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Z20 Engine in 620


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I have a 78 620. I'm removing the smog hardware and when I got the manifolds off, I noticed the engine is stamped Z20. Is this not the orignal engine?


I thought Z engines sat vertical. This one is inclined toward the passenger side like my other 620s.

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The Z identification is always on the left side of the block at the top roughly in the middle. L ID is on the right rear about where the dip stick handle is.


The Z block is almost identical to the L20B with slightly different casting ridges beteween cylinders on the sides. The two that I have taken apart had the fully counterweighted L20B crank in them. The Z20E and Z20S have different rod piston heights from each other and from the L20B but will fit the L20B if kept as a set. The Z20E uses long 152.5 rods and a flattop piston compared to the L20Bs 145.9 rod and 11 cc dished piston. This would give a high 9s compression when used with a pea nut L head and high 8s with the open chamber head.


Engine 'tilt' is determined by the motor mounts used. To have make it work in the L20B position L20B MMs, oil pan and pick-up, timing cover, chain and head were used. If a '78 you probably have a W-58 head on it.

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