I wanted to get some ideas from the members on the use of gas-ported pistons in endurance engines, marine applications in particular. I know they are routinely used in bracket/sportsman and Cup engines and when properly set up get 500 miles or 250+ runs without showing signs of accelerated ring wear.
Because marine engines are cam/duration limited due to exhaust water reversion and torque/power curve placement, a 30 hp increase in a 540 cid N/A 650 hp marine engine is worth a good look IF it can be made reliable for 200-300 hrs run time. The engines will be subjected to both transient and prolonged static running conditions with routine cruise speeds of 2800-4000 rpm and WOT of 5200-5800 rpm. I would appreciate all opinions
1) Best ring material and wall finish?
2) Vertical or horizontal gas ports?
3) The number, size, and placement of the ports?
4) The effects of cylinder pressure? Running 9- 9.5:1 compression pump gas, do we look at increasing cylinder pressure with cam timing?
5) Ring side clearance?
6) Top land thickness?
Thanks in advance,
Bob
Gas ported pistons & endurance engines
Moderator: Team
I did do a search and saw that the topic has been discussed in previous threads but after referencing this article by David Reher I thought I'd try the topic again.
http://www.rehermorrison.com/techTalk/22.htm
Bob
http://www.rehermorrison.com/techTalk/22.htm
Bob
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L98GTA
I used gas ported pistons extensively years ago when I was doing 2-stroke engines and I'll lend what I experienced.
Gas porting and dykes( L shaped) rings are two methods used to regain ring control at high RPMs. The inertia of the ring tries to lift the ring off of the bottom of the grove as the piston changes direction. As engine speed increases this force can become so great that it will cause the ring to "rock" in its grove. When this happens the sealing surfaces of the ring (the face and the bottom) are no longer sealing the cylinder allowing combustion gas(on the power stroke) to blow by. Remember that combustion begins well before TDC.Gas ported pistons allow more combustion gasses to "push" on the top and back of the ring to help battle this.
In my experience gas ported pistons don't make power as much as they allow an engine experiencing a loss of ring control at high RPM to regain the power lost by regaining ring control.
If you look around I think you'll find that the types of engines using gas ported pistons are high RPM screamers.
In the application you mentioned the engine speeds are low enough that I don't think you would see a power increase because your not losing the power that gas porting is used to restore.
Gas porting and dykes( L shaped) rings are two methods used to regain ring control at high RPMs. The inertia of the ring tries to lift the ring off of the bottom of the grove as the piston changes direction. As engine speed increases this force can become so great that it will cause the ring to "rock" in its grove. When this happens the sealing surfaces of the ring (the face and the bottom) are no longer sealing the cylinder allowing combustion gas(on the power stroke) to blow by. Remember that combustion begins well before TDC.Gas ported pistons allow more combustion gasses to "push" on the top and back of the ring to help battle this.
In my experience gas ported pistons don't make power as much as they allow an engine experiencing a loss of ring control at high RPM to regain the power lost by regaining ring control.
If you look around I think you'll find that the types of engines using gas ported pistons are high RPM screamers.
In the application you mentioned the engine speeds are low enough that I don't think you would see a power increase because your not losing the power that gas porting is used to restore.
