Modified piston and fredhead

graydog8josh said:

About to see how much difference in performance a modified piston and fredhead will make on my current bike.

I have a new dax motor with a rt carb and 66 jet. its running teh lame banana pipe and its running super rough. I have a new coil coming in the mail as well as the fredhaed 7 cc chamber and the modified piston.

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If a little extra noise wont bother you, you can cut the end off of that banana expansion pipe to make the exhaust exit about 3/4" inside diameter and it will make the engine come alive with added torque, the tiny little exit pipes they put on the end of the banana pipes are just way to restrictive and kill torque and pulling power on the hills.

I have the little chrome banana pipe on my oldest bike I built back in 2009, it works good on it now that I cut the lower part off and got it to breathe better, look at the pic I included in this message and maybe you will see how I just simply cut the bottom off where the small tube and flat plate it was welded to it to open the end up more, I just got back from cruising a muddy dirt road before this pic, this is a bullet proof old bike but it aint pretty at all...LOL!

The fred head and piston will give you a bit more power all over through higher compression and corrected transfer port duration and timing, but if I were you ....

To get the most out of a high comp motor with a modded piston you should invest in a dremal tool and open up your intake port by grinding it open as wide as you can and rounding it downward into a D shape but only clean up the roof of the port do not grind any off the top just clean it up , then looking through the port wile the piston is at top dead center mark the skirt through the intake port where it hangs down into the port using a sharpy and the remove the piston and grind that marked portion off the skirt.

This is a mod that should be done to add to the tottal intake duration of the motor and it will help out masivly with top end power, midrang torque, and reduce vibes,by further lightning the piston. The only reason nobody sels pistons with the skirt precut is because all motors require a differant amount cut off because of port discrepancys and gasket thicknesses, but it should be done if a fully modded piston is what you are after

Port matching gasket and pipe will give noticeable improvement.

to flow as free as possable and make it into a cheap diy x chamber ! side play where did u get a pre cut skirt piston ?

anyway arebu running a titainium wrist pin ?

and you say u pushed it to 7,800 rpm under load ... if u plan to do any riding over 5,000 plan to run a upgraded needle bearing ... one from a moped or chainsaw like the stihl one thats a mm wider to take up slack and side play and able to withstand 10,000 on the regular a stock bearing will disintigrate at repeated exposure to those high rpms and ruin your whole motor its this reason why i like ghat bronze bushing from juice moto parts .

with a cut on piston and a trimmed skirt yku should notice some lag in low end performance and a bit more blowback cause you should have around 80 to 100 deg duration now vs the stock 60 deg intake duration so more blowback at low rpm but better flow at mid to high rpm...
once you get the carb tunned a cut on piston skirt. trimmed on a ported jug should get you a motor that will rev to 9,000. just be shu to tune the carb ... i mark the throttle with a marker fir 1/4 1/2 3/4 and wide open ... this way i can see whear i am at and ehat jet i am on wile riding.

so if i am riding and i get a bit of a four stroke and i look down at the throttle and the line is pointing at just over tge 1/2 mark ... i know the needle needs to go down some !

also try to port match the inrake and exhaust as mutch as possable it helps out flow a lot and if you runn a stick exhaust you need to cut the tube off and cut it open at the seam and cut out the cat converter and have a muffler shop reweld it for 10$ this wil open up your exhau

I realize this is a really old thread but I seen where it's mentioned about a Fred head modified piston.
I have a Fred head ld90 but my piston doesn't appear modified, can anyone tell me how a Fred head piston should be modified ( other then cutting the piston skirt) thanks