Part 2.
The stock Fuel Pump and in filter FPR needs to service 6 injectors delivering 450cc/min = 162,000cc/hr = 162L/hr at the stock fuel pressure regulators setting of 3.9bar.
Now this includes the 30% head room mentioned in the first post. So really its 113L/hr.

Applying the +25% more fuel requirement for a stacked 1.5bar manifold pressure makes 113Lphr into 140Lphr.

Now looking at the fuel pump curves for the Stock pump, the WalbroGSL392 and the SL55 below.
A NEW stock pump can deliver 165Lphr at the stock FPR pressure of 3.9bar. So it should be able to service the stacked 1.5bar (22psi) condition if you simply change the injectors. However if it's worn and running 10% off spec, say at 145L/hr you going borderline and an upgrade to the Walbro would be recommended.

You can see the SL55 is way off scale and all that excess fuel is simply getting recirculated back through the filter to the tank.


Now if you were thinking you could keep your old injectors and just change the FPR and pump....the stock pump will only do 115L/hr at the 5.5Bar FPR setting - but you need 140!....no dice.
In that case you'd cover it with the Walbro again.
Yes - this is telling us that an FPR of 5.5bar off a new Walbro (or SL55) pump should deliver enough fuel to feed stock injectors fuel to support 22psi boost.

L8tr....I just wanted to check the fuel line losses aren't too significant and it comes out at about 0.2psi for 3/8th" ID steel tubing at 140Lphr (0.6GPM). Which is getting significant and worth keeping in mind.