Two-stroke performance tuning?

[bucketracer]

A "supercharger" is forced induction.

Ergo, an expansion chamber, cannot "force induce" an engine.


Maybe you could "Wikipedia" supercharging.

I am sorry your wrong again. Supercharging is not just forced induction at the inlet. Its forced induction per see.

As I said before, however you squeeze extra air or air/fuel mixture into an engine above what it can normally aspirate for its self is supercharging and is most certainly deliberate in a 2-Stroke.

And from the Oxford Dictionary

supercharger
• noun a device that increases the pressure of the fuel-air mixture in an internal-combustion engine, thereby giving greater efficiency.

http://www.askoxford.com/concise_oed...harger?view=uk

The expansion chamber most certainly can supercharge a 2-Stroke.

Please back your opinion with references otherwise its just your opinion.

.

[F5 Dave]

Yes I see the crankcase as a pump, not a particularly good one. The fact that it can sucked from too (just as Dirty Dorris may overscavenge your wiener as you pop your clogs, - ok now this has R18 rated the thread) doesn't stop it being a pump, in the same way as an engine doesn't stop being an engine if you tow it faster than it can go normally.

But the charging effect is primarily after induction is finished & the transfers are closed.

[SS90]

Yes I see the crankcase as a pump, not a particularly good one. The fact that it can sucked from too (just as Dirty Dorris may overscavenge your wiener as you pop your clogs, - ok now this has R18 rated the thread) doesn't stop it being a pump, in the same way as an engine doesn't stop being an engine if you tow it faster than it can go normally.

But the charging effect is primarily after induction is finished & the transfers are closed.

Well,
I used the Crankcase pump as an example because a few months ago I remember in the ESE thread you maintained that the crankcase was NOT a pump because of the extraction effect...... that's what I remember anyway, feel free to correct me if I remember that incorrectly!

But, can you clarify how pushing "overscavenged" fuel from the expansion chamber BACK into the cylinder constitues "supercharging"?

I don't see it that way.

Your example of an air box suggests that an air box can be considered "supecharging", so do you consider your Trinity engine "supercharged"?

I don't

Think of it this way.

If there was a true "supercharging" effect from an expansion chamber, then "schnürle loop" engines would be redundant, because you would be able to make more power by abandoning the transfer angles (scavenge patterns) and simply increase the port area's by having them "straight across the bore" (which logically will give you more power)

Yet, you know as well as I do, that to make a good long spread of power, you require the port angles to be designed in such a way that turbulence is created in the combustion chamber (as well as stopping as much fuel/air as possible from heading out the open exhaust port.)

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.

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.

[Fooman]

From my favourite reference for this sort of shitflinging (Bosch Automotive Handbook 3rd Ed - note translated from German, so ignore any verbal niceties)

Supercharging Processes (See attached .pdf file)

Summary - The expansion chamber is not a mechanical supercharger, but it provides a dynamic supercharging effect similar to the tuned intake tube charging effect described in the attached document.

From memory, dynamic supercharging (e.g. using inertia of incoming air into cylinder) gives a max of 105% to 110% volumetric efficiency.

I certainly hope this contributes to the thread!

Cheers,
FM

[F5 Dave]

Without wading back through as million pages I probably said that a 2 stroke engine is not just a pump. The crankcase clearly is a pump, & a few other things.

[Yow Ling]

SO what exactly is supercharging? Is it filling the cylinder more than 100% full? If it is then any engine with VE over 100 is supercharged.

Nitrous oxide is not a pump or mechanical but is still supercharging, so if any thing rams more oxygen molecules into the cylinder it would be considered supercharging

[F5 Dave]

From my favourite reference for this sort of shitflinging

That so reminds me of this;
http://www.youtube.com/watch?v=pgUwpb3I98M
Well smeared FM

[F5 Dave]

SO what exactly is supercharging? Is it filling the cylinder more than 100% full? If it is then any engine with VE over 100 is supercharged.

Nitrous oxide is not a pump or mechanical but is still supercharging, so if any thing rams more oxygen molecules into the cylinder it would be considered supercharging

Yeah we're getting into semantics. I'd say there is a supercharging effect, but I wouldn't bother to say it was supercharged unless it seriously pressurised, but you could still argue the toss.

[Fooman]

SO what exactly is supercharging? Is it filling the cylinder more than 100% full? If it is then any engine with VE over 100 is supercharged.

Nitrous oxide is not a pump or mechanical but is still supercharging, so if any thing rams more oxygen molecules into the cylinder it would be considered supercharging

From what I've read, posted above, and can remember from applied thermodynamics course many moons ago, the answer you seek is "Yes".

A supercharger is not the only thing that can supercharge.

Cheers,
FM

[Buckets4Me]

Tecnicaly I thought supercharging had to compress the air before it got into the engine


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

a supercharger compressis the air and shifts it

lets all step back and have a group hug before someone hurts someones fealings

NOS is consintrated N2o so more oxogen (much like compressed air)

But as SS90 points out the chamber dosent force more air fuel into the cylinder so cant be called supercharging

and who cares weather it fails on polution or not (we want fast and warmer weather)

[F5 Dave]

. . .
But as SS90 points out the chamber dosent force more air fuel into the cylinder so cant be called supercharging . . .

um, have you not been reading?

[bucketracer]

.

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

.

[bucketracer]

The whole "scavenge Pattern" concept is to reduce the amount of fuel that gets out the exhaust port.

That's why a two stroke is called a "schürle loop" (closed loop).........

The whole idea is to keep as much fuel in the cylinder as possible,

Nope wrong about that too.

.

[Buckets4Me]

.

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

.

no it's turboed as it uses exaust gass to superchrge the cylinder

(younger audience more add revenue turbo not supercharger with refrence to NOS and drifting)

[F5 Dave]

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