Air intake temperature tests

[03ESPro]

I'm doing a lot of testing on the temps of the air entering the engine using different intakes and such, thought you guys might be interested. Here's a link to it.

[goldstar]

I'm doing a lot of testing on the temps of the air entering the engine using different intakes and such, thought you guys might be interested. Here's a link to it.

A very interesting study and you have provided us with some useful data.

Two comments come to mind. The first involves the location of the best place in the intake duct to measure temperature. The PCM adjusts the A/F ratio in terms of (among other factors) the air density and temperature inputs it receives from the MAF and IAT sensors and, of course, air density is partially a function of air temperature. Consequently, it would seem to make the most sense to measure the temperature of the intake air in the vicinity of both the IAT and MAF sensors because this is where the sensors measure it. In the OEM system, this would be at the outlet of the air box on the engine side of the air filter. If the temperature in the rubber intake hose that couples to the throttle body is greater than in the sensor area, as you have shown, this would seem to be an irrelevant factor since the metering has already been computed on the cooler air before it enters the tube.

I believe the most relevant parameter here is the temperature differential between the ambient intake air and the air in the vicinity of the sensors. Anything that can reduce this differential will be beneficial for power production since HP varies directly as the square root of the change in ABSOLUTE temperature.

My second comment involves the heating of the intake snorkel tube in the OEM system. I, too, have noticed that after a run, although the top of the snorkel tube runs relatively cool, the underside is quite hot due to its proximity to the radiator and the exhaust manifold.

In another thread:
https://www.wihandyman.com/forum/sho...3061#post83061 (post #122), I discuss my attempts to seal up the intake system to take full advantage of ram air effect. I don't want to hi-jack your thread and bring that topic into your discussion but I only mention it because part of the job involved sealing off the 4 drain holes in the bottom of the snorkel. To the degree that the drain holes can ingest hot air, I would expect that sealing these holes will reduce intake air temperature, at least to some degree.

Perhaps, if you have the time, you might want to measure the air temperature both with and without sealing to see if a real difference exists.

Again, thanks for your efforts. I'm sure a number of our Forum members will find your measurements very interesting.

[03ESPro]

That's a good idea about the 4 holes, I remember seeing that mentioned in the thread about modifying the stock air system. As air passes over those holes, its going to produce a siphon effect, and pull in that hot air from the radiator and manifold. Hmmm...

As far as the location of the sensor in the tube, that's also a good point you make about where the PCM measures the temp at. It seems like it would be better for the PCM to measure the temp closer to the throttle body, so it gets a better reading of the air actually entering the intake. Maybe Mazda designed a correction factor into the PCM to account for the increase in temp by the time the air has reached the TB? Also on this, it's great that a CAI can get cooler air to the IAT sensor, but if that air is then heated significantly before entering the combustion chamber and there is no correction for this change, the A/F ratio is going to be off due to a variance in reading vs. actual temp.

Correct me if I'm wrong, but at WOT our cars go into closed loop mode and run a preprogrammed fuel map, overriding any sensors aside from the TPS, right? I'm thinking about the resistors sold on ebay that modify the IAT reading.... they cause your car to run really rich because it thinks the air is much denser than it really is. Forgive me, its late and my brain is starting to fizzle out.... I've done too much thinking today about this stuff. Maybe tomorrow my train of thought will clear itself up.

[goldstar]

03ESPro,

I could be wrong but I think that at WOT and above a certain critical rpm, the PCM goes into open loop mode. It's in the closed loop mode that the PCM is responding to MAF and IAT sensor inputs. Other than that you are quite correct, in open loop the PCM overides the sensors and runs from a preprogrammed fuel map.

There is an informative discussion of A/F ratios at:

https://www.hondata.com/techlambda.html

The stoichiometric A/F mixture is~14.7 to 1 for non-oxygenated fuels (lambda value = 1.0) and according to the article it's best to tune the mixture as close to stoich as possible for moderate loads in engines equipped with catalytic converters and running in closed loop. The PCM uses the Oxygen sensor to keep the mixture near stoich which is the optimum A/F ratio for the cat to work.

The article goes on to state that as engine load increases, the A/F mixture is made progressively richer for increased power, cooler running and less chance of damaging the engine. In a normally aspirated engine, the best power A/F ratio is given as somewhere between~12.5 to 1 (lambda value = .85) and 13.5 to 1 depending on the engine.

Now how does all this relate to making improvements in the air intake system? Clearly, in closed loop mode when the PCM is responding to inputs from the MAF and IAT sensors, anything we can do to increase air density and reduce air temperature in the intake duct will have a beneficial effect on HP output.

I believe the same factors are operating in the open loop mode. There seems to be a consensus on the Forum that open loop operation results in a richer than best power mixture condition that consequently limits maximum HP output. Again, if we can provide cooler and denser air to the combustion chamber than is normally available, in conjunction with the preprogammed fuel map, we are effectively leaning the mixture to some extent and moving it back in the direction of best power A/F ratio.

I don't know how much of an effect any of this would have but on the theory that every little bit helps, modifying the air intake system for increased air density and a reduction in air temperature is certainly a step in the right direction in the search for improved performance.

02 DX Millenium Red

[goldstar]

Re: Air intake temperature tests

While researching another topic, I came across this site:

https://www.mazda6club.com/articles

This is a very interesting and informative group with a number of obviously knowledgeable members. I found an article there that is very relevant to the subject of intake air temperature and provides useful information that I think will interest some of our members.

The article is titled "Why not to do the Throttle Body coolant bypass" and was posted by 'Absolut' in their Tech Articles category. 'Absolut' in turn credits a 'Doctor Wicked' for providing the actual content of the article. Since the throttle body (TB) is supplied with coolant in order to maintain it at a high enough temperature to prevent freezing of the throttle plate in cold weather, does the hot spot created here cause intake air heating sufficient to reduce density and decrease power output? This consideration has given rise to the suggestion that coolant flow to the TB be by-passed with the understanding that this mod is temperature limited-those living in cold climates would have to restore coolant flow in the winter.

Using a Mazda 6 as the test vehicle, the following parameters were established:
1. 80 deg F ambient intake air
2. .0735 lbs/cu.ft air density@80 deg F and 1 Atm pressure
3. 280 deg F coolant temp, and surface temp of the inside of the throttle body
4. TB ID=2.5"; L=2"

It was next necessary to calculate the mass flow rate and velocity of the air entering the engine. The author chose 4000 RPM and the usual 85% volumetric efficiency (VE) as the test point for the engine. Remembering that the 6 is a 3.0L engine this works out to an air flow rate of 3 cu.ft/sec, 180 CFM or 794 lbs/hr. In order to provide a reference point for our own 2.0L (122 CID) engines, I calculated the RPM necessary for an equivalent flow rate at the same VE.

Reference: Auto Math Handbook by John Lawlor

air flow in CFM = RPM x CID(VE)/3456
180 = 6000 x 122(.85)/3456
air flow in lbs/hr = 180 x .0735(60) = 794

Therefore, at 6000 RPM the Protege flow rate is the same as the 6 at 4000 RPM. The author now has all the variables necessary to mathematically calculate the outlet air temp from the throttle body. The outlet air temp turns out to be 81.3 deg F. Thus the entire air temp rise is only 1.3 deg F despite the 280 deg F throttle body temp. This amount of temp rise will result in a power loss of .13%. This represents a loss of .26 HP on a 200 HP engine and .17 HP on a 130 HP engine.

CONCLUSIONS
The first and most obvious finding is that eliminating coolant flow through the TB has no effect on performance. Second, we can at least make some inferences about the effect of intake duct heating on raising intake air temp. Since the TB is undoubtedly the hottest part of the intake duct, it's likely that other less hot sections would have only a minimal effect on increasing air intake temp. This might explain why although the MAF and IAT sensors are located before the flexible hose and TB sections, their outputs are essentially accurate since little heating subsequently takes place as the air flows into the intake manifold. I still think it's a good idea to seal off the 4 drain holes in the snorkel since any air ingested here will effectively create a situation where the ambient air intake temp is raised to a figure higher than its actual value.

02 DX Millenium Red