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The Q code is the Cobra Jet and it is a Cleveland.

by Tom Custom

The Q code engine package was introduced in 1971 as a performance version of the 351C. Here are the different versions of the US 351C

1970:
H code 351C-2V, two barrel engine, 9:1 CR, open 2V style heads
M code: 351C-4V four barrel engine, 10.7:1 CR, closed 4V style heads
The M code used a small cam. It was powerful, but not a performance engine. That is, it didn’t have any “race” parts. Both engine used positive lock rockers and flat top pistons.

1971:
H code 351C-2V, two barrel engine, 9:1 CR, open 2V style heads
M code: 351C-4V four barrel engine, 10.5:1 CR, closed 4V style heads
Q code: Cobra Jet 4V 9:1 CR four barrel engine. Had special parts like high lift cam (same profile as 428CJ), dual point ignition with 4 speed, larger harmonic balancer, baffled oil pan, four bolt mains, big spread bore carb. This engine used open 4V style heads with positive lock rockers. Lower cost, easy maintenance, regular gas performance engine.
R code: Boss four barrel engine, 11.7:1 CR, closed 4V style heads with adjustable rockers, forged pistons, high strength rod bolts, crank selected for a minimum hardness, solid lifter cam, large balancer, four bolt mains, dual point ignition, special exhaust manifolds (not that you could tell by the outside), baffled oil pan, aluminum intake and big spread bore carb. This was a serious performance engine package.

1972:
H code 351C-2V, two barrel engine, 8.5:1 CR (or so), open 2V style heads
Q code: Cobra Jet 4V 8.5:1 CR (or so) four barrel engine. Same as 1971 but with dished pistons.
R code: HO four barrel engine, 9.5:1 CR, open 4V style heads with adjustable rockers, forged pistons, high strength rod bolts, crank selected for a minimum hardness, solid lifter cam (slightly different than the Boss), large balancer, four bolt mains, dual point ignition, special exhaust manifolds (not that you could tell by the outside), baffled oil pan, aluminum intake and big spread bore carb. This was a serious performance engine package, and a low compression version of the Boss.

1973:
H code 351C-2V, two barrel engine, 8:1 CR (or so), open 2V style heads
Q code: Cobra Jet 4V 8:1 CR (or so) four barrel engine. Same as 1972 but got the 2V sized valves in the 4V heads. Cam was retarded in timing 4 degrees sometime starting in 1972. The change is in the cam. It gets an EGR system. Only 4V Cleveland engine option in 1973/74.

1974: Same as 1973. No 4 speed option so no dual points for Q code. Last year for the 351C. In 1975, the taller deck 400 would used with a destroked crank and different pistons to make the 351M. The 400 continued with the 351M until 1980? The 1973 Q code used a special air cleaner housing with the usual snorkel on the right side, a second air inlet controlled by a vacuum servo on the left (US driver's) side, and a chrome lid. Transmissions with the CJ were either the Toploader (only close ratio available in 1973) or the C6 with a special smaller diameter, high stall torque converter. Dual points only with 4 speed. All CJ years cam with a cast iron spread bore intake manifold.manifold


1974:
Same as 1973. No 4 speed option so no dual points for Q code. Last year for the 351C. In 1975, the taller deck 400 would used with a destroked crank and different pistons to make the 351M. The 400 continued with the 351M until 1980?

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