[SD455DJ]

Originally Posted by TRADERMIKE 2012

Mike: Would like to see a Photo of the 1967 428 CI HO Piston Top. I have the Pontiac 1967 "D" Port Heads on the HO YK Code 428 ci Block. That is if you can and have access to that Block and it is 1967. I have never seen the 10.75 CR Piston and I have read there was a Lower CR Piston version used on the Big Body Vehicles. Since I have never had my Heads off the Motor, I am curious to see the difference between them. I have seen photos in Books but I can't distinguish between Low and High compression Pistons. All that I read is that the Low CR is Dished to Lower the CR. So, if you can provide the Two Photos showing both Low and High CR Pistons for 1967 428 CI HO Piston's, would be beneficial to my current research, thanks. Mike out.

TraderMike, The 428HO is a '68 WJ code (manual) for a '68 Catalina 2-dr post coupe my brother is restoring currently. I believe Steve25 is right on with only one dished piston used on the 428 for all 3 years. I don't recall the CC's now. When Dan rebuilt the engine, he used flat-top Icon or Diamond forged pistons to achieve a true 10.75 compression ratio. The dishes would have dropped it down to low 10's. 428's used the same head as the 400's (670's in '67 and 16's/62's in '68/'69). Their combustion chambers all measured in the 72-75 CC range, so needed dished tops to lower. Pontiac went with dished pistons on the 421/428 rather than have specific head castings, like they did for the 455. In the 60's Pontiac adjusted compression ratios by swapping different heads. I attached a copy from the '68 and '79 parts catalogs of the 428 piston P/N's. I see the '68 catalog lists different P/N's for the '67 & '68 428's while the '79 catalog list only one for all 3 years (most likely superseded P/N's over the years to one common part) and most likely very minor differences between the '67 and '68 pistons to notice.

(Got tree'd by tekuhn!)

Dennis