Cowl Induction

[Mkelcy]

I’ve been wanting to do a cowl-hood-to-carburetor-seal for a while now because I was tired of the cowl “cold” air intakes for the kick panel vents ducting hot engine compartment air into the interior of the car. As a potential side benefit I also wanted to get cold air into the engine, rather than the hot air under the hood. I finally (with inspiration from CarlC’s site) got off my butt to do something about it.

I went the 3” by 16” cake pan and “bulb seal” route suggested on Carl’s site. I purchased two cake pans from a local baking supply store and carefully cut a 5” hole in the center of one of the pans with a 5” hole saw from McMaster Carr (and my drill press) and dropped it over the carburetor, only to realize that there are things on the carb that stick up over the air cleaner mating surface (e.g., the accelerator pump linkage), so the cake pan would need to be raised a bit.

I back went into the McMaster Carr catalog and found a “Steel Angle Ring, With 6 Holes, 5" Duct Diameter, 9/32" Hole.” I used nibblers to enlarge the hole in the cake pan by about 0.125” and then slid the “angle ring” in and bolted it up, using the ring itself as a template to drill the holes in the cake pan. The cake pan and angle ring fit over the carb perfectly and cleared everything on the carb nicely.

At about this time I discovered that the carb is not centered under the cutout in the cowl hood but (on my car) was a bit back and to the left. The 3” cake pan was also too tall, but I wanted to get it centered in the cowl cutout before cutting it down for height. I grabbed the second 3” by 16” cake pan (purchased for just such an eventuality) and, using my best guesstimate of the offset, drilled another hole, nibbled it out for the angle ring, drilled the mounting holes and slapped it on the carb. On this trial it looked okay for offset, but the cake pan needed to be cut down about an inch. I used my plasma cutter to cut the cake pan (I held the cutting head upside down on a piece of wood and moved the cake pan past the cutter) and then mounted the “Push-On Edge-Trim Rubber Seal” from McMaster Carr on the cake pan. The bulb seal allows for some error on the height of the cake pan while still getting a good seal on the hood.

Voila! Right height, nice seal to the hood, but because of the offset my 14” air cleaner no longer fit. Right now I have about 6” from the center of the carb to the back of the pan. The cheapest air filter I found that would fit was a 10” Edelbrock air cleaner I ordered from Summit. I got the 10” air cleaner, put it on and drove the car a bit a few days ago.

The cowl hood works just as I hoped. My kick panel vents now give me outside temperature air, rather than engine pre-heated air. I can’t say whether engine performance has improved, but my guess is that it likes denser, cooler air better than hot under hood air. I’m not happy with the 10” air cleaner. It’s only 2” high and seems like it could restrict air flow a bit. I can go either of two ways. K&N makes a 10” diameter, 3.75” high filter, which I could use; there’s plenty of room under the hood for it on my small block, but I like tossing a dirty paper filter element rather than cleaning a reusable filter. So instead, I’ve ordered two 18” diameter, 2” high cake pans to redo the intake with a larger diameter pan that will allow for a full 14” filter. If the 2” cake pan is the right height, I’ll also have to use a different bulb seal to fit over the rolled edge of the cake pan, but McMaster Carr has that covered too.

A few caveats: I wouldn’t want to use the 5” hole saw in a hand held power drill. It’s a big, heavy bit (particularly with the “driving plate”) and things could get pretty exciting if bit and cake pan got out of control. The “driving plate" is optional if one wanted to save some money. You could also simply scribe a circle on a cake pan and nibble out the hole, since I had to nibble the hole out anyway to get clearance for the “Angle Ring.” My drill press has only an 8” reach, so I’ll still have to drill the 18” cake pan off center. Even drilled offset, it should still easily accommodate a 14” filter. The cowl hood has enough of a flat area at the front of the cowl induction opening to accommodate the offset.

List of parts from McMaster Carr:

4066A63 ARBOR FOR 1-1/4" - 6" SAWS, 7/16"DIA, HEX $8.98
4066A83 DRIVING PLATE FOR SAW SIZES 4-1/4" THRU 6" $15.33
4066A72 HIGH-SPEED HOLE SAW, 5" DIAMETER $24.10
1120A562 PUSH-ON EDGE-TRIM, 1/16" EDGE, 3/4" BULB WIDTH 5FT $8.75
1120A432 PUSH-ON EDGE-TRIM, 1/4" EDGE, 5/8" BULB WIDTH 5FT $7.25
1764K43 STEEL ANGLE RING, 5" DUCT DIAMETER, 9/32" HOLE $3.90


A couple of pictures: