Grinding a shallow notch the same width as the exhaust port on the top of the piston?

[BikeBuilder43]

I'm talking about grinding a notch on the exhaust side of the piston. I saw somewhere on here that doing this would help exhaust gasses escape faster. I know it will drop compression and change port timing. Any thoughts?

 

[gary55]

It's called ramping the piston. I used to do this to the exhaust and transfers. If you do both it does not change port timing. You gain a little better flow, but lose a little low end power. Now I just raise the exhaust port. You can get the same effect by ramping the piston only at the exhaust. The pic. shows a transfer ramp, but I don't recommend it there.View media item 60893

 

[FurryOnTheInside]

I'm pretty sure I don't want to experiment with raising my exhaust port, but if I did I would start by ordering a new piston for £4.20 (for the one that fits my engine) on eBay direct from China.
Then I would make a tiny ramp of only half a millimetre on the piston and try that.
If I liked it, I would raise the exhaust port by half a millimetre and try that with the ramped piston (for a total of 1mm change).
If I still like that I would raise the port another half a millimetre (1.5mm change over all).
If I didn't like that and thought I had gone too far then I would swap out the ramped piston for the untouched piston to go back to the point where I still liked it.
The cost is thus kept down to £4.20 instead of whatever the cylinder costs to replace.

In any case (I have read) it's best to go back to the untouched piston once the perfect exhaust port height has been determined.

 

[Rusty_S85]

I'm pretty sure I don't want to experiment with raising my exhaust port, but if I did I would start by ordering a new piston for £4.20 (for the one that fits my engine) on eBay direct from China.
Then I would make a tiny ramp of only half a millimetre on the piston and try that.
If I liked it, I would raise the exhaust port by half a millimetre and try that with the ramped piston (for a total of 1mm change).
If I still like that I would raise the port another half a millimetre (1.5mm change over all).
If I didn't like that and thought I had gone too far then I would swap out the ramped piston for the untouched piston to go back to the point where I still liked it.
The cost is thus kept down to £4.20 instead of whatever the cylinder costs to replace.

In any case (I have read) it's best to go back to the untouched piston once the perfect exhaust port height has been determined.

Interesting. I thought of maybe tweaking my exhaust and intake ports up/down after I get everything broken in from the initial setup. Thing is I will be running a windowed piston to gain the benefits of the Oz reed valve I will be running. Hate to cut notches into the piston on a $25 piston like that lol. Think I will just stick with widening the intake and exhaust ports and forget raising them.

 

[FurryOnTheInside]

Interesting. I thought of maybe tweaking my exhaust and intake ports up/down after I get everything broken in from the initial setup. Thing is I will be running a windowed piston to gain the benefits of the Oz reed valve I will be running. Hate to cut notches into the piston on a $25 piston like that lol. Think I will just stick with widening the intake and exhaust ports and forget raising them.

The pistons with the higher wrist pin hole might be a bit less common so more expensive, but to me $25 sounds like a ridiculous price for a piston. (Although compared to other vehicles it's probably quite cheap)
I'm sure you can cut your own window in the piston.

Idk whether it's the convention to run a raised exhaust port with a reed valve. I think you should get a degree wheel and check the port heights against other people's figures before doing anything permanent. Otherwise, if you want to experiment by yourself you have to pick something to cut. It's either the piston or the cylinder.
I have spent a bit of time modding the cylinder so, although I enjoyed it, I wouldn't want to spoil the work I've already done.

I believe that what I described in my post above is just the conventional way of using a ramped piston to be able to experiment with your port heights at a reduced cost/risk.

 

[Rusty_S85]

The pistons with the higher wrist pin hole might be a bit less common so more expensive, but to me $25 sounds like a ridiculous price for a piston. (Although compared to other vehicles it's probably quite cheap)
I'm sure you can cut your own window in the piston.

Idk whether it's the convention to run a raised exhaust port with a reed valve. I think you should get a degree wheel and check the port heights against other people's figures before doing anything permanent. Otherwise, if you want to experiment by yourself you have to pick something to cut. It's either the piston or the cylinder.
I have spent a bit of time modding the cylinder so, although I enjoyed it, I wouldn't want to spoil the work I've already done.

I believe that what I described in my post above is just the conventional way of using a ramped piston to be able to experiment with your port heights at a reduced cost/risk.

Yep it is the cheaper way to go with by using your piston to experiment. For me I could probably cut my own piston to window it but I figure eh for $25 I rather just buy one already cut vs me having to deal with cutting the window myself then worrying if the piston is now going to fracture from me making the cut the way I did.

 

[gary55]

Yep it is the cheaper way to go with by using your piston to experiment. For me I could probably cut my own piston to window it but I figure eh for $25 I rather just buy one already cut vs me having to deal with cutting the window myself then worrying if the piston is now going to fracture from me making the cut the way I did.

Good thinking. Also a new cylinder is cheaper than the windowed piston your buying so if you were going to experiment you would want to do it with a cylinder.

 

[Steve Best]

Ramping the exhaust or raising the exhaust port have an effect on port timing to raise the rpm slightly, which can raise power.
The ranp does ruin squish somewhat but is a cheap way to test, as Furry points out.
Grinding the port is unrecoverable.

I am in favour of widening the exhaust port at the top only.

 

[gary55]

Ramping the exhaust or raising the exhaust port have an effect on port timing to raise the rpm slightly, which can raise power.
The ranp does ruin squish somewhat but is a cheap way to test, as Furry points out.
Grinding the port is unrecoverable.

I am in favour of widening the exhaust port at the top only.

Are your thoughts on the widening at the top based on that the piston only opens just over half of the port, and if the piston was to open all but 1mm at the bottom of the port would it change your thoughts on this. I'm wondering because the Zeda engines almost completely open the exhaust.

 

[Rusty_S85]

Ramping the exhaust or raising the exhaust port have an effect on port timing to raise the rpm slightly, which can raise power.
The ranp does ruin squish somewhat but is a cheap way to test, as Furry points out.
Grinding the port is unrecoverable.

I am in favour of widening the exhaust port at the top only.

So a trapezoidal shape to the exhaust port wider at the top and stock width at the bottom? Interesting idea. For mine I was thinking of just widening the cylinder side ports in an oval shape then on the exterior side of the cylinder jug take and blend it into a port match for the reed valve and the exhaust pipe to create a smooth transitional funnel to hopefully eliminate any turbulence that could slow down the flow.