Topic: Gas ported pistons?

[PeWe]

I picked up a restored head last week from my nearby shop when we start to talk about higher case pressure with 1000cc that needed additional ventilation via clutch cover.

The tuner mentioned gas ported pistons that can reduce case pressure, better piston ring sealing.
Vertical porting with holes from crown a little bit too radical for street.

He had measured when running an engine on dyno with pressure metering stuff on the ventilation from case and seen less pressure after use of gas ported pistons.
Something to add when order pistons.

I checked my JE 71.25mm pistons. No holes over the top piston rings.

- Is that used on CB750 engines?

I have just mounted the cylinder block, head not yet installed so not too late to make improvements.

I searched and found what we talked about
Scroll down to
"JE calls these lateral or horizontal gas ports. Located directly above the top ring groove..."

https://www.jepistons.com/blog/vertical-and-horizontal-gas-porting 

[Old Scrambler]

Great Info...............I would think the added ring-pressure would be a huge benefit to immediately SEAT the rings on a fresh build........such as an all-nighter in the pits

[PeWe]

I had to look more into this.
Dynoman write that my pistons have "Accumulator grooves".

So I searched more...

https://www.enginebuildermag.com/2018/02/makes-racing-piston/

"Accumulator grooves work on every piston, but work best on gas-ported pistons,” explains Stevenson."

I have a feeling that I should have known this earlier.

[turboguzzi]

for all i know, they are only used in drag racing where you need to seal against huge cyl pressure, not any daily rides or even road racers.
BTW, pressure gets behind the ring in any case as the top of the piston is machined smaller than the skirt. the sealing of the ring is achieved definitely not just by the elastic tension in it..

[PeWe]

OK, good to know.
Additional ring wear might be one thing that does not matter in drag racing. Different for racing and hot street bikes that get longer use.

Edit:
This is what I had in mind.

[dragracer]

I have gas ported pistons in my super comp bike. 1425cc KZ based engine. Not certain I would want to run gas ported pistons on the street.

[MRieck]

I have gas ported pistons in my super comp bike. 1425cc KZ based engine. Not certain I would want to run gas ported pistons on the street.

Vertical, lateral or both Frank?

[dragracer]

Both Mike.
I have gas ported pistons in my super comp bike. 1425cc KZ based engine. Not certain I would want to run gas ported pistons on the street.

Vertical, lateral or both Frank?

[PeWe]

I stumbled on more info about gas ported pistons. Now gas ported rings.
https://www.totalseal.com/rings/gas-ported-rings

Another about beveled rings and why..
https://www.dragzine.com/news/tech-tip-positive-and-negative-piston-ring-twist-with-total-seal/

[bear]

Thanks Per, they say you learn something new every day.

[PeWe]

Hi Brian,
Especially when visiting this forum where lots of info is shared and ideas will grow.

My local shop gave me the initial thoughts about gas ported pistons when I talked about eventual blow by.

 A few days ago I found more about it when searching for something else I have forgotten now

I have an extra set of rings to my 71.25 mm pistons. Just to file grooves ?  
Top ring only 0.8mm thick (2:nd too).  I wonder when they will crack if filing grooves into them.
I guess a 1.5mm thick ring can get some grooves.