Do You Port Pistons To Match Your Porting?

[jayzx10r]

I think if you are porting a cylinder for better flow, you have to do up the piston as well, since this is the bottleneck between carburetor and ignition point after porting, reeding, and going large on the carb.

Feel free to opinionate.

 

I basically keep the same shape piston ports, including radiuses, but make them wider and extend the piston port down as well. Same with the skirt ports, except I raise the port wall a bit there. you do NOT want to only be left with a thin piece between the piston port and the skirt port. This material is important to the structural integrity of the skirt. Overall, I make them wider by widening away from center.

 

The thing to keep in mind is that you don't want to remove any skirt material from the area directly perpendicular to the piston pin, because of the wear caused by piston rocking.

Just to make sure I'm clear on this...if we consider the piston pin to be at the 90 and 270 degree position, then the portion of the piston skirt area I'm referring to would be at the 180 and 360 degree points...the zero point The farther you are from this point(s) of zero , the more material you can safely remove--strictly limiting this statement to the issue of piston rocking force in the bore.

 

I narrow the bridge between ports on the piston a bit (not too much, you don't want to create a potential hot spot). Then I lower the port and raise the skirt port a bit. Then I widen the outer sides of the ports and bevel (angle cut) the outer port piston wall so it looks straight when looking at it from the intake port from the reed cage. I square up the radiuses a little, but still retain a nice, smooth radius.

 

I think the most important part of all this is to get a nice radius on the inside of the piston where the ports pop through. I try to reduce turbulence as much as possible while removing a minimum amount of material. I use sand paper to clean up my tooling marks.

 

Things to keep in mind:

You can't perfectly match the piston to the port because your piston will probably fail at high RPM use...only remove what appears reasonable while retaining structural integrity.

The farther you are from the 180/360 zero degree point, the lower the force from the rod induced piston rocking the piston feels, so you can remove more material relative to the zero point.

You need to remove the same amount of material from each piston because you want the same amount of flow/power in each cylinder. They don't have to mirror each other, but they need to have the same flow characteristics if you have to "individualize" a piston to match up a porting issue..

Smoothing out rough edges is of utmost importance. Ask yourself, what design or shape would running water prefer? I'm not a hippie, but what would nature do in this circumstance?

 

I was thinking that I'll port my next piston set sorta oval...what I'll call a D cut, to look like two back to back D's. My intake ports are pretty wide.

 

It would be interesting to see a dyno difference these mods would make...

 

Jay in SanD...at home, riding on meds....un :cool:

Edited January 9, 2008 by jayzx750

[jbooker82]

You dont really want to opean up the piston windows. It can add a hp or 2 but it is not worth the gain because it will weaken the piston skirts. A broken skirt can wreck a cylinder.

[gumby6t9]

Got any pics to post??

[chase@miamiatv.com]

 

[gumby6t9]

Nice!

[WALLACE84]

 

 

 

Was that on the green meanie chase?

[scotts96fast]

Good luck with the piston porting!!!I notice a big gain,Did that for 3 years ....Also replaced the pistons every year do to crack skirts.

 

 

4 years after that I'm on the same piston just different rings.