04/29/2024
Here is some basic information on the 428 Pontiac. There is much misinformation about this engine on the net and am trying to clarify for the benefit of followers.
The 428 engine option was a very welcome improvement to replace the 421 for the new 1967 Pontiacs. The engine was only produced for 3 model years ('67-9).
There were many overdue upgrades introduced in Pontiac engines for the 1967 model year and they were badly needed. In the prior 2-6 model years, most all other manufacturers came out with either completely new engine designs, or had made considerable improvements to their existing ones. At Pontiac, not a lot changed, performance wise, from 1961-66 comparatively in particular- head design and valve train features. Sales and marketing were strong in those mid years and performance was more than acceptable but, development was pretty modest at a time when others were making big improvements. Pontiac had been lacking behind the other makes in engine development and retaining outdated performance items like- rocker stud oiling, pressed in rocker arm studs, short spring heights, etc. Again, 1966/earlier performance was very good as were sales but, Pontiac was lagging behind in engine developmentand was overdue to some upgrades.
1967 was a big year for these changes and most all Pontiac engines recieved them this year, including the new 428! I only wish these improvements could have been done a few years earlier. When thinking of improvements for the 1967/later model years think- breathing and more reliability as well as making it much easier to swap to larger aftermarket cams, etc.
All 428s feature a 4.12” bore size which is .030” larger than the 421. 428s share the same heads as some of the 400 performance engines of the same year and have the same compression ratio. The exception to this rule is the '69 small valve 360hp 428 standard in Bonneville and optional in other '69 full size models ( most common and produced 428). All 428s have the larger 3.25" main journals as does the 421 and 455. Most 428s, maybe all of them, have the displacement cast into the sides of the block. I believe they were the first Pontiac engines with that feature.
The way the compression stayed the same between the 400 and 428 was Pontiac used a piston with a small dish machined into it for the 428 which makes it easy to identify.
To the novice, since the 400 and 428 now share the same bore size, some think one can swap the pistons for lower or higher compression. However, there is another dimension that is different making it not practical to make that swap. The difference is pin height due to the difference in stroke between the 400 and 428. Both the 400 and 428 used the exact same connecting rod as did the 350.
The stroke is the same as the 421 at 4” and has remained a very attractive stroke choice for many performance fans and racing engine builders. The snout of the 428 crank is slightly longer but, retains the same diameter and can be interchanged with 421s. All 428s were manufactured with cast pistons, rods and cranks and were of adequate strength for most street performance applications. All 1967 and 1968 428s came with chrome rocker covers and nice/new features such as- larger valve heads with 2.11" intakes and 1.77" exhausts with screw in studs, push rod guide plates and ball end push rods. These were all a big improvement over the 1966 and earlier designs. The valves were also now at a better angle and spaced further part. These were shared with most 400 engines including all 4bbl 400s on GTO and Firebird. The 1967 engines with their large valves, still though retained the familiar closed chamber design of previous years. 1968 and 69 engines would get the newer, open chamber head design. Also new for 1967 engines, including the 428 was a redesigned, taller valve cover needed to clear the improved valve train. The same bolt pattern and gaskets were retained gladly.
Remember, 428s were full size Pontiac engines with very good performance, hp and torque but, were not race engines. Still the 428 had/has tons of potential to be an even stronger performance engine.
Another thing that did differ between the 421 and 428 was that most 428s were manufactured with 2 bolt main caps. All 1967 and 1968 428s were 4 bolt main and came with chrome rocker covers and large valve performance heads but, were all fairly low production engines. The only models ever to have the 428 as standard equipment were- 1. the 1967 2+2 and 2 the 1969 Grand Prix SJ and 3 all 1969 Bonnevilles. The 428 was not standard in any Pontiac in 1968.
All 428s used the 4bbl q jet on the excellent cast iron production intake.
For 1969, Pontiac offered, for the first time a milder, lower performance version of the 428 that came with 2 bolt mains, painted rocker covers, small valve heads with pressed in studs. This engine was standard in the Bonneville and optional on all full size models. Over 100,000 Bonnevilles were produced in 1969 and most came with that standard 360 hp 428. It is, by far, the most common of the 428s and they run very well. 428s were available as options on all full size models 1967-9 in 2 or 3 forms. 428s were also avail on 1969 Grand Prix model Js as an option and standard on the model SJ. These '69 GP versions of the 428 did have chrome rocker covers, large valve heads and 4 bolt mains. No GTO or Firebird was offered with 428s though they were and are a popular swap. Some dealerships also offered these swaps. Myrtle Motors of NY and Royal Pontiac of Mi come to mind to name a few.
The top performance 428 was the 428 HO and was offered each year. They were essentially the same engine as the standard ( 1967-8 ) 428 except for a slightly larger cam (068) and low restriction exhaust manifolds. It was not a popular option as the standard 428 was plenty for most buyers and 428HOs were only ordered by a small number of enthusiasts.
I hope this helps you understand Pontiacs great 428 engine.
In the Pontiac Heaven collection, there is currently only 1 428. It is the more common 2 bolt main version. All machining has been done to her and she is ready for assembly when needed. It will be used in the restoration of my '69 Bonneville Safari as part of the planned Pontiac Heaven Museum here in Arizona.
I would like to aquire a 2nd 428 to be used for the Tyrol blue '67 Firebird 400 4 spd in my collection as the original engine is not with the car.
Steve Barcak
pontiacheaven.org
https://www.facebook.com/PontiacHeaven
