I was just about to buy Maces Plenum Spacer and Manifold Insulator. I've got a few other basic mods and upgrades for the near future so I got back in contact with some old friends in the race engine industry. One of his customers brought in an ecotec with a 12mm Plywood self made plenum spacer, straight away I thought oi.... that's a bit how ya going.... But he claimed to have put 70k kms on it since he made it and he had no problems. Now this starts sounding pretty dodgy at first but hear me out, apparently the ply works fine for a spacer but obviously ply isn't a good option for a Manifold Insulator, so what about layering some 6mm Fibre Cement then sealing the whole thing in hi-temp paint so it can't break down over time. I'm a carpenter, we drop fibro down on timber floors when we install fire places and with a fire cranking you can't feel heat in the timber under it after 3x layers (18mm) are down. There isn't a lot of detailed info about making your own spacers and insulators, I was hoping for a bit more than what I found.