PHOTO OF 2.0L FI MOTOR READY FOR DYNO

[sptcoupe]

The TB's on the engine fit onto the manifold (which is made for IDFs) with very little modification necessary - just some porting to ensure a perfect match between the manifold and the TB's to ensure max airflow. The TB's actually look a lot like IDFs, but this box was custom built for this application. When I get to my other computer I will try to post some pics of other air box/indcution systems I have used with IDFs.

[nettxtra]

Thank you

Wher is it possible to buy these boxes?

[azygoustoyou]

How much gain will you get if you were only breathing the cool air compared to the air circulating the engine?

[sptcoupe]

Here are some photos of two other air boxes I did:





I have always thought that the after market airboxes are restrictive to one degree or the other, and have experimented with different designs to try to find one that breathed well, and also quieted down the wonderful wail of those IDFs, only so my wife would take long rides with me.

About 15 years ago I had a full house 1800 on a dyno and tried on/off runs with the Bayless lunch box filters, and the RamFlo, foam element filters. The engine made about 130 HP at the wheels with no box. With the Bayless air filters, it lost about 4 HP, and with the RamFlos, it lost about 7! In both cases, I was losing about as much as I might have gained with the IDFs, so I've been screwing around with different box designs since then looking for the solution to air flow and reduced noise.

I built the black box with the plexi top to see how the airflow would move around the horns with the air coming in from the front of the box, like many standard applications. I simply put a firecracker "snake" (they make lots of smoke) in a mason jar with holes punched in the lid, and held it in front of the inlet and watched the air flow through the plexi top. I wasn't surprised to see that the #1 and # 4 seemed to get less air, because I had noticed that those plugs were indicating a little bit of a rich mixture. The air seemed to simply run around the # 1, and curled nicely up and into the # 2 & 3, but there didn't seem to be as much "smoky air" getting to #4. Of course, it could be that my high dollar smoke generator simply wasn't putting out enough smoke, too. But, when I ran the car with no box, the plugs were a nice even chocolate brown again. That box actually seemed to work real well (I think I stiil have it somehwere), but I could feel the difference with it on and off. That box had about 36mm over the horns.

But that high-tech experiment drove me to try the design that mimics the FI system on later spiders, where the air is brought into the box from the side, and funneled to each air horn by baffling. That box also allowed a full 42mm above the air horns, which allows the air column to really develop well. I was finishing the box up at a shop which had a dyno, and they let me do two quick runs. This engine did 134.2 with no box, and 132.9 with the box (that's a K&N filter on there). This was with no adjustments to jets or mixture or timing or anything else. I am convinced that with some dyno time, that difference would have been under one HP. That system was sold with the motor. But without doubt, that is the best box I have had on the car, and there have been at least 10 over the years.

The box on the engine now has not proven to work yet - about a 10 HP loss with it on. We'll see what happens when we get the shorter horns on there and get it on the dyno. The air on this design comes in through an enormous 3 1/4" hole that runs all the way to the back of the box, with the idea that gobs of air will get to all the bores. But, it has to be sucked up from below the horns and make a turn to get over the top of the horns, and there is no way that can happen with the mere 13mm or so the shop left me after making the horns too long. We'll post the results when we get it out of the paint shop and back on the dyno. If we have some time, we'll experiment with taking the air from in front of the radiator, and then from inside the engine bay.

[manoa matt]

Very interesting and informative write up. You answered several questions I had and some I didn't think of yet. I'll be installing some dual carbs soon and also wanted to make my own air box.

I too thought about how the placement of inlet air hole in relation to the horns/venturies would affect the flow to the 4 horns. My first thought was similar to your current design where the air enters from the front near #1 something similar to these designs:

http://www.flickr.com/photos/bigtimes_fiat/4120543625/

http://www.flickr.com/photos/bigtimes_fiat/4120543627/

http://www.flickr.com/photos/bigtimes_fiat/4120543619/

Ducting would go to the hole in the rad panel with a free flow air cleaner mounted in the grill area, like this: http://www.flickr.com/photos/bigtimes_fiat/4120543611/


I didn't like this design because I figured all the air would be sucked up by #1 and #2 with very minimal air reaching #4. Baffeling in the air box could/would help distribute the air more evenly. The other problem is it frequently rains here in Hawaii and with the air cleaner in the grill area it could get water logged and reduce the flow, or let water get sucked into the engine.

My next thought was to bring air in from the front, but also bring it in from the side (like the FI phlenum) With this design I would have a large air box with an oval filter similar to the turtle back version, but free flowing. There would be two hoses that reach around to each side of the rad effectively letting in twice as much air.

I think you'll find the best flow rates will come from a setup where the filter is in the middle or near the carbs. With the filter at the start of the induction pipe the air has to make it through the filter before it can pick up speed. A funnel like shape at the beginning of the pipe if placed in the grill area would help greatly at highway speeds and if the funnel was properly designed should increase the venturi effect and increase the velocity of the air as it travels down the pipe even when the car is stationary.

Let me know if you have any "old designs" that you want to sell. matt.scarton@gmail.com

[azygoustoyou]

Hi Matt,
Cool carbon fiber covers. Where did you get them?

[sptcoupe]

We actually started with exactly that carbon box. I seemed like it was tall enough, but that single inlet in the front had me worried, so we sent it back. It also didn't seem like it would reduce noise very much.

The turtle backs had baffled tubes that ran all the way back. I think the idea was to get the air to the #2 carb horns, as well as settle the air. They just always seemed to low for me. I did try to improve air flow by using just a small piece of hi-flow element in front of the two inlet holes, on the inside of the airbox. I also tried to run two lunch box filters inside a turtleback (see photo below, from about ten years ago) in an attempt to get more air in the box by eliminating the paper element filter altogether. But they did not give enough clearanec over the horns, even though I had the turleback mounted on an 8mm spacer to increase the room opver the filters. But even that didn't work as well as I had hoped, and I never did feel the turtleback gave me max breathing.

[mdrburchette]

Okay, I've got a silly question. I would think having the filter material further away, such as right at the opening of your box would be more beneficial since the air would have more time to recoup from the flow interruption vs having the little filter assemblies right on the top the horns where air interruption is certain, right? I wonder if you could feed air to each horn better if you had two necks from the box. One on the left side to the front of the car that could feed #3 and #4 and one from the right side feeding #1 and #2. It sure would be an ugly looking thing though.

[azygoustoyou]

If you had two. You would want them to be of equal length to have the same amount of air in each.

[mdrburchette]

Yes, you'd have to consider that or gain volume by making one a little wider.

[engineerted]

Matt, Where did you get the airbox_carbon_back? third photo

Ted

[manoa matt]

Here is the website : http://www.twminduction.com/Home/Home-FR.html

Click on the "air boxes" tab. $295 for that piece of plastic. I saved the picture because I was going to make one out of fiberglass.