No worries mate, love keeping the old 4ac's going hard, lol
The 4ac would probably only need a 2 inch system, but if it's only temporary and you were using a 4age in the future I would go 2 1/4. A 2 1/2 might be too big for a 4ac and make it real sluggish down low. That said I'm just pulling this from work I've done on other cars, but it should be applicable to the mighty 4a motors
