Ah - Injectors by my calculations at stock fuel pressure flow 330cc/min .... that's 15kg/h fuel flow (0.33 * 0.76kg - weight of petrol), times by 6 cyls - 90kg/h max flow, which at 12.5:1 AFR at 326bhp (246g/sec at stoich) nets you about 70.8kg/h fuel flow required. So you're well within injector duty max.


Regarding the plenum. I believe high plenum volume helps you at low and mid range, low velocity of air. A good example of this is if you watch the video on youtube of the Aussie guy that now owns a GT300 Z33 with it's huge plenum. Nismo did this to give them a small boost of mid range torque coming out of corners. When that volume of air ran out, they were then going through restrictors that limited them to 300whp peak.

I think the big thing is getting smooth direct flow, rather than volume for top end. This is very difficult in the confines of the Z's engine bay/bonnet. If you went as far as getting a dry sump and used the height difference to drop the engine down (like the GT300 Z) then it might be a lot easier!