Experimental data for Cold air intake

[emcon5]

Originally posted by tbitz

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.

I don't think this should happen to any significant amount if your engine sheetmetal is intact. Keep in mind that the fan moves an ungodly volume of air in through the grille and out through the cylinder fins/oil cooler/heat exchangers, and right in the middle of the path of that air is the intake horn where you took your measurements.

Originally posted by dave cardone
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.

I remember reading about the intercooler intake Naca ducts on the Ruf Yellowbird ended up working exactly the opposite of how they expected. The low pressure at that part of the car ended up sucking air out of the ducts instead of pushing it in. because of this, the ducts were dropped on the production CTR's. Anyone else remember hearing about this?

Tom

[david c.]

I guess that's why RUF is RUF and I have a 912E! My car runs a little hot in the summer, not all the time, but once in a while. I thought this might be an interesting idea.

My engine bay has a TON of room, and I just removed the heat exchangers in favor of a custom header for a 912E that should be at my house this week. I think I'll take a look tonight to see if there's some way to route air from the front of my car to the back. I have the a/c removed anyway, so I imagine there's space somewhere...

For a track only car,the lexan windows with the ducting seems a lot more feasible. Obviously this would not be a likely choice for a street car.

I don't think I would actually do the fender/window ducting unless/until I build a track only car. That dent has been in my car for two years. Who knows when I'll get it fixed.

I've heard of vaporlock/water problems with the cold air intakes on Honda/Acuras and I wouldn't want to be afraid to drive my car in wet weather!

David

[Superman]

I can only guess that hotter air is coming up from below the engine. I cannot imagine any other way the air can be hotter at the intake than at the grille. In fact, nearly all intake parts tend to stay at outside air temp because of the huge volume of incoming air. Once the engine is shut off, then heat rises into these parts, of course. But otherwise, the air horn should be the same temperature as the tie rods.

I am also curious about the ram air idea. At 6000 rpm my engine cooling fan moves 1500 liters of air per second. No kidding. This must be creating a substantial vacuum, in the same compartment where the engine is trying to draw breath. The engine operates in a vacuum. It's an Anti-Turbo.

[ChrisBennet]

Originally posted by emcon5

I remember reading about the intercooler intake Naca ducts on the Ruf Yellowbird ended up working exactly the opposite of how they expected. The low pressure at that part of the car ended up sucking air out of the ducts instead of pushing it in. because of this, the ducts were dropped on the production CTR's. Anyone else remember hearing about this?

Tom

Tom,
At the Zone 1 Tech Tactics a couple of years ago, Alois Ruf was one of the speakers and he mentioned it.
-Chris

[911pcars]

Bill,
I wonder if the NACA-ducted cool air offsets the hot air coming up from his shroudless engine compartment? I would think he would get better results putting the factory sheet metal back in, then he could make some special air filter housings to receive the ducted air directly.

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

[Vipergrün]

Hmmm, wonder what the affect would be if one were to reverse the air filter cover, having the intake at the passenger side of the car. You'd have to cut the intake a couple of inches to clear the lid hinge, but at least it would be out of the way of the vacuum Superman mentioned.

cheers
-Brad
80SC

[thrown_hammer]

Last night I made a box that I attached to the grill on the inside my tail. I then cut a hole in the bottom of the box. I have a small 4"X4" 12V fan that fits in the box. I attached a short peice of dryer vent hose to the box and CIS snorkel.
The dimensions were not quite right, the hose was in a bind when I shut the decklid but I think with a little time and some brainstorming I may have something here. The idea is to "suck" in the cooler air with the fan and duct it into the airbox.
What do you think? Am I wasting my time?

[911nut]

The thing that we have to remember is that the engine is an air pump. The induction system is going to draw in air from the grill area - high or low pressure.

[tshih]

tbitz,
I re-read your original posting on how you measured the temperature at various parts of the engine bay while driving it at the same speed. However it's not clear exactly how you were making the measurements. Did you try getting an instantaneous read of the temperature by having the thermometer readout on your dash while the car was in motion or were the reading of the temperature obtained after you stopped the car and open the engine lid? The former case presents a mystery unless air was indeed coming up from the ground openings and venting out the lid to mix with the cooler outside air. The latter case is explainable by the fact that the digital readouts are telling you the warmed up temperature (115 deg F) of the inside area of the engine compartment including the air intake duct .

[tbitz]

On my way into work this morning I got some more temperature data. I used my Walmart temperature sensor. The airfilter was removed and the sensor was placed in the airbox (between the airfilter and fuel metering plate). The sensor is in the airstream and is not touching and plastic parts of the airbox.



The ambient (outside the car) air temperature was 72F. After running on the H/W at 110Kph for about 15min the temperature at the sensor was 96F. The difference is 24F. This is less than the 35F difference I saw earlier, but maybe I did not let the engine get really hot. I will run the same test on the way back home tonight.

tshih, All temperature readings are done while the car is moving. I have a digital display in the car that tells me the sensors temperature.

Thrown_hammer, If you do any experimenting, you need to pickup a temperature sensor to see if your mod is helping reduce the intake air temperatures.

[tshih]

Tbitz,

I think the difference of 30 deg F in air temperature does not translate as much in terms of density (of air) and the effect on horsepower generation by a normally aspirated 911 engine is small to insignificant. I am basing this comment on the known effect of higher altitude driving (like in Denver, Co) where air is thinner (less dense) robbing power from normally aspirated cars versus turbo or supercharged motors.

The 911 engine and CIS or later DME were designed to meet emissions and optimise consumption (efficiency). The power generation happens to go hand in hand with these two other factors.....the more efficient motor is usually the more powerful one and gets the most energy out of the fuel and oxygen (20% of air) combination that the design of engine permits (the valve overlap, cam-grind, spark timing, and air flow to achieve the perfect 14:1 ratio of air:fuel during operation). Most after market chips mess with the distribution of maps to skew higher peak power in favor over drivability and emissions and legal issues.

tshih

[Chuck Moreland]

Cool stuff!

Given the amount of air being moved by the fan I am really surprised at the temp increase you are reading. A couple of thoughts:

1) Just to confirm, you are taking the readings while the car is moving?

2) The fan moves less air at highway speeds (say 3000 rpm) than the quote 1500 liters at readline. It would be interesting to see your tests repeated while driving the car at the same speed but 5500-6000 rpm.

3) I am suspicious that the temperature probe is being influenced by radiant heat from the surroundings and thereby giving a false measure of the air temperature. You could fabricate a little shield to wrap around the probe to protect against radiant affects while still allowing airflow to reach the probe.

I do recall reading someplace about a guy who carefully fabricated a cool air / ram air scoop. The author was dissapointed when after all his hard work the car showed no increase on the dyno. I just can't remember the source.

[wckrause]

tbitz --

Here are some links you may find usefull.

Dyno correction factor and relative HP
http://rshelq.home.sprynet.com/cf.htm

On-line calculator to determine relative effects of pressure and temperature on HP.

http://rshelq.home.sprynet.com/calc_hp_dp.htm

I hadn't realized how much of an effect humidity has on hp.

[tbitz]

Chuck,

1) Yes all readings are taken while the car is moving.

2) I tried this on the way home tonight ambient air temp was 81F. Driving at 120Kph in 5th at about 3500rpm intake air temp was 111F. I then shift to 3rd doing same speed and about 5000rpm, after a minute the temp went UP to 113F. After shifting back to fifth the temp went back down to 111F. So it looks like more rpm mean higher intake air temperatures.

3) Look at the picture above on how the sensor is mounted. The sensor is IN the airbox and is not touching anything. Unless the plastic is re-radiating heat (which I doubt very much) I think the temperatures I am measuring are that of the air.

[tbitz]

OK,

I've fabricated a quick cold air intake using aluminium dryer hose. I know it is not a practical solution as it points up and thus rain will go straight in the intake, but I just want to see if the air temperatures drop. The sensor is still in the airbox as pictured above.

On my way to work tomorrow morning I'll see if this helps (Let's hope it doesn't rain tomorrow).

Here are some pics of my 5 minute cold air intake. This is kind of a diversion for me as when my CIS-to-EFI project is complete the intake path will be very different.

[JMPRO]

Here is the answer, Cool Collar to the rescue

[Vipergrün]

Originally posted by JMPRO
Here is the answer, Cool Collar to the rescue

Bwaaaahaahahahahahahaha. Just about pee'd my pants on that one Too funny


-B
80SC

[tshih]

tbitz,

your experiment with higher rpm running and 3 degrees "higher intake air temperature" is totally indicative of increased engine bay temp since the engine oil temp is increasing at higher rpm running. This is more to support the theory that there is lack of proper insulation of your probe from the radiant heat encountered in the engine bay area near the intake opening.

[tbitz]

Well folks I came into work this morning with my "home made" cold air intake pictured above and here is the data.

Ambient air temperature was 74F. After driving for about 25minutes on the highway the intake temperature was only 77F!! That is right, only 3F increase in intake temperature. I cannot believe how well this has worked!

Yesterday (without the cold air intake) my intake temperature was 96F with a lower ambient air temperature than today.

Based on the following calculator
http://rshelq.home.sprynet.com/calc_hp_dp.htm
This drop in temperature translates to 5Hp gain for my car. Not bad for $3 and 5 minutes of work.

I believe the oil temperature was lower too, but I will hook up my ECU to the oil temp sender and get real data to prove this.

I cannot believe, Porsche has not seen this flaw in the intake design.

It would be very advantageous to the group if someone else tried this to prove there isn't something specific to my car that is causing this problem. The sensor are cheap and only takes a minute to setup.

[Peter Kelly]

Originally posted by tshih
Tbitz,

the more efficient motor is usually the more powerful one and gets the most energy out of the fuel and oxygen (20% of air) combination that the design of engine permits (the valve overlap, cam-grind, spark timing, and air flow to achieve the perfect 14:1 ratio of air:fuel during operation). Most after market chips mess with the distribution of maps to skew higher peak power in favor over drivability and emissions and legal issues.

tshih

This is completely false information. Most race engines are tuned to run an air fuel ratio in the high 12's (12.7 to 12.9 to 1 air fuel ratio) The literature is full of proof that max power is achieved at around a lambda of .87... .87 x 14.7 = 12.789

The only thing 14.7 air fuel ratio is optimum for is emissions.