Piston windows

[Atomic Monkey]

Is there anything to be gained by opening up the windows in the pistons? I also see pistons with an added window for the boost port, not sure what there is to be gained from that either???

It would be interesting to see some dyno numbers to show the differences... if any

[trickedcarbine]

Slight gains. On these things there are so many minute things that can be done. Most think mods for minimal gains are a waste of time. But if you do a handful of small things, they can definitely add up

[Tedder]

I had a well known builder tell me that the windows were there to aid wrist pin lubrication.

[m671054]

^^^^^^this. Wouldnt no windows with boyesen ports help initial transfer velocity? Just thinking out loud.

[Atomic Monkey]

I'm going to do it then, at least make them as wide as the port... possibly even add the boost port opening to the piston.

I hogged a lot of material out of the intake, so it might not be such a good idea to make them the same overall size of the port.

I also added some small "Boyesen" ports, but without more welding, I don't see where they'll be big enough to make much difference.

[J-Madd]

I would think that the windows would leave more room for the charge to be stuffed in the crankcase. Where there is not piston there is air. JMO.

[m671054]

But picture the underside of the piston trying to compress the mixture. With no windows the skirt seals the intake port earlier creating a smaller area to compress the charge. With windows you are pushing back against the intake tract until the windows clear the port.

[Atomic Monkey]

But picture the underside of the piston trying to compress the mixture. With no windows the skirt seals the intake port earlier creating a smaller area to compress the charge. With windows you are pushing back against the intake tract until the windows clear the port.

I see the logic in that, but that's what reeds are for. I've seen 2 strokes that open directly from the intake area to the transfers. Those engines also didn't have windows in the pistons.

[trickedcarbine]

Bump

[Atomic Monkey]

Lol! Somebody's been thread-mining! But you did bring it up at the right time. I was looking at those new pistons the other day wondering if there would be anything to be gained by opening those up??? And then a part of me just wants to try them "as is".... hmmmm

[LCW]

Probably minimal gains vs the chance of the skirts rattling off or having an out of balance rotating assembly. I just rebuilt a motor that the previous guy had built. The pistons were hogged out and wore out. I didn't touch the new ones. Just cleaned up the new cylinders a bit.

[jbooker82]

But picture the underside of the piston trying to compress the mixture. With no windows the skirt seals the intake port earlier creating a smaller area to compress the charge. With windows you are pushing back against the intake tract until the windows clear the port.

 

Yea but the banshee uses reeds. They are the mechanical seals that allows the crank case to pressurize. The idea of the windows is to allow the engine to begin to pull air and fuel in to the crank case from the time the piston starts to go up instead of waiting for the skirts to clear the intake ports.

[m671054]

Most cylinders that run well have boyesen ports. With those in i dont feel windows are as important. You guys are right about stock cylinder needing windows. I havent dealt with stock cylinders for awhile