Originally Posted by inimmini

The stock scoop & IC work reasonably well. Various figures have been reported for thermal efficiency of the stock set-up (i.e., [Tin-Tout]/[Tin-Tamb], so that at 100% efficiency the outlet temp = ambient). These range from 55% to 70%, and mostly sit around the low 60's. My own tests have shown 55% to 68%, which is in line with what others have measured.

To do better than stock, paying $500-$800 for a bigger IC seems to be the rule. I could find a thermal efficiency posted for only one after maket IC, the M7 DFIC, at 71%. You can do better than this, for less than $50 and a bit of time! Follow these steps to get a reliable TE of around 80%:

Insulate the IC
That's right - the IC has many surfaces exposed to hot air from the engine, not exposed to cold flowing air. These include the front and back, and the bottom surfaces of the channels (between the fins, facing the engine). I think many of the after market ICs really suffer from heat absorption, especially those that extend back over the spark plugs. I'll go out on a limb and say that the main benefit of the M7 DFIC is relative immunity from engine heat, due to its horizontal orientation. You can do just as well, though, with some insulation on the stock IC.

Here is a pic of my IC with the ends insulated with silicone foam, and the bottom insulated with self-stick woven glass fiber with reflective aluminum (not great for reducing heat conduction, but good for radiant heat transfer).

https://www.northamericanmotoring.co...=&ppuser=16996

I've also insulated the inlet manifold from the radiator hose and the SC exit horn. These are very hot items, and close to the air inlet manifold. Although the IC outlet air temps are not directly affected by the downstream intake manifold, it just seemed like the right thing to do, and very easy as well.

https://www.northamericanmotoring.co...=&ppuser=16996

Make a better IC diverter
The stock diverter, as many have attested, could use some improvements. It doesn't use the air from the right side of the scoop, it has only one fin to divert the air downwards, it leaves gaps on the left and right sides of the IC, as well as a big gap between it and scoop. You could buy the Alta version, or make you own that is probably better. Here is mine. It has 2 fins, and additional foam to prevent leakage. I've left the stock foam "U" in place. As you can see, my diverter extends much farther forward than than stock piece, so it can meet up with the scoop (more this later).

https://www.northamericanmotoring.co...=&ppuser=16996

To get the diverter to mate up well with the scoop, I found I had to remove the two front IC mounting brackets. These hold the diverter up too high, so if extended it runs into the scoop instead of under it. Here is a pic of the IC on the car. If you look closely at the far left side, you can see a black "undermount" bracket I made, so that the IC is at least held on 3 of the 4 corners:
https://www.northamericanmotoring.co...=&ppuser=16996

Open up the stock "mailbox slot", and eliminate the scoop - diverter gap

The stock scoop has two pieces - the outer painted part, and a black plastic inner piece. The bottom section of the inner piece forms an overly narrow slot, and also interferes with extending the diverter forward to eliminate the gap. Cut the bottom of the inner scoop off, like this:

https://www.northamericanmotoring.co...0&ppuser=16996

This probably gives at least 20% more area for flow. Next, glue some rubber strips on the bottom of the painted outer scoop, so they extend over your diverter. Here are the rubber strips I glued on:

https://www.northamericanmotoring.co...0&ppuser=16996

Since the rubber is black, you can't see them from the outside. The scoop looks totally normal. The idea is to have the scoop and the diverter mate up like this drawing tries to show, so that the engine can move back and forth without opening up a gap:

https://www.northamericanmotoring.co...0&ppuser=16996

If you do all this, what do you get?
Here is some data I logged today, under a variety of conditions. I forgot to mention in the table that ambient temp ranged from 60 to 62 F, so I used 61 F for the calcs. The best TEs are found during acceleration, probably because the thermal mass of the IC helps cool the inlet air during these brief periods. Averaging just the cruising values, though, gives 79.9% TE .

https://www.northamericanmotoring.co...0&ppuser=16996

If you do nothing else, take the first step and insulate the IC. I did the diverter/scoop mod first, but adding the insulation makes a noticeable in the seat-of-the-pants, particularly after idling the engine a while.

Also keep in mind, I have no OCC! So there is still room for some small improvement!