Gas Ported Pistons

[R_Redding]

Are gas ported pistons allowed in current F1 engines .. I assume they are as I see no mention of them in the tech regs ?...

And do we know if any teams use them ?... It would seem that having the ring tight to the bore on the power stroke , but looser on the other strokes would save a lot of friction.




Rob

[riff_raff]

The piston compression ring gas porting shown in your pictures is that used on long stroke drag race engines that have far higher linear acceleration rates than the current 12krpm short stroke F1 engines. It is used to prevent ring flutter, but does not reduce friction losses from the compression rings.

[autogyro]

The piston compression ring gas porting shown in your pictures is that used on long stroke drag race engines that have far higher linear acceleration rates than the current 12krpm short stroke F1 engines. It is used to prevent ring flutter, but does not reduce friction losses from the compression rings.

We used this idea way back on dragster engines.
It uses gas pressure to increase the clamping force on the top compression ring and helps prevent piston 'topple'.
In the early days we simply machined away much of the skirt on the forged pistons used and fitted teflon buttons.
It certainly works on long stroke short endurance engines but at the expense of increased oil contamination.
I cannot remember ever using it for petrol fuelled engines ours were mostly methanol/nitro.

[R_Redding]

The piston compression ring gas porting shown in your pictures is that used on long stroke drag race engines that have far higher linear acceleration rates than the current 12krpm short stroke F1 engines. It is used to prevent ring flutter, but does not reduce friction losses from the compression rings.

I read about gas ported pistons on this Reher Morrison Racing Engines page..

http://rehermorrison.com/tech-talk-45-w ... horsepower

Are their engines used for drag racing only ? ...the car shown certainly does look dragster-ish .
Rob

[gruntguru]

All piston designs rely on gas pressure behind the top ring to hold it against the bore. Gas ports only become necessary if piston acceleration near TDC holds the top ring too tightly against the top land - blocking the access of combustion gas to the back of the ring.

[autogyro]

All piston designs rely on gas pressure behind the top ring to hold it against the bore. Gas ports only become necessary if piston acceleration near TDC holds the top ring too tightly against the top land - blocking the access of combustion gas to the back of the ring.

One reason to machine a larger bore clearance on race engines gg.

However that results in more piston topple on large bores.
Methanol based fuels burn slower than petrol and have less chance of 'unsticking' the ring from the top land on the power stroke, reducing piston clamp pressure.

[Brian Coat]

I believe this type of *vertical* gas port is used on Pro Stock and NASCAR Pistons but not TF/FC/TA/TAFC.

These are unblown gas/petrol engines with big bores (typically ca. 110 mm IIRC).

[autogyro]

I believe this type of *vertical* gas port is used on Pro Stock and NASCAR Pistons but not TF/FC/TA/TAFC.

These are unblown gas/petrol engines with big bores (typically ca. 110 mm IIRC).

Have you any more details as to why Brian?

[Brian Coat]

I have enough detail to allow some semi-informed speculation ...

I think the really powerful engines in drag racing go for dykes rings - friction and wear not are the over riding concern in those classes - they just need to SEAL in those vast pressures (top fuel BMEP is over 100 Bar!!)

But Pro Stock and Cup the engines are very constrained by hardware rules - they are almost spec engines so naturally every lil pony counts which means sealing & friction become really important.

And they have big bores and run pretty high piston accelerations so ring flutter is an issue.

The solution appears to be very thin top rings, modern coatings, very light ring tensions and vertical gas ports to prevent flutter and allow the lowest possible friction. They also run auxiliary vacuum pumps on their sump systems. I know gas ports look like they are a risk to top land durability but at least in pro stock there is a min piston mass rule so they're chunky anyway.

I assume you can get a low tension ring pack to work on an F1 engine without resorting to vertical gas ports.

[autogyro]

Thanks Brian, what you have posted makes good sense.
I only asked because my experience was over 25 years ago when we were trying all sorts.
Interesting to know what current F1 practice for rings is.

[gruntguru]

I think the really powerful engines in drag racing go for dykes rings - friction and wear not are the over riding concern in those classes - they just need to SEAL in those vast pressures (top fuel BMEP is over 100 Bar!!)

Dykes rings are similar to gas porting in the sense that they can still make use of gas pressure when piston acceleration is holding the ring tight against the top land.

As an alternative to the gas porting seen above, I wonder if anyone has tried milling some little channels across the horizontal face where the top ring contacts the top land? This would provide gas access to the back of the ring without direct exposure to the combustion chamber and the carbon buildup issues, not to mention superior piston strength.

EDIT. Just noticed one of the standard porting designs is exactly what I mentioned above.

[riff_raff]

All piston designs rely on gas pressure behind the top ring to hold it against the bore. Gas ports only become necessary if piston acceleration near TDC holds the top ring too tightly against the top land - blocking the access of combustion gas to the back of the ring.

Actually, piston rings rely on installed preload to ensure the optimum amount of radial contact pressure for most of an engine cycle. The aspect ratio of a piston ring cross section (width/height) is also important, as this will affect the performance of the ring in terms of friction and dynamic flutter. As the image below illustrates, the reason compression ring gas porting becomes necessary is when the normal combustion gas flow path thru the annular gap between the piston top land and bore surface is too restrictive to allow sufficient gas pressure levels in the groove space above/behind the ring to ensure adequate sealing and prevent dynamic flutter. The gas ports used on drag race pistons simply provide a more direct/efficient flow path for the combustion gas to the groove space above/behind the compression ring.



Here is a link to a good explanation of piston ring issues like flutter: http://korihandbook.federalmogul.com/en ... 9.htm#1218

[hardingfv32]

1) I am suspect of the gas port systems. From MY research, I have never seen them used outside of drag racing. I have not seen them used in F1 or NASCAR. No major RACE engine manufacture uses them that I am aware of.

This statement holds for Dykes rings too.

2) Piston ring side clearance on the top ring groove of .001" are common, so I doubt there is an issue about combustion gas flowing to the back of the compression ring.

3) NHRA PRO Stock does not have a constrained engine rule set. The NASCAR piston and ring rule sub-set is not constrained.

4) I have not seen any physical experiment/research paper demonstrating what is termed 'ring flutter'. There are some who doubt that it exists.

Brian

[Brian Coat]

http://www.federalmogul.com/en-US/Media ... 976080.pdf

This is quite interesting re flutter.

[olefud]

It’s fairly common to use combustion gas pressure behind the top ring to increase ring pressure during the power stroke while allowing reduced ring pressure otherwise in performance engines. The ring face is advantageously curvilinear to prevent the ring from scoring the cylinder wall should it tilt a bit.

I have no idea of F-1 usage.