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I doubt 30 can be done in a street drive-able trim. It would have to be a big turbo so without fancy variable vanes etc its going to be rubbish at low revs. You could look for obstructions in gas flow ie air intake system exhaust system air filters etc. All will choke the turbo. Also you might be at the limit of the injectors. If they cant inject more fuel then the only answer is bigger injectors. By the time you have a 4 inch no bends or mufflers exhaust and a straight 5 inch inlet pipe with no air filter 50% larger injectors and up the pumping capacity you should go a little better. Then add lpg injection and Mr Plod will confiscate your car under boy racer rules but a 13 second quarter in a 2 ton 4wd always looks impressive.
The other possibility is that your boost gauge doesnt read above 18

Are all Belt driven pumps right spin and all gear driven pumps left spin?. Looking at the Belt and the Gear driven 4j engines with the timing covers removed it would seem that way.
i have eyes on a gear driven 4jg2 pump but i can't see the VE4 part number so i don't know if it is left or right spin

All gear driven pumps run opposite to belt driven, if you get complete engine you can just swap everything onto your engine