I just picked up my HR heads from Gord Bush who cleaned them up for me and flow tested them. We of course have previous numbers from the non-revup heads that I had Gord Bush port – so let’s compare! Visually looking at the HR heads you can see just how much bigger the intake port is than the non-revup heads, and the numbers prove it – the HR heads flow the same as the ported DE heads (infact substantially more at low valve lifts). The exhaust doesn’t flow quite as well as the ported DE exhaust did, but it is still substantially better than a stock DE at high lifts.
One reason the exhaust flows less at low valve lifts may be due to the fact that the HR has smaller valves. While this may be counter intuitive to those of you that go out there and buy the biggest valves you can, a smaller valve shrouds the combustion chamber less, and in-fact promotes flow at higher lifts. My imagination tells me you want the smallest valve and biggest port you can get away with, without overheating the valve.
Once these HR heads are ported, we should be able to get a decent bit more exhaust flow and hopefully crack the 400whp barrier with shorter intake runners and exhaust runners. Wish us luck!