Proflow does not sacrifice quality for a low price- you get both with our aluminium cylinder heads. Our LS3 cylinder heads are designed for street / race performance engines to give the ultimate in flow at a competitive price. Cast from A356 aluminium, these 15° LS3 rectangle port heads are designed to fit LS series engines with a 4.00" or larger bore. These bare 275cc heads accept 2.165" diameter intake valves and 1.60" exhaust valves and have a 0.625" deck thickness. Suits 6-bolt standard or LSX block designs.