well. I have sort of the same question. but I think it has to do with the vtec signals and the P28 only has 1 and the P72 have 2. It's allows you to do both cams at the same time. that's my theory not sure. but I have a Gsr turbo and am using a chipped p28 ecu that has a 8500 redline and works great. vtec comes on at 5100. late