Experimental data for Cold air intake

tbitz · 06-22-2002, 07:32 PM

I am in the process of converting my 911SC from CIS to EFI. A couple of days ago I installed the ECU with all the sensors connected to it. The fuel injectors have not been installed yet.

Since the ECU has an air temperature sensor, I decided to take some air temperature readings in the engine bay while driving. All the readings were done on the same highway and all within about 10 minutes of each other.

The first reading was done with the sensor attached to the grill of the deck lid and then the decklid was closed.

While driving at about 120Kph for a couple of minutes the temperature read 80F (27C or 300K).

Next I attached the temperature sensor at the intake of the air box.

Again driving at the same speed, the air temp was 115F!! (46C or 319K). I could not believe the temperature had risen by 35F (19C). I repeated the experiment and got the same results. I also put the air temperature sensor in the air box and was still reading 115F.

The increase in temperature results in a 6% reduction in air density and thus a 6% loss of horsepower.

A cold air intake seems like a great idea here.

masraum · 06-22-2002, 10:46 PM

excellent data, that's good info for the SC guys. Now someone needs to do it for the 3.2's

dean · 06-23-2002, 03:45 AM

Please keep us posted on the EFI conversion. I would love to get rid of that crappy CIS. What sys are you going to run?
Good luck

tbitz · 06-23-2002, 06:01 AM

Guys,

It would be nice to get more experimental data on this from other vehicles.

It is simple to do. Go out to Walmart and pick up a digital thermometer (they are about $5-$10) like the one below:

Place it at the positions I show above and report your data. Make sure the sensor is not making contact on any surface. We only want to measure the temperature of the air not any metal/plastic surface.

Take a picture of your setup and report your data in this thread.

Blown, you can follow my CIS-to-EFI progress here:http://www.geocities.com/tbitz/cis_to_efi.html

RarlyL8 · RarlyL8's Garage

And you all thought Ram-Air was an urban myth:

pwd72s · 06-23-2002, 08:55 PM

For years, no make that decades...the hot rod set has known that the cooler the intake air the more horsepower, all other things equal. Heck, even my wife's lowly '99 Ford Ranger has a stock intake system that gets the original air from outside, not the warmed up underhood air....

island911 · 06-23-2002, 09:11 PM

If you want to have better confidence in the temperature of the intake air, move the sensor in to the airbox. I'm just guessing it's picking up some radiant heat at the sensor . . .radiant heat goes right thru air, without significatly absorbtion.

fwiw, some v8 guys would dump ice on their intake manifold to keep the intake air dense. . .for a 1/4mile.

widebody911 · widebody911's Garage

This solution worked well with the Big A$$ Wing:

And the one I built for Jack

Jack Olsen · 06-23-2002, 09:47 PM

There's a $190 version selling on ebay.

And then, as you can see above, there's Pelicanite Thom Fitzpatrick's
hand-crafted 'Sheißflau' model.

tbitz · 06:35 AM

island911,

The picture above shows the sensor infront of the snorkel intake, but I also tossed the sensor in the airbox and got the same results.

This morning I decided to use my Walmart temperature sensor (pictured above). The ambient air temperature was ~64F. I taped the sensor so it hangs in the middle of the air intake hole. After driving on the highway for 20mins the temperature was indicating 96F. This is a 32F difference!

On my way back home tonight. I will throw the walmart sensor in the air box and try again. I will set it up so that the sensor is not touching the plastic cover. I only want to measure the air temp.

I am starting to think that due to the rear 911 body style a low pressure is created near the grill on the decklid. This results in air being sucked out (instead of into) the engine bay. Since the engine needs air to breath it is taking it from below the engine, where it gets 'pre-heated' by the muffler. Just a though.

It would be nice if someone else tried this. The walmart temperature sensors are cheap ($10).

wckrause · wckrause's Garage

Tbitz -- Do you have any holes or gaps in your engine sheet metal, or gaskets?

It would be interesting to measure air pressure within the engine bay, within the airbox, and near the grill. You've got to measure temp and pressure to determine air density.

tbitz · 06-24-2002, 07:18 AM

Wckrause,

When I had the engine out this winter to rebuild my transmission, I fixed up all the rusted sheet metal. There is a hole (2.5" dia) on the left side of the rear sheet metal which I am not sure what it was for. Maybe the pipes from the EGR passed through it? I don't have EGR anymore. I have plugged this hole with some aluminium tape.

My fuel injection ECU (Megasquirt) is a "pressure density" system, so it has a pressure sensor built in. I will place the sensing tube at various locations in the engine bay and gather some data. The ECU plugs directly into my laptop so I can get real-time data as I drive. When gathing the data I will try and keep the conditions the same (speed, rpm, etc...).

dickster · 06-24-2002, 07:27 AM

sports bikes have been using ram air for years-but it only works at higher speeds.

although, i guess with the temp being alot lower you could get the benefit of both lower temps (at low speeds) and ram air for higher speeds.

how about a scoop under the car? like the brake cooling ducts.

david c. · 06-24-2002, 08:39 AM

I know this might be called blasphemous, and it would break up the lines of the rear of the car, but why not a little naca style duct under the rear quarter window(s) with air hos(es) to the intake/airbox/CIS box or what have you?

I have a dent in my quarter panel on the pass side in an area that would require repainting where such a duct would fit. I've been (very informally) thinking about having something like that installed when I get the dent fixed.

David

thrown_hammer · 06-24-2002, 08:50 AM

I have thought about using the ducts on my rear fenders to duct air to the airbox(drivers side) and oil tank.(pass. side)

tshih · tshih's Garage

All this talk of cooler air (via ducts and scoops which channels cooler air into the intake snorkel) is fine but don't forget the dreaded water swallowing problems of the earlier 944 series which destroyed many engines by ingesting water from an intake scoop too low to the ground (where air was cooler!, and deep puddles during rainstorms flooded). Design is a carefully thought out solution to a technical challenge.

Last note, did the 1979 SC have an air conditioner condenser mounted under the rear decklid?

I've also seen some race cars like the GT1 with the top of the roof scoop or the Tiger striped 911 GTS race car of Bodymotion (NJ race shop Porsche-repair shop) that ram charged air for the intake.

Tom

Bill Verburg · Bill Verburg's Garage

Heres another nice way to duct cool air to the intakes, from a friends RSR;

911pcars · 06-24-2002, 11:53 AM

On many race cars (couldn't tell in your pic, Bill), each air intake hose connects to a NACA duct attached to the rear quarter window "glass" (usually lexan). Putting ducts in the bodywork is pretty radical for a street car and usually against race regs. (depending on the race org.).

Water ingestion is always an issue, moreso if the air intake faces toward the heavens or is low next to puddles and other water sources.

Sherwood Lee
http://members.rennlist.org/911pcars

Bill Verburg · Bill Verburg's Garage

Yup, there's a NACA duct and a lexan dam in each quarter window. The car is new to him this year, havn't heard what's done in rain.

Bill Verburg · Bill Verburg's Garage

Here's a pic of the engine compartment, looks like there is no issue that all the other cars with that sort of air cleaner setup won't have