[ID67goat]

The 69 GTO that my mother bought new was a 3 speed manual car and not a RA3 and it had 48 heads on it.

[Dragncar]

48s are the best D port head, they have the RAIV chamber. And 350 ones get down to 65.5 ccs.

[25stevem]

Thanks for the correction on usage!

[25stevem]

The 48 casting does not use the RA4 chamber .

Here is a photo of a RA4 chamber, take a good look at this and then go back to post 12 in this string and note that in all of those heads pictured the top cut back goes all the way down to the chamber floor in every D port head ever cast other then the 1968 1/2 RAII head which due to its round port exh does have what became known as the RA4 chamber.

[Kenth]

Still, NO pictures of the "large chamber" #48 heads next to the "small chamber" #48 heads we here have seen pictures of.

https://forums.maxperformanceinc.com...=846583&page=6

So far it would be safe to say that there never was a "large chamber" #48 head.

[Jay S]

Originally Posted by tom s

Im building another engine right now with stock 48s and the chambers are 69 CCs.Tom

Curious what the date code is on those?


I think the $700 for pair 48 head cores mentioned early on in this thread is pretty close for value from what I have seen. If you find someone looking for a particular date code they are worth that easily.

A local guy to me just bought a 69 4 speed 350 HP GTO which he was told by the seller that the engine was original, with the original heads. He bought it thinking it was original. But the car has a late 60s era set of small valve 46 heads and the engine code was originally a 69 400 2bbl. Would be cool to see 48s on that car again, but it goes to show how some people are completely oblivious to original Pontiac engine code combos, in that case it was the seller and the buyer.

From the heads i have looked at, 12 heads and 48s have the same chamber. But the chamber on the 12s is slightly deeper, adding a few cc’s. Still smaller chambers than other d ports though. I recall Rocky Rotella has the data for that, the blueprints show the 12s have a couple more cc’s, .030” deeper IRC. I had a very late 48 head that appeared to have the same chamber depth of a 12, and when I checked came out about 70 cc, upper 69s. The date code for the 48s I had was a few days from when 12s were made. The edge of the chamber is a little further from the spark plug, and with with a head gasket on the edge you could also see the chamber was further away. Not much difference between the 12s or the 48s that I can see, on the 48s it could be just differences in the timeframe of production or variations in mass production too.