Cool, thanks for the explanation.My fault, I skipped the important part.
Unfortunately it's because the hpfp can't flow the fuel to the injectors in the first place. On 93 the limit of the hpfp's flow is ~350whp. To get beyond that you need to supplement the fueling somehow, and the best way to do that is to split the flow just prior to the hpfp, and route it to additional injectors mounted post throttle body.
They are hard to find over here, i had a good look and looked at costs. As i would need a custom exhaust manifold and buy the head (which is similar cost to a second hand engine over here) i deemed it a no goTobad you can just swap to the FRPP head that has individual exhaust ports.
Sent from another garage.