308 carb airbox restriction discovered

Nick, No I didn't.
Just cut it all out and then sandblasted/stripped back and painted.
You just know it will breath so much better before you have done it.
Have you done it to the GT4?

 

No I have'nt yet. I am worried it will be too noisey; once done it can't be undone - and that worries me.

Regards
Nick

 

I felt it was my duty to Enzo to rip that garbage out of there. Its a Ferrari for Gods sakes, not a Geo.

Actually its not that much louder, just adds some rawness, and really, it only makes noise when you open it up. Just cruising its quiet as a lil mouse. You bought a performance car, and someone that Enzo trusted, and obviously shouldnt have, plugged up the air intake so it cant get its legs. Come on, its like making a Greyhound breath through a straw while trying to chase a rabbit.

 

Nick, I know what you mean, and I thought the same thing.
But you have to do it to make it breath right. It is a real comporomise the way it is.
Yours is a RHD yeah?
If that is the case you will hear it louder from your driving position like me.
It is a bit pulsey/throbey at low revs, but you won't be able to wipe the smile off when you wind it out.
I have my exhaust off at the moment. As soon as it goes back on I am going to record the sound from the cockpit and let you hear it.
Maybe within the week.

Steve.

 

Ok Steve, 75% there
Apart from it sounding better, does it go any better? My car has lasted 30 years with that stuff in there, and even spent some years doing track work at Castle Donnington; Surely this mod is older enough or recognised amongst the racing community?

Cheers
Nick

 

They go remarkably better. Remember, the airfilter is stuffed up against the packing and can only admit air into the airbox through a very small hole. Or in the case of this GT/4, 3 small holes. The rest of the air filter is totally useless. It would be akin to jogging and trying to breath through a straw. I believe the original poster stumbled onto it when he noticed only a small area of his air filter at the throat was getting dirty, the rest of the filter was clean, doing absolutely nothing, because no air was going through it. That alone is a good reason to clean out that crap.

As far as how old the mod is, no one probably knows for sure. All I know is that in over 10 years of being associated with various online Ferrari forums, I never heard of this mod until this thread started, and neither has anyone else. In most racing the stock airbox was usually tossed aside and individual air cleaners were used. Those who did that have always reported significantly better throttle response, and have immediately had to swap jets up richer to keep from backfiring in the exhaust and running lean. I think most have reported around a 10HP or so increase on a dyno with open carbs vs the plugged up airbox? If you go back and read through this thread from the begining, modding these airboxes has required the same kind of jetting changes, so it was obviously highley restrictive as it was, and equal to, and perhaps much more efficient than individual filters with it uncorked and pulling (maybe pressurizing slightly) cold air in from the body side vent.

Which goes back to the begining. If your going to uncork the airbox, plan on rejetting.

 

Does the mod require the removal of the iron bit at the cleaners entrance - the bit with 3 holes?

 

OK Bit the bullet, got out the angle grinder
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This is what happens if you stick a mic in the air intake on the side of the car - enjoy
The 1st one is at tick over, the 2nd, well listen for yourself!
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shall we assume your happy with the mess you made?

But why did you leave the tubes at the other end? You still blocking air flow man, LOL.

 

I think I am happy, if it ever stops raining here, I might get it out on the road!

Oh the holes, they are to stop birds and other small animals being sucked in at speed

Nick

 

I have just been for 21 mile "thrash", and my initial findings are that it certainly revs much free'er than before.. But at what cost! It's so loud, at over a 100 you have to have the windows closed, and on narrow town/village streets it sounds terrifying! I wish there was an airbox muffle switch..

 

you shouldn't be going over a 100 on rarrow twon/villages street anyway, what if some stepped out from a side street???






Manufactures sped a lot of time trying to solve intake noise. Just stuffing up the intake does stop noise, but costs a lot of hp. On ewer cars you'll see all kinds of odd shaped boxes in the inlet path all designed to cancel some noise at some rpm. You might try taking a look at some of the stuff on other cars and then add something similar.

 

Dr. Barry and I have reviewed this, there are two different part numbers...

If you order an early 308GTB box for a 1975-76 fibreglass car, or a Euro version, you get the different one from the fibreglass packed ones we have in our 1977s, I have not yet compared #20405 to my 1977 cars, I will soon..

The visual indicator for the early boxes is the Firing Order metal plate or at least the rivet holes drilled for it, in the cone snorkle.

HTH.

 

I guess you wouldnt care for a 59 pontoon fendered 250 TR then? All 6 of those fat and unfiltered velocity stacks right out there in in the open behind a mesh screen? How terrifying. I think its not that its so loud, its just that we have all become so accustomed to sound proofed cabins and silenced engines. Your now hearing the engine exactly as Enzo had intended, not the government mandated silenced version. Its like removing the gag from lady Liberty. Go put some more miles on the car, I think within a day you will grow to love that sound.

When I was 14 I took the cover off the aircleaner on my Dad's 440 Chrysler and flipped it over upside down. The snorkle on those cars was very restrictive, and more than that, it was really a big silencer. With the cover flipped over, the aircleaner was now open all the way round and it could not only breath, you could hear it, and you could "feel" it, the car had a lot more power. Dad didnt like it at first, he kept putting it back on right. But after we took a trip and he seen over 2 MPG better fuel mileage, well, a few days later Dad had a big fat Cal Custom aircleaner on it.

There are compromises in everything. When guys put individual air filters on the 308's, it was noted the engine recieved much hotter air. But it was also proven the cars made more HP on dynos. So a an unlimited supply of heated air can still make more power than a more restricted amount of cooler air. But it was also noted that the individual air filters are really loud. The gutted airbox is probably the best compromise. Additionally, Russ and others have pointed out dynamic airflow within the airbox, that coupled with increased air pressure from the side vent at speed, may make even more power than having open carbs. Look back at the different designs and work Russ has done, only to end up back to the original. If your really not liking the noise, try carefully painting the inside of the airbox with underbody soundproofing, as well as inside the snorkle, perhaps even placing a piece of insulating material on the floor and roof on the airbox and inside the snorkle. Also make sure they airbox is structuraly sound. If it can twist or flex excessivly, it will resonate off the engine, and carb noise will exacerbate that resonance. You could also try lining the car body intake with thin sheets of insulating material. It probably wouldnt take much to "tone" it down. Just make sure nothing you do could get sucked into the engine.

 

We used to flip the airbox lid on an old Caddy! LOL!

Man, thanks for the memory...he died a long time ago.......

 

it was on a freeway,,, honest officer! who said mph

 

here is what i did to my 308, sounds from the drivers side is very nice now. i had individual air cleaners and dumped them, once the car got hot - it ran like crap.
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Yes it does.
In fact the perforated tubes are connected to the inside baffle and the plate at the entrance.
You have to cut out the entrance plate to be able to get the tubes and all the crap back out through the airbox.
It's made pretty solidly really. Back from that entrance tube, there is a raised rib that the bellows goes over.
I made sure that I retained it, be it that the distance from the end of the entrance tube to the rib is now about 3 or 4 mm less.
Have a small angle grinder and Dremel at hand, take it slow.

I had the same problem with dirt markings on the air filter.
Here's some figures to ponder.

I had my car breathing through 3 x tubes basically jammed straight onto the filter.
The total surface area of these three tubes and hence total usable air filter surface totalled 3,400 square millimetres.
Keeping in mind that the air filter has a "Z" type configuration that increases the actual usable surface area, but for these comparisons it doesn't really matter.
If you can free up the air box and allow access to the full surface of the air filter you go from breathing through 3,400 square millimetres to 43,750!
43,750 is the total surface available from a filter that is approx 35mm high and a circumference of approx 1250mm.
Now if the figures were close you could say it doesn't quite matter.
BUT, the surface area gained is nearly 13 times!
If you wanted to be a purist, sure, the flow around the back of the filter would be more hindered, but hey, the comparison between these two figures is immense.
Added to this are things like the performance of the car is not likley to change quickly over time due to air filter clogging etc.
Go for it I say!
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My tubes pulled straight out without having to touch the end part. I certainly can't see that leaving it in place can do any harm, the combined area of the three holes is larger than the area of carb's chokes, so there should be enough air getting to them.
Any way, seeing the bits that get pushed in the air intake, its probably a good idea to leave some restriction in place,

 

Hi BigTex!
What do you mean lip the airbox lid?

 

He meant "flip" the lid. The older American cars with V-8's had big round flat aircleaner housings with a big lid on top. With the lid in place, not unlike a 308, all incoming air is forced to come through the snorkle. Some cars, even big 440 Chryslers, had snorkle openings so small you could barely get your hand in the end. But some covers could be flipped over, and the wing nut could still be used to tighten it down. Because the lid pressed against and sealed the air filter to the housing, it didnt effect the filter at all, but the outer edge would now sit an inch or two above the lower housing leaving a large area to pull air in from. Just like a lot of aftermarket V-8 air filters are just a top and bottom that leave the whole airfilter surface exposed for better breathing.

But now when you stepped down on that big ol 4 barrel, instead of hearing almost nothing, you now heard this lovely honking sound. I assume the Caddy was simular.

 

can you let us know why you abandoned the dual plenum setup?

There was also mention of venting the airbox to stop pulsing waves being generated or something, and on that note, how does the crankcase breather plumbed into the airbox change the dynamics of the airbox?
I know, so many questions.......