How much power does cold air induction add?

[bvolcko38]

I had problems with a too hot air induction to my Aero-injector. I added a small NACA inlet 3" in front of the air cleaner...problem solved, runs like a bear now. Carb temps dropped 100 degress! Now, if I chose to enclose the air cleaner and utilize ram air, I don't see a problem as long as the fuel tank is vented to the ram air enclosure. The fuel tank and the carb would be seeing the same air pressure. Mixture setting would not change. Just my thoughts.

[racaldwell]

Bill,

I can't say how much power you will gain but it would be an improvement. Probably too small to measure though. For a data point, there is 0.3 inHg decrease in manifold pressure on my RV6 when going from outside ram air to inside the cowling air while at 135 kt.

Rick Caldwell
Xenox 0057

[WesRagle]

Hi Guys,

Look here for a chart of potential ram air gain http://www.luizmonteiro.com/Article_Pitot_Static_Blockages_02.aspx.

Ram air isn't very much at 110 Kts. Only about 1/2 in.hg. The real gain is to be had with the decrease in density altitude by providing cool air.

The reason I asked Jeff earlier "why the concern about ram rise" is because when I built my Sonex I built it with a "closed" cold air induction system. I didn't provide an escape route for the induction air other than through the AeroCarb. I wasn't aware of the possible problems when I did it. I didn't have much ram rise because I took the induction air from a NACA in the side of the cowl, emulating what Tony Spicer had done with his Ellison carb.

The reason I'm interested in this is because I've seen posts from other folks who have implemented cold air induction and they don't seem to be near as impressed with it as I was. And, the only difference is that my system was sealed and their systems were not. I'm just curious, could it be that the induction air is taken in gulps/pulses causing some hot air to to be ingested so they weren't seeing the full effect?

I'm going to say this again, and then I'll go away while the eyes roll:

When I built my AeroVee I built it with 8:1 compression and, like I said, I provided the AeroCarb (at the time) with outside air. I installed the standard 54-44 Sensenich propeller. WOT speed was 150 MPH @ 3750 RPM. Typical solo climb rate was 700 FPM (and it's hot down here). My standard cruise was 135 MPH @ 3500 RPM. Probably not smart but it just felt good there. The only thing I can think of that I did different was installing a sealed/closed cold air induction system.

Edit: Oops, I also used a larger K&N filter.

Wes

[Rynoth]

This is a very interesting conversation, and I'm seriously considering adding a very small naca duct to blow cold air over my air filter.

That said, from my personal experience in the Aerovee Turbo, climb power is entirely limited by CHT. So my question is, would having cooler/more dense induction air result in any sort of difference in CHT? My impression is that if the engine is making more power (with more fuel in the mix) as a result of more dense air intake, it's going to be making more heat. If the cooling airflow over the engine remains the same, would having cooler intake air actually result in lower CHT while making more power? Or for that matter, the same power at a lower CHT?

[sonex1374]

Ryan,

Colder induction air will certainly lower CHTs, and improve detonation margins. This is why turbo intercoolers are so often used. Having said that, if you can get away with not using any of these things and the engine still performs adequately, there's something to be said for a simpler approach. I think blowing a bit of cool air over the air filter would certainly help, and the loss of "full-time partial carb heat" might not be a big deal considering the extra heat the turbo adds to the system.

For me, I think cold air induction is the way to go on an AeroVee. On the Jab, meh... maybe.

Jeff

[NWade]

For those considering a cold air scoop or NACA duct like the one Ryan Roth mentioned:
Remember that if you just add ram air into the lower cowling near the Aeroinjector/carb, you are pressurizing that lower cowling area and likely reducing the pressure drop between the upper and lower plenums - cutting down on the cooling airflow around your engine and past your engine cylinders!

It’s important to keep all of these interrelated systems In mind, and think about how they interact before you jump in to making something that may or may not yield a net improvement.

Take care,

—Noel

[WesRagle]

Hi Guys,

I going to ramble a little bit and maybe add some perspective to what were are talking about here. I'm not an engine guy so these comments will be based just on what I see and think. You guys tell me where I'm wrong.

On my present build I pulled cold air from the front of the cowl with a 2" diameter tube. The cross sectional area of the tube is pi (3.14 sq.in.). So as not to complicate things, lets assume our engines have a 100% volumetric efficiency. For this example I'll use a 4 cylinder engine with a total displacement of 2180 cc.

Since this is a 4 cycle engine there are two intake strokes per revolution. So the total volume of air needed per revolution of the engine is 1090 cc. Converting to cubic inches, 1090 cc = 66.5 cubic inches.

Since my intake has a cross sectional area of 3.14 sq.in., my intake will have to move 66.5/3.14 = 21 inches of air per revolution of the engine. So, if we're climbing out at 3100 RPM that would mean I need 3100 * 21 = 65100 inches per minute of air through the tube. Converting to MPH that is 61 MPH. So, for my induction system the average velocity of air in the intake tube is 61 miles per hour.

Just looking at the way the engine works, the air demand isn't constant. The air demand is directly related to piston velocity. The piston velocity will be maximum when the rod bearing is in the horizontal plane of the crank. I suspect what the demand will look like is a rectified sine wave. That is a series of humps. The peak value of these humps will be approximately square root of 2 times the average or 1.414 * 61 = 86 MPH.

86 MPH through a 2" tube is a lot of air. I don't have a good feel for how effective just directing a little air toward the filter would be, but again, were talking a lot of air here. Even more for the turbo.

Wes

[Msing48]

Wes, that photo is from the 1st or 2nd “Great Southern Sonex Gathering” in Conroe, Texas. I was very much impressed with what a fine job you did building it. I’m sure your Onex will be just as nice if not nicer.

[Rynoth]

For those considering a cold air scoop or NACA duct like the one Ryan Roth mentioned:
Remember that if you just add ram air into the lower cowling near the Aeroinjector/carb, you are pressurizing that lower cowling area and likely reducing the pressure drop between the upper and lower plenums - cutting down on the cooling airflow around your engine and past your engine cylinders!

It’s important to keep all of these interrelated systems In mind, and think about how they interact before you jump in to making something that may or may not yield a net improvement.

Take care,

—Noel

Noel, thanks, that’s definitely on my mind and I’ve ordered the smallest naca duct I could find. This will be an experiment after all, and the nice thing about a fiberglass cowl is it will be easy enough to patch the hole back up if I’m not happy with the results.

The air filter on the turbo is very close to the bottom of the cowl, so I'm thinking a small vent very close to the filter may provide a decent cooling effect without introducing a ton of air to the low pressure side of the baffles. Since it's also not very far from the cowling exit, maybe there will even be a flow-through effect that helps "pull" air out of the cowling, but that's beyond my ability to calculate.

[WesRagle]

Hi Mike,

Wes, that photo is from the 1st or 2nd “Great Southern Sonex Gathering” in Conroe, Texas. I was very much impressed with what a fine job you did building it. I’m sure your Onex will be just as nice if not nicer.

Yep, a long time ago but I remember that day very well. And thanks for the complement but I'm afraid I don't have the patience I had back then. So, the Onex won't be nicer, but I'll bet it flies :-) And thanks for putting on such a great Sonex event.

Oh yea, I almost forgot, thanks for my first flight ever in a Sonex!

All the Best,

Wes