A buddy of mine who races XC gave me 2 junk heads to practice on. One stock, one that they ported, and one to port for him to race with this season. I have only messed with the stock practice head so far, and I documented pretty much everything. I have 16-20 hours into this intake port, and it will never even run.
But I found huge flow increases, and I forever have a template to refer back to.
Here's some pics of what I changed.
Here's the combustion chamber. One side of the intake is unshrouded, the other is stock. Easy to see the difference. Once I had the chamber finished, this head flowed better than his ported head at lower lifts, and as good as his ported head at higher lifts.
Here's the finished intake port.
I couldn't get rid of the valve guides completely. Because it was a junk head, I pushed the limit, and broke through the spring seat trying to eliminate as much guide as possible.
This one is unfinished, but the shape is there.
I added epoxy to the short side radius and port floor. This was tricky to balance. It hurt flow first, and I gradually lowered it and layed it back until it helped. If I had only tried it once, I would have abandoned this idea because it hurt flow that bad, even at motoman's suggested 65% of valve diameter theory. Once I got it right, it helped flow from mid lift all the way to full lift.
For easy comparison, here's before and after
I have not figured out how to turn this into CFM readings yet, but here's the before and after data.
All tests were done at 20" of water (50/50 water and antifreeze actually) and I used a 2.507" orifice straight cut in 10 ga. steel.
Valve lift - Inclined manometer inches of water. (air flow)
.100" - 0.5"
.200" - 2"
.300" - 3.75"
.400" - 4"
.100" - 0.625"
.150" - 1.75"
.200" - 3"
.250" - 4.25"
.300" - 5.25"
.350" - 5.5"
.400" - 5.5"
I think lower lift flow would have been better with some different valves or a fresh valve seat cut. Stock valves were used, and I don't have any means of valve seat cutting right now. The stock valves just have one straight 45 degree seat.
The best part of all of this is that I got to add about as much material as I removed, so the power should improve from idle to redline, and this is for a XC bike.
I can't wait to get the real one finished and see what it does on the dyno. The local tech school has a dyno, and we can rent it for donation. I think a bunch of us might rent it for a day and do some hard core tuning.
I thought you guys might be interested since it's 450R stuff. Questions, comments, arguements, tell me I'm ugly and can't read good, whatever.