The 221SP's cylinder head was created in 1973 year, and manufactured until 1982, more than less, and it's based on the original USA stock cylinder head from a 200 cid engine. Basically, is the same head with a removable intake manifold and different exhaust system.
Later, the 188 MAX ECONO cylinder head appears in 1989 year. "MAX ECONO" means MAXimum ECONOmy.
The 221SP's head flows much better than a 188 MAXECONO's head. But the MAXECONO's combustion chambers are better and had larger exhaust valves. This head only needs a good work of "porting" and it could be better than a 221SP head.
The 221SP had more modifications than just a cylinder head. It came with a Holley 2300 based two barrel carburetor, a different camshaft (a litle more agressive than stock, with 272 degrees of intake/exhaust permanence, with solid lifters) and a slightly modified distributor. And more mechanical improvements.
Here, in Argentina, the 188 and 221 cid engine had 7 main caps.
Sorry again by my english...
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