8 moves more fluid & 6 was used w A/C cause it had a faster pulley ratio (to spin the fan faster to move more air at idle/low speeds cause of the added A/C heat in the condensor) which made up for 2 less blades as Ma thought an 8 would then cavitate at higher rpms w the faster A/C pulley ratio moving the vanes too fast. Use an 8 & tack weld the 5 dollar anticavitation plate on the vanes & you have the best of both worlds.