thought this would be interesting and helpful to some of you guys

http://www.datafan.com/TunersHandboo...efiltered.html

i will add more links soon.

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i cant get the link to come up

javascript:mox();i have been having a hard time with links on this site. try this one tho.


i think most of this info should apply to nitro and gasoline, only the piston ring section is not relevant for nitros of course.<br type="_moz" />

Hey nothing wrong with piston rings,Top Fuel drag engines use them 7000+ hp !!!

True, but these are small scale engines, and designed without the use of rings.

D.DJ    small scale engines,where are the full size ones,what do they use them in?</p>

But they don't turn 40,000 rpm.

lol. i was just saying that the section of that article about piston rings, does not apply to nitro engines, because they dont have piston rings.

If you're talking model car engines then no, they don't use rings, but I have about 12 different model engines with rings. And none of my 80 or so engines are nitro engines either because I just use methanol and oil for fuel so I just call them glow engines .

Thanks downunder,my point as well,if i put some nitro in my lawn mower,is this now a nitro motor?

wow got to go get a better calculator for that stuff

Some scale engines do use rings, but they are usually 4-strokes or large capacity engines that dont spit out huge RPMs.
The ones that do go say 20K +, they just use a slightly conical piston sleeve to create its own seal.

The Super Tigre 40 is ringed and I have an old .29 that's ringed but the smallest ringed engine I've heard of was a .15 from many years ago. Most heli engines are ringed too because they're much more dirt tolerant than ABC.

The very first Super Tigre G20 did use piston rings,i think they were 15mm bore,not to sure a about tapered bores with piston rings,from my old engine rebuild days i recall 4 thou to the inch,racing clearance for air cooled engines.The piston ring end gap would be reduced at T,DC.

That was back in the day, so I assume they found it didnt work well and so we have tapered cylinders in these engines. Just my theory.

Rings work very well in model engines from around the .30 size and upwards but are limited to around the 20,000 rev mark because then the ring can't quite follow piston movement so they start to flutter in the ring groove which wears the groove and the seal gets lost. There's a class of control line speed that's been running for a very long time and the engines were limited to 2.5cc (.15) but rings weren't successful in those small engines and especially at the revs they were running so the only type of piston used was lapped cast iron. These were (and still are) very good except they're quite heavy compared to an alloy piston with rings. Back in about the early 60's Super tigre .15's were one of the world's best speed engines but the pistons were starting to give problems with consistent runs as they developed them further and further. So Super Tigre experimented with ABC which gave an instant fix and allowed their engines to keep setting world speed records. Other manufacturers caught on and virtually all speed engines were then ABC. It wasn't long before ABC made its way into normal consumer type sport engines and now it's about the only type most modellers know of.

ABC isn't the ultimate though because an even better arrangement is AAC where the liner is aluminium and chrome plated. Even better than AAC is AAO where the alloy liner has a kind of anodising which is much harder than even chrome but so far only the Russians can do this properly.

Exactly, im not saying ringed engines are bad, just that they cant rev as high without suffering ring flutter. If only they could be stable at high speeds, then we wouldnt really have to worry about getting a whole new P/S set, just replace the rings and break THEM in. I would think they would be much cheaper, but until technology advances in that are, the ABC engines, other other types like AAC or whatever, they will still be the way to create a consistant seal (before it wears out)

why do the smaller ringed engines have such a hard time with rpms? the gassers get up to 22K with out flutter issues, and those have the 30mm stroke. just seems strange to me a motor with a 15mm stroke would have more trouble sustaining high rpms than a motor with a 30mm stroke...

i think the small engines really yank the piston up and down, while the larger ones have a smoother transition between the up and down stroke, due to the stroke length.? idk, just a guess.<div></div><div></div><div>too bad we cant use an o ring lol. that would make a perfect seal, without flutter. but you would have to replace it every few minutes.</div>

Hehehe, i think engines with a larger stroke make less flutter because they travel more than those with a shorter stroke, causing the ring to hit the "edges" and bounce back, see what im saying? it like shaking a can of juice for example. If you shake in small quick shakes, the juice just touches the ends, but if you make the shakes bigger like the Monkey Dance (lol?) they really hit the ends of the can. Im no expert on 1:1 engines, just a fair bit of knowledge behind them.

That's a very good question because I didn't know that gassers (and presumably similar sized glows) could turn revs like that so it got me checking in to ring flutter. It turns out that ring flutter depends mostly on combustion leakage past the top ring and getting trapped by the second ring which can then lift the top ring off the piston groove which leaks even more pressure and power drops considerably. A fix is a larger ring gap on the lower ring (which reduces sealing anyway) or using a single compression ring. Either way, tolerances have to be kept very close but as engine size gets smaller the tolerances have to be even more precise because of scale. Ring tension (how hard it springs out against the liner) is also critical because if it's not enough then combustion pressure can force it away from the liner (especially if it's been lifted off the piston groove seat) and then obviously loses the seal. Too much tension causes high friction and wear. Once again, things like this are easier to control the bigger the ring is.

With smaller engines, all these problems with rings are overcome by using no rings, as with ABC, but there's a crossover point where ABC becomes a disadvantage. This is because ABC relies entirely on holding a correct piston/liner clearance with metals that expand close to the same amount but as the bore gets larger any slight difference in thermal expansion gets exaggerated. It appears the crossover point is at around a 1" bore which is about a .90 size engine. The largest ABC engine I know of is a 1.08 but mostly it's around the .90 size that you see some engines ABC and others as ringed.

well, according to the article i posted, the more pressure in the chamber, the more the ring pushes against the cylinder wall. the pressure pushes it outward.