Quote:
HUH??
A wedge combustion chamber [no matter the manufacturer] is a wedge. If you use hemi valve placement, then you got either a hemispherical or a pent roof type chamber.

A wedge chamber is VERY EFFICIENT at keeping production costs down, while at the same time, providing an acceptable design. It is not more efficient as a cross flow cylinder head design as the exhaust ports have a somewhat less than ideal bend. Once again, it is adequate, but it is not more efficient.

The hemispherical shape is expensive to manufacture & it's bulky, but valve placement is optimised & the chamber has a lower "surface to volume" ratio than any other design. This means that it has a much better "heat rejection" figure. [less heat lost through the chamber walls into the cooling system.] The central plug placement also optimises flame propigation & this has customarily meant that this design can run a full point of compression more that other designs on the same grade of fuel.

The problem with the "dirty engine" syndrome revolves around the lack of combustion chamber swirl, which would lead to the ability to burn leaner mixtures. This has been addressed by one piston manufacturer & good results are being achieved. Combined with EFI,... great results are being achieved.

GM has long been the producer of an entirely adequate, but low cost wedge chambered engine, & this has been proven to be extremely popular. Chrysler corp just plain built a legend, & to hell with the cost,... quality of design & manufacture came first.

DATSUN, on the other hand, came up with a ledgend of their own, starting with the A10. This very basic, low cost design has been developed into the almost buletproof range of engines that just will not die.
39 years after this engine went into production [sept '66] this automotive icon is still in production & still manages to comply with the relevant smog requirements where it is sold. I am not aware of any plans to end production anytime soon either.
Compared to the contemporary Toyotaaargh Corolla pushrod 1200 engine, which was scrapped by the manufacturer decades ago, well,.... the Datsun engine just simply can't be compared.

Very few engine designs have enjoyed a continuous production run as long as that, & i don't think any other design that was in production in the 60's has been good enough to survive into current production.
Thats gotta speak volumes for any of the A series family members. These engines are simply greater than the sum of their parts, & remember, none of these A series engine versions has ever been a dud.
VIVE' Datsun pushrod A series powerplants.

I gotta admit, i am both surprised & impressed at how many members are Mopar savvy. Thanks for the support blokes.