One of our faithful Ace supporters in the UK got himself one of those new production Hitchcock's Big Heads last year. The one with the normal(smaller) ports.
He rode around with it for a while, and it was okay, but nothing to jump up and down about in the performance department. So, he contacted me to see what we could do with it.
Well, after a thorough examination and some preliminary flow bench work, it was found that it flowed a bit better than the normal head, and probably around the level that one of the typical "tuned, gas-flowed heads" would do. The regular Ace/Mondello head did quite a bit better, so we thought we might have a chance to make this Big Head even better than our Ace/Mondello head.
And it turned out that we were right. After some careful porting and valve job work with new custom Manley Racing valves and the full custom Ace valve gear with the beehive springs and titanium retainers, along with a flowed/matched manifold stub, we were able to improve upon the normal Ace/Mondello head by about 10%-12% on the flow bench with this new Ace Big Head mod. It flows a little bit over 220 cfm at the same .350" lift that the Ace Magnum Cams have, and he has those cams on his bike already. That's somewhere around 45 cfm better than when he sent it in to us, which is about a 25% increase in peak flow from stock to now.
And the ports aren't oversized with this mod. It still uses the 32mm manifold I.D. for our Mikuni TM32 that we like to use. It just flows better.
The Big Head has a pretty stiff price tag, just for buying the head alone. Then add the Ace modifications to the ports, and this becomes a big ticket item. I don't expect very many people to be doing this. But, it did come out well.
Before we send it back to him, we are looking into something we might be able to do with the rocker arms.
If that happens, I'll update and post some pics.