The Motordyne plenum spacer flat spacer yielding the best overall gains, the motordyne 1/2"-5/16" plenum spacer outperforms the competition while keeping your strut bar and engine cover in place. This stealth modification adds 11hp-15hp and is the simplest to install. All motordyne melt proof plenum spacers come with quality parts, pre-attached gaskets and self sealing plenum internal supports for oem reliability.