Like Purdy says,driveability.I can hit the hill at 45 and top it at 45.The exhaust smells cleaner.Runs cooler.Fuel mileage up.I have a low mile roadster that was a pretty zippy car.I put a BF head on my pickup and now the roadster seems like a dog.I monkeyed with it for a while,looking for something wrong,but figured out it was the same as ever.The head just made that much of a difference in the truck.I have installed a few Snyder heads for customers,those are always,while it's in the garage let's do this or that.They seem to work well,the people I installed them for have nothing to compare them to except their before and after performance.I still have one new BF head,that one is going on the roadster.That was just a lucky find.I bought a bunch of parts that were from the estate of an A owner.There were 3 or 4 heads in the pile.I leaned them in the shed between the studs,and a couple years after I put them there I happened to look at one while setting out mouse poison.It had BF cast in the top of the head.At a close look it seems to be new.Funny thing was is that I bought the pile from a Model A dealer and appraiser,and he never noticed it.I never noticed it when I bought the stuff,I never look at the heads as they have gotten to the point where you have to take them when you buy the good stuff.He probably thought the same as I did,more iron to take up room and get rid of.