[U47]

1969 Pontiac has three engines, 350, 400, 428. that use the # 48 big valve head. Since all the engines use flat tops with valve relief's, this means the chamber volume has to be different. Is there any way to tell them apart besides cc ing the head?

D.

[b-man]

#48 heads never came on 428 engines, all of which had dished pistons so you can rule that one out.

[Steve Barcak]

Originally Posted by U47

1969 Pontiac has three engines, 350, 400, 428. that use the # 48 big valve head. Since all the engines use flat tops with valve relief's, this means the chamber volume has to be different. Is there any way to tell them apart besides cc ing the head?

D.

I will agree that I have never heard of #48s installed on a 428. What is your info source who told you that?

Further, what you state does not mean that #48 heads had to have a different chamber size. That would only apply if they had the same compression. The 350 ended up with less compression using the same head as the 400.

Also, if you have never seen a 428 piston, they are dished, not a flat top.

[U47]

The 350 H-O 330 Hp. M/T block WV or A/T block XU use # 48 head at 10.5 compression.
The 400 RA3 366 hp M/T block WS use #48 head at 10.75 compression.
The 428 390 hp M/T block WJ use #48 heads at 10.75 compression.
From Pete McCarthy's book. Could this be incorrect?
My 68 & 69 service factory manual shows a picture of all three pistons (350-400-428) together and all three have relief's.

I bought a fresh rebuild/ never fired up 428 from a friends wife who had it for sale after he passed away. A bore scope revealed it had dished pistons. I was certain it was built with dished pistons to lower compression to run on today's gas. Pontiac division had been doing this on all low compression engines from 1955-1963, However reading "Pontiac high performance engine design and blueprint assy" from H-O racing it says " all pistons used by Pontiac have flat tops with valve reliefs". I'm thinking they are talking about high performance engines.


D.

[Half-Inch Stud]

pretty sure the 1969 390 HP YK 428 HO with TH400 Class III hitch TOW Package in a Bonne Conv had 48 heads, and Long Branch Manifolds. 62's? i've never owned a set.
So, perhaps Pontiacs that were special-order got ...a premium engine combo?

Might even had the dual vac-pot distributor, but that could have been the 68 375 HP 428 HO with 16 Heads and Long Branch Manifolds, in a BONNE Conv, that had 3.42:1 Posi, and the dual Vac-pot distributor. But I digress.

[U47]

Originally Posted by Half-Inch Stud

pretty sure the 1969 390 HP YK 428 HO with TH400 Class III hitch TOW Package in a Bonne Conv had 48 heads, and Long Branch Manifolds. 62's? i've never owned a set.
So, perhaps Pontiacs that were special-order got ...a premium engine combo?

Might even had the dual vac-pot distributor, but that could have been the 68 375 HP 428 HO with 16 Heads and Long Branch Manifolds, in a BONNE Conv, that had 3.42:1 Posi, and the dual Vac-pot distributor. But I digress.

YK has # 16 heads.

['ol Pinion head]

'69 YZ's & WQ's had 48's. I've owned several '69 YZ's. I don't trust Pete's book on everything on engine codes, numerous exlclusions & several mistakes.

[Bill Eveland]

As mentioned the 428 were dished, here's a pic from the 428 I had to show the dish.