How To Fab a Cold Air Intake from the Fog Lamp Hole
This mod is a cold air intake fabbed to the S&B airbox on an '06. Your truck may be different but many of the procedures should be similar. This will interest those with "nothing else to do” or those who think many small improvements will pay off.
Air boxes like the S&B draw air from the stock fender location plus a large hole in the bottom of the box. This hole allows warm engine compartment air in which is less dense than outside air. Not good. Dense means more oxygen content which is good. A fog lamp was sacrificed for the cold air intake duct. The goal was not to create a “ram air” intake, although this mod will no doubt pressurize the air box a little.
The standard, late model S&B
View of the hole from below. It's larger than the fender intake so any improvement made here should pay off nicely. The charge air tube runs right by it with 300-400 degree air in it sometimes. That's it at the bottom of the photo. And the radiator is directing hot air into the area.
Since we need a stiff pipe with a flange for attaching to the box, we used an air vent designed for clothes dryers and kitchen vent hoods. A common hardware store item with a 4 inch pipe. We will cut the hood off leaving just a simple flange.
This very “cool” flexible aluminum ducting will run to the fog lamp hole. When bent the segments expand. In this project it was cut to 16 inches long.
Lamp and hole are somewhat oval but the duct tube will bend into shape. The opening is cone-shaped, which is good as you will see.
The idea is to glue a rubber piece like a grommet onto the end so when the tube is inserted from the front and pulled up to the air box it’s tight enough to pull the rubber into the cone-shaped hole where it seals the gap and stays put. http://i160.photobucket.com/albums/t...odgeCAI009.jpg
We spotted a Trucklite lamp mounting grommet at a truck parts department that was about the right size. Had to trim the ID with a razor to fit over the duct. Easy. Glue it to tube with silicone adhesive.
Another way to do it would be to slit the length of a 3/8 inch OD rubber hose and push it onto the edge of the duct, and glue into place. This would be smaller and allow it to sit deeper in the lamp hole than what we used which might be important if you want to hide it behind one of those louvered things that come on some Dodges.
Remove the inner fender so you have room to work. This is also the easy way to service your oil filter
Oops, the duct hits a plastic deflector. Need to cut it up a ways.
The deflector is part of a big molded piece that includes the fender air intake piece. It’s held on by big plastic buttons that can be pried up, but you’ll find that the A/C line blocks removal of this unit.
Screw it - we’ll cut it in place! A saber saw or Sawzall is perfect for this but loosen the bottom of the deflector so you can pull it rearward as you cut, so the blade doesn’t hit something expensive.
The finished cut, round to match the duct tube. The deflector will help support the duct as it bends around it.
This is about the right amount to remove.
If the duct is tight and not too long (about 16 inches in this case) the front will stay secure in the fog lamp hole.
View of duct from above
After un-riveting and cutting the hood sheet metal off the vent, it left a flat flange that can be trimmed to fit the bottom of the air box and screwed on. We left the air box in the truck for this step because it was nice and secure while we were forcing the sheet metal past the air filter mounting flange on the S&B. This was the trickiest step because you have to make sure the sheet metal lays down under the filter flange with enough clearance so the filter can slide on.
View from below. If you use a dryer vent like this, leave it full length because the end of the tube has a reduced diameter that will allow the duct to slide on.
The dryer vent came with a screen so we trimmed it to size and pressed it into the bottom of the air box. You can screw it down if you like. This will keep birds and rodents out.
The assembled CAI
View from underneath with inner fender installed. Nice and cozy.
Finished duct in fog lamp hole. We are going to try it like this and probably use a pre-filter. Might add a Dodge louvered whatever-you-call-it if this tends to pull in too much stuff. Since the box also breathes through the fender there shouldn't be much suction as if this was the only opening.
“Cool,” sure, but did it help? We decided to measure the air temperature between the filter and turbo with the unit installed, and then with the flex duct removed and pulled down from the pipe. This is where further testing is recommended, because it would be better to remove the sheet metal and test like a standard S&B unit with the big hole in the bottom. The installed duct pipe breathes from a place below the charge pipe and we're thinking it might be cooler air down there even without the flex duct attached. We didn’t do it this way because complete disassembly would have taken too much time and the afternoon was cooling off.
This is our BBQ thermometer with probe, sender, plus a wireless receiver that will sit in the truck
A hole was drilled in the S&B for the probe right after where the two halves fit together. A towel was stuffed in to catch the plastic chips, but the chip came out on the drill bit. This hole will end up taped and the big strap that secures a sensor wire wire will slide over and conceal it.
Being anal we insulated the exposed end of the probe with aluminum foil because that’s how we do it in the BBQ. The sender was taped to a safe spot and the wire was kept away from the battery terminals.
After a flat freeway approach we went up the Waldo Grade at 60 mph heading for the Golden Gate Bridge. We thought building some heat would be good but the CTD wasn't working too hard (as usual!!!). Made two runs with the setup connected. 60 degrees to start, which was about the ambient outside air temp, and noted 57 and 56 at the top of the hill, reflecting the ambient air decrease of 3 degrees as the elevation increased, as noted on the Dodge thermometer.
Stopped to unhook the duct from the tube. The intake temp went up to 82 because it was now drawing some air from the engine compartment while motionless. Then I noticed when driving back to the freeway that twice the intake temp changed 5 to 6 degrees very fast. Probably the thermostat was cycling and the radiator was dumping heat. Or not. At that point we decided to take a long freeway approach to the test to let things equalize.
Despite the ambient air dropping a degree or two by then, the intake temp rose to an average of 62, and at the top of the hill it was 64, which was 7 to 8 degrees warmer than with the CAI assembled.
So it supplies cooler air to the turbo. The definitive test however would be with a more toasty engine compartment. EGT never went above 950 on the hill and the water temp barely changed. Not a long enough hill for serious engine heat soak either. No doubt the gap in intake temps would be greater with a heavy trailer and/or the fuel on kill which it wasn’t. And if the S&B box is tested unmodified it will probably be drawing a higher percentage of hot air than it did with the 4” pipe sticking down below the charge tube.
We have driven in the rain with no troubles yet, but not through big puddles and not down any farm roads in the hay harvest season if you know what I mean.
Hope this helps someone.
Foul weather status report - no problems in the big rain we've been having. Hit some big puddles and had water come over the windshield too.
Update - I put the fog lamp back in so it wouldn't draw attention during my smog test. Left the duct behind the bumper. I'll leave it that way because the air will be about as cool and I don't think the ram effect is very important.
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