Air Box Replacement

Everybody knows that the C5 (and most cars) can use some help in the breathing department. Forced to breathe through four small holes, the engine doesn't get nearly all the air it can use. There are many ways to solve this problem. A fair number of people just cut holes in their air box cover or clamp a conical K&N filter right to the MAF. Another popular option are the many aftermarket products available. There are two basic types, engine compartment feeders (like the TwinFlow, LS6/TPIS/Donaldson) and bottom feeders (such as the ProFlow+, Vortex and MTI). The engine compartment feeders take air from the front portion of the engine bay via some type of expanded filter system. This air is usually very warm from the engine and is mostly stagnant. The bottom feeders pull air through a hole cut in the radiator shroud. This type draws fresh, pressurized air from beneath the car. Drawing air from beneath the car is the best way to go. The area is pressurized by design to force air over the radiator.

With all this in mind, I ordered the MTI Performance Air Box because it look to be the best, most professional design. One of my requirements was that the system use a K&N filter and not some unknown "wonder" filter. I placed my order with MTI in February and finally received the air box at the end of April. I was immediately shocked by the fit and finish of the product. All the components were modified Chevrolet parts with the exception of MTI's new filter cover. The modified Chevrolet parts looked like someone did the work in their garage with a hacksaw. The hole in the shroud was very rough and irregular. The air filter fits in the stock Chevrolet bracket that has been poorly riveted to the shroud (and had the original air box clamp area hacked off). The MTI cover is simply a piece of hard plastic that is a virtual copy of the bottom component of the stock air box. It fits poorly over the air filter bracket with considerable gaps. The whole thing sits so far forward in the engine compartment that you have to cram the cover past the front crossmember. This causes the shroud to bow and create further gaps. To top it all off, the air outlet tube built into the MTI cover tapers along it's entire length. This means that no mater how hard you crank down the hose clamps, the hose still wants to slip off. The whole assembly is a bit too long and prevents the stock air tube from snapping into it's mounts. If you force it down, the MTI cover slides off the frame creating more leaks. The instructions are also terrible. They skip many steps and forget to mention several electrical connections and fasteners. Needless to say, I was not pleased. Since I already had the system installed, I went out for a test drive. I noticed a seat of the pants difference from the stock setup. Three 0-60 runs with the G-Tech/Pro yielded an average of 5.34 seconds. This is better than my stock testing which had an average of 5.48 seconds (and had one bad run). This increase cannot be totally attributed to the air box change. I'm getting better and launching the car and 0-60 isn't all that great of a benchmark. I sent the MTI unit back for a full refund and took a closer look at the stock air box components.

Since the MTI system used so many stock components, I figured a lot could be done by taking a close look at what I already had. Cutting holes in the stock air box would work but it's not ideal. My first thought was to turn the filter cover and frame over, cut a hole in the shroud, and mount the whole works up. This would essentially duplicate the MTI system. This is harder than it seems. The angle of the air outlet tube on the stock cover doesn't allow it to sit flush with the shroud. Since it's a rubber hose, an extension would have to be rigid on one side and flexible on the other to mate with the MAF. I'm still looking into this idea. I next decided to just leave off the stock air box cover. I clipped the filter frame and cover together and then hooked the whole thing up just like stock. Since I was testing and didn't want to drill a mounting hole in the filter cover and shroud, I just used two short burgee cords (no laughs please) to secure the filter assembly against lateral motion. Testing 0-60 times with configuration yielded an even better 5.21 second time. Again, this really can't be taken as a true benchmark. I don't see why the times would get better drawing air from the engine compartment rather than from below the car. It's most likely I just launched better.

I'm going to test this configuration for a while before I make my next move. A bottom feeder is still most attractive and I may yet go with the ProFlow+ if I can't create something that works well on my own.

During this whole ordeal I also removed my MAF screen. In hindsight, since I ended up replacing the MAF body later, I wouldn't have done this. If you want to remove it anyway, it's pretty easy. To remove the screen I disassembled the MAF by removing the four torx screws. Be very careful not to touch the wires inside the MAF itself. I banged out the filter with a screwdriver and a rubber grommet. It's pretty much impossible to do this without damaging the screen. Be sure to remove all debris before reassembling the MAF.

Please see the Pro Flow+ installation for the happy conclusion to this saga.

Air Box Installation Images


The installed MTI air box on the left and my modified stock air box on the right


The MTI rig (with poorly made cover) and a view of my modified stock air box and filter


The disassembled MAF and the MAF inlet with screen removed

Common Air Box Replacments


The bottom feeders: ProFlow+, Vortex Rammer and two views of the MTI


The engine bay feeders: TwinFlow and TPIS/LS6/Donaldson


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