428

[rchrdwjohnson]

Hi. I'm Richard and I have a 1969 Pontiac Grand Prix SJ powered by a 428. I am getting ready to overhaul the engine and was wondering how to tell if it is a h/o or not. Any help available on this? I have the engine tore apart. Thank-you.

[Larry]

There is little info about the HO other than it was an option. Nothing I have goes into any detail of what the differences were. With only 20 HP gain, it couldn't have been much of any significant change. Perhaps just carburation, cam, and/or exhaust manifolds. That's about all you would need for just a 20 HP gain.

However, the blocks were stamped differently. Check this link for the 370 vs. 390 HP block codes: https://www.pontiacregistry.com/members/online_magazine.php?view=2&article=243&page=2

Also, in one of Pete McCarthy's books he does mention that the 370 HP had #16 heads and the 390 HP had #16 or #48. If yours are #48, that would help ID it.

We found this as part of a discussion at Pontiac Heaven: "The top 428 for 1969 was again the 390hp rated "HO" version with the low restriction manifolds and slightly larger '068/tripower' cam." You can read the entire thing at: https://www.facebook.com/PontiacHeaven/posts/the-428-was-pontiacs-top-engine-for-3-short-years-1967-9-the-bore-is-the-same-as/623219591159710/

Let us know if you find more information that we can pass on to others.

[rchrdwjohnson]

Thanks. On front pass side I found 152410 above the letters XG. Does that make it a 390hp? Another question. When I pulled the engine I unbolted it from the transmission thinking that would be easier. I couldn't get it out. Eventually I tore the starter to pieces and got it out. What is the best way to put it back? Trans & engine bolted together with starter on? I don't think a starter can be changed without pulling the engine. Am I wrong?

[Larry]

Looks like you got yourself a 390 HP 428! The only problem with those ID numbers is that they were used over again in various years. But the chance of a different engine, from a different year, with the same two ID letters is slim to none.

OOPS on the starter deal. I've changed many a starter even with headers and never had a problem. A pain, but doable.

The only thing to be careful of when putting the engine with flywheel and torque converter mounted on it is to make sure the transmission and torque converter engage properly. It can be tricky and you have to fool with it sometimes. If you can't get the engine to seat squarely against the flywheel, don't force it. That can ruin the oil pump.