The original dual idler gear drive. No timing chain to stretch. As simple to install as a stock timin.5.5g chain. Dyno test show no loss in horsepower and the ultimate in cam timing accuracy. Fits under stock cover. Complete kit includes offset cam bushings, roller thrust button, bronze thrust ring, locking cam plate and bolts. These dual idler kits are available two ways - Relatively quiet or (N) noisy (mild supercharger sound).