Ok - so the plenum i've got waiting for my engine 'looks' a bit on the small side...

It'd be a real shame not to use it as its a very well made bit of kit.

Is there a formula i can use to see if its up to the job?

Or are there any 'rules of thumb' i.e

For 'XYZ' power you'll need a plenum of 'ABC' and a minimum throttle body diameter of '123' etc.

Cheers