ESE's works engine tuner

[F5 Dave]

With all this talk of carb mounting flanges it just occurred to me - why don't we use 4T style mounts? Typically only 2 bolts but that works on 4Ts, and often we have an adaptor somewhere in the whole carb/reedblock/engine assembly so why not have one screwed to the reed block and then the carb mount to the adaptor? Mostly nice and straight. For a "real" race bike it would add undesirable length but as an option for us it would seem OK.

Used one on the 50 for decades but that was easy as not full reed.


The 100 has the shortest 4stroke inlet I could (Z750 i think) find bolted to a 10mm plate bolted direct to the reed with some filler in the reed corners to blend nicely. I couldn't use Frits` idea of the O-ring plate as that made the carb clash with the cases.

[wobbly]

As Frits has said the higher the ring position the better, up to the thermal limit of the supporting land.
The higher you go the less unburned trapped mixture there is in the clearance crevice.
In a back to back test of 1mm stock ring with a 0.8mm so called A Kit ring, the thin ring was worth around 0.3Hp from 8000 to 13,000
so in this case the friction reduction gave a power increase, with no apparent issues of loss of heat transfer.

Wossner have made some special pistons for me with 8 radially placed gas ports in the top of the ring groove.
This piston combined with a very low tension ring pressure on the bore, is worth around 1 Hp at 8000, dropping to 0.3 Hp at 13,000
due to the drop in friction, and the better ring seal at lower rpm reducing blowby.
Thus you can pick up around 1 1/2 Hp simply with small details in the piston assy.

[husaberg]

Used one on the 50 for decades but that was easy as not full reed.


The 100 has the shortest 4stroke inlet I could (Z750 i think) find bolted to a 10mm plate bolted direct to the reed with some filler in the reed corners to blend nicely. I couldn't use Frits` idea of the O-ring plate as that made the carb clash with the cases.

[F5 Dave]

.. . .
In a back to back test of 1mm stock ring with a 0.8mm so called A Kit ring, the thin ring was worth around 0.3Hp from 8000 to 13,000
so in this case the friction reduction gave a power increase, with no apparent issues of loss of heat transfer.
.

Erm in the same piston with an extra .2 clearance? would have thought the ring would have been more prone to twist. Or a dif piston with other variables?

. . .
Wossner have made some special pistons for me with 8 radially placed gas ports in the top of the ring groove.
This piston combined with a very low tension ring pressure on the bore, is worth around 1 Hp at 8000, dropping to 0.3 Hp at 13,000
due to the drop in friction, and the better ring seal at lower rpm reducing blowby.
Thus you can pick up around 1 1/2 Hp simply with small details in the piston assy.

If I'd seen this on an A'mercan website I'd have sneered & filed it with rifled squish areas. But it didn't & I trust what you've posted, so I'd have to ask -what is happening? the ports create more seal, but pressure being equal how does this push the ring further into the bore at lower revs when pressure is lower? And what in particular is a low tension ring?

[wobbly]

Yea right, so I put a thin ring in a wide groove, don't think so.
Honda did the A kit pistons with thin rings, so I wanted to see why.
They also had the ring pin at the back so the B ports could be made large and symmetric, that made a heap more power than could be gained from the vanilla customer piston.

The gas ports allow the combustion pressure down in behind the ring to create a better bore seal,quicker, at lower rpm.
There is a very limited vertical clearance to allow this, so the ports work well in combination with a ring that doesn't need as much static
radial tension on the bore to create a natural seal action without the gas pressure - thus less friction when the gas seal has been dissipated below EPO.

[husaberg]

Yea right, so I put a thin ring in a wide groove, don't think so.
Honda did the A kit pistons with thin rings, so I wanted to see why.
They also had the ring pin at the back so the B ports could be made large and symmetric, that made a heap more power than could be gained from the vanilla customer piston.

The gas ports allow the combustion pressure down in behind the ring to create a better bore seal,quicker, at lower rpm.
There is a very limited vertical clearance to allow this, so the ports work well in combination with a ring that doesn't need as much static
radial tension on the bore to create a natural seal action without the gas pressure - thus less friction when the gas seal has been dissipated below EPO.

Wayne are we talking about ports like a Oil control ring on a four stroke (Bottom of pic)or to the top of the piston like in top of this picture?
Edit he does say combustion......

[wobbly]

If you look at the pic I posted you can see they are 1/2 moon slots cut into the top of the ring land to transfer combustion pressure
to the space behind the rings back face.
At lower rpm there is more time for this pressure to build and be effective, at high rpm it doesn't seem to work as well - I believe simply
due to the lack of time.

[F5 Dave]

Yea right, so I put a thin ring in a wide groove, don't think so.
Honda did the A kit pistons with thin rings, so I wanted to see why.
They also had the ring pin at the back so the B ports could be made large and symmetric, that made a heap more power than could be gained from the vanilla customer piston.

The gas ports allow the combustion pressure down in behind the ring to create a better bore seal,quicker, at lower rpm.
There is a very limited vertical clearance to allow this, so the ports work well in combination with a ring that doesn't need as much static
radial tension on the bore to create a natural seal action without the gas pressure - thus less friction when the gas seal has been dissipated below EPO.

So this would happen sooner after TDC when the pressure is pushing the piston down & the ring hard against the top of the land after swapping from the bottom of the land (on the way up).. . .No hold on, the piston would be taking the ring for a ride after Ex Port opening, but the pressure would be trying to blow past the ring at TDC pushing the ring down driving the piston as well. . . Now my head hurts.

But you are saying the piston ring ports would swap the ring to bottom of the land bearing pressure quicker reducing time of blow by I guess. I'm still not sure how the low tension ring is made differently but you are saying that for >190degrees there is less friction.


Have you tried just milling some ports on a conventional set up to see how this would work? I mean how much is less friction of this open EX port time? & how much is decreased blowby?, which has to counter the downside of more area lost to combustion, similar to having the ring slightly lower.

Does sound compelling to try this, thanks for sharing.

[husaberg]

The conformability of the rings increases exponentially as the thickness of the rings is decreased. If you reduce ring thickness by half, conformability goes up 8X. Plus, the reduced tension reduces frictional losses.

reducing the ring-to-piston vertical and groove back clearances can aid in reducing cylinder pressure loss. But he warns it is possible to go too far. “The top compression ring needs combustion pressure behind it to hold it out against the cylinder wall during the high pressure portion of the combustion cycle.

Gas ported pistons (vertical or lateral) also help with ring sealing. The ports provide a more direct path for cylinder pressure to get behind the top ring. Gas pressure helps force the ring out against the cylinder wall. In high rpm applications, gas porting helps thinner, lighter rings be more stable, reducing the tendency to bounce or flutter in the ring groove (which can break the seal).

As a rule, the higher the power output of the application, the more end gap you should allow for thermal expansion.

Foul stroke tid bits
http://www.enginebuildermag.com/2011...ct-horsepower/

* Gas porting: consists of drilling small holes through the tops of the pistons, which allow cylinder pressure access to the back of the top ring to force it out making it seal more tightly to the cylinder wall. They are most effective with tight ring grooves and high ring positioning. I do not recommend vertical gas porting (holes drilled through the top of pistons) for street applications. First, the engine probably doesn't develop enough cylinder pressure to unseat the rings and second vertical ports plug up with carbon in a street engine after a short time. which will be a potential source for pre-ignition. Also, you most definitely do not want one or two to plug up and apply unequal force circumferentially around the piston. As a result vertical gas ports are most often use for drag engines and horizontal ports (drilled through the side of the pistons) are used on circle track and road race engines (and on street engines...sometimes). Unless you have 600 hp or more, do not to worry about gas porting. Gas porting is needed in race engines, but it’s done because of the type of rings used and the absolute need for total ring seal at high rpm. Titanium and Chrome nitrite top rings are typically the type used, and in a 1.2 mm size. Both of which last very well, but are difficult to seal. Gas porting gets them to seal. Molly seals very well, but will not last in a race engine for very long. Also, machining the gas ports is a trick best left to the manufacture. JE happens to be my favorite and I’ve never had an issue with them, ever. Wiesco is a back up. Leave it up to them to determine placement, size and number of ports for the ring type, ring size and how long the race is. I’d also recommend that if you do go this route, coat the bottom of the top ring land, or the bottom of the ring itself with a dry film molly lubricant to keep the ring from welding in the grove. Make sure you use a good Indian stone to de-bur the groves too. Just hit the edge lightly. You’ll also want to take an exacto knife to the ports to make sure that there are no bur’s that will promote carbon build up, or hot spots. Make sure you do all this port and land prep before you mock up the assembly. Bur’s throw off your measurements. And don’t forget to polish the piss out the pistons with a light scotch bright buffing wheel. The deal with gas ports is they allow tighter ring land clearance since pressurization is accomplished with the ports. This tighter clearance is how flutter is controlled, this can be worth 20 to 30hp since it allows higher rpm with out ring seal loss.This also adds power by taking less piston movement to start building pressure,similar to moving top ring up on piston.Lateral gas ports are more street friendly since they wont carbon up as quickly as vertical ports. Ifin you still want to do this..get a gas port drill kit from Goodson..they make all kinds of trick stuff for race car engine builders...


https://www.physicsforums.com/thread...essure.316225/

[TZ350]

Ring tension is nowhere enough on its own, gas pressure behind the piston ring is necessary to ensure ring sealing against compression and combustion pressures.

http://alfatune.fi/cms_naytasivu.php?sivu=100

Simplified description of compression ring fluttering.
In the normal engine operation, the cylinder pressure on compression and on power cycle should keep the first compression ring steadily pressed downwards against the bottom of the piston ring groove. The pressure above the piston ring will find its way back of the piston ring, which again pushes the piston ring against the cylinder wall and securing the sealing. In standard applications, the pressure will be directed via the ring to groove clearance. In some applications this occurence may be helped by arranging more direct paths for the cylinder pressure to penetrate behind the piston ring using specific gas ports. The gas ports may be drilled vertically from the piston top or grooved laterally on the top surface of the piston ring groove.
The cylinder pressure fights against inertia of the piston ring and cylinder wall friction. Inertia of the piston ring is related to piston acceleration and to weight of the piston ring. If these opposing forces become greater the piston ring loses its contact to the bottom land of the piston ring groove, thus pressure behind the ring will escape under the ring and the force against the cylinder wall is lost. In standard application also the pressure path behind the piston ring will be closed and the pressure area above the ring is reduced making the problem even worse and last longer on the power stroke. This malfunction is called as piston ring fluttering.

Causes of piston ring flutter.
When the piston ring fluttering happens, rings lose their contact and result will be excessive blow-by. Furthermore the oil control does not work right anymore and these malfunctions cause long list of problems, including following:
- Power losses by excessive blow-by
- Ring and groove wear or failure
- Oil in burning chamfer will provoke knocking which may cause several mechanical failures
- In endurance applications high oil consumption may lead to lubrication problems and related failures
- High blow-by may pressurise the crank case and cause oil leakages and further power losses

[ken seeber]

Rings and heat rejection from the piston.
For many years, perhaps mistakenly, I was of the understanding that a very large percentage of heat from the piston was passed thru the ring. This in part was due to us (when I was at Orbital) dealing with some large vehicle manufacturers in working on the durability of the injected 3 cyl 2 stroke engine. They went on and on about the heat path via the ring, but they maybe were influenced in their thinking by their experience with diesels which had/have lots of compression rings and oil scrapers.

Since my resurgent interest in performance 2 strokes, I am starting to have other thoughts. One thing that I still believe in though is the fact that if the oil gets to be above 290 or so, it will carburise and if this occurs within the ring groove, the ring will stick and then, the sadness.

There is also no denying that the hottest part of the piston will be the crown, with the temp down the skirt, pretty much the same as the bore temp.
So, where does all the heat get dissipated to? My thoughts are:
1. Contact with the parts of the piston that are hotter than the bore to the bore. In this case, namely the ring and the top land.
2. From conduction down the piston behind the ring groove and bosses to the rest of the lower skirt and then to the bore and also to the pin bearing and rod via the piston pin
3. Radiation both upwards and downwards. Obviously if the underside of the crown and upper internal bits are around 250 or so, they are going to kick out some heat. There is going to be some thermal radiation from the pin and big end bearings, but I suspect these would be minimal and easily dissipated by the mixture.
4. Convection. There is a high level of gas flow under the piston, capable of removing lots of heat. This is in conjunction with the latent heat of vaporization of the fuel within the mixture. Also there is the flow across the piston crown during the transfer period.

To me, the biggies are the contact and convection, followed by the conduction and then radiation.

For max contact, I consider the fact that the ring land and ring spend a big percentage of the cycle at TDC and BDC at very low velocity, giving more time for heat transfer. As these have the highest temp gradient relative to the bore and rest of the piston, then these have the most opportunity to dump the heat. This is why the focus of cylinder cooling should be at TDC and BDC. BDC means the cooled water from the radiator passing under the exhaust port (in addition to cooling, or at least minimizing the thermal input, of the unburnt charge in this passage prior to being returned with the reverse exhaust pulse) and also underneath the cup handles of the A & B passages, which in addition can assist in cooling the mixture passing through these passages. Again at TDC, it is desirable to have a ring of coolant passing around this level prior to passing into the head. I often wonder why there isn’t an internal horizontal baffle in the cylinder to force the coolant around this path, instead of potentially short circuiting into the head.

Convection cooling. Knowing the airflow and therefore being able to infer fuel flow, one should be able to determine the convection effect, given temperature rise. So, it would be interesting to have the thermocouple readings, say between the carb and reed valve, just downstream of the reed and then in the transfer passages. Assuming there is a temp rise, then one could calculate the thermal input into the mixture. Still, it’s just one bit of info one could have, but unless we know the heat input into the piston, one could not calculate the heat loss via the contact and radiation.

Gas ports in pistons. The primary function of a ring is to seal compression and combustion pressure from leaking down past the piston. To achieve this, the ring must both seal against the bore and also its seating face. Sealing against the bore is achieved using both the spring force in the ring and gas pressure acting behind the ring, in the case of a common kart piston, the 1.0 mm height. To seal against the seating face, this means the gas pressure acting downwards on top of the ring, in the case of a common kart piston, the 2.2 mm radial depth. All going well, as the pressures rise above the piston, the pressures proportionally rise in the ring groove to act on to the ring. To achieve this, there must be a gas flow into this area. However, there are things that can prevent this from occurring as it should:
• Too great a gap behind the ring. Obviously this will require a greater gas flow to fill this volume, this will take longer and retard the sealing.
• Too tight a ring side clearance. If there was no clearance, there would be no gas flow, hence no sealing. However, in reality, it appears that most manufactured clearances, although pretty tight, seem to have adequate flow area. A heavily carboned ring and groove might create this effect however.
In saying all this, a Dykes ring offers almost no restriction to the gas flow to behind the ring.
I always thought that the gas ports were mostly used in nitro dragsters where the charge is heavily liquefied and that this might prevent a responsive pressure force acting on the ring. Hence the gas holes provide more access for the gas/liquid flow. An example of this is that small aero motors, like Frit’s 6.5 cc engine, don’t have rings, sealing is performed by the viscous film between the piston and ring. So, pretty interesting to see Wobbly’s thoughts. Certainly easy to try.

Ring tension. To me, this is a function of the ring gap, prior to fitment. All things being equal, a smaller gap will create a lower tension ring.
My thoughts anyway.

[Frits Overmars]

Rings and heat rejection from the piston... where does all the heat get dissipated to?
Convection. There is a high level of gas flow under the piston, capable of removing lots of heat. This is in conjunction with the latent heat of vaporization of the fuel within the mixture. Also there is the flow across the piston crown during the transfer period.

I don't know about the high level of gas flow under the piston, but there certainly is a high level of gas flow over the piston. Jan Thiel found out that this makes all the difference between a borderline and a thermally sound high-performance engine.

I often wonder why there isn’t an internal horizontal baffle in the cylinder to force the coolant around this path, instead of potentially short circuiting into the head.

So do I. But the baffle need not be in the cylinder; it can also be in the head, or the baffle role can be performed by a suitable head gasket.
Coolant, rising from the crankcase and passing along both sides of the exhaust duct, can all too often move straight up into the head, so there is hardly any horizontal coolant circulation in the upper part of the cylinder. Blocking the flow from cylinder to head right above the exhaust and opening a path to the head above the C-port will force the coolant flow to take the long way. Once in the head, it should then flow closely along both sides of the spark plug hole. This will usually take some more baffling and some venting.

Gas ports in pistons: even a tiny bevel from the top land to the ring groove caused detonation in the Aprilia engines. Any place where mixture could hide from the direct flame, was detrimental. So gas ports, either radially inward like Wobble showed, or axially top-down as used in nitro dragsters, were out as far as Jan Thiel was concerned.

The primary function of a ring is to seal compression and combustion pressure from leaking down past the piston. To achieve this, the ring must both seal against the bore and also its seating face. Sealing against the bore is achieved using both the spring force in the ring and gas pressure acting behind the ring... However, there are things that can prevent this from occurring as it should:
• Too great a gap behind the ring.

this is in line with our findings. The ring should be able to just disappear into the groove radially; the less the better. But too shallow a groove will cause the full thrust force to act on the ring instead of on the piston skirt. Then we have a very efficient oil scraper and the mother of all seizures.

• Too tight a ring side clearance. If there was no clearance, there would be no gas flow, hence no sealing. However, in reality, it appears that most manufactured clearances, although pretty tight, seem to have adequate flow area.

We found that a really tight fitting ring brought a considerable amount of extra horsepower. We start with a narrow groove and a ring that won't fit at all.
Then the ring thickness is ground down in tiny steps and retried over and over until it will barely enter the groove. It may sound like a lot of work, but it is one of the easiest ways you'll ever discover of finding power.

a Dykes ring offers almost no restriction to the gas flow to behind the ring.

Those 100 cc direct-drive kart engines of yesteryear all depended on Dykes rings, or L-rings as they are called over here. Detonation was hardly a problem as the cylinder filling of these engines was modest, in return for an ultra-broad power band. But with a good cylinder filling the gas volume above the L-ring will cause detonation problems.

.. small aero motors, like Frit’s 6.5 cc engine, don’t have rings, sealing is performed by the viscous film between the piston and ring bore.

Viscous film, you can say that again, Ken. The obligatory fuel is methanol with no less than 20% oil.
But wait, there's more. The cylinder bore is not cylindrical but very slightly conical. When the engine is cold, it can hardly be turned over by hand because the piston will literally jam near TDC. At running temperature the piston will just be able to move, with zero clearance.

[wobbly]

The real trick to getting the benefit of the gas ports in a 2T is the low radial tension of the ring that is allowed due to the extra
( quicker ) access of the combustion pressure into the clearance volume behind the ring.
This radial tension is created when the ring is manufactured, and a low tension ring has a smaller gap when relaxed, out of the bore.
Thus when assembled, it does not have as much natural static spring force on the bore surface.
Reducing the friction component of the ring when it isn't subjected to gas pressure for sure gains power, as my testing has shown.

I am next going to start working on the VHM piston/head idea of a radius on the timing edge as they are selling these as a kit to fit into KZ2
125 race engines and the published power tests show an improvement.
How much is due to the effective port timing change, as opposed to the flow bench improvement remains to be seen.
But as to why a radius on the timing edge doesn't deto, and Jans tests showed that a chamfer did seems at odds.
Except to say that the VHM head squish shape conforms to the piston shape, thus no extra trapped end gas is invoved.
The KZ2 engines will deto at the drop of a hat, so this effect needs to be tested to death before using it in a race situation.

[Frits Overmars]

..why a radius on the timing edge doesn't deto, and Jans tests showed that a chamfer did seems at odds.

Maybe we misunderstood each other Wob. I didn't mean a chamfer on the timing edge, but a bevel (albeit ever so slight) at the upper edge of the ring groove.

[F5 Dave]

The real trick to getting the benefit of the gas ports in a 2T is the low radial tension of the ring that is allowed due to the extra
( quicker ) access of the combustion pressure into the clearance volume behind the ring.
This radial tension is created when the ring is manufactured, and a low tension ring has a smaller gap when relaxed, out of the bore.
Thus when assembled, it does not have as much natural static spring force on the bore surface.
Reducing the friction component of the ring when it isn't subjected to gas pressure for sure gains power, as my testing has shown.

I am next going to start working on the VHM piston/head idea of a radius on the timing edge as they are selling these as a kit to fit into KZ2
125 race engines and the published power tests show an improvement.
How much is due to the effective port timing change, as opposed to the flow bench improvement remains to be seen.
But as to why a radius on the timing edge doesn't deto, and Jans tests showed that a chamfer did seems at odds.
Except to say that the VHM head squish shape conforms to the piston shape, thus no extra trapped end gas is invoved.
The KZ2 engines will deto at the drop of a hat, so this effect needs to be tested to death before using it in a race situation.

Ahh thanks for explaining the low tension ring, I only really thought of it as being in the bore with a particular gap. But you are perhaps saying that if you used a low tension ring that in itself might be a bad choice, but in conjunction with ring ports creates less friction when ex port open & can seal real well when it needs to.

So manufacturers actually make low tension options for some applications? Or you could perhaps heat it and position it to take a set at a lower tension position.