qzilla

I can tell you right now that it's so freaking hot here in the metroplex that any real gains you are seeing are probably diminished strictly based on the factory ECU backing off everywhere due to incredible IAT temps. We have been doing some monitoring and when IAT is over 170 in the shade at idle, there is no efficiency left.

Now if you do some back to back you can tell but, on a moving average and looking for gains from spring to summer or something, that is an uphill battle!

Rednax

I've been under the impression that, to a point, hotter is better for fuel economy. But I don't have a number for CTD's where efficiency falls off. I've seen a gasser graphed past 105F ambient and FE climbs the whole way, from below freezing temps.

qzilla, at what temps do things start to change for the CTD in re FE. Good or very good until what temp?

And, specifically, what is meant by:

We have been doing some monitoring and when IAT is over 170 in the shade at idle, there is no efficiency left.

as to "efficiency"?

Thanks

.

ajpulley

Can I install the MPG_CITY on an MMM that's been upgraded to a XZT?

AH64ID

Holy crap those are HOT IAT's, I am not sure I have ever seen over 140* once the motor is running (that was stock intake pulling a grade at 32 psi on a 95* day), and the hottest I have ever seen is 150* with the motor off.

What kind of intake are you running?

That is the principle the MMM is running on. It's an IAT fooler that tells the ECM it's hotter than it is so the timing gets advanced, but at a certain point the timing is maxed and just can't go any more.

I know a few folks who are wiring resistors onto their 2nd gets for IAT fooling and seem to get the best mileage with IAT's of 140*.

Shorts

I appreciate the thoughts on this. Yeah it has been brutal hot here so figures it would be influencing numbers. For the readership we've been over 100* for the past 27 days. Even our overnight low of 86 set an all time record for hottest low


I've been meaning to grab a thermometer sensor so I can monitor the temp in the box for my own info.

AH64ID

I have been running one that is attached to the outside of my OEM box for the last week. It's always hotter than the air in the box by 10-60*+. The temperature rises as boost does so the charge air tube must radiate a lot of heat, 2-3 seconds of high boost will show a 10* or more rise in IAT, while pulling a hill will put 60* on the OEM intake air, as measured by the IAT sensor. Towing last weekend every hill I hit that needed sustained power would put the underhood temp above 160*, where the gauge just said "HI", while with the home depot CAI and stock box my IAT's were never over 123*, even in 93-99* weather.

I also am running turbine/manifold blankets that keep the underhood temps MUCH colder than without. They keep enough heat in the manifold that I can hold my had on the manifold immediately after pulling a hill with sustained 1000* EGTs.

Shorts

Thank you for the numbers. That gives me an idea what's going on under there. I saw your manifold wrap in one of your other threads and they look good. I was wondering though, can the wraps negatively affect the manifold or bolts at all? Just thinking in terms of the trapped heat under the blanket making the temp range more extreme and causing metal cracking or anything like that. Don't know if that's possible, but it came to mind.

AH64ID

I am not sure if they will have any effect on longevity. They are used in boats on most installs and don't seem to effect anything negatively, other than bolt removal is a little more difficult!

I wonder if the EGT's read higher as there is less heat loss.

qzilla

Actually lower IAT's allow the ECU to run more advaced timing.

And we were measuring on a totally stock truck but, it was a 6.7 and it was 109 outside and the truck ambient temp reported 114. It has been brutally hot.

The problem with turbo charged diesels and intakes and intercoolers to some extent is this. We want to grab cool air, the turbo them compresses it which super heats it, then we attempt to cool it to ambient which is really not possible with such small intercoolers than we run it back into a hot intake stream and manifold.

I don't know where the line is for fuel economy for sure as far as ambient temp is concerned, that is one of the things we are trying to learn. I just know if you try and take average numbers that were derived mostly in the spring and compare them or average them into summer time numbers you will always be disappointed. The heat kills the efficiency.

Also there is a point the trucks are looking for that is too cool for the ecu to want to advance the timing but, that is more for "detonation" fears than efficiency. If they allow a high advance on a cold engine and it does have a detonation event then you can loose a head gasket pretty quickly.

The guys running resistors are simpy lowering the signal, not raising it. The problem with doing it this way is that you get the same drop across the entire curve and these sensors are not 100% linear. Plus a 10% drop at 1v is a lot less than at 4v. That is why either some sort of smart digital resistor or a small microcontroller is really needed to map the change to be totally effective.

AH64ID

I don't know about the 08+ trucks with the smaller IC, but my 5.9 only has minor intake mods and it maintains 6-12* over ambient at the MAP on a normal cruise day, +45 was the hottest I saw with the stock turbo (30 psi, 95* out, towing) and +30 is the peak with the new turbo.. They do a pretty darn good job.

They are actually raising it. 2nd gens have a different setup and run about +40* from ambient almost all the time, regardless of boost. So in the winter or spring, or even mild summer the IAT is much less than 140*.

Shorts

I see - thanks. That's a good question about EGTs. Are you thinking about doing a measure/comparison? Would it be as simple as measuring EGTs with/wo the blanket?


So if cooler IATs allow for advanced timing, does the heat & ambient temps prevent or limit the ECM from running any advanced timing even with the M3? For example I'm running the City tune. Is the timing the ECM will run at 65* the same as at 90*? Does truck ECM have final authority over the timing or does the M3, I guess would be another question?



I've gone through these reads a time or two. I'm going to run through them again for a refresher. The 'airbox' article actually gets into the weeds of IATs and HP which might be applicable here.

http://www.genosgarage.com/GenosGara...irCleaners.pdf

http://www.genosgarage.com/GenosGara...R59_AirBox.pdf


I suppose if I were comparing mpg numbers on record I could go back the past two years and compare them by the month. That will give a slightly better comparison to the trend with regard to outside temps.

AH64ID

It would be that simple. Find a hill and pull it at "x" speed to see what the EGT's are, and then pull the blanket and do it again, all I would need is 4 more of the clamps.

I may, but I am not really worried about it, 1250° is as hot as I have gotten in 6th and 1210° in 5th..

But if you think there are 50° from the blankets (a real possibility) my EGT's are quite low!

I would guess the blankets also only effect EGT's while towing, as there isn't enough time around town to make a difference on a heavy acceleration run.

qzilla

That is interesting, I wonder what affect altitude has on these numbers? I know down here we get stupid IAT numbers in this dry heat and it has been HOT! I also wonder if the efficiency of the IC changes based on the Ambient temp? So at 90deg it might be really efficient but, at 105 it might loose a lot of that?

That is correct, sorry I think what I meant to type and what I typed late at night was confusing.

Most all temp sensors are resistive so lowering the signal raises the temp.


Cooler is not ALWAYS better. There is a too cool point and a too hot point and of course there is a sweet spot. The factory is worried about detonation, headgaskets under boost etc. So when they are really cold they retard the timing and when its too hot the retard timing.

Ultimately the ECM gets to decide how much timing to use. Boxes like the M3 change signals to get the ECU into that sweet spot for the greatest advance or efficiency.

There are a lot of factors going into this. On the M3 for the newer trucks there is actually several minor things we do. We run a little more rail pressure down low but, the peak remains completely stock. Anytime there is more pressure for a given duration it advances the timing. The flip side of that is on the upper end we tell it less rail pressure which causes it to change the duration slightly to compensate and it will also command a different timing value.

Same holds true for boost and/or IAT. Remember these are somewhat minor changes and we don't change them all the time, just when the factory readings get out of those zones.

Basically we are trying to stabilize everything regardless of conditions.

Same theory that people are doing with the resistors except we use "smarts" on board to allow it to change and adapt based on conditions, it is not a static change.



I also wrote on another board about changing the IAT while having another box on board that alters timing. I think there are some unique anomolies that happen there. A box may want to advance timing a certain amount but, cannot because of whatever the factory requirement is. You can only get away with so much of a change at once without going out of bounds. Well if yuo fool the ecm to change something with something like a resistor and then the ECU makes a change that is different than normal, your box could possibly in theory be able to make a larger change than normal resulting in unexpected results.

Basically they were looking at a timing box on a 2nd gen with an IAT fooler. Using that seems to all the box to advance timing mroe aggressively than on a stock truck because fooling the ecm also fools the timing box. So instead of a 2deg advance you might get a 3 deg advance.


Its all theory to some extent. It would be a lot simpler if there was just a manual they produced that said max efficiency = xxxx but, they don't!

I am certain different trucks, different air and different temps will all have slightly different results.

What we do know is that cooler air to the actual combustion chamber and more timing advance = more efficiency. Getting there is the tough piece of the puzzle.

AH64ID

I find it very interesting that rail pressure is added down low as when I call you guys twice I was assured it did zero for rail pressure.

From what I have seen its a very sharp bell curve. At 95-100° F it will run +10° but takes longer to get back there if you stop or pull a big hill. City driving puts it about +15-20°. The same is true in winter, the difference gets much larger as you drop below 25°.

My turbo had the biggest effect on my IAT's, but each of the cam, MIT, GDP horn, and Home Depot CAI all had effect's as well.

Rednax

Thanks for the replies, insights and continuing speculation in the above.

Looking for the most work from a gallon of fuel, but never compromising reliability and longevity, is an important subject.

Commuters ought to have records which can be compared against average monthly temperatures as well as altitude and terrain. Truck spec should be noted (plus changes from stock) for purposes of comparison.

(I have records going back two years, graphed, and -- as I am not a commuter -- the variations aren't noteworthy as we essentially have no "fall-winter-spring" as is experienced farther north. Plus, due to climate the single decisive factor in my mpg over a calendar year is extended idling to to heavy A/C use in "summer" [May through October]).

The single point of comparison may be average speed (as deduced from miles over hours [E/T]). From that point we may be able to back into truck spec, climate and terrain to account for differences among CTDs (insights) where use is fairly comparable.

My "thinking" (as of today) is that, where usage is at least 30-40 miles minimum [as engine oil, trans & axle oil need this far to come to op temp; tires maybe longer] and an average speed is noted -- on a solo vehicle -- comparisons might be made across truck spec, climate and terrain for a beginning.

Then there is the problem of solo versus towing. Any mods that restrict towing capability need to be noted (and discarded) for purposes of discussion. That which threatens longevity or reliability for mpg or HP is a dead end.

As always, gains in FE are not measured in mpg (one tank versus another; short of A-B-B-A testing), but in percentage increases to average mpg.

.