Planet Minis

LongMooie

you can see my atempt on page 1 first pic is intake port marked for xr70 intake
the seconed pic is exhaust outlet i marked lines so i could see how much to take off
the next to photos are after i ported them

cyclerider57

There is a little miss information posted. When I said flat short side radius I meant when looking in the port and not at a side view. The bottom of the port when it starts to turn down toward the combustion chamber should become a little bit of a D shape. The D shape with the flat part toward the combustion chamber changes the pressure difference through the cross sectional area of the port by increasing volume. This creates a smoother pressure difference as the particles make the turn and keeps them following their path rather than pulling off the wall and creating turbulence.

Yes, a straight port is good. You have to pay close attention to the approach angle into the combustion chamber and against the back of the valve though. Hogging the bottom of the port down is an absolute no-no. You can create a lot of unwanted flow characteristics when you do this! (Especially once the charge starts to enter the combustion chamber) Don't just cut down the bottom of the port to straighten it when you can help it. Always try raising the rest of the port farther away from the valve rather than cutting down until you see valve seat all the way around. The APPROACH angle directly behind the valve is CRITICAL to good cylinder filling and fuel mixing. Like I said, within one inch of the seat is the most important part of a port. You can have as straight of a port as possible but it needs to be held as tightly as it can to the valve stem angle rather than a horizontal axis in line with the bottom of the head. A straight port that is really low will not fill as well as a port that has a pretty large turn but holds the approach angle of the port behind the valve close to the valve stem angle.

Also, keep in mind that a valve stem does take up some port cross section and the charge going through the port does not like drastic changes in port cross section (which also changes velocity and pressure) and a big change can create a lot of disrupted flow and poor air-fuel mixture. It is sometimes necessary to increase port diameter to help keep the actual flow cross section change at an acceptable level.

__________________
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LongMooie

ah shiiiit now you tell me... ha ha ha
this was done on a stock xr50 head that i dont intend keeping so if it dont work ah well!
i like building my bikes and cars and this was something i have never done, ill post the photos of the rest of the porting tomorrow and maybe you could show where i went to much or too little i think this is an interesting thread rather than check out my new stickers lol
thanks for you info

arlindsay1992

Cycle rider knows his stuff. Trust him over me for sure.

Big Daddy P

I just got a new Tak top end kit and looking at the head it looks like it's already been ported...I see it's already been hit with a dremmel. Do all heads come that way?

CGrumley

I have porting done to my manifold intake from who ever did had my bike before and it isn't that great. haha