One of the plans for the rebuild of my "good" engine is to port the head. A couple of weeks ago I spent a morning with Dave Andrews whilst he ported one set of ports for me on my head. The idea is that the set of ports he did would serve as a template for me to finish up the rest. He also gave me some burrs to do the work with and some mandrels to help get the bit down into the long ports on the cosworth head.
The trick to getting the port sizes correct and consistent down their length is to use some machined down valves, in this case I believe that it's 22 and 21mm.
Before embarking on the YB head I thought that I'd have a practice on a pair of subaru heads that I had spare. I didn't want to spend a lot of time widening the runners since I could learn the tools and techniques from sorting out the valve seats and cleaning up the runners. The subaru heads have pretty well sized ports and well shaped runners off the shelf but the valve seats are pressed into the head slightly offset which means that there's a lot of work to be done to remove the lips on either side.
Above you can see the lips that I mentioned in the pictures above.
The pictures above show me roughing out the valve seats, the far right shows a before and after. At this stage I've really just removed the lip and blended the seat into the head itself. I've not tries to make it particularly tidy, to straighten the port nor to blend any further than the seat/head interface.
Now you can see me working from the manifold side, I've used the big bertha of burrs here as there's space to get it in and it removes a lot of metal quickly, leaving a nice smooth profile on the larger curves. The right hand image shows it after some more work, with the port pretty much finished.
After the final porting and polishing you can see the result in the valve throats on the left, the exhaust ports have polished up nicely and the inlets let you see quite a decent amount of the valve as you look down the ports.
It's taken a bit of getting the hang of which burr to use where and how much speed/pressure is appropriate but porting really doesn't seem that difficult. The hard bit seems to be working out what you need to do where. I'm pretty glad I had a practice run though. The work is nothing like up to DVAs very high standards but it's quite enough for me to get an idea of what's involved. The other thing I discovered is that even with 1KW of halogen lights and another 1KW of flourescent lights still isn't bright enough when you're poking about way down inside a port.
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