Hi Mace ECOTEC PERFORMANCE 12MM PLENUM SPACER Holden 3.8L V6 VS VT VX VU VY - Mace Engineering Group I have given up on the aluminum spacer and try the plenum the space as per the link above. Quote from the website "Plenum spacer is a special spacer that sits between your plenum cover and intake manifold. Its main purpose is to improve air distribution (like our twin throttle manifold) between cylinders by slowing down the air speed inside the plenum chamber. As a result there is less of a pressure drop inside the plenum chamber between cylinders, and less air momentum, resulting in better air distribution and power. Not only will our spacer help you make more power, it will also help prevent any costly rebuilds through dangerous lean outs that occur with these standard manifolds in high horsepower/boost applications (due to poor air distributions). In addition to improving air distribution between cylinders, the increase in plenum volume also increases low down torque." I would like additional infromation in how increasing the plenum chamber volume and slowing the down the air speed increases low down torque. There is not enough science in the above statement as to the how the evening out of the distribution and less pressure drop increases low torque over and above what Holden did with the original plenum design. Did Holden get it wrong ? Does your R&D work and calc's to resizing the plenum spacer thickness prove Holden wrong ? It is also sold as it improves throttle response ie quicker. How can the throttle response be quicker if there is a slow down in air speed. Engine builder has told me with the plenum spacer the throttle response will be less responsive and slower due to the slow down in the air speed. These are genuine questions not internet trolling to take the mickey out of you.