Aussiespeed Ford crossflow and OHC plenum pig insert reduces plenum volume for faster acceleration and better throttle response. We have found that some engines respond different due to cylinder head mods, camshafts and RPM ranges with some engines not needing the CFM or sometimes engines with larger camshafts may need a bit of help getting into the power band.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 make your engine produce better torque at lower RPM for better throttle response.This pig is designed to fit our AS0015 and AS0014 Ford Cross Flow and EA to AU overhead cam engines. The AS0241 AussieSpeed Plenum Pig inserts sit over the top of the existing shaped plenum floor and requires a single bolt hole to be drilled through the manifold floor once the insert is in position,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 and 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 and supplied with 1 bolt,washer & nyloc nut. Due to the even flow of Aussiespeed manifolds we suggest that power valve sizes be reduced. We have found that increasing the main jet size by 2 sizes from standard and on some engines going as low as a 2.5 power valve can stop the fuel from laying in the bottom of the manifold and upsetting the air flow.