Two-stroke performance tuning?

[gav]

Care to share your "research" Skunk?

I would like to read a credible source that shows that "supercharging" is ANYTHING that simply increases VE (be it over 100% or not)

That's quite an interesting point, because we all seem to be stuck on definitions here.

Although, this is getting a little tiresome.......

Can anyone quote a source that defines "supercharging" (and in particular, it's relation to VE)

Anyway, if a Two Stroke chamber really "supercharged" a cylinder, would that not make them ILLEGAL in GP racing?

And, just to make a point,perhaps you should consider yourself when it comes to insults.........

Heres an example of "supercharging" being referred to in regards to the action of the expansion chamber. 3/4 of the way down the page.
http://www.southernskies.net/page_in...okeengine.html

This pulse is timed to reach the exhaust port after the transfer ports close, but before the exhaust port closes. The returning compression wave pushes the mixture drawn into the header by the negative pressure wave back into the cylinder, thus supercharging (a bigger charge than normal) the engine. The straight section of pipe between the two cones exists to ensure that the positive waves reaches the exhaust port at the correct time:

[Sketchy_Racer]

Don't forget Skunk, I feed myself and keep a roof above my head by tuning two stroke engines.... I must know something....

Just because you do something for a living doesn't mean your any good at it though does it? Just because someone pushes trolleys for a living doesn't mean that only they know the correct way to push a trolley...

Everything I read from you is either an insult, a critisism or you boosting your own ego about how great you are at two stroke tuning.

You strike me to be one of these people that can read a book, or article about something, pick up what the book is saying and use the technical jargon to make it seem like you know what your on about. You don't seem to be able to think outside the square, nor change a preset view on something even though from an outsider looking in, you have been wrong! (as everyone is at some stage or another)

I've said it before in another thread, but it got me in trouble, so I wont say it again, I will however link you to it just to remind you - http://www.kiwibiker.co.nz/forums/sh...&postcount=242

[Rodney007]

You strike me to be one of these people that can read a book, or article about something, pick up what the book is saying and use the technical jargon to make it seem like you know what your on about.

this is kiwibiker, its what we do,

[bucketracer]

I've said it before in another thread, but it got me in trouble, so I wont say it again, I will however link you to it just to remind you - http://www.kiwibiker.co.nz/forums/sh...&postcount=242

You got into trouble for that!!!! I did too, for something similar. Thats interesting, Hmmmm

a bit of topic, but does anyone else remember the character Tod from the film "Wedding Crashers"?

.

[Fooman]

Are you saying the return is mainly from the port to flange area and not so much from the header area?
My understanding is the fresh charge will exit the exhaust port by 100 or more mm (generalisation) before being pushed back.
I also understood that scavenging was to clean out the cylinder of old charge as completely as possible (even if it ends up in the pipe).

Am I correct in any part?

I was being asininely picky on behalf, etc. I just saw a comment in a paper saying that the fresh charge does not necessarily go into the pipe a reasonable distance - depends on the config of the engine as a whole.

One would think that a 2T motor that minimised or eliminated the charge lost down the pipe, but pushed all the exhaust out would be rather desirable - that doesn't imply a lot of charge going out the pipe is desireable...?

I know less than you about the "art" of two strokes, but know a reasonable amount on thermodynamic cycles and the engineering thereof.

I did some quick reading after I posted this - VE is the wrong expression for 2T engines for precisely your last comment - it is not just how much you can stuff into a cylinder, but how much fresh charge you can put in, after extracting all the old charge. Scavenging efficiency is the term used in 2T terms, due to the combination of intake and exhaust flows. I'll try and track down some papers etc tomorrow - There was a nice 1949 MIT thesis on the web, but that probably didn't take into account any spanny!

Cheers,
FM

[bucketracer]

.

Essentially, an expansion chamber pushes "HALF FUCKED" over heated low density air, fuel, and particle matter back in to the combustion chamber.
.

SS90 you’re starting to get it, the supercharging thing.

And now there is the loop scavenge systems flow patterns and how they are designed so the incoming mixture push's the exhaust ahead of it while minimizing mixing and there by dilution of the incoming mixture as it enters and fills the cylinder.

A series of pictures on page 2 show how loop scavenging works and the dilution of the incoming mixture by residual exhaust gas and the supercharging effect of the expansion chamber. http://www.fluent.com/solutions/automotive/ex204.pdf

The less dilution of the incoming mixture as it fills the cylinder and then down into the first part of the exhaust port/expansion chamber is the aim of improving scavenging flow patterns.

The better the separation between the fresh mixture and the exhaust gas the less "HALF FUCKED" the new mixture is when the bulk of it that has been drawn into the exhaust tract is energetically pushed back into the combustion chamber.

Scavenging flow patterns and expansion chamber supercharging is all about removing the exhaust gas while minimising the dilution of the incoming mixture ie., scavenging efficiency, and how much fresh charge is squeezed back and then trapped in the cylinder.

.

[B.Crump]

DKW and NSU had them

what bikes are they? i dont know much about bikes that arnt main streeam

[diesel pig]

what bikes are they? i dont know much about bikes that arn't main stream

He's talking about motorcycles that were raced in GP's 70 years ago.

[SS90]

J

You strike me to be one of these people that can read a book, or article about something, pick up what the book is saying and use the technical jargon to make it seem like you know what your on about. You don't seem to be able to think outside the square, nor change a preset view on something even though from an outsider looking in, you have been wrong! (as everyone is at some stage or another)

Your confusing me with Teezeetreefiddy.

So, what exactly have I been wrong about, given your "expertise" in two stroke tuning.......(nice expansion chamber by the way.........)

Maybe you could list 3 things I have been wrong about.......... (I don't think you can)

[SS90]

One would think that a 2T motor that minimised or eliminated the charge lost down the pipe, but pushed all the exhaust out would be rather desirable - that doesn't imply a lot of charge going out the pipe is desireable...?

My experience tells me that is quite correct.

The fact that a (normally aspirated two stroke fitted with a SUITABLE expansion chamber) (in my opinion) simply DOES NOT qualify as a "supercharged" engine, any more than power valves do (because, a power valve improves the VE of an engine.....does that make a power valve assembly a supercharger?....a mechanical one at that!), or perhaps even a Reed valve? That increases VE as well (sort of)

Because IF that was true, then all 2 strokes would be banned in MotoGP!

Would you consider larger valves in a four stroke engine "super chargers"? because larger (or multiple) valves increase the VE of a 4 stroke engine, if so, an engine with mulitple valves, is a "supercharged" engine, and the (bigger or multiple) valves are "mechanical superchargers"



If it could be considered a "supercharged" engine, such efforts to keep the charge inside the cylinder would be negated, and we could increase our power by simply increasing the size of the transfer ports (angles required by scavenge patterns REDUCE the area of the ports)

And, as such, we could simply design expansion chambers that "supercharge" the cylinder (an easy task, if it where true), ignore all the efforts of the last hmmmm....... 50 years and have our transfers pointing straight across the bore.......

Fooman, you seem well schooled,(and appear to be presenting a (thankfully) unbiased position) and I see that you advocate that "supercharged" doesn't mean "how much air you can stuff in", rather "how much FRESH charge you can put in AFTER extracting the old charge"

In my opinion, basically, a Two stoke (currently) has a reletively LOW VE, due to the SUBSTANTUAL LOSSES inherent in ALL (current) two stroke engines, not the least of which is the fact that the (returning) fuel/air/particle matter is as far removed from "fresh charge" as can be.

I'm not saying that this "returning over scavenged" charge is "unusable", but, because if this (as one example) you shouild not consider a two stroke (with expansion chamber) as "supercharged"

That is, because of the LOSSES, (inclusion of particle matter along with charge dilution) a two stroke can not be considered "supercharged".

The FIM seem to see it that way as well!

I don't see the effect of increasing the negative pressure of the cylinder on the intake stroke, combined with returning "over scavenged" charge back into the combustion chamber as "supercharging".

Granted though, it would be correct to say "there is a Dynamic Supercharging effect" (meaning the increased negative pressure in the cylinder caused by the expansion chamber.

But that's not "supercharging"

[SS90]

Heres an example of "supercharging" being referred to in regards to the action of the expansion chamber. 3/4 of the way down the page.
http://www.southernskies.net/page_in...okeengine.html

This pulse is timed to reach the exhaust port after the transfer ports close, but before the exhaust port closes. The returning compression wave pushes the mixture drawn into the header by the negative pressure wave back into the cylinder, thus supercharging (a bigger charge than normal) the engine. The straight section of pipe between the two cones exists to ensure that the positive waves reaches the exhaust port at the correct time:

Ok, this is where alot of people get a little lost.


You must be VERY wary of what you read on the net.

I concede that you could consider there is a slight "Dynamic supercharging effect" from an expansion chamber.


However, this "effect" does not constitute a "supercharged engine", anymore than an airbox (or power valve) does.

I feel it is important to note the difference when designing an exhaust that is suitable for a given situation.

If you enter in to the task with the concept that "an expansion chamber "supercharges" a cylinder", then you (in my opinion) are going to neglect important factors in both your engine design as well as your pipe design.

As with "scetchy racers" design, he demonsrarted a lack of knowledge when it came to checking his final calculations, and ended up with a lemon.

(F5Dave pointed out "a few" mistakes in the design)

It's something we all have done, but some experience would have told him that it was "off"


For example, you need ALOT more information to design an expansion chamber than simply exhaust port specs and intended RPM range.

[SS90]

.


SS90 you’re starting to get it, the supercharging thing.

And now there is the loop scavenge systems flow patterns and how they are designed so the incoming mixture push's the exhaust ahead of it while minimizing mixing and there by dilution of the incoming mixture as it enters and fills the cylinder.

A series of pictures on page 2 show how loop scavenging works and the dilution of the incoming mixture by residual exhaust gas and the supercharging effect of the expansion chamber. http://www.fluent.com/solutions/automotive/ex204.pdf

The less dilution of the incoming mixture as it fills the cylinder and then down into the first part of the exhaust port/expansion chamber is the aim of improving scavenging flow patterns.

The better the separation between the fresh mixture and the exhaust gas the less "HALF FUCKED" the new mixture is when the bulk of it that has been drawn into the exhaust tract is energetically pushed back into the combustion chamber.

Scavenging flow patterns and expansion chamber supercharging is all about removing the exhaust gas while minimising the dilution of the incoming mixture ie., scavenging efficiency, and how much fresh charge is squeezed back and then trapped in the cylinder.

.

hahahaha,

Your becoming quite the legend in the workshop here Bucketracer, can you PM me your address, my boss want's to send you a Tshirt! (serious!)

[SS90]

then why do we have a chamber and not a straight pipe ??????? like a 4 stroke ????????

Erm,

Not all expansion chambers are designed the same.
Look at Kartsport for an example.

[Buckets4Me]

Erm,

Not all expansion chambers are designed the same.
Look at Kartsport for an example.

ye but they are nothing like a 4stroke ????
any why is that ???? I'm even more confused with that answer

[SS90]

ye but they are nothing like a 4stroke ????
any why is that ???? I'm even more confused with that answer

Really?

Perhaps if you and your mates spent less time frantically trying to prove me wrong (and not actually reading what I write) all this may be easier to follow....... it get more and more disjointed every night I read it.

I wonder if you have less interest in two stroke tuning, and more interest in (trying, though never succeeding) to prove me wrong.

Just for fun, roll back read THE WHOLE thread...... you will see what I mean.

There is a dramatic difference between debate and pointless critisism...