Using my engine model I've gained some additional insights into the effects on engine performance due to increasing the air filter inlet temp. I ran my model for air filter inlet temps of 70F, 130F, and 190F, and as I'll discuss, this is about the worst case for comparing a cold air intake (70F) to an open element under the hood intake when towing on the flat (130F) and for pulling a steep grade in a lower gear with the cooling fan locked up (190F). Please hold your fire concerning these temps because the whole point of this post is to pass along some new and interesting findings regarding how the engine adjusts CFM and MAF for a given BP as the driver applies more throttle to maintain his original BP in an attempt to regain the lost MAF and RWHP due to the increases in air filter inlet temp so that the truck can continue doing the same workload as before.

At a top level, if the throttle position is held constant as the air filter inlet temp increases, the CFM remains constant, and the MAF and RWHP decrease, and the truck can't maintain its previous workload. The air density, AD, of the air flowing into the air filter decreases by 11% for 130F vs 70F inlet air temp, and by 22% for 190F vs 70F inlet air temp. Since MAF=CFM*AD, if the CFM flow into the air filter remains unchanged as the AD decreases due to increases in air filter inlet temp, the MAF into the air filter will decrease by this same % decrease in AD, and since RWHP is directly proportional to MAF it will also decrease by this same % decrease in AD.

The problem with this top level analysis is that usually the throttle position isn't held constant as the air filter inlet temp increases, because if it were the truck couldn't maintain the desired workload, and would have to slow down until the workload was reduced enough to be accommodated by the lower available RWHP. To find out what happens when the driver pushes harder on the throttle so that he can maintain his previous workload as the air filter inlet temp increases is a more complicated problem, and the solution requires running my engine model.

I ran my engine model for air filter inlet temps of 70F, 130F, and 190F. The reference run at 70F used the input parameters shown in the data table here... https://www.ford-trucks.com/forums/654024-maf-and-rwhp-with-and-without-an-intercooler.html#post5148711 , and air filter inlet temp is the only parameter that changed from one run to the next. The ambient air temp is 70F, and as is indicated in the table, the air flowing through the IC heat exchanger picks up 20F, and has a 90F temp due to the waste heat from the A/C condenser. From my previous analysis of the cooling system here... https://www.ford-trucks.com/forums/653632-high-altitude-effects-part-1-cooling-system-1-of-2-a.html#post5141462 , the RAM air flow through the radiator picks up an additional 50F due to the waste heat from the coolant, so that the air entering the engine compartment from the radiator is about 140F. This air mixes with some cooler air from a Zoodad hole and other sources to give about 130F for the air filter inlet temp using an open element air filter. If you slow down to pull a grade in a lower gear you lose most of the RAM air flow through the radiator, the air temp exiting the radiator increases to 205F which triggers full lockup of the cooling fan, and the air filter inlet temp using an open element filter increases to about 190F. I've confirmed these kinds of temps by using my remote thermometer attached to the under hood fuse box.

The curves in pic #1 give the bottom line as to what happens if the driver applies enough additional throttle to maintain a constant boost pressure as the air filter inlet temp increases. Except for a slight variation with increasing boost, what's basically happening is the following. For 130F vs 70F, the AD decreases by 11%, but if enough throttle is applied to maintain a constant BP, the CFM increases by 7% so that the MAF and RWHP only decreases by 4% instead of the 11% decrease that would occur for a constant throttle and constant CFM condition. Likewise, for 190F vs 70F, the AD decreases by 22%, but if enough throttle is applied to maintain a constant BP, the CFM increases by 14% so that the MAF and RWHP only decreases by 8% instead of the 22% decrease that would occur for a constant throttle and constant CFM condition.

Now keep in mind that these results are for an early 99 engine, and it's possible that for a 99.5 with its larger turbo, IM, boots, and plenum, and less restrictive IC, that just maintaining a constant BP might result in hardly any decrease in MAF and RWHP as air filter inlet temp increases. For my early 99 my model indicates that instead of just maintaining BP, I need to increase the BP by about 3 psi to get back the last 4% in MAF and RWHP for 130F vs 70F, and to increase the BP by about 5 psi to get back the last 8% in MAF and RWHP for 190F vs 70F. These numbers seem to match my SOP when towing under the assumed conditions. It's possible that for a 99.5 no additional increase in BP is required to get back to the original MAF and RWHP as air filter inlet temp increases, and just applying enough throttle to maintain the original BP might be sufficient.

Also keep in mind that 70F vs 130F and 190F is about a worst case comparison when towing. When running empty, it might be more like 70F vs 100F for the difference in a cold air intake vs an open element intake, and this is only a 5.5% decrease in air density, and that only leaves a 2% decrease in MAF and RWHP at a constant boost for my early 99, and maybe no difference at all for a 99.5 engine. I point this out not to diminish the advantage of a cold air intake, but to illustrate that it would be hard to tell any SOP difference when running empty.

The curves in pic #2 give the actual CFM, MAF, and RWHP for constant BP vs increases in air filter inlet temp at 2800 RPM, and pic #3 gives the turbo outlet air temps and inlet manifold air temps. As can be seen in pic #3, at a BP=15 psi, increasing the air filter inlet temp from 70F to 130F to 190F increases the IMAT from 149F to 174F to 199F, but he actual turbo outlet air temps increase from 287F to 370F to 453F. So at a constant 15 psi BP, 60F step increases in the air filter inlet temp result in only 25F step increases in IMAT, but result in 83F step increases in TOATA. The larger increases in TOATA are due to the combination of 60F increases in the turbo inlet air temp, and the increased workload on the turbo as the throttle is applied to increase the inlet CFM for the hotter inlet air so as to maintain the constant 15 psi BP.

Even though the IC recovers a lot of this increase in TOATA , and allows the MAF and RWHP to be maintained almost constant by applying more throttle to keep the boost constant, doing so runs the turbo at a much higher operating temp than with a cold air intake. Also, my model only gives the compressor side increase in air temp, applying more throttle to maintain a constant BP as air filter inlet temp increases requires more drive pressure on the turbine which also leads to more heating of the hot side of the turbo. This is yet another reason why I think my turbo wore out within several years of switching to an open element cone filter. Typical wear out models indicate that the rate of wear increases exponentially with increases in operating temp.

 

Gene- Now that is some great stuff that is really making me reconsider my 6637 given the amount of towing I do. And what you show corresponds perfectly with my real workd towing results. When towing heavy up a grade I am fine EGT wise so long as I can maintain speed. Once I slow down much, then the EGT's start getting out of hand which causes me to slow down even more, and so on.

So what I gather from your example is that without a fresh air intake and when under heavy load, the truck is in a nasty closed loop cycle. Engine heat causes Air filter intake temp to go up. Higher intake temp results in less power and more throttle. More throttle results in higher boost and more engine and IC heat, which then causes higher air filter inlet temps, and just keeps going in a degenerative loop. Where with a fresh air intake, Turbo inlet air temp stays mostly constant regardless of engine bay temp and road speed. So the higher the load and engine compartment temperature, the larger the benefit of a fresh air intake.

I may very well have to find a fresh air intake, a local mountain and do some before and after testing noting AIT, MAT, EGT, and boost at a given road speed. I know I haven't always agreed with some of your analysis, but this one I'm all over

 

The "degenerative loop" is an appropriate description, and when that radiator cooling fan starts locking up things really degenerate as that fan starts draining 20 to 40 more HP (depending on RPM) from the engine, and you've got to push even harder on the throttle to regain that lost HP.

Wait until you see my analysis of the effects on the turbo and engine due to operating at high altitude. There are several other factors involved as well, but when you start climbing a mountain grade the atmospheric air pressure starts to decrease, and this has an even more dramatic effect in reducing air density than increases in air filter inlet temp. Now the "degenerative loop" quickly tightens into a "noose" that really starts choking performance big time, and requires a lot more throttle to get the boost much higher to get the lost HP back. Of course a fresh air intake can't undo the effects of lower atmospheric air pressure, although RAM air does help a little, but it can help with the reductions in air density caused by hotter intake air, so at least you don't have to battle both of those factors at the same time.

I'm considering wrapping some shiny metal tape around the black rubber inlet boot to the turbo, and around as much of my AIS box and snorkel that I can reach without removing it. Every little bit helps stabilize the "degenerative loop", even if only a little bit.

 

Gene, I took my AE with me on a trip tonight and noticed something interesting. My MAT was always lower than my IAT. No matter what boost pressure I was running, it was lower after the IC than what the filter (pre turbo) inlet temp indicated. My IAT sensor is located directly under the open element 6637 filter, zip tied to a bundle of wires there.

I'm curious about your thoughts on this? How could my MAT temps be lower than my IAT temps? I even recorded about 45 min of it if you'd like to see the data log, just email me.

On a side note, I could see increases in the engine temp compartement when I would give the truck more throttle, as indicated by an increase shown on the IAT sensor.

 

Any thoughts Gene, on why my MAT was lower than my IAT?

 

Jeremy, this is the info I have been asking for repeatedly. I'd like to take a look at what you have. But can you just post a couple examples here of what you saw? I've been putting off buying a copy of AE, but now that I'm back at a full-time job, it may have just been bumped up on the priority list...

Also, I was told some time ago that those to sensors display their data in two different units (one is in C, the other F). Can you confirm?

EDIT: Also, do you have the ability to try a different intake (like putting the stock box back in, etc.)??

Joe

 

Well you are in luck Jeremy. I just logged the heck out of some stuff today too testing the 6637. My IAT was alot higher than my MAT too. All the time. I have a good idea why too. As Gene has pointed out, there is a lot of hot engine compartment air getting sucked into the filter. That hot air, despite being compressed by the turbo gets a significant cool off in the intercooler.

At least that is my theory. I was not looking at those numbers when really getting into the boost up a hill so I will have to review the tape. Curiously, it was in the low 90s and I was running tha AC. The MAT still ran lower than the IAT the times I looked at it.

Oh, Jeremy, I noticed that my manifold boost number on the AE was consistantly 1-2 PSI lower than what my gauge was showing, even allowing for the sampling rate. Have you noticed that too?

I will not be posting my numbers on the 6637 unless someone is really wanting to see them. I do know that I was able to pull over 10'' of water at 21psi.

 

Mike,
That was exactly what someone posted a long time ago. And that's why I've been asking repeatedly for exactly what you guys just provided.

When are you going to swap to a different intake? You've been running the 6637 for some time now with the current test setup...

 

Joe, they were both in F on mine, I just pulled up the file on the laptop. I monitored AIT, MAT, Manifold Gauge pressure, ICP pressure, ICP duty cycle, Engine RPM and barometric pressure for this particular run today.

I filmed the event. I am going to try to burn it onto a DVD or at least my DVD recorder hard drive for starters. I may be able to upload something sometime but not tonight for sure. I will try to get something for you.

 

My AE says both are displayed in *F. A few examples, IAT/MAT: 115/104, 111/102, 117/111, 108/100, 120/106, 104/102. Ambient temp at this time was fluctuating between 88 and 90.

I do not have any other form of intake to test. I threw away the stock stuff a couple years ago.

I also notice that boost displayed on AE is consistently 2 or so psi below what my Autometer displays.

 

Man Jeremy, I gotta review the tape. I thought mine was a lot more of a diff than that. I can't do it right now because the Titans are spanking the Saints.

 

Keep in mind this was running empty at around 75 MPH. I tried to slow down at the bottom of hills and give it throttle to accelerate up the hill and raise boost pressure, but I70 towards St. Louis from Columbia is pretty flat.

Looks like the Titans just sealed the deal with that interception.

 

Yeah, give me a few minutes to look at that tape again just for those #s.

 

OK, 136/115/5.1, 138/115/7, 140/117/8, 125/109/2, 129/111/4, 136/115/7.5, 140/118/6.5, 143/126/11 .

Just some #s from different hills where IAT/MAT/Manifold Gauge Pressure. I will say that the manifold gauge pressure psi is way off from what my Dipricol was showing. Way off. Sometimes as much as over 10 psi. If this is what the PCM is seeing, I may need to fool with my OBA ****. What do you guys think?

 

I would like to know what BP corresponds to these IAT/MAT values? From this report it sounds like a BP of about 5 psi? If it was, a BP=5, MAT=111, and a TIT=110 is consistent with the pic #1 below. My measurements in the brake cylinder/fuse box area where your IAT is located indicate that's a relative hot spot due to the stagnant air there. Your IAT is probably reading a little higher temp than the actual turbo inlet temp (TIT) due to your Zoodad hole bringing some fresh air to the front portion of your air filter.

Since your IAT is in stagnant air as opposed to being in a 30 mph RAM air stream where it's supposed to be, there's no convective cooling of your sensor, and that will also make it read hotter. 1) Thanks to all who've taken an interest here. 2) I've been neglecting FTE some because my 65th birthday present was a nice case of SHINGLES. At least my new MEDICARE card came in handy! 3) I need data like Tenn gave that includes BP to see how MAT vs BP matches with my model. 4) In pic #1 below, I highlighted in green a few BP vs MAT points that seem to match Tenn's results fairly well. Pic #2 is the table of input values for this run. As you can see in that table, there's a number of parameters that effect MAT. My IC and turbo aren't as efficient as the 99.5 version, and those efficiency #'s greatly effect the MAT, does any one have those #'s, like maybe jtharvey for your upgraded IC and turbo?

In closing I hope that the comments about the MAT being lower than the IAT aren't leading people to think that by lowering the MAT the IC is somehow compensating for having sucked into the turbo the hotter IAT air to begin with. As I tried to explain in the link I gave in this thread, to my thread on the IC, that's not the case at all.

The IAT along with the CFM going into the air filter inlet is what determines the MAF (lb/min) that flows into the cylinders. This MAF is given by MAF=CFM*AD, and the AD here is determined by the IAT and not the MAT. This MAF is really the # of air molecules per min that flow into the air filter, and these molecules get hotter as they go through the turbo, and then they get cooler as they go through the IC and into the engine, but their #/min and lb/min flow remains constant from the air filter inlet all the way into the cylinders.

The MAF (lb/min) starts at the air filter, and it's determined by the IAT and CFM into the filter, and the same MAF (lb/min) exists at each and every point in the entire air flow path from the air filter to the intake valves. Heating or cooling the air flow on the way to the intake valves only effects the air flow CFM so as to keep the lb/min a constant. If the lb/min weren't the same everywhere, lbs of air would be piling up somewhere, or the opposite, a deficit would develop. If you cool the air, it gets more dense, and the flow CFM reduces so as to keep the lb/min a constant. When you heat the air flow the opposite occurs.

So why do we have an IC if cooling the air and reducing the MAT doesn't put more lb/min into the engine? Because with an IC we don't have to run the BP as high to get a given lb/min into the engine. This means the turbo doesn't have to work as hard, and when it hits its max BP, the max lb/min into the engine is higher with an IC than without. However, once you establish a given CFM and IAT at the air filter inlet, that establishes the lb/min that's going into the filter, and that's the same lb/min that's going into the cylinders. Having a good IC to get a lower MAT just means that it takes less BP to push this given lb/min past the restriction of the intake valves and into the cylinders.

The turbo is a constant volume or CFM compressor. You push on the throttle to drive the turbine, this spins the compressor, and that establishes a given CFM at the turbo inlet and at the air filter inlet. Now it's up to you (not your IC) to determine the IAT of the air that this CFM sucks into your turbo. If you decide to suck hotter air than is necessary into the filter at this given CFM, that determines a lower than is necessary lb/min flow into the turbo, and all that an IC can do at this point is to lower the MAT which then lowers the BP required to force this lower lb/min into the cylinders.

I know I've been repetitive here, but I've tried many times in different ways to emphasize the importance of not sucking in hot air, and I just got a little carried away! BTW, there's a good review article on the 6.4L in the new PSR magazine, and it explains how fueling is done almost exclusively by using the IAT1 and MAF sensor at the air filter, but they do adjust fueling some with the IAT2, which is what our MAT is called on that truck.