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Mopar1973Man

Intake Temp Vs. MPG.

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Now for the last 2 winters here I've been studying the impact of the intake temperature vs. MPG. I keep coming back to finding myself desiring warmer air over winter cold air. The breaking point where I see a absolute fall in MPGs is right at 50-60*F outside and then the MPG's start failing and continue to fall as outside temp get closer to 0*F. So to give you a feel of the change in MPG's.

60*F outside air temp = 100*F IAT Temp = 23 MPG

0*F outside air temp = 50*F IAT Temp = 19 MPG

So for the MPG game you need all the warm air you can get... But if you looking to pull hard on the rollers (dyno) I would which back to running cold air for the HP/TQ performance.

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A lot of people say they lose mileage when they switch to winter fuel too.

I really don't... I've been holding 19-20 MPG most of the winter. But I see a increase in MPG once I get down south where its warmer it always rises. Come back to the cold and watch it fall... Remember I can see instant MPG number not doing hand math...

1996 Dodge 1500

[ame=http://www.youtube.com/watch?v=8I7JOW3tFUo]Ride in the 96 Dodge - YouTube[/ame]

2002 Dodge 2500 Diesel

[ame=http://www.youtube.com/watch?v=SRQdoPs_tLo]New Meadows Valley - Cruising at 55 MPH - YouTube[/ame]

So I can compare outside air temp, intake manifold temp and MPG all in one shots to see changes from environment. Like saying I'm cruising around Caldwell, ID and Ontario, OR at 60*F and looking at 23 MPG on the very same tank of fuel now get to New Meadows, ID and start see a loss of about 3 MPG (20 MPG) because the sun has gone down and the temp is already 20*F out...

Edited by Mopar1973Man

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Hmmmm, New Meadows ~3900' elevation, Caldwell ~2400' elevation. A variable, but not a GIANT one.

As previously noted, D2 has more Btu/gallon than D1, which contains more than kerosene. That wouldn't affect same-tank numbers, though. Irritatingly, kerosene costs more than D1, which costs more than D2. Sooo, you pay progressively more for progressively less. Grrrr!

Can you bypass the intercooler? :bat::td::nono::puke:

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This is interesting! I have always suspected this but usually everyone is after bigger power numbers than anything so they always lean that direction. I have not got set up yet to do any checking like you have been doing. Good job!

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My range of elevation from McCall, ID to Riggins, ID is from 5,200 down to 1,800 ft.. Of course it takes more fuel and energy to climb that to roll down.

Now to eliminate the variables of the ECM I've been running what I call a "MPG Fooler". I've got a 2.2K ohm resistor plugged into the IAT sensor plug that fools the ECM to seeing 143*F in the manifold constantly. Last 2 years now I've never been below 19-20 MPG all winter. But now unplug the fooler and hook the IAT up and the MPG will fall down to 16-17 MPG.

Winterfront adds only at best a +10*F gain to the IAT temps so even on cold days I start to slide in MPG's But the winter front does help a bunch.

But still the line in the sand is about 50-60*F outside temp where I still see a instant climb in MPG's.

This is interesting! I have always suspected this but usually everyone is after bigger power numbers than anything so they always lean that direction. I have not got set up yet to do any checking like you have been doing. Good job!

Well there is a few things most don't talk about... Like big power truck must run high cetane fuels which is like running winterized fuel its low in BTU content but the ignition quality is fast and hot. So to keep building power at high R's you need a fast burning fuel and lots of it. So here comes the cold air to control the excessive amount of heat you generating and also cold air is denser so you get more in the cylinder giving you more power.

But hey wait amoment we are daily drivers... With low cetane fuel that burns slower and hotter. So if you increase the air temp the fuel burns better and ignites easy.

attachment.php?attachmentid=5225&stc=1&d=1330379944

This table above is from the ASTM testing labs for testing diesel fuel. You can plug in the numbers from your local fuel station and where the 2 lines cross is the cetane.

Point of reference gasoline is right around 115K to 120K BTU's. Depends on where yo look for BTU's listing...

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Edited by Mopar1973Man

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good ideer on the ecm fooler :ok:

sure is nice they came out with these ELECTRONICS TO IMPROVE OUR MPG :wall:

Actually it did improve the MPG's but the band of the tune is right there in the summer time temps. It just the colder weather I think the fudged a bit and guess the table on because it could be better.

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Ok to give you a change report... I've now switched off my 265/75 R16's to my 235/85 R16's (ST Tires). Now started out my morning at 6*F above in New Meadows, ID for a low and head for Donnelly, ID my high temp for the day in the truck was 33*F outside temp.

attachment.php?attachmentid=5232&stc=1&d=1330465476

Explain the display...

MPG - Instant for the second

Cmg - Current MPG for today's travel (21.3 MPG)

Tmg - Total MPG for the Tank (20.6 MPG)

MPH - Speed

So even with crappy cold weather I'm still pulling excellent mileage with so called "Winterized Diesel" those suppose to loss 2-3 MPG for the winter. I've got my grill completely covered...

attachment.php?attachmentid=5233&stc=1&d=1330465850

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Edited by Mopar1973Man

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What I managed to prove is intake air temp is a KEY factor in MPG's and the old school of CAI (Cold Air Intakes) are not what you want if your looking for MPG's.

  • Warmer intake air does increase MPG's.
  • Lower cetane fuels will increase MPG's.
  • Warmer IAT Temperatures will increase MPG's (need to be ran against a ehancement box).

Here is from Quadzilla Performance.

No doubt, stabilizing the IAT will help, I agree 110%. There is a too low and a too high number. If the IAT drops too low the ECU retards the timing just like too hot due to fears of detonation and stabilitiy of combustion in diesel fuels. No doubt winter blend fuel hurts this as well.

So you can definitely stabilize things but, I think the anomoly in the summer time is that when running a box with timing advance you actually get a steeper timing advance curve from the box by fooling the IAT.

The way the timing and fueling works on the can bus on these trucks is that we all just basically go to the MAX allowable advance and fuel number as soon as the VP computer will let us without locking it up. We can physically demand more fuel and timng but, the VP computer will shut down thinking there is an issue. As a matter of fact our peak numbers for fuel and timing can already be reached on a stock truck, its just that we can re-shape that curve and reach those max #'s when and where we want.

So basically fooling the IAT retards the timing and the box sees the opportunity to make an even bigger change going to max and it does it sooner.

Sort of complicated but, I can see where it works.

What we need to do on these older trucks is some tracking of the IAT across the actual timing advance range at the pump and not via the OBD port since its slow and suspect on that sort of parameter, I know when we start changing the fueling the timing numbers the obd reports some weird stuff that is not exactly right.

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I've got a few questions about this for you. I even have an idea that you might try. . . . :cool:

The 2.2K Ohm resistor you used: Is it replacing the sensor altogether or is it parallel across it? Oh, by IAT, do you mean the one just after the air filter in the hose before the turbo inlet? I would like a wiring diagram please!! I want to try this also! I think my Common Rail has a temp sensor in the intake manifold that is integral with the same sensor that also reads boost pressure. So I will have to wonder how I will approach doing this if mine has this 'extra' temp sensor in there as well. I am wondering if I have one of these sensors reading bad in my truck and if that is what is killing it's mileage. It makes sense! One (or more) of these sensors could be feeding the wrong ambient info to the computer and it could be using a calibration that lowers the timing too far or something. Only things I have ever noticed about this truck is it gets lower fuel mileage than it should and it is low on power compared to others. I may want to get ahold of a Scan Tool that can read the different sensors of the truck and see if they are accurate. If one were way out of cal I don't believe that would set any codes and if a tech wasn't actually looking he would never notice one being out of whack!!

Do you know of anywhere that it is listed what the resistance would be from these different sensors for a certain temp or pressure? If I could find that info then I can test them myself!

Do you know what the OEM winter front looks like? If not, I can post up a pic of the one I made that is similar to it. I saw your grill covers and wonder what your IAT manifold temps would be with a winter front that covers up the coolers better like the OEM one does? If it is under 20F out and I'm running empty I usually don't have a problem leaving it on fully covering up the coolers. But I don't have any way of measuring what is going on inside the engine except for EGT. I can say that when it is cold out like that then the EGT's fall into the basement! I just made a run like this Fri and Sat and pulling a steep hill at 80 only got it up to almost 600F. Going down the other side dropped it off to under 300F! Anyway it would be interesting to see what covering up the coolers better would do to the MPG numbers......

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Well as for CR I can say what works and what doesn't... I know the IAT sensor is in the manifold...

As for the 24V mine is near #6 cylinder...

attachment.php?attachmentid=5276&stc=1&d=1330989720

So I unplug the sensor and plug in a resistor

attachment.php?attachmentid=5275&stc=1&d=1330989720

As for ECT and IAT sensor values for 24V engines at the bottom of the page...

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/26-engine-systems/59-intake-air-temperature-sensor-iat-sensor

Being that I love to tune mine in and play more... I plugged a rheostat in to the plug just like the resistor and I can dial in the temp I want the computer to see... Since I got a ScanGauge II I can plug in resistors and get a temp result in seconds. As for using this mod the is no pre-grid heater any longer. In other words when you turn your key on the WAIT TO START will light up but go right back off without any voltage drop. Then when you start the grid heats come on for posting heating. Why? Well the best that I can explain is that ECM checks the ECT and IAT against the battery temp sensor. Since the ECT and Battery temp are correct then the ECM use that for heat figures. Now even on cold days 0*F or colder I've seen the ECT at 190*F and the IAT at 143*F then shut down the engine and go into a store grab a cup of coffee or soda come back out fire up and still have post grid heat. The only sensor at that point seeing cold is the battery temp sensor. I don't have a overhead console with outside temp so that the only thing left check for outside temp...

Here is how to build a fooler... (First switch just need to use IAT plugs and proper ohm resistor)

high-idle-mod.jpg

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Edited by Mopar1973Man

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