For the same reason they want 440 heads on their 383's
Same deal with 1.6 and 1.7 rocker arms!
IMO I have discovered like many other builders that a HV oil pump isn't needed in most cases, especially if all your clearances are within tolerance.
HV pumps take a HD drive like has been mentioned and takes extra horsepower to turn it. Those who say they have never ran out of oil with one and a stock 4-5 QT pan has never run there car for a extended periods of hi RPM to know. My
My current 340 with a 7 qt pan has a used standard oil pump in it. I ran it hard and long at 4500-5000 rpm for over 5 miles at time on the salt flats. It held up and the gauge held steady oil pressure the whole time. With a used standard oil pump when I put it togeather in 2007.
