The decision should really come down to which one is going to perform best in a motor being built for strong mid-range torque in a car that lives in the steep and winding roads between the South Coast, the Southern Tablelands and the Alps. Power is needed most from 3,000 to 5,000rpm. Specs include NB8B pistons, stock NB cams and lifters, mildly ported head, long 4-2-1 headers, tunable ECU, 91 fuel.
I'm setting up an NB8A head right now. It's pleading me to bolt a manifold on and throw it on the car. I have NA8 and NB8A manifolds sitting beside it on the bench, as well as an adaptor flange that lets me bolt the NA8 manifold direct to the NB8A head. I've had no luck finding an NB8B flat top manifold.
The NA8 manifold is in better shape and is much much easier to fit, despite some detail issues.
The NB8A manifold is rougher and is missing a couple of bits (NB fuel rail and VICS solenoid). I may also need to swap the ECU or at least install an RPM switch to activate VICS, assuming it's worth the effort.
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