ESE's works engine tuner

[koba]

They made a device so they could adjust the inlet length. Then they ran the motor, changed the tuned length of the inlet and plotted the peak torque point. After step by step changes and plotting the results it was clear if you could have an automatically varying tuned length you could have a very long, Phat flat and high torque curve.

I can't help thinking about what could be done with an electric power valve actuator and a couple of pieces of pipe that slide inside each other.

.

I think the current R1s have somthing like that, I think its just a two stage job tho, essentially long trumpets and short.

[SS90]

There was heaps of research done by Fujio Nagao (of Kyoto Univerisity) on the subject of the resonance effect of the intake side of a two stroke.

Alot (most) two stroke tuners use his data in their books, and I have been lucky enough to read several portions.

Basically, It is quite simple to calculate the resonance frequency in an exhaust system as it's frequency is ALMOST exclusively a function of it's length.

But, the intake side is termed a "resonance flask" (as it consists of the crankcase, and the inlet tract.)

(Another example of how important the crankcase is, and how much modifications can effect the engine!)

And, there is a simple formula for determining the resonance frequency of a flask, but, when you look further into it, it starts to get complicated when you try to use it, as there are so many variables when it comes to a specific example.

One of many examples of a variable is Sonic speed, ( which is dependent on temperature, and how do you calculate the temperature of gasses when it is not only being cooled by evaporating petrol, AND heated at the same time by the metal of the engine when it is being).

there are many variables, but it is pointed out the biggest problem in calculating the correct length for a specific engine is that the volume of the intake in question (which includes the crankcase) changes constantly with the movement of the piston.

Couple this with the fact that the intake tract (as is the case of a GP125, is not just a simple tube)

Not only the shape, but the area varies all through this length, which is not only difficult to measure, but in being so, difficult to calculate, even if you could measure it accurately (as there are so many different formulas needed for such a complex shape)

You could waste an amazing amount of time on this calculation, and , even today it is considered acceptable (even with some of these very clever computer programmes (MOTA, coupled with a rendering programme like CATIA for example)) to simply experiment, but in a scientific way.....

One method involves isolating the effect of the inlet tract on the engine.

Which, in itself is a basic concept, you must of course, design and build a "stub" exhaust that will be too SHORT to operate effectively with-in your projected operating speeds, BUT be long enough to prevent the "Kadenacy effect" which will cause "back breathing" into the combustion chamber and also upset mixture strength.

Kadency effect , basically, is the name given for the reason a high pressure will balance out a low pressure, an example of which is the Crankcase/combustion chamber scenario...... So this effect is not always a bad thing!

There are a few more steps in this method, but, it is quite time consuming (and noisy).

It is well documented (and I suspect that some people may know), that the closer you mount the carb to the cylinder (in the case of piston porting), or, such as is the case of a GP125, the disc valve, that MAXIMUM air delivery (permitted by the carb size, and primary compression ratio that is) is delivered to the crankcase.

Great!

Not quite.

When you get that close, the wave activity at such a location creates MASSIVE pressure fluctuations, and the carb really has trouble doing it's job of metering the fuel.

Myself (and thousends and thousends of peoole before me) have found that using a reed block helps dramatically (and also the distance of the reed block from the disc (in a disc valve example) has profound effects when only increased/decreased by 3-4mm

My personal experience has been 5mm can be as much as 200RPM more effective range.

But that does vary from design to design, and cannot be considered a rule by any means.

With such a small carb, could it be an idea to go to the effort of adapting a reed block (a short one, so that it doesn't end up wider than a Benelli Sei') to the inlet (and, also increasing you inlet timing to maximum, as now the reed block will only allow fuel in as a result of the piston pressures).

It's just a thought (and perhaps inpractical), but with a little carb, maybe there are some tangible gains having the carb as close as possible to achieve MAXIMUM AIR DELIVERY (with your piddly little 24mm carb.)

Just a thought.

[F5 Dave]

I dont get this bit.

I'm not trying to be personal or anything either but I just don't understand it.

Small hole = high airspeed = cool inlet charge right?

My Volkswagen has a 28mm carb on a 1500cc four-stroke engine, the small hole and long inlet manifold lead to manifold icing! yeah, none of this cold air induction shit, it needs to be heated in winter so it doesn't freeze up!

While this is a totally different example I would have thought the theory would carry over at least in part.

Could you give us an idea of why? even without data to support it yet.

Oh come on Mal, if you'd done any reading on 2 strokes this would be evident.

[SS90]

No, I don't take it personally.

What we are dealing with here is the "pumping efficiency" of the engine.

Having a smaller carb (in particular an excessively small carb, rather than just 1 or 2mm smaller than ideal) increases the pumping loss (the horsepower the action of "drawing the air in" through a smaller hole.

This " higher than normal pumping loss" in turn adds to the overall temperature of the engine.

A four stroke (like your Käfer, (beetle)) for example has less "pumping losses", particularly in the intake stroke, as the inlet valve opens after the piston has started its downward stroke, and there is alot more energy from one four stroke power stroke than one two stroke power stroke, and the crankcase is not pressurised on a four stroke (it's actually vented to atmosphere) making pumping losses more of a factor on the two stroke.

This may or may not include VW's!

I think a good example would be if you had a syringe (with an opening of 1mm and extracted the plunger, and paid attention to how much energy was required to do so (perhaps using a spring scale), then, with the same syringe, decrease the opening to 0.4mm, and did the same test, you would require sigificantly more energy to perform the same task. (due to the fact that the opening has decreased it size, and there is more energy required to perform the same task. The air you draw through this smaller hole will also be quite a bit hotter than the air you draw through the larger hole.

This is a pumping loss.

[F5 Dave]

Ahh, So you are saying the frictional increase of pushing the same amount of air through a small orifice compared to a bigger orifice will mean an increase in heat.

. . . However this does ignore the latent cooling effect of the petrol in the gas mixture.

And, and more importantly I would argue is that you aren’t pumping the same amount of air through. You are sucking less in (aided by some extent by inertia I concede). You have a given amount of suck & there is a restriction so you can’t get that much in. That is why it is a restriction in the rules as it restricts power from the larger 125 engine (from the 100s which can run any size & be watercooled).

[speedpro]

Ahh, So you are saying the frictional increase of pushing the same amount of air through a small orifice compared to a bigger orifice will mean an increase in heat.

As mentioned by you a bit later in your post, the air is being sucked through the hole. There is therefore air at atmospheric pressure outside the hole and a reduced pressure area on the other side of the hole and the air moves through the hole accordingly.

The air outside the hole as it moves through the hole to the inside of the crankcase will reduce in pressure, it wouldn't move otherwise, and what happens to a gas as it's pressure is reduced , , , , hmmmmm?

And yet somehow or other the theory is that we end up with a hotter engine. Actually when you take all the friction and combustion going on I'd be very surprised if the temp change is anything other than academic.

[Buckets4Me]

Pushing pulling pocking and prodding
I would be hot uner the collar to

[saxet]

One way to look at it could be that the motor has to work harder with a smaller dia. hole. Heat would be the natural outcome of the extra energy used ...I sound like a tech tutor.........maybe I was listening.

[TZ350]

Hopefully this leads to an animation of the complete 2-stroke process.

http://www.atvriders.com/articles/twostroke.html

And this page has a description of the various 2-Stroke types.

http://en.wikipedia.org/wiki/Two-stroke_cycle

* 1 Applications
* 2 Different two-stroke design types
o 2.1 Piston controlled inlet port
o 2.2 Reed inlet valve
o 2.3 Rotary inlet valve
o 2.4 Crossflow-scavenged
o 2.5 Loop-scavenged
o 2.6 Uniflow-scavenged
o 2.7 Stepped Piston Engine
* 3 Power valve systems
* 4 Direct Injection
* 5 Two-stroke Diesel engines
* 6 Lubrication
* 7 Reversibility
* 8 Sources
* 9 See also
* 10 External links
.

[koba]

No, I don't take it personally.

What we are dealing with here is the "pumping efficiency" of the engine.

Having a smaller carb (in particular an excessively small carb, rather than just 1 or 2mm smaller than ideal) increases the pumping loss (the horsepower the action of "drawing the air in" through a smaller hole.

This " higher than normal pumping loss" in turn adds to the overall temperature of the engine.

A four stroke (like your Käfer, (beetle)) for example has less "pumping losses", particularly in the intake stroke, as the inlet valve opens after the piston has started its downward stroke, and there is alot more energy from one four stroke power stroke than one two stroke power stroke, and the crankcase is not pressurised on a four stroke (it's actually vented to atmosphere) making pumping losses more of a factor on the two stroke.

This may or may not include VW's!

I think a good example would be if you had a syringe (with an opening of 1mm and extracted the plunger, and paid attention to how much energy was required to do so (perhaps using a spring scale), then, with the same syringe, decrease the opening to 0.4mm, and did the same test, you would require sigificantly more energy to perform the same task. (due to the fact that the opening has decreased it size, and there is more energy required to perform the same task. The air you draw through this smaller hole will also be quite a bit hotter than the air you draw through the larger hole.

This is a pumping loss.

Hmm, I get the idea.

Ahh, So you are saying the frictional increase of pushing the same amount of air through a small orifice compared to a bigger orifice will mean an increase in heat.

. . . However this does ignore the latent cooling effect of the petrol in the gas mixture.

And, and more importantly I would argue is that you aren’t pumping the same amount of air through. You are sucking less in (aided by some extent by inertia I concede). You have a given amount of suck & there is a restriction so you can’t get that much in. That is why it is a restriction in the rules as it restricts power from the larger 125 engine (from the 100s which can run any size & be watercooled).

But I also see what you mean...

As mentioned by you a bit later in your post, the air is being sucked through the hole. There is therefore air at atmospheric pressure outside the hole and a reduced pressure area on the other side of the hole and the air moves through the hole accordingly.

The air outside the hole as it moves through the hole to the inside of the crankcase will reduce in pressure, it wouldn't move otherwise, and what happens to a gas as it's pressure is reduced , , , , hmmmmm?

And yet somehow or other the theory is that we end up with a hotter engine. Actually when you take all the friction and combustion going on I'd be very surprised if the temp change is anything other than academic.

And your angle...

Pushing pulling pocking and prodding
I would be hot uner the collar to

I do know all about what you are talking about but thats another story...

One way to look at it could be that the motor has to work harder with a smaller dia. hole. Heat would be the natural outcome of the extra energy used ...I sound like a tech tutor.........maybe I was listening.

I think I'm confused

Tee Zee, CAN you test this by whacking a bigger carb on and measuring heat and all that?
It would be interesting to see.

[Buckets4Me]

I'm sure he can test the theory but no one is to complain at the next gp ok

[koba]

I'm sure he can test the theory but no one is to complain at the next gp ok

Hmm, good point.

TeeZee, Maybe it would be a waste of time testing that theory

[SS90]

Hmm, I get the idea.



But I also see what you mean...



And your angle...



I do know all about what you are talking about but thats another story...





I think I'm confused

Tee Zee, CAN you test this by whacking a bigger carb on and measuring heat and all that?
It would be interesting to see.

This is all very interesting, however, I feel that some of the basic understandings are being compromised by irrelivent references to technical terms.

Speedpro...........

In the case of the intake stroke of an internal combustion engine.............the air is not "sucked through a hole"

....... It is "pushed".

(by the higher pressure air behind it)

A highschool science teacher will teach that.

Let's not get lost here!


I have written earlier (as discovered by air-cooled 125GP developing engineers) when you are calculating the required length of an inlet manifold, while it is easy to find a suitable formula to suit the occasion, as is subjected to too many variables (and therefore too many variables in the equation) to be a worthwhile exercise.

Four Strokes are somewhat different (an example of which has been offered.....ironically, a VW Beatle.

It would be a good idea to point out now, that the generalised standard for the calculating the length of a four stroke inlet manifiold, is from the back of the inlet valve to atmosphere (I am sure there are other variables, but this is considered a constant......, whereas the two stroke includes the Crankcase volume (.....which changes)

As such, every two stroke engine must undergo it's own developing procedure.

Lets us all remember that we can get "lost" using big words, and forget some basic principals.

This is one area in particular that the levels of gains to be made (compared to a four stroke) are quite significant, due to the in-nefficienty of a two stroke engine.

Pumping losses are considered critical on a Two stroke engine.

More pumping losses mean more heat.

An example of pumping losses being so important, is attention to the correct primary compression ratio.

(for a given engine, in a given situation)

[saxet]

Perhaps another thread needs to be started for this sort of discussion( two stroke tuning thread) so TZ350 can have his thread back???

[SS90]

That's a very good idea.

I would contribute to both, (to the best of my ability,and with-out any hidden agenda)

It would be very cool to contribute to the "resurrection" of New Zealand in the race bike scene.

We have been absent for a while...........