Effect of vehicle speed on IAT

[aldive]

You do not get similar results with your 2nd gen front end? Maybe the 2nd gen front end cools under the hood differently. You were measuring IAT's, not underhood air.

I will soon be conducting an evaluation of under hood temperature vs, IAT vs, truck speed.

 

[spindlecone]

IMO
temps as measured at the mAF and reported to the OBD connector are worthless, with the MAC intake, they could be a hell of alot hotter at the TB due to underhood temps and radiant heat
Am getting a needle probe tomorrow and measure temps at the silicone sleeve, just before the TB, and if need be, header wrap my intake tube.

 

[JDraper]

Very interesting 410 about the turbulance starving the intake, last dyno run I had the dyno guy hit the intake direct with one of the fans they use (3rd pull) it killed the engine,why?

This is likely due to the MAF being confused due to turbulence. The Mach 1's are VERY sensitive to the turbulence flowing past the MAF. If you are already running a little lean, introducing a cross wind across the MAF could cause a stalling condition.

(I'm gonna use the Mach as my example because I'm familiar with it's setup)

In the Mach 1, Ford puts a metal screen directly to the outside of the MAF. The purpose of the screen is to straighten out the airflow to give the MAF consistent readings. One of the common mods to the MACH is the K&N CAI setup. The instructions in the K&N kit tell you to install the stock MAF housing and sensor into the K&N kit without putting the screen back in place. With the vehicle set up this way, stalling is a constant problem. If you modify the setup and add the screen back in, the stalling goes away. I had done this mod to my car and had the same issues. I then switched to the C&L setup, and I have had no problems. The C&L doesn't have a screen with it, but the MAF housing is larger, designed differently, and sits the MAF slightly farther back in the housing than the stock one does, which should help promote laminar air flow past the MAF.

I would assume that the Explorers could have the same issue, especially if the air intake is modified.

 

[spindlecone]

Interesting
My A/F is 12.7 at wot, not lean by any means, so JD you feel just turbulant air, via the the filter could cause a stall?
Those MAF wires are awful fine, could imagine seeing them get tossed around

 

[JDraper]

Interesting
My A/F is 12.7 at wot, not lean by any means, so JD you feel just turbulant air, via the the filter could cause a stall?
Those MAF wires are awful fine, could imagine seeing them get tossed around

If just removing the wire mesh in front of the MAF is enough to cause driveability and stalling problems with a realtively constant airflow, then yes, I think a quick change in direction of the airflow across the filter (especially if there is a decent velocity change) might be enough to cause a stall on the dyno.

If you have a way of monitoring the voltage off the MAF, monitor it while the vehicle is idling, and then turn the fan on it...I'll bet you see a voltage swing. MAF sensors are VERY sensitive to changes in air flow by design, so any change in air flow will affect them. If the airflow past the MAF is turbulent it will give constantly changing readings, which may cause driveability problems.

I'm not exactly sure how the Explorer computer uses the MAF readings (I.E. how many samples it takes over a period of time, if it uses discrete data or averaging during sampling, or how quickly it responds to changes in the MAF data), but I do know the MACH is EXTREMELY sensitive to changes. One of the Mach 1 Registry members had lost his MAF screen, and was trying to make one out of screen material, and found that even a slight change in mesh hole size affected how the MAF read.

 

[JDraper]

Just thought I'd copy this post over...this is from one of the Mach 1 Registry people who is in the business of calibrating Mach 1/Bullit/05 GT Mustang computers and doing custom flashed chips...

Actually the screen is there for a reason - hence the stalls experienced with removing it. The screen is actually there to help remove the turbulence coming in through the upstream inlet. It does a rough job of "straightening" the airflow so that the air meter element will read an accurate amount of airflow. With swirls and backflows over the element, an incorrect air mass reading will be measured.

Sometimes it will be too high (which will result in overfueling and a closing of the idle speed control valve) other times too low (and thus too little fueling). These measurement errors will be most pronounced (larger percentage) at low total air mass readings - like decels and idles where you will be ingesting say <1 pound per minute of air. This is attributed to the stalls people are finding. (Note: we idle at roughly 0.7 pounds per minute of airflow while WOT @ 7000 will be 34 pounds per minute for comparison).

Now the turbulence issue I mentioned before can rear its head. It is a combination of what air inlet hardware is on the car - K&N, a heavily oiled K&N (which coats the air meter element), or other intake system components.

Furthermore, stalling issues result from a stack up of errors. If you happen to get a high spec flow ISC valve then you will be less prone to stalling out with the screen removed. That is why some people here changed an ISC valve and haven't stalled. However that is expensive to try overall.

The air meter transfer function in the calibration is flowed with the entire air inlet system intact – from the silencer tube to the t-body. It is even positioned on the flow stand in the exact orientation as in the car. Changing the tube between the air meter and t-body can significantly affect the overall transfer function resulting in measurement errors. The basic rule of thumb is that any change within three air meter diameters (before and after the air meter) can have an impact on the transfer function.

 

[410Fortune]

good info! I ditched that screen years ago! hahaha
My aftermarket 4.0L MAS did not have a screen either...

 

[Mbrooks420]

Please explain how this would work.

In stop and go traffic, max speed about 15 MPH, there is verry little air flow, ducted or not.

When there is little air flow underhood temeratures soar. If your intake was sucking air from outside as opposed to the hot engine bay it would be cooler, even if the ambient temp was 90. Although you would still get heat soak into the intake piping, I still think that the IAT would be lower.

 

[Rhett]

I will soon be conducting an evaluation of under hood temperature vs, IAT vs, truck speed.

That is good. When I typed my previous post, at the end, I finally realized that you and I had measured entirely different things.

I had measured under hood air temp vs. truck speed.
You had measured IAT vs. truck speed.

I'd be interested to see your underhood vs. truck speed results. When I did my testing it was an 80degF ambient day.

 

[Rhett]

The purpose of the screen is to straighten out the airflow to give the MAF consistent readings.

I once read about some of the Corvette/LS1 guys removing their MAF screens, the idea being that the screen hampered air flow. I had never thought about the screen actually serving some useful purpose, other than yet another way to keep debris out of the intake.

I do wonder how sensitive Explorer MAFs are. Surely not as sensitive as the MAch1 maf? I don't have a screen on my Granitelli MAF. I can't even remember if the stock maf had a screen on it.

 

[Rhett]

When there is little air flow underhood temeratures soar. If your intake was sucking air from outside as opposed to the hot engine bay it would be cooler, even if the ambient temp was 90. Although you would still get heat soak into the intake piping, I still think that the IAT would be lower.

That's the exact theory that I was operating under when I heat-taped my intake tube 4 years ago.

 

[aldive]

I do wonder how sensitive Explorer MAFs are. Surely not as sensitive as the MAch1 maf? I don't have a screen on my Granitelli MAF. I can't even remember if the stock maf had a screen on it.

I too am confused by this "screen thing". I did not have one on my stock MAF, on a Granatelli MAF that I had, on a Pro M that I borrowed, nor on my C & L.

 

[410Fortune]

The gen I Explorer's had a screen just before the MAS. When I went 4.0L I was like, "pfft I'm not gonna get any leaves in here behind the filter" and took it out. I figured the screen takes up a tiny tiny bit of volume with that wire mesh, so in theory taking itout gives me a larger opening. hahahahahaha. Yeah yeah I know it won't do anything, but every little bit helps.

Some of the later Gen I's had the conical air filter box, I am pretty sure I have seen a screen in there in front of the MAS too. Not sure about the Gen II trucks though...
My aftermarket MAS (70mm Granatelli) is nothing more then a fox body Mustang MAS body with a re-calibrated factory sensor.

I have never has a MAS issue with stumbling or shutting down. Maybe the bigger the injectors the more sensitive the readings from the MAS?

 

[aldive]

I have never has a MAS issue with stumbling or shutting down. Maybe the bigger the injectors the more sensitive the readings from the MAS?

I too have never had a problem with any MAF ( well actually we had some issues with the Pro M on the dyno, but resolved them with computer tweeking ) I have used.

 

[aldive]

I will soon be conducting an evaluation of under hood temperature vs, IAT vs, truck speed.

http://www.explorerforum.com/forums/showthread.php?t=143801

 

[DieselDean89]

so how much is this screen, and would having it help my idling problem? i
remember not seeing one when i took my maf out to clean it. Relating to the underhood temp discussion, ive heard a common drag racing technique to lower underhood temps pretty dramaticaly is to wrap the headers (using header wrap, of course.) its supposed to drop temps by at least 20 degrees F.

fun fact: every 20 degree F temp drop in the engine equals out to about 1 hp

 

[Mbrooks420]

Header wrap is only for racing apps. It ruins headers in short order. A better way to lower under hood temps is with a real hood scoop.