Twelvz

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

SStrokerAce

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

LameRandomName

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.

amean94ta

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

94bird

From Reher Morrison's article:

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.

stealthblack

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.

SStrokerAce

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

jonaddis84

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?

racer7088

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!

SStrokerAce

http://www.cppistons.com/PDF%20Files...0Page%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

Twelvz

thank you, very informative.

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

andy katzelis

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.

jimlab

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

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

94formulabz

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

just curious here.

-brent

andy katzelis

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.