Differences in 308's rear deck vents

I'll take a stab at trying to help you with this. I'm sure there are others on this board who will know for sure.
I seem to think that the early carbed cars had the full center section with out the louvers and starting sometime in 1980, with the injected cars, Ferrari added additional louvers.
This seemed to be the definitive design as it carried over to the Qv cars and the 328 series.
There is another rear deck that was installed on the turbo cars. The body colored center section was raised in order to clear the larger airbox.
Zebra

 

I wish I knew that BEFORE I jumped through hoops to make my supercharger intake fit under the stock hood....

 

I believe that the extra louvres on the engine cover were introduced when catalytic converters were added to the 308GTB/S on the '77 JAPANESE and '78 US versions (and were included on all cat-equipped 308 B/S thereafter, but all non-cat version 308 B/S have the small vent area on the engine cover).
Like the roof on a B, the extra body color of the small vent set-up just adds to the coachwork beauty IMO (i.e., ain't no 308 B/S coachwork better looking than a non-cat B ).

 

I just checked a euro 308 GTS QV, two separate vents.

 

My '78 US car does have the extra louvers behind the center section if that helps.

Edit: The interesting thing is I never noticed the difference on other cars!!
I think Zebra has it backwards and 91tr is closer.

 

I knew someone would have a better answer. I guess the cats are the key?

 

Looks like 91tr is correct.

Looking through my pictures, the first US 308 I found with the connected vents is #23467, a 1978 GTS manufactured in January 1978. #23267, a 1978 GTB manufactured in December 1977, has the split vents.

Looks like US models manufactured since January 1978 have the connected vents. I assume that is also the date the catalytic converters became mandatory. Euro models seem to have kept the split vents.

 

born feb, 1978 *23785*

 

SPOT ON. The extra lovers were to get rid of the heat from the cats. Even more observant eyes will notice that the panel under the car and behind the rear tires got louvers too at this time.