[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.