Rear diffuser on a 328

Have you pics ?

What do you mean by "rear diffusers" ? The rear bumper grill ?

 

Pictures please? I own a 328 and have no idea what you are talking about. There are really 2 versions, one with rear fog lights and one without rear fog lights.

 

There is no rear diffuser on a 328

 

I'd guess that the OP is talking about the difference in the "diaper" grill (to use the unflattering 308 term) between the US (with cat) and euro (no cat) versions.

 

The grills are exactly the same size. One has fog lights. The other does not.

 

I believe the US version grill has one more horizontal bar above the tailpipes that runs across the entire width (that the euro does not have) so is a tad bigger, or makes it look bigger (at least, that's what the SPC shows - 5 horizontal rows for US vs 4 horizontal rows for euro).

 

The first one ( top ) is euro type. The third is US type one. And as say Brian the biggest difference is the presence or not of fog lights.

I "think" there is a visual différence in the length of the outlets exhaust. But I don't remember the reason yet

@nerofer should have his opinion ........

 

Look at this pic.

The positioning of the grid is different between the Euro and US type. The US type is "more remote"
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Euro type
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Where can you purchase this pictured grill version if damaged?

 

Just to add that Euro versions(excluding Swiss market)don't have a slot cut out in the centre of the rear bumper which US and any other market that had cats..
The slot was there to facilitate cooling of the exhaust/cats,,well at least that's what I was told.

 

Well, it's actually very simple:

The standard "euro" cars (with the exception of the swiss cars after mid-1987) do not have a catalysator ("W" engine). Their rear grill is fitted recessed under the rear bumper in such a way that the four tail pipes protrudes quite notably out of the grill, about four inches I would say.

The US cars ("X" engine) and Swiss cars after mid-1987 ("C" engine) have a catalysator, which is fitted in front of the exhaust box; to put the whole exhaust system in the same space than on euro cars, the exhaust box itself has a different shape on cars with catalysator, and is pushed slightly backwards compared to an "euro" car without cats.
The consequence is that the grill itself is fitted pushed slightly more rearwards than on euro cars, about two inches; and that the tail pipes are shorter, and protrude only about two inches from the grill vs four inches on "euro" cars. This to avoid having tailpipes protruding "out of the bumper", or longer than the total length of the car.

Of course the cars with catalysator also have a different rear bumper, which has a "letterbox" air extraction slot just beneath the registration plate. Note that it also has three small holes for air extraction in the middle of the black indentation line (swage line, blood line or whatever you call it)

(we could nitpick here about the "Middle East" variant, Bertrand, which, as you know, has the rear bumper with the hot air extraction outlet but NO CAT (= "W" engine), this for additional cooling of the engine compartment under a very hot climate, but that model is rather rare...)

Rgds

 

The two exhaust boxes here under:

The "Euro" (= NON CAT) exhaust receive gases from the two manifolds from each side:
- the rear manifold (rear bank of cylinders) goes on the left (driver's side on LHD cars) and discharges in the left entry elbow, via a short intermediary pipe (elbow);
- the front manifold (front bank of cylinders) is routed on the right (passenger's side on LHD cars and discharges in the right entry elbow, via a long straight intermediary pipe.

The "WITH CAT" exhaust has a single catalysator (missig in the picture, figured by a test pipe) in front of the exhaust box, bolted to a single entry elbow.
Compared to a non-cat car, the rear manifold is reversed: it discharges on the right (passenger side) into a "Y" pipe which receives gases from the front manifold at right, and then brings both exhaust flows into the single cat.
To leave space for the catalysator pushes the exhaust box to the rear (even if it is shorter than the euro box, and actually higher) so the grill is pushed rearwards, and the exhaust pipes have to be shorter in order not to protrude out of the total length of the car.

As many of you already know, the manifolds are différents between cars without cats and car with cats:
- on car without cats, see the last picture (rear OEM manifold illustrated, note it discharges on the right; short elbow intermediary pipe missig), the tubes are plain to be seen, i.e not wrapped in anything, there is no ports for the "sniffer tubes" (and no port for a lambda probe on the cat)
- on car with cats, the tubes are wrapped in a metal sheet, giving them a kind of "doughnut" aspect, and have ports for sniffer tubes.
Rgds
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Well I hope that you have understood now that the two different 328 grills correspond to a different version of the exhaust system: one for cars with cat, one for cars without cat; and to a different bumper also (with hot air extraction slot for cars with cat, without it for cars without cat)...
So the answer is NO, the grills are not interchangeable: it depends if the car is fitted with catalysator ("X" engine, mainly US, Australian, and some Japanese cars; "C" engine: Swiss cars after 1987, Swedish cars) or not ("W" engine, standard euro cars).

Rgds

 

Thats all true of course but surely the most obvious difference is the size of the grill. 3 bars on Euro and 5 on US.
On the Euro the area which is occupied by the top 2 bars of US grill is black painted fibreglass, part of the valance, with the fog lights at each side of it.

 

At the usual Ferrari parts suppliers I suppose....