actually, its quite substantial. Head flow stock for stock features a huge advantage to the poly over the LA. In stock form, they flow over 220 cfm, ported, they can reach 300 cfm. with the port spacing and heights to have a good to great velocity as well. compare that to a stock 318 LA head that maybe 150 cfm max out of stock, 302 style LA heads, 135 cfm out of other swirl port heads. For comparison, a Eddy Victor set of LA heads flow 295 fully ported and polished per Hughes Engines.
