Editing Pontiac V8 engine (section)

===400===
[[File:Pontiac 400ci V8 in 1976 Trans Am 50th Anniversary.jpg|thumb|A L78 400 4bbl engine in a 1976 Y82 Limited Edition [[Pontiac Firebird#1976|Trans Am]] ]]
For 1967, Pontiac retired the {{cvt|389|cuin|L|1}} and replaced it with the 400&nbsp;cu&nbsp;in ({{cvt|399.95|cuin|L|1|disp=out}}), a 389 [[bore (engine)|bored]]-out by +{{cvt|0.06|in|mm}} to {{cvt|4.12|in|mm|1}} and retaining its [[stroke (engine)|stroke]] of {{cvt|3+3/4|in|mm|1}}. The 400 remained in production through the 1978 [[model year]], with 1979 cars receiving engines produced the previous year.

In basic 2-barrel form it produced 290 horsepower and 428&nbsp;ft. pounds of torque in 1968.<ref name=400specs>{{Cite web|url=https://itstillruns.com/pontiac-400-specs-7621192.html|title=Pontiac 400 Specs|website=It Still Runs}}</ref> This was the engine installed in the [[Pontiac Executive]] line of large cars<ref>{{Cite web|url=https://www.automobile-catalog.com/car/1969/2792405/pontiac_catalina_hardtop_coupe_400_v-8_2-bbl_turbo_hydra-matic.html|title=Detailed specs review of 1969 Pontiac Catalina Hardtop Coupe 400 V-8 2-bbl Turbo Hydra-Matic offered since September 1968 for North America|website=www.automobile-catalog.com}}</ref> and its largest station wagon, the [[Pontiac Safari]].

In 1967, the [[cylinder head]] design was improved for the 400 4-barrel engine. The [[Angle seat piston valve|valve angle]] was reduced from 20 degrees to 14 degrees for better breathing. 1967 was the last year for closed-chambered heads. The "670" head was a 1967-only [[casting]], and the only PMD head to have a closed chamber with the new 14 degree valve angle. The 400 2-barrel and big car AFB 4 bbl kept the 20 degree valve angles for '67; starting in '68 all Pontiac V8s went to the 14 degree valve angle. Pontiac went to open-chambered heads in some 1967 models and all 68 and up to improve power, engine breathing and reduce [[Exhaust gas|emissions]]. The valve size increased as well, to {{cvt|2.11|in|1}} intake and {{cvt|1.77|in|1}} [[exhaust valve]]s on high-performance heads. Low-performance and two-barrel applications, the standard engine in [[Full-size car|full-sized]] Pontiacs, got {{cvt|1.96|in|1}} [[intake]] and {{cvt|1.66|in|1}} exhaust valves and pressed in [[rocker arm]] studs.

In 1975, to assist in meeting CAFE emissions standards, Pontiac drastically modified the structure and metallurgy of the 400 blocks being produced. The 2bbl option was no longer available, and the sole 400 available for all model lines became the L78 400 with a 4bbl Rochester Quadrajet. This 400 engine was relegated to only produce 185&nbsp;hp (or less depending on application) for the remainder of its production. These blocks were cast from 1975 through 1977, and were last used in 1978 model year vehicles. The block had metal shaved from the inner journals, and was made with a reduced nickel content to reduce weight from the completed engine with the goal of making the engine lighter, which would in turn reduce the overall weight of the vehicle, alleviating the emissions it produced. These blocks were denoted with casting numbers starting with 500, such as the "500557" blocks found in 1975-78 Firebirds. Pontiac did re-introduce the older, more durable block but the 400 no longer could meet the tightening emissions requirements, and block casting ceased in 1977. These stronger cast blocks were assembled and stockpiled for the 1978 and 1979 Firebirds equipped with the W72 Performance Package.<ref>{{Cite web|url=https://www.motortrend.com/how-to/picking-a-pontiac-400-or-455-block-for-performance-use/|title=Picking a Pontiac 400 or 455 Block for Performance Use|date=April 13, 2016|website=MotorTrend}}</ref>

The four-barrel 400 was a popular performance option for many of Pontiac's cars. When fitted with other high-[[airflow]] components, it produced a good balance of low-end [[Torque#Machine torque|torque]] and higher-RPM power. In the 1968 Pontiac GTO it was given a 10.75:1 compression ratio and tuned to deliver 360 horsepower and 445 foot-pounds of torque.<ref name=400specs/>