Benefits of gas ported pistons?

yeah...what are they...when/why would someone use them?

Another one for later...

Look at the quote in my sig, he writes a excellent article about gas ported pistons in his tech talk series.

Bret

yeah...what are they...when/why would someone use them?


They used to be real popular on destroked chevy small blocks back when people were pushing them over 10,000rpm. (287ci if I remember correctly.) Basically they use combustion pressures, channeled through tiny little "ports" from the piston surface to behind the top ring, in order to use combustion pressures to push the ring out against the cylinder wall and ensure sealing at very high RPM.

i thought it was to bleed off pressure faster on the downstroke and force tension on the up? sort of like a vaccume pump

From Reher Morrison's article:

The fact is that the second ring is not a compression ring - its purpose is strictly to control oil. Any pressurized gas that leaks past the top ring accumulates in the volume between the rings where it unseats the top ring and diminishes its sealing ability. That is why many Pro-style pistons now have an accumulator groove machined between the top and second ring grooves. The theory is that leakage past the top ring will have a larger volume to fill before it disturbs the ring seal.

I'll take issue with his first statement in this quote. The 2nd ring does most certainly still serve a function to limit blowby. His quote about accumulator grooves is right, but heck, we've been using accumulator grooves for many years in normal old production engines. It's nothing unique for racing.

Gas ports do seem to have some intriguing possibilities to help reduce friction, but I can't readily see a benefit in helping the rings seal to the bore. I'd love to see a good comparison with a properly optimized ring design for use without gas ports. None of this A-B test he mentioned. The test was not proper since he didn't optimize the rings for each type of piston design.

my own limited understanding was that it was only used in drag race applications above 8000 or so RPM.The theory being that much lower ring tension could be used to help the motor build rpm faster,yet combustion pressure would promote a more positive ring seal when applied through the ports to the ring at high rpms.since it is short-duration,and low rpm manners are inconsequential when youre coming off the t-brake at 5000,along with vacuum pumps or other crankcase evac systems common on drag cars to help with the low rpms blowby.I am not aware of circle track or road race motors using this,but that might just be me not knowing they do, as that isnt my arena.Ports are generally drilled down from the top of the piston around the edge at an agle to the top/rear of the ring in the applications i have seen.

Hopefully this is more helpful than not.

Side Gas porting will work well on longer term engines..... the top gas ports are a more drag race style deal.

RMRE probably gets the most out of their ring setups.... from what I have seen from Darrin Morgan's wrighting on the subject of ring seal and bore finish the guy knows what he's doing. They don't have the R&D on the non gas ported deals but even if it was optimized it will give them less power. A dry sump, vacuum pump motor really likes these things.

Bret

Side Gas porting will work well on longer term engines..... the top gas ports are a more drag race style deal.

Bret

By longer term Bret Im assuming you are still speaking strictly racing appications right?

I was under the impression the gas ports will clog up relatively quickly and simply become a regular non-ported piston, and a big waste of money on any kind of street application.

Is it not gas ported pistons that the top ring fit is extremely snug? For lack of a more technical term, but the tolerance of the ring groove to the ring are extremely tight so that all the combustion pressure is pushing out on the ring and not leaking into the 1-2 gap?

Edit: Sorry, didnt read your post throroughly enough Bret, you said side gas ports...fill me in here, never heard of side gas ported pistons. Where are the ports?

There's vertical gas ports on top of pistons and there's horizontal ports used on the sides of pistons. Like was said the top are "mostly" used in drag racing but also in some endurance racing even NASCAR. Mostly they use the side or horizontal ports for endurance though.

You use lower radial wall back cut rings almost always with gas ports and it cuts down on ring flutter by inceasing the differential on the rings and by lowering their weight as well. Also you will pick up even more by tightening the ring side clearance but the rings and lands must be very flat to do that!

http://www.cppistons.com/PDF%20Files/SmallBlock350Chevy%20-%20Page%2011.pdf

Look at the top ring groove on those pistons.... You can see a small hole/semi circle above and touching the ring grooves. That's a horizontal gas port. Much less likely to get filled with carbon deposits.

Bret

Another one for later...

Look at the quote in my sig, he writes a excellent article about gas ported pistons in his tech talk series.

Bret

thank you, very informative.

by the sound of it I would think a decently revving supercharged street application would benifit from these

To further expand this topic.

What's super sweet about the whole gas ported piston deal is the low tension ring technology it employs. As I understand it, the single bigest friciton loss in the engine.

Appearantly the LT1 has a lower tension ring package? And, certainly the LS1 is utilizing low tension rings.

Additionally, low tension ring packages have been and are continuing to be developed that allow using traditional engine vacuum as a crankcase evacuation source rather than a vacuum pump now employed by many racers (to expensive and the system, engine life between rebuild, is more than I can take).

What's the super sweet part? We get to reap the benefits of all this energy being expended by others. More power and better fuel economy.

Here's a little clearer picture of side-ported pistons...

http://home.gci.net/~jimlab/images/Pistons/PB140038.jpg

Additionally, low tension ring packages have been and are continuing to be developed that allow using traditional engine vacuum as a crankcase evacuation source rather than a vacuum pump now employed by many racers

How does that work at WOT? Some automated valves? Do you have any more conceptual or detailed info on this?

just curious here.

-brent

Same way the current system does, which is probably not as well as a dedicated vacuum pump would work, I suppose.

I'm not aware of any thing other than the PCV valve, anyone else?

I would also say low tension ring packages are not new, OEMs have used them since the 70s. Seems like they are getting more attention lately.

I'm not aware of any thing other than the PCV valve, anyone else?


I thought that was what you were eluding to, some sort of modified/altered PCV circut that had the ability to maintain crankcase vacuum at WOT. PCV is effective for part throttle cruising, but not WOT which is what most of us are interested in :D

-brent

Nope, as far as I know it's low tension rings that still maintain a seal well enough to use the existing technology. I didn't mean to mislead.

Realistically, on a street car, or even a dual purpose street/strip car, how often is WOT a concern, from an OEM or personal standpoint.

Maybe if the CARB starts checking emissions at WOT OEMs will devise a system.

Im pretty sure Ive heard people talk about this, but couldnt you hook up a factory AIR pump to turn on with a "window" type switch at say 50% throttle to suck crankcase pressure and evacuate into either the intake or, for non-tree huggers, to the atmosphere. AIR pumps are able to make about 5-8psi into the exhaust stream so wouldnt that be enough vacuum to suck WOT crankcase vapors?

The stock LT1 air pump is good for this use. Old schoolers use them as crankcase pumps as you say (cheap pump-advantage). Vent to the atmosphere only. At 100% duty cycle the pumps don't last long (drawback). A trigger is a good idea.

Gas ported pistons are an "optomization" of the standard piston. During operation compression and combustion pressure pushes on the backside of the top ring forcing it ******ds. Gas ports increase the area available and offer a more direct path for the pressure to accomplish this. When building an engine to this consideration the ring is usually backcut to reduce its radial tension lowering the friction during the intake and exhaust stroke. Combined with a thin ring package gas porting can provide an optimal seal and reduced motoring friction. The loading on the rings and cylinder walls increases though during compression and power strokes greatly increasing the wear of those components, thus providing a short life. Side porting is generally used as a "cheat" when the rules specifically disallow gas ports. During a head off inspection the side ports cannot be seen. ie: Stock and SuperStock. Carbon buildup is not a problem for wot only applications, but deffinitely is unsuitable for street use. Dykes and headland rings are varations on the gas porting thinking. The dykes ring is stepped like an L and allows combustion pressure to get behind the vertical part of the L pushing the ring ******d.

TotalSeal offers a gapless top ring that will really seal up a engine and testing during prostock truck times showed a need for less jet on the carburetors, the signal improved substantially. Plus a 5-8 hp increase on a highly optimized combination.
Tight ring seal improves the response and power of any engine, but good seal during the intake stroke will improve it further.

Why is o-u-t-w-a-r-d a dirty word on this forum?

Why is o-u-t-w-a-r-d a dirty word on this forum?

Try out-ward.

Thanks.

Well with the Total Seal Gapless Top ring quote you are going to find some friction from some of the members here..... I'm not one of them.

Good seeing you here Mark.

Bret

I thought that most of the problems were with gapless second rings.

Yeah but that poison is still in the water for most guys....

Yea, well, I’m not sure that I’m really over it, but OTOH, I’m not really in the mood to build anything NA lately so I’m willing to give up a little in overall efficiency in the interest of overall durability… I can always turn up the boost ½psi to make up the difference.

If I had a serious belief (hell, convince me) that it would be as durable a setup I would probably use them in my next build… Maybe I should anyway just to get some empirical data on my own.