Sea Level vs Altitude Tuning

[soutthpaw]

Ok so I was right on the Timing, I remember reading something about someone doing dyno testing in Boulder then they went back to the flatland somewhere and said they had to retard timing 5 to 10 degrees.... that seems like a lot to me but who knows. So I want to add fuel for the low boost to try and help it spool up quicker... guess i need a different turbo and injectors.... Ill wait and see what Bill has to add... Having been at Edge in Utah he must have had an opportunity to work with some high altitude tuning

[soutthpaw]

I was looking at the ALtitude and Sea level Timing maps and what I see is the pic below, My question is that the sea level tunes are all different, showing 6 different maps yet the Altitude map is the same for all six maps... Do I need to copy the Maps from the sea level over to the high altitude map for each tune or is the high altitude disabled somehow...
If so, I am open to suggestions on how to figure out by how much to change the altitude maps.... I/ or You can remove the image link if you want as its propitiatory

[cleatus12r]

I certainly don't think there's an issue with the graphic posted. Bill seems pretty ok with screenshots.

As far as the altitude table goes, the SOI is already higher than the sea level map in certain areas (and across the board on the stock map). I am not going to give potentially destructive advice on high-altitude SOI. Bill will probably be more helpful. I would THINK that it would be possible to "crank up the timing" on the high altitude SOI map....but I'm not going to say one way or another.

Now, Jack....

The thing we have to remember about diesel engines is that they use the control of FUEL to alter engine output. In a perfect (and naturally aspirated) world, there will always be 7.3L of air expelled per every two crankshaft revolutions. We know that's not possible due to volumetric efficiency and other factors that alter flow. That being said, there is A LOT of air being pumped through a diesel. Yes, it is possible to attain 30, 40, 70, 90, 120 PSI of boost; it's usually not really hard to do.

We need to get a little into engine mechanical design to see where this boost is coming from. First, the airflow potential comes into play. I've already discussed that. Secondly, the camshaft plays a very large role. Turbo diesel engines use a camshaft that creates very little or no valve overlap. This is very important because under high-load conditions there will be more pressure in the exhaust manifold-to-turbocharger plumbing then there is boost in the intake. If both valves were open at the same time (intake and exhaust for any given cylinder), what would happen? Passive EGR would be the result. We both know that's bad for performance. However, the downside to high drive pressure (pressure in the exhaust before it reaches the turbine housing) is that the pistons themselves are pushing against that pressure when the exhaust valves open....robbing power.

On a stock setup (99 and up 7.3L) the turbine housing (exhaust side) is very restrictive. This is GREAT for low-speed spool up. However, it begins to become a hinderance above about 2500 RPM....especially under load and ESPECIALLY with more fuel (chip, injectors, etc.). The pressures exerted on the turbine wheel are massive and the drive pressures can exceed 40 PSI on a stock (or near stock) truck. With 40 PSI driving the turbine wheel and subsequently the compressor wheel, there is a lot of "power" to drive the compressor at very high speeds.....this equals boost. Without getting into turbocharger maps and usage, it's easy to see where this boost comes from. Adding fuel at the right time or adding MORE fuel puts more heat into the drive side of the turbocharger. The more heat that is dropped across the turbine wheel (hot gasses expand as they cool) when the pressure is no longer there, the more efficient the drive to the compressor.

Now, with more correctly timed and injected fuel, the boost level will exceed 25 PSI. Using a stock turbocharger at these kind of boost levels is dangerous.....the drive pressures can skyrocket....like 60+ PSI on a stock turbocharger at boost levels around 30 PSI. Under load with a stock turbocharger, this means that there is the possibility of damage due to axial loading of the turbocharger shaft.

More boost does not always equal more power. Once the stock compressor housing creates about 25 PSI (changes with altitude), it's not efficient anymore and it is merely adding a TON of heat to the intake charge for the intercooler to try to cool off. Airflow (and quality of air) is far more important than a higher boost level on a near stock truck. Adding a more efficient turbocharger (I'll use the Garrett GTP38R ball bearing unit as an example) will allow more air to enter and exit the engine. The added boost from the larger compressor (even though it is shrouded/ported) is largely due to the amount of air it can move from the atmosphere into the intake tract. There is less resistance to shaft rotation with the ball bearings and the exhaust housing is less restrictive. This means more (or the same) boost levels as stock, less exhaust restriction (for the pistons to push on), and cooler pre-intercooler air temps.

My fingers are tired.

[cleatus12r]

http://www.youtube.com/watch?v=9ITmlyKzzg8

http://www.youtube.com/watch?v=oB4Ug...eature=related

http://www.youtube.com/watch?v=hwQBj...eature=related

My favorite...The guys who put a boost/vacuum gauge on a diesel.
http://www.youtube.com/watch?v=ffO-Hmcgw7c&NR=1

[soutthpaw]

Ok I think I am gonna leave all the WHY questions to you now Cody.. then at some point I am going to put them all in one thread and get Jack to make them a sticky... Excellent explanation as usual. I give it

As for my previous post, It looks like the Timing is an actual setting and not a modifier? that's why I thought it should be different for each different map... Here is the Stock sea level vs altitude map

The part that is Highlighted in yellow I thought was interesting.. Reason being is that we know the burn(Combustion) time is a constant at the selected altitude.. so if the engine is turning faster you should need to start the Burn earlier given the same amount of fuel. Right?
so why does the stock setting retard the timing so much in the higher RPM's in that sea level map.. also it seems like there is a mid RPM range that requires retarding the timing a bit that I am wondering the reasoning behind it (is there another modifier somewhere in the parameters that justifies the retarding of the timing that I am missing)

[soutthpaw]

Originally Posted by cleatus12r

My favorite...The guys who put a boost/vacuum gauge on a diesel.
http://www.youtube.com/watch?v=ffO-Hmcgw7c&NR=1

What do you expect from a guy driving a Dodge
And they even know their trucks suck cuz they never refer to them as a Dodge, always as a Cummins... cuz they know the packaging it comes in is

[Jackpine]

Cody, thank you. That was a very good explanation of the details of diesel turbocharging and I appreciated the videos too. I had no idea it was possible to attain that much intake manifold pressure. I also hadn't thought of the undesirable effects of compressive heating on the air charge on the intake side. It's a bit of a balancing act, isn't it?

And southpaw, I really didn't mean to sidetrack the thread with an argument over the amount of boost possible. I was really just trying to answer one of the questions you asked in your first post: "The Turbo in general is supposed to offset the effects of altitude found in naturally aspirated engine. So I am wondering why the altitude parameters are needed..." And, I'm going to stand by my original response: That 28 psi boost you have at sea level is not going to be possible with the same turbo in Colorado Springs. Since the ambient pressure there is 11.77, you're probably going to see 23.5 psi. As the ambient pressure drops, the turbocharger has less input to work with - it cannot make something out of nothing. Therefore, altitude has to be a factor in any tune for the engine, right?

Since Cody's a moderator, southpaw, he can make any thread a "sticky" - I don't have to do it! And I agree with your opinion of his answers!

- Jack

[soutthpaw]

I also need to ask Bill if I/he can post the last paragraph of page 36 of the Minotaur manual. its one of the best explanations about the importance of Oil selection for a diesel and its many functions....

Ok, My son went down for his nap so I was able to get my test tunes loaded along with the one Cody sent me... Ill go try them out after he is awake again...
One of my test tunes is with the torque converter locking in all 4 gears.. took a quick spin around the block and seemed drivable so thats a good start ...

[cleatus12r]

Originally Posted by soutthpaw

Ok I think I am gonna leave all the WHY questions to you now Cody.. then at some point I am going to put them all in one thread and get Jack to make them a sticky... Excellent explanation as usual. I give it

As for my previous post, It looks like the Timing is an actual setting and not a modifier? that's why I thought it should be different for each different map... Here is the Stock sea level vs altitude map

...........we know the burn(Combustion) time is a constant at the selected altitude.. so if the engine is turning faster you should need to start the Burn earlier given the same amount of fuel. Right?
so why does the stock setting retard the timing so much in the higher RPM's in that sea level map.. also it seems like there is a mid RPM range that requires retarding the timing a bit that I am wondering the reasoning behind it (is there another modifier somewhere in the parameters that justifies the retarding of the timing that I am missing)

The problem with tuning the 7.3L is that there is no table ANYWHERE that sets start of injection. There are numerous factors that come into play and the the SOI tables are just another "modifier". Injection pressure control, engine oil temperature, boost pressure, etc. all play a part in when the PCM DECIDES to initiate SOI. It's not a simple "oh, 7 degrees BTDC is the "timing" and that's it." The PCM bases fueling rates and SOI on a large number of things.

Here's a hint as to why the timing table has a dip in it. Compare the MFD in the "ICP desired" map. See a trend? As the ICP ramps up quickly, the SOI takes a dip. Increased injection pressure actually advances the ignition point of the fuel in the combustion chamber due to better atomization and higher fuel rate (more fuel in less time).

Higher boost pressures in the higher RPM ranges affect the ignition point as well. More boost = higher dynamic compression = earlier ignition point. So therefore, a slightly less advanced SOI.

[soutthpaw]

here is a table I Just made that compares the Offset at altitude compared to sea level of the stock map as a way to look at different patterns.. I may put these values on a map just to see what it looks like in 3D


The highest advance group is at high RPM in the low to mid throttle range Based on the fact that there is a low mass fuel desired value (found in low torque demand situation).. which would most likely be found at high crusing speed... thus more advance under low load and best fuel efficency
oh the 55/2200 value is a typo, its supposed to be 9 not 90 heh