260z
My engine-
F54 block, bored .040
e31 head with 504/310 cam
forged pistons, lightened flywheel, balanced and knifed edged crankshaft, 3.90 diff, close ratio 5sp.
currently running SU's with SM needles. I have a set of Mikuni 40's that I'm going to install. I'm wondering if I need to go with a electric fuel pump or would I be able to use existing mechanical pump? I also have a set of 44's that will eventually replace the 40's, they need to be rebuilt.

Your thoughts?

Thanks,
Patrick

The existing mechanical pump will keep up with your mikuni's. The SU's have a very touchy float and anything more than 2.5-3 psi overpower the floats and needle valves, spewing fuel everywhere.While I can't speak to how well the mikuni floats and needle valves hold up to the pressure, If you go electric, be sure to buy a low pressure unit. You will also want to invest in a low pressure regulator to dial in the right pressure.

Pepper,
With the 40's, I installed a Carter electric pump for carbed cars and a Holley fuel pressure regulator.

The mechanical pump keeps up with the S.U.'s just fine. I still run that set up on my track car actually.

And, your car originally had both. So it's both wired and plumbed for an electric pump to be used in conjunction with the mechanical pump. The only problem with an electric pump is the "safety" - how to make sure it shuts off in case of a crash... Nissan tried all sorts of things before they had an ECU capable of controlling the fuel pump. Still, it shouldn't be hard to wire the safties back up if you decide to re-install an electric fuel pump in your 260Z.