gas ports.

Anyone ever seen vertical or lateral gas ports on a 4t mx piston?

I havnt

Wonder why?

Anyone ever drilled any?

Some people used to drill holes between the top and 2nd ring groove to vent gas from behind the upper ring.  This supposedly helped the upper ring bite into the cylinder wall for a better seal and prevent a phenomena called ring flutter.  Since modern dirt bike pistons only run one compression ring this practice would no longer be necessary.  The other solution was to run a wider ring gap on all rings below the compression ring but this was much to the contrary of the recommendations by the makers of Keith Black pistons (they ran the top ring very close to the top of the piston and recommended almost double the ring gap for the top ring over the 2nd ring.  Keith Black ran something called an attenuator groove where they relieved the area of the piston between the top and 2nd ring to allow space for gases to accumulate without causing an increase in pressure to unseat the upper ring.

Edited by 1987CR250R

Yup, those were gas ports to boost ring tension, but tests often showed that it was fairly easy for these ports to cause combustion pressure to leak behind and the under the ring if not done exactly right.  Modern ring design uses the pressure of the combustion gasses to increase sealing already, so this step is mostly unnecessary.

87 I think were talking about something different?

Gray racer were almost on the same page.

I don't think its fair to say old rings didn't use combustion pressure to seal as well as new ones and well any top ring on an internal combustion engine.

Dikes rings aren't modern but that's what they use on blown alcahol and nitro cars they let pressure behind them so well they tear up the bore.

What I'm taking about is verticle or horizontal gas ports.

They are drilled from thr piston top (verticle) down to behind the ring where it will be half round and half thr ring depth.

Or they are drilled half round on the top ring land the depth of the ring groove.

These allow lower ring tension and ring side clearance since there is a path to allow the ring to be pressurized other than the clearance. Halving that clearance allows the ring less of a chance to bounce from the top groove to the bottom groove "flutter" we actually always want the ring resting on the bottom of the groove but it doesn't want to stay there on the intake stroke. We want it on the bottom because we want all the clearance at the top to allow pressurization.

With gas ports you can use lower tension thinner rings that are low friction on 3 of the 4 strokes.

This isn't anything archaic as implied by gray.

Or extremely exotic. They are found in racing clases from late models on up, modifieds, figure 8, pro 4, Sprint cars and midgets, and comp eliminators to pro stock (fuelers run dykes rings an even more extreme solution)

I was actually expecting to see horizontal gas ports on my Honda piston.

http://rehermorrison.com/tech-talk-22-the-importance-of-gas-ports/

Rher Morrison serious credentials (pro stock builder) says they lost 50 Hp on a 550hp engine when they used non ported pistons.

But I think it may be that that had the thin rings and tight ring clearance and didn't seal well because of that. Maybe the difference between pistons and rings meant to run without gasports vs the low tension package would be a smaller difference like 25hp.

Makes me wonder if there's 2 or 3 Hp on a 450 in drilling 12 x 0.03" holes

I don't think its fair to say old rings didn't use combustion pressure to seal as well as new ones and well any top ring on an internal combustion engine.

 

 

It wouldn't be, but I never said that.

Most piston cooling occurs through the rings, too.  Do the gas ports have any affect on that?  It's only on more modern gas engines that under piston oil jets to aid cooling have started to show up.

Edited by 1987CR250R

heres an example of a trx450 piston, gas ported see the half round holes on the top of the ring groove

trx450_piston2-lg1.jpg

A yam-haha piston

YFZ450coatedCPPiston_zps22873ada.jpg

Heres a crude tool for drilling them

http://www.goodson.com/technical_support/instructions/Cylinder_Head_Rebuilding/GPT-043,%20062,%20078.pdf

personally id use a mill instead of that jig

 

heres the verticle gas ports as ran in an engine masters competitoin engine.

although more effective in sealing things up and doing so in a hurry they are succeptible to being plugged with carbon so they are suitable for methanol or drag racing only.

1303phr-14-o%2B2012-AMSOIL-engine-master

 

 

 

the mac daddy is the dykes ring tight in the bottom of the "L" section but room for pressurization.  ive heard it seals so well that its hard on the cylinder walls

the diagram is exaggurated dyke.gif

 

this is an actuall top fuel ring

I plan on using something like this a stainless steel dykes ring thats about 100$ a piece for a twin screw supercharged, intercooled 4 cyilnder road race engine that will make 750 from 2.7L

tf011-500x333.jpg

I was honestly like wtf i expected to see them on the oem piston. it only has one thin ring?!?

our jawa uses them.

I guess the question is is there a reason not to use them???

Most piston cooling occurs through the rings, too.  Do the gas ports have any affect on that?  It's only on more modern gas engines that under piston oil jets to aid cooling have started to show up.

I dont think it would it just forces the ring to the cylinder faster and harder for a better seal on the power stroke.

Most piston cooling occurs through the rings, ...

 

Most piston cooling is done by the incoming intake air and fuel charge. 

 

The natural thermal barriers set up by heat having to move across the spare bit of contact between piston and ring, through the less conductive steel ring, then the insulative effect of the moly filler in the ring face, then interfered with by new heat generated by ring friction, and finally through the small contact at the bore wall cannot possibly do enough to be significant.   Heat transfer through the lubricant on the skirt is apt to be far better.

Logical.

I have heard that too. But you make it sound like a fairy tale..

Vertical would clog up with carbon on the service life most these motors are expected to run. Think even the circle track guys gave up on it because of that.   Drag  racers? another story.   Used dykes rings without the bottom rail ring on 1000cc twostroke prostock and radar runners, and like your description they get a free ride back up the bore with no to little tension, was worth maybe 10hp leaving the rail ring off.

Edited by highmarker

Vertical would clog up with carbon on the service life most these motors are expected to run. Think even the circle track guys gave up on it because of that. Drag racers? another story. Used dykes rings without the bottom rail ring on 1000cc twostroke prostock and radar runners, and like your description they get a free ride back up the bore with no to little tension, was worth maybe 10hp leaving the rail ring off.

Verticle I wouldn't consider but lateral sounds good to me.

And I know the Sprint cars and dirt late models run verticle gas ports because the methanol doesn't carbon up as bad as gasoline.

Vertical would clog up with carbon on the service life most these motors are expected to run. Think even the circle track guys gave up on it because of that.  

 

This is the biggest problem with gas porting regardless of how it's done.  It really is only suitable for engines that are run very hard for almost all of their operating time, don't run for comparatively long periods, are disassembled often, and are used in situations in which every last single horsepower is critical to success. 

This is the biggest problem with gas porting regardless of how it's done.  It really is only suitable for engines that are run very hard for almost all of their operating time, don't run for comparatively long periods, are disassembled often, and are used in situations in which every last single horsepower is critical to success. 

so it would be useful to say pro twin and pro single flat track racers then? especially the smaller disp? i understand the service interval would be much more often, but say "In a perfect world"

so it would be useful to say pro twin and pro single flat track racers then? especially the smaller disp? i understand the service interval would be much more often, but say "In a perfect world"

Wouldn't doubt it it some or many of them have horizontal gas ports.

Is be supprized to see verticals tho.

Maybe on a team that opens it between every race.

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