Editing Pontiac V8 engine (section)

===428===
[[File:1969 Pontiac Grand Prix SJ, 428 V8 engine.jpg|thumb|A 390&nbsp;hp 428 V8 in a 1969 [[Pontiac Grand Prix#1969|Grand Prix SJ]].]]
In 1967 the 421 was enlarged to {{cvt|426.61|CID|L|1}} by increasing its bore to {{cvt|4.12|in|1}}. Both Chevy and Ford had 427 cu in performance engines, so Pontiac simply referred to its 427 as a 428 to one-up them. It retained the 421's {{cvt|4|in|1|adj=on}} stroke and {{cvt|3+1/4|in|1|adj=on}} main journal.

Offered from 1967 to 1969, it produced {{cvt|360|and|376|hp|0}} in 1967, {{cvt|375|and|390|hp|0}} in 1968 and {{cvt|360|,|370|and|390|hp|0}} in 1969. The crankshaft in the 428 had a "N" cast on them (designating nodular steel) as opposed to the 421's Armasteel. In 1969, Pontiac also used a revised crankshaft out of a Pearlitic malleable-iron, although it still used the "N" casting letter. This new material had stronger alloys in the iron. All 428 cylinder heads received the 14-degree valve angle; closed chamber only in 1967 and open chamber the next two years.

The 428 was factory installed in large cars only. However, a few dealers would offer them in the GTO or Firebird and do their own installations, such as Royal Pontiac who offered the "Bobcat" conversion.<ref>{{cite web | url=https://www.caranddriver.com/reviews/a15142469/1968-pontiac-gto-428-royal-bobcat-road-test-review/ | title=Tested: 1968 Pontiac GTO 428 / Royal Bobcat }}</ref> It was replaced by the 455 for the 1970 model year.