ESE's works engine tuner

[Frits Overmars]

I am currently working on an engine that has two rings and I am looking for a piston with only 1 ring that I cannot find. If I remove the bottom ring is that the groove will serve as a bypass between the transfer and the exhaust. I think the groove is so small that maybe it doesn't show. what do you think about it? thank you.

The groove will indeed constitute a bypass. Whether it will actually serve as a bypass, depends on the exhaust and transfer pressures.
As you say, the effect may be small. Just try it; you've got nothing to lose.

[ken seeber]

Good morning all . I am currently working on an engine that has two rings and I am looking for a piston with only 1 ring that I cannot find. If I remove the bottom ring is that the groove will serve as a bypass between the transfer and the exaust. I think the groove is so small that maybe it doesn't show. what do you think about it? thank you.

Over herein Oz around a century ago, there was an engine used in karting for little kids, it was called the Comer S80 or SW80.
It had a chrome bore and a 2 ring piston. The tuning trick of the day was to reduce friction from the second ring. The rules stated that both rings must be in place.
What the "gun" tuners did was to reshape the second ring such that it was tensioned into the ring groove, ie making no contact with the bore, but still there to prevent short circuiting and also satisfy the rules.
To achieve this, the ring was squeezed into an "undersize" ring, such that the ends must have overlapped, ie forming a helix. Then it was heated, presumably to some annealing temperature, maybe 800 - 900 C for cast iron, less for steel.

Then it was fitted to the groove such that it was tight to the bottom of the ring groove. Clever ??

So, if you have old rings to play with, maybe this is the go.

No guarantees though.

[lohring]

"The only thing I would insist on , that many ignore , is to get a one way clutch , as is sold for tractor pto drives for mowers etc.
Then if an engine locks up , the dyno inertia wont keep driving the crank around to complete its destruction. "

Amen to that. I've never seen an engine as completely destroyed as when we seized one at over 10,000 rpm on the way to a 20,000 rpm pull. We had a centrifugal clutch and a square coupler that linked the engine to the wheel, but not a one way clutch. The coupler was twisted 180 degrees before the clutch let go. Fortunately it was a 26 cc engine. A bigger engine would be a lot more expensive.

Lohring Miller

[TZ350]

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2Stroke Stuffing. Was that really 30hp????? https://youtu.be/MIDaSh3o380https://...be/MIDaSh3o380 I am not sure about the durability of the results but I am very impressed by his energy, honesty and resourcefulness in developing that supercharged 50cc engine.

[KKT]

This may well be really dumb questions..

Looking from the bottom of a cylinder for a two stroke: Is there a relation between the area of the transferducts and the area of the cylinderbore, and the volume of all transfers vs the cylinder volume ?
How do you know if the transferducts are large enough for a given cylinder capacity ?

[ken seeber]

Been thinking about 2 Stroke Stuffing. If we had an in-cylinder pressure trace it would be interesting if there was significant pressure decay prior to exh port opening, as is pretty much normal. Now, to get more power, it’d just so useful to have a higher pressure in the cylinder before EPO.

He has the ability to pump in more charge because he has a blower. This is on the basis that it can provide a greater gas flow than the blower than can be achieved with regular crankcase/exh tuning flow.

Going back to current tuning stuff, the usual thing is to go for a high CR (ie small head volume) to maximise the efficient burn of the available charge, consistent with detonation control etc.

Now if Alex can provide more mass flow thru the cylinder, he is ultimately limited to a total trapped volume of the cylinder trapped volume after EPC plus the head volume.

So, what if he increased the head volume? This would mean more charge mass in the cylinder at EPC and therefore more mass of charge to burn and reduce the pressure decay prior to EPO. This would/could mean more power.

Free lunch ???

[Frits Overmars]

Free lunch ? Pretty much. But first:

He has the ability to pump in more charge because he has a blower.

Right, but more importantly, he has the ability to keep in more charge because he has a rotary exhaust disc that closes the exhaust before the transfers, so he can really supercharge the cylinder.
Next: an increased combustion chamber volume makes it possible to pump more mixture in because the pressure rise will be less steep (that is also true for a conventional two-stroke with an expansion pipe).
A lower compression ratio equals a lower expansion ratio which again would be great if he were to use an expansion pipe because the pipe would then be fed with high-energy exhaust gas. But even without such a pipe a low expansion ratio is good for power because it means a smaller pressure drop between maximum pressure and pressure at exhaust port opening, in other words, a higher mean pressure during the expansion stroke (this is how you make 1000hp-per-liter dragsters survive: a verging-on-tolerable peak pressure that hardly drops off).
For Alex however, lunch will not be completely free because in his case the exhaust gas energy is wasted. And with fuel prices these days....

[wobbly]

I was recently amazed to learn of a Volvo stern drive boat engine that is supercharged as well as turbocharged.
On part throttle the supercharger is designed to increase mid range power and economy , then when giving it a handful the turbo spools up and uses the " free " exhaust energy
to dramatically increase top end power.
I sure don't want Alex going off on another weird arse tangent , but Frits mentioned the only partial free lunch due to loss of exhaust energy.

[pete376403]

Some big GM diesel two strokes are both turbo and supercharged.

[ken seeber]

I was recently amazed to learn of a Volvo stern drive boat engine that is supercharged as well as turbocharged.
On part throttle the supercharger is designed to increase mid range power and economy , then when giving it a handful the turbo spools up and uses the " free " exhaust energy
to dramatically increase top end power.
I sure don't want Alex going off on another weird arse tangent , but Frits mentioned the only partial free lunch due to loss of exhaust energy.

"The lunch will not be completely free "

I guess that means just another half sandwich (ham, cheese and tomato) then...

[husaberg]

I was recently amazed to learn of a Volvo stern drive boat engine that is supercharged as well as turbocharged.
On part throttle the supercharger is designed to increase mid range power and economy , then when giving it a handful the turbo spools up and uses the " free " exhaust energy
to dramatically increase top end power.
I sure don't want Alex going off on another weird arse tangent , but Frits mentioned the only partial free lunch due to loss of exhaust energy.

In the 4t world the Nissan march engine that was about 900cc was a super turbo as were a few fire engines in the states
The later Detroits were supercharged scavenges with an additional turbo, which i suspect was also for noise reduction as well.

Surely as its hot a tubo might help burn off unburnt fuel and possibly emissions in a 2t

https://en.wikipedia.org/wiki/Nissan_MA09ERT_engine

[vro46i]

Stepped pins can be made to be reliable , but its so much easyer to use a CNC spark errosion process.
A good operator will know what copper electrode size to use and can adjust the current to get a dead straight sized hole on exactly the correct stroke.
Ive done this several tines now , with only one hole being a little tight.

Edit - its really good for destroking , as you make the new hole on center , but oversize , and use a spacer sleeve to re establish the press fit.
That way the actual new hole size is immaterial , as long as they are all the same.
Depending upon the flywheel OD lengthening the stroke this way could make the web too thin above the pin hole.

Hi Wobbly, I have arrived at the stage of destroking the engine from 125cc to 110. Using an oversized big end pin (24mm dia) where previously a 22mm dia. The machinist is going to offset bore it to fit the new big end pin to achieve the required stroke. Can you please tell me, how much of an interference fit does the big end pin to the new crank web hole is acceptable? 2 -3 thou? Thanks in advance.

[Vannik]

I was recently amazed to learn of a Volvo stern drive boat engine that is supercharged as well as turbocharged.

https://deltahawk.com/

One of the lead designers is on this forum

[husaberg]

[136kg136ps]

I worked on 2 stroke 16V149 Detroits Diesels that had 4 turbos, two bypass superchargers, intercooling, ceramic coated piston tops and chambers to produce just under 1 hp per cubic inch in the 1980s. The piston skirt and top were seperate and they used 4 exhaust valves per cylinder.

Used for industrial and military generators and marine propulsion. They were something to behold. Leaky, noisy and prone to fires caused by oil spray from turbo oil lines soaking lagging and catching fire. I had to rescue a coworker once using a firefighting oxygen unit when he was overcome by fumes from a fire.

The bypass kicking off could be heard through supposedly soundproof enclosures and felt as a pressure change.

I got to thinking about the role crankcase pressures played a part in two stroke operation with them because when all cylinder block leaks were sealed, a catastrophic failure was likely imminent.