Err, no, not complete bollox.
@Mr. Dazzle 's post is factually correct, as I read it anyway- -when the exhaust gases flow out they expand , and in that create a vacuum at the exhaust port which pulls more charge into the cylinder
Maybe you'd like to share the reasoning that makes you say his post (and I guess mine too now ) is complete bollox?
That's how I saw it. If the pressure difference at the exhaust port ie the suction from the falling piston was greater than that created by the escaping pressurised exhaust gases, the exhaust gases would flow backwards ergo there must be a - relative - vacuum at the exhaust port. The expansion chamber will increase the suction as a given volume of gas can expand/reduce pressure more than if the chamber wasn't there. That's got to add to the suction on the incoming mixture.
That's the idea yes. I'm sure you've heard the term "scavenging" in this context before?
It's a big part of the reason the inlet and exhaust ports are on opposite sides of the cylinder.
Err, no, not complete bollox.
@Mr. Dazzle 's post is factually correct, as I read it anyway- -when the exhaust gases flow out they expand , and in that create a vacuum at the exhaust port which pulls more charge into the cylinder
Maybe you'd like to share the reasoning that makes you say his post (and I guess mine too now ) is complete bollox?
That's how I saw it. If the pressure difference at the exhaust port ie the suction from the falling piston was greater than that created by the escaping pressurised exhaust gases, the exhaust gases would flow backwards ergo there must be a - relative - vacuum at the exhaust port. The expansion chamber will increase the suction as a given volume of gas can expand/reduce pressure more than if the chamber wasn't there. That's got to add to the suction on the incoming mixture.
That's the idea yes. I'm sure you've heard the term "scavenging" in this context before?
It's a big part of the reason the inlet and exhaust ports are on opposite sides of the cylinder.
Yup. I'd heard of 'scavenging' but never really applied the ol' brainium to understanding it. I'd also spent my yoof blithely considering that 2T exhaust design was important re performance and that you could stick any old dustbin on a 4T. Turns out that's tosh as well.
Doubt is not a pleasant condition.
But certainty is an absurd one.
Voltaire
Mr. Dazzle wrote: ↑Wed Feb 02, 2022 12:22 pm
Yeah I turned those off in my CBR
I wonder if anyone's done it on a 2T though.
It has, on late RGV250s, they also have solenoids in the carbs opening and closing air jets.
The variable exhaust volume is how Honda's ATAC works, Yamaha used a barrel valve to vary exhaust port height, Suzuki and Kawasaki have used variations of both, KTM use a very complicated system of variable port heights that's a copy of a Yamaha setup.
Rotax made an engine with an adjustable power valve, it was hydraulically damped and you stiffened the damping to make the power valve open slower.
Mr. Dazzle wrote: ↑Wed Feb 02, 2022 1:57 pm
You can do it the other way too - you can blow on the inlet instead. That's why supercharged two strokes are so common in really big stuff.
Supercharged two strokes work differently to conventional two strokes, they don't suck the mixture into the crankcases before squirting it through the transfers to the combustion chamber.
Watched Pete Gibson make some expansion chambers for a TZ250 racer back in the mid 1990's Formed by hand from flat steel, filled with sand , then blown into shape with compressed air. Thats the shortened version anyway.
Well respected and so used by many on race bikes where as other brands ended up on production racers.
I had a Piper 3 into 1 on my Suzuki GT550. Sounded brilliant at full chat, but completely buggered up the power delivery. I recall one fast ride along the A508 & A505 (Buntingford to Amptil) got me about 15 mpg.
That's the idea yes. I'm sure you've heard the term "scavenging" in this context before?
It's a big part of the reason the inlet and exhaust ports are on opposite sides of the cylinder.
Yes, they are on the opposite sides of the barrel, but the fuel mixture doesn't get into the combustion chamber via the inlet ports.
A while ago you admitted that you had never even seen a 2 stroke engined bike. But now Google makes you an expert. Maybe if you looked at a barrel, you'd understand.
Yorick wrote: ↑Wed Feb 02, 2022 3:13 pm
Yes, they are on the opposite sides of the barrel, but the fuel mixture doesn't get into the combustion chamber via the inlet ports.
No it goes via the transfer ports if you're being pedantic - seems that everyone else knew what I meant. In fact I didn't evne use the term "inlet port" in the bit you described as "complete bollox"
I've never said I've not seen a 2 stroke bike 'cause it's not true. I've not ridden a big old fashion 2 stroke for sure, but I've seen plenty of stuff about them.
And it's not Google which gives me knowledge in this area
Yorick wrote: ↑Wed Feb 02, 2022 3:13 pm
Yes, they are on the opposite sides of the barrel, but the fuel mixture doesn't get into the combustion chamber via the inlet ports.
No it goes via the transfer ports if you're being pedantic - seems that everyone else knew what I meant. In fact I didn't evne use the term "inlet port" in the bit you described as "complete bollox"
Well, I knew what you meant and it was me asking the question, so I'm a happy bunny.
(I knew about inlet port and transfer port from spending many 'happy' hours polishing them in an attempt to screw another 0.0005hp out of ageing Lambrettas ).
Doubt is not a pleasant condition.
But certainty is an absurd one.
Voltaire
Yorick wrote: ↑Wed Feb 02, 2022 3:13 pm
Yes, they are on the opposite sides of the barrel, but the fuel mixture doesn't get into the combustion chamber via the inlet ports.
No it goes via the transfer ports if you're being pedantic - seems that everyone else knew what I meant. In fact I didn't evne use the term "inlet port" in the bit you described as "complete bollox"
Well, I knew what you meant and it was me asking the question, so I'm a happy bunny.
(I knew about inlet port and transfer port from spending many 'happy' hours polishing them in an attempt to screw another 0.0005hp out of ageing Lambrettas ).
Not all 2 strokes even have transfer ports - the kind you find in motorcycles and chainsaws are a very narrow sub-set of what you can build. The big stuff in ships and trains etc. does it a different way so you can use a 4 stroke style bottom end, which is why they don't make the 2 stroke smell. But then again, they also don't need spannies, sooooo.....
) is complete bollox?
In fact I didn't evne use the term "inlet port" in the bit you described as "complete bollox" 
