piston rings & sealing against cylinder wall
piston rings & sealing against cylinder wall
(OP)
I had someone telling me about drilling small holes, down from the piston crown into the small space "behind" the top piston ring, purportedly to allow the combustion pressure to get into that space and force the ring out against the cylinder wall. The theory is that the gap between the top face of the ring and the adjacent land is too restrictive to permit this pressurization from occuring fully/fast enough. Anyone here heard of that, tried it? Does this really work? This is in the context of race engines. I have difficulty believing that blow-by between the ring & the cylinder is a big concern (that would rob power) in a race engine, which has fresh rings, good cylinder walls, etc.
Thanks
Thanks





RE: piston rings & sealing against cylinder wall
In my experience, on small displacement road race engines, the small holes tend to carbon up. At least on the one engine that I used them on. I'm sure there is a performance advantage to match the additional expense on some of the big bore drag race engines, I just did not see any difference in performance on mine.
Perhaps Pat P. or someone closer to drag race engines would be a better authority on "piston porting".
Rod
Rod
RE: piston rings & sealing against cylinder wall
The big driver, as I understand it, is not an excess of non-conforming areas between the ring face and the cylinder wall, but rather radial "flutter" of the piston ring under conditions of rapidly changing cylinder pressure. With four bolts per cylinder, the bore distortion will tend to have fourth-order and lower components, to which most compression rings could readily conform. The concern is that cylinder pressure will rise much more rapidly than top groove pressure due to restricted flow between the top land of the piston and top groove. When the pressure acting on the exposed portion of the ring face is sufficiently high compared to the pressure in the groove, the ring can lift off of the cylinder wall and allow large amounts of gas to bypass. This problem is compounded if the piston top land distorts significantly due to temperature and/or firing pressure, further reducing ring side clearance.
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
Now, Compositepro...You have been on this forum for enough years to know who we are and you certainly must know we are not going to let you off with such a flippant post---Please explain yourself, sir!
Rod
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
Another major consideration I had in my comment is that this technique is something I have not heard of and is not used commercially to my knowledge. In a business as competitive and mature as auto racing, when I hear about secret performance enhancing techniques that are discussed in public forums my reaction is "snake oil". I don't mean to be insulting to anyone but I'll believe it when I see some data. People can easily be made to believe almost anything.
Of course drilling holes will also lighten the piston and therefore improve performance. If the piston and rings are really poorly designed to begin with then maybe drilling holes will help. But, again, I see better approaches.
RE: piston rings & sealing against cylinder wall
About 10 years ago I was asked to evaluate such a design for a racing team sponsored by a major OEM.
Ported pistons couldn't be used in "production" applications because of the carboning concern Rod mentions (and the additional cost of multiple drilling operations).
What superior approaches do you have in mind?
RE: piston rings & sealing against cylinder wall
It is mainly used on low tension rings.
I agree with all that ivymike says.
I also think that rings distort or rock a little in the groves, and to limit this, the axial clearance above the top ring needs to be minimal to avoid flutter and twisting and breaking at very high engine speeds. Serious drag racers run piston speeds higher than F1 as they do not need to last nearly s long. A race might be 700 or 800 turns of the engine. Most other forms of motor sport involve tens of thousands of turns and street motors do several million turns of the engine.
Only high budget teams tend to bother with ported pistons and it is done 2 ways. One is to bore about 8 or 10 holes from the piston top to the back of the ring grove. The other is to mill notches in the edge of the top land so you have areas where there is much more clearance between the piston and the bore, but still substantial areas to support the top outside area of the ring.
Regards
Pat
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RE: piston rings & sealing against cylinder wall
Thanks to all who responded, this is a great forum.
Gregg
RE: piston rings & sealing against cylinder wall
It was also mandatory to align bore with a torque plate mounted to simulate mounted heads.
Was the practice of directing combustion pressure to the backside of the rings effective? One must first delve into the 'black magic' of hotrodding to understand that every theory in the book was at some point applied in the quest for response. Radiused rings where a companion to the pressure assist.
RE: piston rings & sealing against cylinder wall
sometimes down thru the dome to intersect the back of the ring groove.
Alternatively, a series of grooves milled into the top (non sealing) face of the ring groove
Bill "Grumpy" Jenkins talks about them a bit in his "Chevrolet Racing Engine" book.
h
They were hot high rpm drag race technology in the mid/late 70s when combined with tight ring side clearance, reduced back clearance and crankcase evacuation. The shop I worked in drilled and milled a lot of tiny holes in pistons for folks who asked. Even pistons with standard ring clearance.
It was almost like those stainless steel mufflers with large openings are today.
AIR in some piston or ring tech article Kevin Cameron mentioned the late new England cam grinder Domenic Ravesi was developing an engine and among other things tested very "tight" ring side clearance. I believe the result at some tighter than stock value was power shutting off at high rpm.
RE: piston rings & sealing against cylinder wall
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RE: piston rings & sealing against cylinder wall
Larry Coyle
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
you beat me to it!
I have no theory or first hand experience to offer, but my observation is that this seems to remain a serious topic of discussion since over 30 years ago.
Changing the subject slightly, Grumpy also propounded the reflective paint (or ceramic?) coating on the piston crown as a barrier against heat transfer, for increased performance. So far I haven't seen this migrate into commercial engines, any thoughts from the "experts"?
RE: piston rings & sealing against cylinder wall
Regards
Pat
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RE: piston rings & sealing against cylinder wall
Aren't "Dykes" rings much the same thing for the same purpose.
Does any oem still use them on 2 strokes? (Does anyone make 2 stokes, come to think of it!)
Harry
www.tynevalleyplastics.co.uk
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
Anyway, the only Dykes I could find still in use was down at the radio control hobby shop for a quarter scale something or other. I don't fly much anymore, don't have enough $$$ left after bills. (I still like to window shop, perhaps when I get too old to race).
Rod
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
However, since all seem to know about "gas ported pistons", it's about time to consult the "experts" <smirk> I am refering to JE as I am currently using their "vertical gas ported" pistons in my race car and I sorta knew where to look...Page 6 of their on line pdf catalog.
http
http://ww
Shucks...You will need to open the Home page and then go to the pdf catalog. I get a "Forbidden" if I try to link directly.
Rod
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
There are 2 different types of gas ports. "Vertical", that are drilled in the top of the piston. And what's know as a "Lateral" port. Drilled on the side of the piston just above the top ring. Vertical is traditionally used in drag racing. Lateral in circle track and road racing.
(carbon build up is greatly reduced with lateral.)
Yes there is a certain amount of blow-by caused by these ports. But to offset the effects piston makers cut an accumulator grove between the first and second ring. This grove gives the gases a controlled place to go. This actually helps control "Ring Flutter" by providing a cushion between the two compression rings.
From my work with NASCAR Cup teams,NHRA pro teams, and
amature weekly racers, there is merit to this technology.
RE: piston rings & sealing against cylinder wall
I made a little plug with the same number of holes on one end and a 1/4 npt on the other that I could hook up a air hose. The amount of air coming out was pretty small. The boss's wife liked it on her watering can for the office plants.
I think this was before the dyke ring caught on for drag racing. The gapless ring has pretty much taken over I think.
RE: piston rings & sealing against cylinder wall
It should have said "lateral gas ported". I guess I just had vertical on my mind as the subject of this thread....Sorry...I have not used a set of drilled, ported pistons in over 30 years. However the current pistons seem to be just fine...in fact, if you did not know in advance you might not even spot the difference.
Rod
RE: piston rings & sealing against cylinder wall
If you think a shop makes money gas porting a set of pistons, tell me how much you charge because it is not a money making proposition. You have to contend with breaking a drill bit off and making sure you get half the diameter of the drill bit into the back of the ring land. Placement is critical if this technology is to work properly. No money to be made I assure you as there is no universal setup for doing this. The advent of cnc machines definitely makes it worth while to have the manufacturer do this for you when you order a set.
Larry Coyle
Managing Partner
Cylinder Head Engineering, LLC
CNC Porting
De Soto, KS 66018
RE: piston rings & sealing against cylinder wall
RE: piston rings & sealing against cylinder wall
Regards
Pat
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