Editing GMC straight-6 engine (section)

==Group 1==
The Group 1 engines were the smallest in displacement and outer dimensions, and differed most significantly from the larger Group 2 and Group 3 engines by having only four main bearings (whereas the Group 2 and 3 engines had seven)<ref name="meyer"/>{{rp|15}} and a different [[firing order]] (1-5-3-6-2-4, whereas the others are 1-4-2-6-3-5).<ref name="motor"/>

===228===
GMC replaced the [[Pontiac straight-6 engine#223 Pontiac/GMC|Pontiac 223]] with their own {{Convert|228|CID|L|1|adj=on}} '''228''' in 1939.  This OHV ([[overhead valve]]) engine was produced through 1953. With a cylinder bore of {{Convert|3.5625|in}}, this is the smallest low-deck engine. All four low-deck engines have a stroke of {{Convert|3.8125|in}} and used 7 inch long connecting rods.

===236===
The {{Convert|236|CID|L|1|adj=on}} '''236''' was introduced in 1941 and only in limited production through [[World War II]]. This is a low-deck engine, with {{Convert|3+13/16|in}} stroke and {{Convert|3+5/8|in}} bore. Production ended in 1946.<ref name="motor"/>

===248===
The {{Convert|248|CID|L|1|adj=on}} '''248''' was released in 1939 alongside the 228. The 248 was similar to the [[#236|236]]. The bore was {{Convert|3.71875|in}}. Stroke is 3.8125. Power in 1955 listed as 100 HP @ 3100 rpm; torque 202&nbsp;lb ft @ 1000 rpm. The 248 was discontinued in 1955.

===256===
The {{Convert|256|CID|L|1|adj=on}} '''256''' was similar to the 236 and 248. It was also an OHV/pushrod engine, and was built for just two years, 1940 and 1941. This is the largest low deck engine. Bore was 3.78125 and stroke was 3.8125. Power listed as 91 Net HP @ 3000 rpm; torque 201 Net lb ft @ 1000 rpm.

===270===
The last GMC-only straight six was the {{Convert|270|CID|L|1|adj=on}} '''270'''.  It was produced from 1941 through 1963, and was an OHV/pushrod engine. This is a raised-deck engine. The bore was 3.78125" (same as 256) and stroke was {{convert|4|in|1}}. Power listed in 1963 as 133 HP @ 3600 rpm; torque 244&nbsp;lb ft @ 1300 rpm.

===302===
The {{convert|301.6|CID|L|1|adj=on}} GMC inline six was produced from 1952 to 1960, when it was replaced by the V6. It has a [[Stroke ratio#Square engine|square bore/stroke ratio]] of {{convert|4x4|in|1}}. This is the largest raised-deck engine. It was originally designed for the GMC military M135 and M211. It was used in military 2{{frac|1|2}}-ton trucks with the [[Hydramatic]] transmission; however, the engine was a sealed engine for snorkel/submersion use, had an electric fuel pump, and other features such as a deep sump oil pan. From 1952 to 1959, GMC manufactured the civilian 302 engine, which was not sealed, had a mechanical fuel pump, and used a standard oil pan. Power listed in 1959-160 HP @ 3600 rpm; torque 268&nbsp;lb ft @ 1600 rpm. This engine was popular with hotrod enthusiasts because it delivered tremendous power for an inline six engine at the time (although now obsolete), is built with a heavy cast block, and can take quite a bit of abuse.