I agree with Jeffrpm about the repeat ability of CNC porting vs hand porting to some extent, but. I have seen some CNC porting that did not work better( or even as good) than hand ported heads, Why?
The cnc ports were simply poorly designed and while they flowed tons more it was all at lifts that no cams reached. This was no fault of the process but the programming Ie who decided where to cut and where to weld.
As anything experience counts for some things and a trained set of eyes to make decisions on what should be done is always one of the most important. I can not tell you how many times I have heard Mr. Meyers let a customer know a head was not worth porting based on the casting in his hands. That some times was due to the base ports would need so much material added the costs would not be worth the effort and some times because the owner won the head lottery and all the head needed was some clean up work. Castings and production machining are just that , good enough for production. Neither are intended to be the best and often can be improved but that experience may let you know if it is truly going to make a difference that is worth the work (and cost).
Jprecision does good work no doubt but I can not say I have seen any measurable benefits over traditional ported heads done by a EXPERIENCED porter such as Mr. Meyers, Mr. Ferracci, Mr Axtel (sp) and probably others. Do not kid yourself into thinking CNC is doing anything more than making the process more profitable as it is automated and performed by someone other than the guy who came up with the files. This is not a knock on cnc porting or Jprecision as I know that some of those big name's have used their services with good enough results, that would not happen if they thought it would not be up to their standards.
That said the number of people who are able to do this work and have the experience is shrinking, these guys are getting older and the work can be hard on you. This is likely why many are switching to cnc portiing they can inspect what they have in front of them and then request specific things done , or not done. This may be the reason to send your heads to someone like Mark Sutton who has experience to ask the right questions of who ever they are having the work done by. They are the quality control who might get the head back and know that something is not right vs an end user getting the head back and thinking..... mmmmmmm... pretty ports, without knowing if it will flow better at the lifts you need.
In the end it is your motor and I think The Op is doing the right thing to ask the question. It would be easy to let OCD take over and want "the best" in which case , all those who do it to claim that it is them. They are no different from racers who all think themselves fastest yet all have their day, but will be guaranteed to be proven wrong at some point. As a street bike and not chasing maximum power I see no need to drive yourself crazy looking for the best, that said if it is done by someone with a proven track record of performance and they can give you proven results you should be much more interested in the improvement than the name attached to it.
I have heard no names mentioned here I would not be happy to send a set of heads off to for work, all should be able to use their experience to give you a product improved from production or a answer as to why you may not want to have the work done. Talk to your engine builder and see what they have experienced for gains with ported heads on a similar build and decide for yourself if the cost justified the expense. Either way you have the satisfaction of building something you enjoyed and hopefully it lasts a long enough time that you forget the costs and headaches that happen along the way.
