bench years ago. It is a nice head, if someone needs a 48 we don’t have plans to use it.

I would have thought if there was a small cc 48 it would have had some sort of factory identifier to keep it separate from the other 48s.

I noticed the other day Butler still list 62 heads only going on 68-69 a/c cars. I have never seen a 62 on a 68 car. Maybe it exist somewhere. Lol And they list 16s only on 68 manual cars? My sets of 16s I have had came off of 68 t400 cars. A lot of info out there, and of course the internet is never wrong.:)

I always felt the same way...If there were two versions of the 48s they would've had 2 different #s....the end.

That's not the case since we have D port number 16 castings with the long exh air injection passage running above the Exh ports and without it, and you would have thought that with such a big change in the casting that the factory would have assigned a different casting number, but they did not.

The best explanation I have ever heard is that a certain number of 66 CC casting 48 heads went thru a abbreviated maching process of the chamber to get leave it at 66 CCs and not 72 , and these where to be used on the 350 HO option coming up in 69 that Pontiac had high hopes for sales wise.

When those big sales numbers did not come to pass then these heads where used on the manual transmission RAlll motors only!

I've got a set of 48's.
K308 date code on both.
I cc'd them at 65cc. They were surfaced once in my 30 year ownership. No idea how much but was only for a uniform finish after a bake, shot and shake.
FWIW
They been on the bench apart for a while now.
Anything I can check, measure or photo on them to help the discussion or identification of they're the unicornz 48's?