Pretty much exactly where I think I'd find out that I ran out of knowledge 8psi ago.
Boost is not the killer.
High EGTs is.
Even then, it takes really high EGTs, over extended periods of time.
An older well known Aussie cruiser guru once posted pics ( on now defunct lccool forum) of exhaust manifold glowing red after driving 100's of km at 160km/hr on Aussie desert highways. EGTs steady at 800⁰C.
I don't suggest this is a good idea. In normal driving, with a diesel you'll typically only see peak EGTs for a few seconds at a time, maybe a few minutes of you're climbing mountain passes on the highway, foot flat to the floor, or pulling a heavy boat/camper/horse trailer etc.
I've tuned boosted and NA things on megasquirt, etc before.
Forget at least half of what you learnt about tuning if it was with gas engines.
Tuning a diesel is similar, but also some of it is kind of the opposite in a lot of ways.
In a gas engine, lean AFR means high combustion temps. Engine RPM is controlled by throttling the amount of air that the engine pulls in. Too much fuel cools combustion temps/EGTs and reduces power.
In a diesel, air intake is completely unthrottled, power & engine speed is controlled by how much fuel you squirt in.
Lean AFR means low rpm, and/or low power.
Turn the fuel down too much, it'll drop idle speed and you'll have no power.
Too much fuel creates heat, and raises EGTs.
Running a diesel with a lean tune means low power potential, low combustion heat.
More fuel generally means more power, but with a heat penalty and smoke.
You G-Turbo upgrade increases air flow at pretty much all engine speeds. More air in = leaner AFR = lower combustion temps, lower EGTs.
The turbo performance is also heavily dependent on his much fuel you squirt in. Lean AFR means low heat, but also relatively little exhaust gas expansion through the manifold and turbo.
The gas expansion is a big part of what drives the turbo. Old turbo conversions relied on smokey tunes to create a lot of heat and expanding gas through the turbo to drive poorly matched turbos from gas engines. This is risky.
Adding the Gturb, and not touching fuel settings is going to be safe. You may not see an increase in power. And performance may be dissapointing until tuned. But, you have a lot more air, and lower EGTs.
The other thing that controls EGTs is your right foot.
Even if your tune is currently ridiculousy rich, and you added the GTurbo as is, watch the EGT gauge, the EGTs climb high, back off on the throttle. Problem solved immediately.
Pushing a diesel hard at low RPM, high load, full throttle dumps a lot of fuel into a slow revving engine. This is when EGTs become high and dangerous.
Being aware of this, you can drive accordingly. Instead of pushing hard to crest that mountain pass in top gear with the engine struggling, downshift slow down a touch, let the engine rev. It'll thank you for being allowed to breath.
Diesels are slow revving compared to a gas engine, but they are happier at high RPM when working hard rather than laboring at low RPM
