Two-stroke performance tuning?

[bucketracer]

Combine the above technique with a copper combustion chamber (all the rage in high performance two stokes, perhaps even a copper finned base gasket) a little "ahead of it's time" and exhaust pipe and port specs and you got your self a weapon.

At last, SS90 is right about something.

.

[Skunk]

[Fooman]

ie a turbo shifts more air but dosent compress it :P

That's a pump. Which can compress the air, after exit from the pump, if it is pumping into a smaller volume. A turbocharger is a supercharger powered by exhaust gases via a turbine. Doesn't use mechanical power to drive, just waste energy in the exhaust, so increases the efficiency of the engine.

Cheers,
FM

[Buckets4Me]

That's a pump. Which can compress the air, after exit from the pump, if it is pumping into a smaller volume. A turbocharger is a supercharger powered by exhaust gases via a turbine. Doesn't use mechanical power to drive, just waste energy in the exhaust, so increases the efficiency of the engine.

Cheers,
FM

so supercharging is ANYTHING that pushes more than 100% air charge into the cylinder

[bucketracer]

so supercharging is ANYTHING that pushes more than 100% air charge into the cylinder

Yes, thats anything that makes the engine achieve greater than 100% volumetric efficiency.

Any extra air or air/fuel mixture squeezed into an engine above what it can normally aspirate for its self is supercharging.

The expansion chamber most certainly supercharges a 2-Stroke.

.

[koba]

In all the guff for my MR2 it reffered to the "Inertial supercharging effect" provided by tuned length intakes in the TVIS system.
So I guess Toyota must see it that way.
(And Yamaha maybe as the built the engines..?)

[Ooky]

http://homepage.mac.com/rg500delta/d...pe_design.html

for Rg500 but its alot about pipes

[Yow Ling]

ok I'm getting seriously bored of this. When are we going to get onto the serious business of whatever it was we were talking about?


. . . Think it was polishing the fins on a go-cart wasn't it

Yea I thought we were going to talk about NSUs and deeks

[TZ350]

.

you could read a book called "the two stroke tuners hand book" By Gordon Jennings.....
It's a really good place to start, many top tuners have recommended it to me, it is well written, and while SOME aspects are dated, if you read it carefully, it is a little "ahead of it's time"

If the expansion chamber supplied any degree of "supercharging" such requirements would be redundant and the level of attention a tuner must pay to scavenge patterns (such as is required now) would be negated, and all the attention would be on increasing the (I believe non-exsistent) "supercharging" effect of the chamber.

Jennings talks about the expansion chamber as a lot like having a supercharger. P53 and refers again to the supercharging effect of inertial wave action on P83.

P105 scavenging, P108 for a description of the Loop Scavenging System or Schnerurles Loop. P115 cylinder flow patterns, 117 & 118 residual exhaust gases.

Cylinder scavenging flow patterns are all about preventing short circuiting of the incoming fresh mixture directly out the exhaust and maintaining separation of the spent exhaust gases as the incoming fresh mixture sweeps up and over filling the cylinder and sweeping the old gases before it and eventually expelling them out the exhaust port.

Much effort has gone into refining scavenging flow patterns to minimize the mixing of old and new and thereby minimize the dilution of the incoming fresh mixture. This mixing is a problem whether the motor has a carburetor or is direct injection as dilution of the fresh with exhaust reduces the amount of oxygen in the new mixture.

With a typical scavenging ratio of 80% or so, any improvements in the scavenging flow pattern that maintains separation and reduces dilution means more fresh air/mixture can be trapped in the cylinder by the action of the expansion chamber.

Jennings book is a good place to start with understanding the basics of scavenging flow patterns and their roll in reducing charge dilution and the supercharging effect of the expansion chamber.

It's smart to have a grasp of these basics before tackling the intricacies of 2-Stroke Tuning.

A link to Jennings book can be found on page 80 of the ESE thread.
.

[TZ350]

As it is, a correct scavenge pattern coupled with the correctly designed exhaust are JUST 2 (of many) CRITICAL things to consider in a two stroke engine design.

Thats true, now the first 2 things have been covered, I would be interested to hear more about some of the other critical things in two stroke engine design.

.

[Skunk]

There are plenty of computer programmes available that will design a pipe for you, using just port time areas,RPM intended etc.

My experience is that all these programmes that only require a small amount of data (specifically in relation to exhaust port only) return essentially the same expansion chamber..... (dated)

Obviously, the more you spend on the software, the better the expansion chamber you end up with....but you have to "answer the right questions" this software asks......it's quite complicated.

There are a lot more factors you must consider when designing an expansion chamber.

That is the difference between an expansion chamber designed in the 70's, and one designed recently.

So instead of telling me it's all dated and wrong how about telling me the modern and correct way.

Or is it so secret (because of the Asians) that no one is allowed to know?

[TZ350]

http://homepage.mac.com/rg500delta/d...pe_design.html

for Rg500 but its alot about pipes

Thats some very interesting reading there.

.

[SS90]

.

So a 2-Stroke "is" Supercharged by its expansion chamber and its wrong to claim it does'nt.

.

No it's not.

Sshhhhhhh Bucketracer....the grownups are talking!

[SS90]

Yes, thats anything that makes the engine achieve greater than 100% volumetric efficiency.

Any extra air or air/fuel mixture squeezed into an engine above what it can normally aspirate for its self is supercharging.

The expansion chamber most certainly supercharges a 2-Stroke.

.

OK, so tell us Bucketracer.......WHAT IS THE VOLUMETRIC EFFICIENCY OF A PERFORMANCE TWO STROKE ENGINE?

[SS90]

.





Jennings talks about the expansion chamber as a lot like having a supercharger. P53 and refers again to the supercharging effect of inertial wave action on P83.

P105 scavenging, P108 for a description of the Loop Scavenging System or Schnerurles Loop. P115 cylinder flow patterns, 117 & 118 residual exhaust gases.

Cylinder scavenging flow patterns are all about preventing short circuiting of the incoming fresh mixture directly out the exhaust and maintaining separation of the spent exhaust gases as the incoming fresh mixture sweeps up and over filling the cylinder and sweeping the old gases before it and eventually expelling them out the exhaust port.

Much effort has gone into refining scavenging flow patterns to minimize the mixing of old and new and thereby minimize the dilution of the incoming fresh mixture. This mixing is a problem whether the motor has a carburetor or is direct injection as dilution of the fresh with exhaust reduces the amount of oxygen in the new mixture.

With a typical scavenging ratio of 80% or so, any improvements in the scavenging flow pattern that maintains separation and reduces dilution means more fresh air/mixture can be trapped in the cylinder by the action of the expansion chamber.

Jennings book is a good place to start with understanding the basics of scavenging flow patterns and their roll in reducing charge dilution and the supercharging effect of the expansion chamber.

It's smart to have a grasp of these basics before tackling the intricacies of 2-Stroke Tuning.

A link to Jennings book can be found on page 80 of the ESE thread.
.

Teezeetreefiddy "old boy", once again, you have managed to use 1000 words to over complicate things.

I am quite confident that I have more experience with scavenge patterns than you.

In any event.

To summate your post.

Scavenge patterns essentially stop the incoming fresh charge from heading out the open exhaust port.

The end.