During the development of our Aussiespeed Manifolds we have found by changing the shape of the plenum can be an easy way to increases torque, horsepower and in some engine produce better torque at lower RPM for better throttle response without a loss at the top. Aussiespeed Plenum pigs can be easily removed and are easy to fit.The pig can be fitted to most 2 or 4 barrel manifolds where the bottom of the manifold can be easily accessed. AussieSpeed Plenum Pig inserts sit flat on bottom of manifold sometimes trimming of Plenum pig or manifold may be required. It is very important that the Manifold and Plenum pig insert are absolutely free of contaminants. These include fuel, oil, sand, filings etc. It is a good idea to use a degreaser or cleaning fluid before installation.It is also recommended that the pig & bolt have a small amount of fuel resistant sealer on the bottom. Once installed fuel mixtures will need to be checked, Due to better atomization in most cases your carburetor may require leaner jets. The pig comes drilled & supplied with 1 bolt, washer, nyloc nut. Some manifolds may require longer bolts when fitting in universal applications.