Air intake cat/diff/cv cooling duct delete?

After removal of my own cats, I found a new, longer hose which was of the correct I.D. and then pointed it to blow air onto the alternator.

Tucked up under the front header as it is, I can easily imagine that the alternator gets pretty cooked, and I figured that any fresh air that I could steer that way would certainly help.

 

iifc reading here that duct was for the rr inner cv joint. There are twin metal ducts on the rear wheel well that cool the cats. One each side.

 

I don't think that blocking off the cv branch cooling duct will have any effect on engine intake air flow. Ferrari didn't design a 2.927 liter eight cylinder engine that consumes (x) cubic feet of air per minute at 7,700 rpm and then plumb it to an intake tube that will only pass (x-5) cubic feet of air per minute.

 

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+1

 

It wasn't to cool the cats; it was to cool the diff and cv (particularly their grease), because the the cats generated excess heat by trapping exhaust gasses. I deleted my airbox sound baffling (deceptively harder that it looks in the forum pics) and useless pneumatic flap, and I think it's made a difference in performance, but a HUGE difference in sound I kept the secondary branch tube to the diff, and can tell you the car can be run to its limit without suffering a loss of air to the engine.

 

Obviously didn't measure with an airflow meter, but makes a notable difference to have the sound baffling gone. Bear in mind, the passenger (front bank) header literally kinks around the passenger axle, and the rear header coils up right atop the diff, so certainly couldn't hurt to keep some cool circulation there.

 

Lemme see if I can find the pics from my restoration that will better illustrate it. Basically, the perforated mesh that retains the fiberglass batting is actually seriously tough steel. Snips won't do the trick. It is tack welded to the airbox along its periphery, but they're good welds. So you've got a piece of heavy metal mesh and solid welds that need to be ground off by a grinding tool, but the airbox metal itself is relatively thin and susceptible to cutting. At first I tried grinding into the middle of the mesh and trying to pry away the mesh from the welds. No dice, and the burning fiberglass was no fun. In the end, several careful grinds at the wider part of the airbox, but the real difficulty is when you get to the narrow snout section (and you'll find that normal grinding tools don't reach). I found that a sharp chisel and careful blows with a heavy hammer made quick work of the welds. Also twisting the snout section mesh with a pair of good pliers helped pry it off. There's a ton of fiberglass stuffed in there, so wet it or wear a mask when you pull it out.

 

Pics. Note the difference in air inlet size before and after...

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It makes a nice sound difference.

I always thought the drop pipe was to prevent some sort of ram air effect


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Here is what came out of my airbox!

Regarding the cooling tube coming off the bottom of the fiberglass air intake, everyone has a speculation and a new theory. Its really simple. Its a cooling tube for the passenger, inner CV joint because that joint is surrounded by the exhaust tubes. Its not for the cats, its not for the differential. Its for the CV joint.

If you attach a tube to the fiberglass opening it makes a natural path to the CV joint area. The cats are cooled by air under the car, going through the engine compartment and out the extra, side to side vents that are in the USA cars. Think of how big that vent is and how small the CV cooling tube is and do you really think the Ferrari engineers would design such a small tube to cool two super hot catalytic converters. Use logic and common sense. Also the differential has huge metal fins surrounding it to dissipate the heat. A small tube is not going to cool it down. Use logic and common sense.

To all the speculators, please give the Ferrari engineers some credit. They got most of the 308 correct. Isn't that why you own one and enjoy driving it?

 

Is there some hard data to prove this? I'm pretty sure the most restrictive point in the entire system are the intake valves, not the air filter or its inlet. Why on earth would they design an air cleaner that couldn't pass the amount of air the engine would demand at full rpm? It would be the easiest component to change in order to accommodate what is required. I get the desire for more noise but I don't think you're getting more air from this alteration.

 

'73-'77 US version only have air injection (no cats); '78-'79 US have air injection and cats so the underbonnet temp situation is more difficult.

The online 308i-2V SPC are only euro version (never seen a US 308i-2V SPC online after FDB shut down - and not sure FDB even had one). Although the euro don't have the dedicated tube, I believe that they do have a sort of crescent moon shaped opening in the bottom of the duct to let some air into the engine compartment and to let any rain/water that enters drain out (rather than being forced into the intake tract).

 

Thanks for the link Paul, that is an interesting thread. Still, I've seen these sorts of discussions in other forums through the years which entail a good deal of "armchair engineering" based on what people perceive simply by looking at the appearance of things but not on any actual math. In my opinion you need to look at the size of the intake valve in the cylinder and realize that only one of those is open at any given instant. So it seems to me that any limit on the "flow" of air through the entire intake system is going to be determined by that. Maybe I'm wrong but that's the way I've always seen it.

 

Additional data point, fwiw - my 84 Euro QV side air inlet duct does have the side outlet for the CV joint cooling tube (if we're going to refer to it as such), but my car, when I got it at 29 years of age, did not have an actual hose connected to that outlet.

My car was very original and complete when I bought it, but not guaranteed - so we can say that the intake duct on Euro QVs did also have that side outlet, but may not have had the hose to direct air onto the right side CV joint.

 

Just came across this other pic showing the airbox obstruction. That entire opening becomes unblocked if the sound baffling is removed. Also, there's a pic of the condition in which I found my branch tube. My notes say that the replacement I sourced is a GATES 28081 hose, for anyone interested.

I remember being told by my mechanic at some point that these hoses are attached in a somewhat clumsy way, and that - because they are directly in the way of doing the belt change, they often are just ripped out and not carefully replaced.

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