Well, still plugging away at my track bike when I can. I wanted to show what I'm doing to my head
This was supposed to be part of the track bike post but it came up separately after I got logged out and logged back in... Anyway, I reduced the intake port size to create a "choke point" for the incoming air/fuel charge. What that does is similar to what happens when you pinch the end of a garden hose, the water flows faster and with more force. The difference, though, is that instead of the pressure coming from a "push" it's coming from the pull of the piston's intake stroke. I didn't come up with this idea, I'm just relating it in this thread in case someone else wants to do it.
I recommend this mod for bikes used for road racing or other events where the throttle openings vary along the entire r.p.m. range. The result is a more linear power curve; when you twist the throttle the power tracks right along with it instead of dipping or tapering off. Torque is also increased. This mod would hinder a bike used mainly for W.O.T. activities due to the extra air intake needed at the higher r.p.m.s. This is the second time I've done this mod, the first was on the first Hayabusa I built and the result was
extremely improved acceleration up through the entire r.p.m range! I posted a few pictures back then but they were too small, I didn't explain what I did either.
Okay. To start off you'll need to completely disassemble the cylinder head and clean and degrease it thoroughly. If you're a DIYr I'm assuming you already have basic hand tools and some mechanical know-how.
Some special tools you'll need are:
> A Dremmel tool
> 0-1" and 1-2" micrometers or a Vernier caliper
> a pack of 60 grit Dremmel sanding drums
> a "T" gauge set
> one or two sticks of modeling clay
> a few tongue depressors
And last but most important, JB Weld to build up the intake ports.
The intakes will have to be roughened in order for the bonding material to adhere. Use the Dremmel with a 60 grit sanding drum and come in from the valve side to roughen the bottom area of the port about a 1/4 of an inch before the intake valve opening. Be
very careful not to damage the valve seat! To be on the safe side, stop and start the tool after inserting in the port.
Clean out the debris and wipe the surface with electric contact cleaner or denatured alcohol. Once you've got the head prepared you'll need to measure one of the intake valves to calculate how far to shrink the port down. The "magic" number is 30% smaller, or the recommended
65% of the valve size. To find that out, measure the valve diameter:
Next, take your measurement and multiply it by .33. Subtract your result from the
initial valve measurement.
The formula is simple: Valve dia. - (valve dia. X .33)= "New" port height OR Valve dia. X .654= Choke point height
You now have the measurement you need to transfer to your "T" gauge: