Clarkmac, the normal
procedure for porting is to do the port modifications without the guide in place, because, well, it's in the way of doing a good job. But it's a bit of a chicken and egg problem, because you need to do the seat work in order to do the port work, but the seat work has to be referenced to the guide.
The way we do it is:
1) Cut the seat using the existing guide as a reference, but leave .010" of material
2) Do the port work
3) Install the new guide
4) Do the final seat shaping and blending using the new guide as the reference
5) Put the final profile on the seat
This is really the best way to do it, but of course, if you're trying to hire out the seat work but not the port work, it means sending the heads out twice.
We can certainly swap the guides and do the seat work, and leave the port work to you, but just keep in mind the guide will be somewhat in your way.
By the way, here's the program we use for the seat work, developed in-house:
As you can see, there are a lot of options, but basically, at the top we enter some generic information, then on the left is operations we want to do to the intake valve and on the right is exhaust valve.
The first thing we do is a "locate" operation (greyed out above because the "Cut Intake Seat I.D. box is checked). In this operation, the machine positions the head and we use a precise locating device called an "Indicol" to accurately located the center of the guide. We enter the exact X, Y, Z, and A positions into the program.
Then we do the "Cut Intake Seat I.D." operation. As you can see, we have the choice of doing a "Rough Cut" (with a specified amount of material to leave) and/or a finish cut. Either one of these operations requires entering the final valve size so the program knows how big to make the cut. It also takes in your target spring installed height so it knows how deep to make the cut. It also gives the option to unshroud the valves, which essentially blends the whole top radius cut of the valve job into the chamber.
There are some options as well for doing complete seat removals and cutting new seat pockets, but it doesn't sound like you're planning to change seats.
Once all the options are selected, Hammer Dan hits "Generate CNC Code" down at the bottom and this program writes the G-Codes and downloads them to the CNC machine. We then run the G-code program on the machine and it goes off and cuts and shapes the seats:
Although the above process gets the seat shaped properly and blended into the chamber and bowl, at the end of our process we also use a precise seat cutter of our own design to put the final valve job onto the seat:
The CNC machine has already shaped the seat, so very little material is actually removed at this step, it's just to put the final profile on the seat. The shape the seat is cut by CNC machine closely matches this profile, they're designed together. This is critical, because if your final seat profile doesn't match the shaping and blending, you end up with a turbulence-inducing mess where the profile cutter begins and ends. It's really the whole purpose of all this CNC automation I'm describing, to get the two to flow together precisely.
We put a lot of work into automating this whole process as shown to bring the highest quality valve jobs possible. Valve jobs are incredibly important for performance even though they really don't show up on a flow bench very well at all. With proper exhaust augmentation, the intake can see 100" of vacuum or more at the moment the intake valve comes off it's seat, and momentary velocities are through the roof, which makes this profile and the accuracy of the cut and blending just incredibly critical to the power the motor makes. That's why we put so much effort into getting it perfect.
Read more about our process automation here
. Also you can see our ala carte head service prices here
. Be advised that we're essentially shut down this week due to a major move of our shop, but we expect to be back up and running before the end of the week.
Good luck with your project!