Editing Pontiac V8 engine (section)

==HO engines==
===326 HO===
A higher-output version was offered, called the 326 HO (High Output). It had a four-barrel carburetor, dual exhaust, and higher compression, and was good for {{cvt|280|hp|0}} for 1963–1964, and {{cvt|285|hp|0}} for 1965 - 1966 and the final year, 1967.

===350 HO===
In 1968, there was also a 350 "HO" which had increased power with the addition of higher compression #18 heads (#17 and #46 were the most common 2-barrel heads), a four-barrel carburetor and matching intake that was also used on the 400 and 428 engines. There was also the addition of dual exhaust, and for vehicles equipped with a manual transmission, a slightly more aggressive camshaft.

In 1969 the 350 HO was upgraded again with the addition of the 400 HO cam, commonly referred to by enthusiasts as the 068 cam. Also added was the #48 casting number heads with a {{cvt|68|cc|2|adj=on}} chamber for higher compression, along with larger {{cvt|2.11|and|1.77|in}} valves. Free-flowing exhaust manifolds from the 400 Ram Air were used late in the model year. This was underrated at {{cvt|330|hp|0}}.

===400 HO===
Officially named the Quadra-Power 400 for 1967 and renamed 400 HO for 1968, the 400 HO was first offered for 1967 as the third engine in the GTO line after the automatic-only 400 2-barrel and the standard 400 4-barrel (the 400 HO would not be offered in the Firebird until the 1968 model year). For the 1967 GTO the engine was rated at {{cvt|360|bhp|kW PS|0}} and had the cast-iron headers. The camshaft was the HO cam with 288/301 duration. It was the top-of-the-line engine unless one opted for the "Ram Air" V-8 derived from it. As Pontiac's 1967 performance brochure said, "You can add the Ram Air induction hood scoop and new high output cam and valve springs to the Quadra-Power 400 for better top end breathing." But the "Ram Air" 400 also mandated steep 4.33:1 gears(or 3.90:1 in Firebird), making the Quadra-Power 400 (400 HO) the top practical street engine option for most drivers. Standard ratio with the 400 was 3.55:1(except 3.36:1 in Firebird for 1969) regardless of transmission(3.23:1 for cars with air conditioning). The 400 HO was offered as an option for 1967-1970 for GTO and 1968-1970 for Firebird. For 1969-1970 GTO the 400 HO included driver operable Ram Air induction and was renamed "400 Ram Air" for 1969 and just "Ram Air" for 1970. In the Firebird Ram Air induction for the 400 HO was a separate option for 1969 (included with Trans Am) and included with the engine(optional in Formula; included with Trans Am) in 1970.

===400 W72 "T/A 6.6"===
At the end of 1976, Pontiac was no longer able to continue production of the 455 (7.5 L) V8 motor due to the tightening emissions requirements. As Pontiac still wanted to offer a performance motor to compete in the performance market, they looked back to the 400 Pontiac and how it could be improved to offer greater performance while meeting CAFE standards.

In 1977 the {{Convert|400|CID|L|1|adj=on}} T/A 6.6, ([[Regular Production Option|RPO]] code W72) was created to fulfil the performance engine gap in the Pontiac line-up. The W72 offered many improvements over the standard L78 400 Pontiac. One of the key upgrades were the 6x4 heads. The standard head seen on an L78 400 Pontiac was the low compression 6x8 head, while the 6x4 head seen on the W72 had hardened valve seats for a higher RPM operating range, improved air flow, and higher compression. These heads can be distinguished from 6x8 heads through a small stamped "4" on the top of the front boss. The head design was incorporated from the earlier 1970s 350 Pontiac heads, and could satisfy emissions in all states except for high-altitude emissions states and California. The W72 also featured a camshaft with a higher duration, finer tuned 800cfm Rochester Quadrajet, insulated fuel line, larger 60PSI oil pump, chrome valve covers, a larger harmonic balancer, and the "T/A 6.6" Shaker decal.<ref>{{Cite web|url=https://www.angelfire.com/wa/angryclown/CanAmW72.html|title = The T/A 6.6 (W72) Pontiac 400 Engine}}</ref> All of these improvements provided the W72 with a power rating of {{cvt|200|hp|PS kW|0}} at 3600&nbsp;rpm and {{cvt|325|lbft|0}} of [[Torque#Machine torque|torque]] at 2400&nbsp;rpm, while the standard L78 400 only produced {{cvt|180|hp|PS kW|0}} at 3600&nbsp;rpm and {{cvt|325|lbft|0}} of [[Torque#Machine torque|torque]] at 1600&nbsp;rpm.<ref>{{Cite web|url=https://tran-zam.com/fhistory/1977Engines.aspx|title=Tran-Zam.com|website=tran-zam.com}}</ref>

The W72 engine was standard in all 1977 [[Pontiac Can Am]]s (bar the 1977 Can Ams sold in California/High Altitude states which received the [[Oldsmobile V8 engine#403|L80 Oldsmobile 403]]) and was optional in all 1977-79 [[Pontiac Firebird]] Formula and Trans Am models. The W72 package was a standalone option, and although was discounted when ordered in conjunction with the Y82/Y84/Y88 Special Appearance package, did not come included with Special Edition Trans Ams, it remained an extra cost option. With some WS6 "Trans Am Special Performance Package" bundles in 1978, the W72 engine was incorporated with the WS6 option group and not listed on the dealer order invoice. However, it can easily be determined by examining the cost price of the option, where the package excluding the W72 engine cost $251, and with the engine, cost extra at $324.<ref>{{cite web | url=https://www.hitmantransam.com/Pages/ws6ws7.htm | title=Hitman's Pontiac Trans Am Site - WS6 and WS7 }}</ref>

All 1977-1978 Trans Ams ordered with the 4-speed Borg Warner Super T-10 manual transmission received the W72 T/A 6.6 engine. There are no manual transmission equipped Trans Ams that came factory with the standard L78 400 motor in 1977–79. The W72 Performance Package also included an upgrade to the rear differential ratio, setting the rear gear ratio to 3.23 for all 1977 and 1979 W72 Firebirds, with the exception being 3.42 for 4-speed equipped W72 Firebirds in 1978 only.

All W72 equipped Trans Ams featured the "T/A 6.6" shaker decal. A common misconception made by enthusiasts was the notion that all Pontiac engine equipped Trans Ams featured the "T/A 6.6" decal on the shaker, however, it was exclusive to the W72 engine that was featured on less than half of all Trans Ams made during this period. All L78 Pontiac 400 equipped cars received the same shaker decal as the [[Oldsmobile V8 engine#403|L80 Oldsmobile 403]], being "6.6 LITRE". This may have been propagated by the only authorized company that is licensed to reproduce these decals not including the "6.6 LITRE" in the Trans Am decal kits, and only including "T/A 6.6" with no extra cost.

For the 1978 model year, Pontiac re-incorporated the earlier thicker cast cast engine block denoted by the cast number 418988 and a "XX" cast into the side of the block. The earlier 1975-78 blocks had metal shaved from the journals and bottom end as well as a decrease in the nickel content of the block in an attempt to decrease the overall weight of the vehicle to help alleviate emissions and cost. The camshaft was also revised to have a slightly higher duration, the carburetor jets tuned and a dual exhaust was implemented allowing the power to increase to {{cvt|220|hp|PS kW|0}} at 4000&nbsp;rpm and {{cvt|320|lbft|0}} of [[Torque#Machine torque|torque]] at 2800&nbsp;rpm.<ref>{{Cite web|url=https://tran-zam.com/fhistory/1978Engines.aspx|title=Tran-Zam.com|website=tran-zam.com}}</ref> By mid-1978, the W72 could no longer be ordered in conjunction with the MX1 [[Turbo-Hydramatic#THM350|3-speed Turbo-Hydramatic 350]] automatic transmission, and could only be ordered with the 4-speed manual transmission.

By 1979, Pontiac was no longer allowed to produce the 400 engine as emissions further tightened. Pontiac had prepared for the forthcoming cancellation of the venerable 400 by producing large volumes of the stronger cast "XX" 400 blocks in 1977 that were assembled in 1978, and stockpiled at a warehouse by the assembly plant for later use. The 1979 Firebird model line was the last year for the Pontiac 400, and by this point not only was it required with the 4-speed manual transmission, it also required the WS6 Special Handling Package as mandatory equipment. The W72 was only available for a very short time, with the majority of 1979 model year W72 Firebirds ordered in late 1978. By early 1979, orders for the W72 package were being rejected by dealers as they supply had run dry. Instead, they were substituted with the [[Oldsmobile V8 engine#403|L80 Oldsmobile 403]], or the [[#301|L37 Pontiac 301]] if they still requested a 4-speed transmission. On the invoicing for the 1979 model year Firebirds, they had the option listed as L78, however, every 1979 400 equipped car received a W72 engine.

According to the June 2019 issue of ''Muscle car Review'' magazine, during dyno testing performed during that era, the National Hot Rod Association (NHRA) rated this Pontiac W72 400 T/A 6.6 engine at 260 to 280 net horsepower instead of the 220-hp rating published by Pontiac. The 1979 W72/WS6 equipped Trans Am was considered to be one of the overall best performing cars of the decade due to having a powerplant that produced more power than any other competitor on the market at the time with handling equipment to supplement the performance.<ref>{{Cite web|url=https://www.hemmings.com/stories/article/1979-pontiac-trans-am-2|title = 1979 Pontiac Trans Am}}</ref>

===421 HO===
First offered as an option in 1963, the 421 HO came in a 4-barrel engine of {{cvt|320|hp|0}} and one Tri-Power HO version with a hotter cam and efficient iron exhaust manifolds and rated at {{cvt|370|hp|0}}. Pontiac offered this to the public as a streetable version of the 421 SD. The engine came with 543797 (4-barrel) and 9770716 heads for the tri-power and special exhaust manifolds and a 7H cam with 292deg. intake duration and later 1964 L with 288deg intake essentially the same as the 068 cam. #9770716 aka "716" heads featured a 170cc intake port volume, and were considered a milder "street" version of the vaunted SD421 Super Duty heads. These same heads were also used on the 1964 GTO 389 tri-power engines. By 1965 and 1966 the same combinations would be rated at {{cvt|338|hp|0}} for the 4bbl and the two Tri-Power versions would be rated at {{cvt|356|hp|0}} and the HO version at {{cvt|376|hp|0}}.

=== 428 HO ===
This engine was first offered in 1967 as the top engine option in full-size Pontiacs. It was rated at 376&nbsp;bhp in 1967 and 390&nbsp;bhp in 1968 and 1969. For 1967 only Pontiac called this engine the Quadra-Power 428. It was renamed 428 HO for 1968.

===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.

===301 W72 "T/A 4.9"===
While not related to the 400 W72, the concept was the same. The W72 301 was a tuned L37 301 Pontiac V8 with some minor upgrades. All 1980 Trans Ams received this engine as standard with the option to delete this engine choice as a credit option for the standard L37 301. The main upgrade for the engine was the ESC, (Electronic Spark Control)<ref>{{Cite web|url=https://tran-zam.com/fhistory/1980Facts.aspx|title = 1980 Firebird and Trans Am Fact Sheet|date = 2 November 2021}}</ref> which provided slightly more power at {{cvt|170|hp|0}}for the 1980–1981 model years. For 1981 this engine was officially called the 301-EC [EC standing for Electronic Controls] in the 1981 GM factory service manual and is referred to as "high performance" The RPO W72 option was no longer used as a result, similar to how all W72 engines in 1979 were coded L78.<ref>{{Cite web|url=https://tran-zam.com/fhistory/1981Engines.aspx|title=Tran-Zam.com|website=tran-zam.com}}</ref>

One of the key modifications over the standard 301 4-barrel was the 301 Turbo block. The 301T block was significantly more durable than the standard 301 block and received a thicker bottom end. This included the ESC (Electronic Spark Control) distributor and controller borrowed from the 301 Turbo, which allowed for higher timing without the penalty of engine damaging pinging or preignition. A larger {{cvt|4|in|1|adj=on}} ram air flex duct to the air cleaner from the left-hand fender, specific carburettor calibration for the Rochester Quadrajet, a "T/A 4.9" callout on the shaker, 60 psi oil pump, and cam similar in grind to the {{cvt|220|hp|0}} 400 from the 1978–1979 model year were also included. Unfortunately, there were no improvements in the casting number "01" small-valve high-velocity heads, which would have yielded greater improvements in power. Additionally, the 301 W72 never received the option to come equipped with a manual transmission like the standard 301 received in 1979, and disappointingly, production for all Pontiac V8's ended soon after as GM sought to "corporatize" engine production.