If your looking for improvements in economy and are considering smoothing out the castings; it might be worth seeing if you can get a better manifold first. Not sure if there are any available for your engine?? But I know from experience on other cars better flowing inlet manifold, ones that have better angles and bigger tubes are a good place to start if you're looking at doing some mod work in that area of the engine. Years ago extractors were also a way of improving economy although I'm not sure if it will make any diff to your car. I'm more referring to old Holden's that we used to drive and play around with back in the 80s.
@losh1971 Yes mate that is exactly what I am trying to do, I'm not trying to increase the horse power (although any positive benifits I get out of the changes are welcomed). It would be great if I could find a new one but the price would probably kill the joy of finding it, Hahahaha!
Also about extractors? Haven't all the Commodores got headers now? Would there be much difference? Between the headers and extractors? I suppose there would be an improvement with extractors, I'll think about that one? I do have a 2.5 inch single system of the headers now, so that will do for a while until it needs to be changed, and that's when I'll think about the extractors. Good point though losh1971.
I just picked up a second hand Plumen and Inlet Manifold of a VY V6 Ecotec for $100 which I think is a great price. It means I can play with this off the car and not damage the original one. It also means (when I have time to play around) I can test the difference between the original Plumen and Manifold and the port and polished Plumen and Manifold and? With and without the insulator spacer, so that should be fun.
Eventually I will port and polish the heads, but I wont do that until they need to be removed, plus I'll look at the cost of new heads versus reconditioning the heads? Recoditioning could mean shaving, which leads to a higher compression? And I'm not sure if I want that to happen. But anyway that's in the future, don't need to think about that now. Can you suggest any good brands for new heads?
Also? I found that High Voltage Coil packs will add an improvement, the information and feedback I have read from this is that? It improves the idling? What's yout thoughts on High Voltage Coil packs?