Editing GMC V6 engine (section)

{{Infobox automobile engine
| name = GMC V6 engine
| image = 1960 GMC V12 702cid.JPG
| caption = GMC "Twin Six" heavy duty engine {{convert|702|cid|L|1|abbr=on}}
| manufacturer = [[General Motors]]
| production = 1959–1974
| configuration = 60° [[V6 engine|V6]], [[V8 engine|V8]], and [[V12 engine|V12]]
| valvetrain = [[Overhead valve engine|OHV]] 2 valves × cyl.
| fueltype = [[Gasoline]] and [[Diesel fuel|diesel]]
| fuelsystem = [[Carburetor]]
| coolingsystem = [[Radiator (engine cooling)|Water-cooled]]
| block = [[Cast iron]]
| head = [[Cast iron]]
| displacement = {{Unbulleted list|{{convert|305|CID|L|1|abbr=on}}|{{convert|351|CID|L|1|abbr=on}}|{{convert|379|CID|L|1|abbr=on}}|{{convert|401|CID|L|1|abbr=on}}|{{convert|432|CID|L|1|abbr=on}}|{{convert|478|CID|L|1|abbr=on}}|{{convert|637|CID|L|1|abbr=on}}|{{convert|702|CID|L|1|abbr=on}}}}
| bore = {{Unbulleted list|{{convert|4.25|in|mm|abbr=on}}|{{convert|4.56|in|mm|1|abbr=on}}|{{convert|4.87|in|mm|1|abbr=on}}|{{convert|4.875|in|mm|abbr=on}}|{{convert|5.125|in|mm|abbr=on}}}}
| stroke = {{Unbulleted list|{{convert|3.58|in|mm|1|abbr=on}}|{{convert|3.86|in|mm|abbr=on}}}}
| power = {{convert|150-275|hp|0|abbr=on}}<ref>{{Cite web|url=https://www.motortrend.com/how-to/ccrp-1212-702-ci-thunder-v12-gmc-engines-horsepower/|title = 702ci Thunder V12 GMC - Car Craft Magazine|date = 16 October 2012}}</ref><ref>{{Cite web|url=https://silodrome.com/702-cubic-inch-11-5-litre-gmc-v12/|title = There's a Rare 702 Cubic Inch (11.5 Litre) GMC V12 for Sale on eBay|date = 24 January 2020}}</ref>
| torque = {{convert|260-630|lbft|0|abbr=on}}<ref>{{Cite web|url=https://www.curbsideclassic.com/blog/the-gmc-twin-six-v12-702-cubes-275-hp-at-2400-rpm-630-ft-lbs-at-1600-rpm/|title = The GMC Twin Six V12: 702 Cubes, 275 HP at 2400 RPM, 630 Ft. LBS. At 1600 RPM|date = 4 October 2021}}</ref><ref>{{Cite web|url=https://gmauthority.com/blog/2015/06/remember-when-gmc-produced-a-v12-engine/|title = Remember when GMC Produced a V12 Engine?|date = 9 June 2015}}</ref>
}}

The '''GMC V6''' is a family of 60-degree [[V6 engine|V6]] engines produced by the [[GMC (automobile)|GMC]] division of [[General Motors]] from 1959 through 1974. It was developed into both [[Gasoline engine|gasoline]] and [[Diesel engine|diesel]] versions, and produced in [[V8 engine|V8]] and [[V12 engine|V12]] derivatives. Examples of this engine family were found in [[pickup truck]]s, [[GMC Suburban|Suburbans]], heavier trucks, and motor coaches.

A big-block engine, variants were produced in 305-, 351-, 401-, and 478-cubic-inch (5.0, 5.8, 6.6, and 7.8 liters respectively) displacements, with considerable parts commonality. During the latter years of production, {{convert|379 and 432|CID|L|1|adj=on}} versions with enlarged [[crankshaft]] [[Plain bearing|journals]] were manufactured as well.

GMC produced a {{convert|637|CID|L|1|adj=on}} 60° [[V8 engine|V8]] with a single [[camshaft]] using the same general layout (bore and stroke) as the 478 V6. The 637 V8 was the largest-displacement production gasoline V8 ever made for highway trucks.

The largest engine derived from the series was a {{convert|702|CID|L|1|adj=on}} "Twin Six" [[V12 engine|V12]], which had a unique block and crankshaft, but shared many exterior parts with the 351.

Diesel versions of the 351, 478 and 637, advertised as the '''ToroFlow''', were also manufactured. These engines had no relationship to the well-known [[Detroit Diesel Series 71|Detroit Diesel]] [[two-stroke diesel engine]]s produced by General Motors during the same time period.

All versions of the GMC V6 used a six-throw crankshaft, which when combined with the 60 degree included cylinder angle, produced a smooth-running engine without any need for a balance shaft. [[Spark plug]]s were located on the inboard side of the [[cylinder head]]s and were accessed from the top of the engine. This position allowed for shorter spark-plug wires and kept the spark plugs away from the hot [[exhaust manifold]]s, something which was emphasized in sales literature. It was also perceived as being easier to access for maintenance. These GMC V6 engines were noted for durability, ease of maintenance, and strong low-end torque.

In 1974, GMC discontinued the V6 engine; all gasoline-engine models were powered by Chevrolet straight-six and V8 engines, while diesel engines were dropped from medium duty models and would not return until 1976.

{| class="mw-collapsible mw-collapsed wikitable"
! colspan=8|GMC 60° Engine Family
|-
!Fuel
!Cylinders
!Model
!Displacement
!Bore
!Stroke
!Power (Net)
!Torque (Net)
|-
|rowspan=16|Gasoline
|rowspan=14|6
|305A<ref name=6066-gas-data>{{cite web |url=https://6066gmcguy.com/EngineData.html |title=GMC Big Block V6, V8, & V12 Engine Data |date=12 May 2008 |publisher=6066 GMC Guy |access-date=17 August 2024}}</ref>
|{{convert|304.6|CID|L|1|abbr=on}}
|{{convert|4.25|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|125|hp|0|abbr=on}}
|{{convert|240|lbft|0|abbr=on}}
|-
|305B<ref name=6066-gas-data/>
|{{convert|304.6|CID|L|1|abbr=on}}
|{{convert|4.25|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|127|hp|0|abbr=on}}
|{{convert|245|lbft|0|abbr=on}}
|-
|305C<ref name=71-trucks>{{cite web |url=https://xr793.com/wp-content/uploads/2019/08/1971-GMC-Conventional-Models.pdf |title=GMC Conventional Models, Series 4500-6500 |date=1971 |publisher=GMC Truck and Coach Division, General Motors Corporation |access-date=17 August 2024}}</ref>
|{{convert|304.6|CID|L|1|abbr=on}}
|{{convert|4.25|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|142|hp|0|abbr=on}}
|{{convert|250|lbft|0|abbr=on}}
|-
|305D<ref name=1962-trucks>{{cite web |url=https://xr793.com/wp-content/uploads/2021/11/1962-GMC-Pickups.pdf |title=GMC Pickups |date=1962 |publisher=GMC Truck and Coach Division, General Motors Corporation |access-date=17 August 2024}}</ref>
|{{convert|304.6|CID|L|1|abbr=on}}
|{{convert|4.25|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|142|hp|0|abbr=on}}
|{{convert|260|lbft|0|abbr=on}}
|-
|305E<ref name=1963-trucks>{{cite web |url=https://xr793.com/wp-content/uploads/2021/11/1963-GMC-Pickups.pdf |title=GMC Pickups and Stake Racks, Series 1000-2500 |date=1963 |publisher=GMC Truck and Coach Division, General Motors Corporation |access-date=17 August 2024}}</ref>
|{{convert|304.6|CID|L|1|abbr=on}}
|{{convert|4.25|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|142|hp|0|abbr=on}}
|{{convert|260|lbft|0|abbr=on}}
|-
|351/351C<ref name=71-trucks/>
|{{convert|351|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|155|hp|0|abbr=on}}
|{{convert|288|lbft|0|abbr=on}}
|-
|351E<ref name=6066-gas-data/>
|{{convert|351|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|190|hp|0|abbr=on}}
|{{convert|304|lbft|0|abbr=on}}
|-
|351M<ref name=6066-gas-data/>
|{{convert|351|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|190|hp|0|abbr=on}}
|{{convert|304|lbft|0|abbr=on}}
|-
|379<ref name=6066-gas-data/>
|{{convert|379|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|170|hp|0|abbr=on}}
|{{convert|266|lbft|0|abbr=on}}
|-
|401<ref name=6066-gas-data/>
|{{convert|401|CID|L|1|abbr=on}}
|{{convert|4.875|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|178|hp|0|abbr=on}}
|{{convert|351|lbft|0|abbr=on}}
|-
|401M<ref name=67-trucks/>
|{{convert|401|CID|L|1|abbr=on}}
|{{convert|4.875|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|210|hp|0|abbr=on}}
|{{convert|348|lbft|0|abbr=on}}
|-
|432<ref name=6066-gas-data/>
|{{convert|432|CID|L|1|abbr=on}}
|{{convert|4.875|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|190|hp|0|abbr=on}}
|{{convert|336|lbft|0|abbr=on}}
|-
|478<ref name=6066-gas-data/>
|{{convert|478|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|206|hp|0|abbr=on}}
|{{convert|400|lbft|0|abbr=on}}
|-
|478M<ref name=67-trucks/>
|{{convert|478|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|225|hp|0|abbr=on}}
|{{convert|410|lbft|0|abbr=on}}
|-
|rowspan=1|8
|637<ref name=6066-gas-data/>
|{{convert|637|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|250|hp|0|abbr=on}}
|{{convert|560|lbft|0|abbr=on}}
|-
|rowspan=1|12
|702<ref name=6066-gas-data/>
|{{convert|702|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|250|hp|0|abbr=on}}
|{{convert|585|lbft|0|abbr=on}}
|-
|rowspan=5|Diesel
|rowspan=3|6
|D351<ref name=65-engr/>
|{{convert|351.2|CID|L|1|abbr=on}}
|{{convert|4.56|in|mm|abbr=on}}
|{{convert|3.58|in|mm|abbr=on}}
|{{convert|118|hp|0|abbr=on}}
|{{convert|234|lbft|0|abbr=on}}
|-
|D478<ref name=65-engr/>
|{{convert|477.7|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|135|hp|0|abbr=on}}
|{{convert|266|lbft|0|abbr=on}}
|-
|DH478<ref name=65-engr/>
|{{convert|477.7|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|155|hp|0|abbr=on}}
|{{convert|298|lbft|0|abbr=on}}
|-
|rowspan=2|8
|D637<ref name=67-trucks/>
|{{convert|637|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|185|hp|0|abbr=on}}
|{{convert|440|lbft|0|abbr=on}}
|-
|DH637<ref name=67-trucks/>
|{{convert|637|CID|L|1|abbr=on}}
|{{convert|5.125|in|mm|abbr=on}}
|{{convert|3.86|in|mm|abbr=on}}
|{{convert|205|hp|0|abbr=on}}
|{{convert|444|lbft|0|abbr=on}}
|}