On my '85 Quantum TD I removed and plugged the line from the compressor section to the wastegate, so now I have no wastegate at all. That raised the boost from 9 psi max to 12.5 psi max, and gave me a noticable increase in acceleration.
I think lean/rich applies to diesels. But of course it's not uniform throughout the combustion chamber like it is with gasoline motors. On a diesel some areas in the combustion chamber (right near the injector spray) are getting much more fuel than others (dead space in the main chamber). The areas with more fuel are rich (sometimes too rich, if it's smoke) and the areas with less fuel are likely lean. Increasing the fueling beyond the smoke level will make some of the areas overly-rich, but will also make some of the areas that used to be too lean richer. That's why turning up the fuel even when there is smoke will continue to give more power. Because mixing isn't as good in a diesel (where the fuel gets milliseconds right before TDC to mix) as in a gas engine (where fuel is mixed close to perfectly before it enters the combustion chamber), the diesel will make less power for a given air quantity than a gas motor.
Stan, I bet if you plugged the outlet hose on your safety valve, you'd find the boost would be over 25. If your wastegate is disabled, likely the poor little turbo is just screaming, but the safety valve limits boost as it should to around 12 psi. At that level, the turbo will be making way too much heat too. I bet you'd go faster if you did plug the safety valve outlet, and make a simple, gated boost controller to make the wastegate limit pressure to 12 (or whatever you want) thereby reducing the heat being generated by the compressor.If you want, I can show you how to make a simple, reliable gated boost controller.
Combustion temperatures have a bell-shaped pattern in relation to the fuel-air ratio, with its peak just lean of stoichiometric (which not coincidentally is the point of optimum thermal efficiency in any engine, the reason of which can be attributed to thermodynamics). At either side of the peak, combustion temperatures fall off pretty quickly, and when you get to the fuel-air ratio regime that a Diesel operates in (> 18:1), the bell shaped curve has pretty much flattened such that there's not a heck of a lot of difference when you change the F/A ratio. Note that the bell-shaped pattern is surprisingly pretty INVARIATE REGARDLESS OF THE FUEL USED (comparing within hydrocarbon fuels; hydrogen and alcohols are slightly different).
If you want, I can show you how to make a simple, reliable gated boost controller.