Editing Pontiac V8 engine (section)

===455 HO===
;'''1970'''
The 455 HO designation made its debut in 1970; Rated at {{cvt|360|or|370|hp|0}} (depending on which vehicle it was installed into) and {{cvt|500|lbft|Nm|0}} of torque, it differed from the regular full sized car 455 by large valve heads with smaller combustion chambers, and a larger camshaft.

The 1970 '455 HO' was a conventional "D" port engine. It was rated at 360&nbsp;hp at 4300&nbsp;rpm in the GTO and 370 at 4600&nbsp;rpm in the Grand Prix and other full-size Pontiacs. Ram Air induction was optional in the GTO, though power ratings were unchanged. Late in the model year the Ram Air 455 HO was made an available option for those GTOs with the optional "The Judge" package.

;'''1971'''
The "455 HO" moniker took on a whole new meaning with the introduction of the 1971 model year;

Intended as a low compression progression from the previous years Ram Air IV engine, all 1971 455 HO engines used a heavy duty 4 bolt main block, round port cylinder heads (casting #197; with 8.4: compression), "Ram Air" style exhaust manifolds, and a two-part aluminum intake manifold.

The 1971 Pontiac 455 HO was Pontiac's first engine to receive a special {{cvt|800|cuft/min}} Rochester Quadra-jet carburetor with specific jetting.

The 1971 455 HO was rated at {{cvt|335|hp|0}} at 4,800&nbsp;rpm and {{cvt|480|lbft|0}} of torque at 3,200&nbsp;rpm ([[Horsepower#SAE gross power|gross]]).

The 1971 455 HO was available in the Firebird (optional in Formula; standard in Trans Am), the GTO (standard with "The Judge" package), and the 2-door LeMans, LeMans T-37 (including GT-37), and LeMans Sport. Ram Air induction was optionally available with the 455 HO in the Firebird Formula(standard on Trans Am), GTO (standard with "The Judge" package), and 2-door LeMans Sport when the T41 Endura Styling Option was also ordered.

;'''1972'''
The 455 HO moniker was again carried over, this time as a near-exact repeat of the 1971 offering, the only changes were the carburetors (they used a conventional {{cvt|750|cuft/min}} unit this year), and the head castings (casting #7F6).

According to GM mandates horsepower was now rated in net figures as opposed to gross, so on paper the 1972 455 HO appeared to have a significant drop in power, but in fact it was very much the same engine, and performance figures reveal this to be true.

The 1972 455 HO was rated at {{cvt|300|hp|0}} at 4,000&nbsp;rpm and {{cvt|415|lbft|0}} at 3,200&nbsp;rpm.

The 1972 455 HO was available in the Firebird (optional in Formula; standard in Trans Am) and 2-door LeMans (including those with the GTO option) and LeMans Sport convertible. Ram Air induction was optionally available with the 455 HO in the Firebird Formula (standard on Trans Am), and the 2-door LeMans (including GTO).

;'''1975'''
After the 1974 SD455 was dropped the 1975 Firebird's top performance engine was an 'L78' Pontiac {{cvt|400|CID|L|1}}.

Pontiac still offered the regular 455 (RPO L75) in its full sized cars, and after a negative public reaction for dropping the 455 engine, it was re-introduced mid-year as an available option for the 1975 Pontiac Trans Am. However, the engine used in these Trans Ams was the same regular production 455 taken from the big body cars Pontiac was producing, and output 200 HP with a torque rating of 330&nbsp;lb⋅ft at 2,000&nbsp;rpm.<ref>{{Cite web|url=https://tran-zam.com/fhistory/1975Engines.aspx|title=Tran-Zam.com|website=tran-zam.com}}</ref>

The 455 HO package was only available to late model year Pontiac Firebird Trans Am's, and was mandatory with a 4-speed transmission. The shaker wore the decals "455 H.O." like the earlier 1971-1972 motor, but it was not the same motor, and featured standard d-port heads with a very conservative camshaft.

The 1975 455 HO package received some negative press/reviews as some buyers expected to see a return of the 1971-1972 engine, and were disappointed when they received the lower output motor. Upon reflection, many did not consider that it was the only large displacement engine still on offer for any performance car on the market, and reconsidered Pontiac's position between the rising CAFE emissions restrictions.<ref>{{Cite web|url=https://www.hemmings.com/stories/article/unsung-muscle-75-455-ho-pontiac-trans-am|title=Unsung Muscle: '75 455 HO Pontiac Trans Am}}</ref>

;'''1976'''
The L75 455 engine continued as an option into the 1976 model year for the Trans Am, however, Pontiac opted to drop the "H.O." moniker from the shaker due to the disappointing public approval as the motor was not deemed to be "High Output".

The 455 was fundamentally the same for the 1976 model year, albeit the shaker decal now just read "455". This was the last run for the 455 (7.5 L) motor from Pontiac, and production ceased on the 455 this year as it could no longer meet the emissions requirements any longer.