Boost Bottles

[OzzyElsie]

https://www.youtube.com/watch?v=E35g6AXw3bY

I don't mean to scratch an old scab but the above is an interesting article. The speaker is a bit hard to take at times when he goes off on a tangent but he knows what he's talking about with engineering and physics and is very precise with his use of words during explanation.

Ciao, enjoy

[hybrid]

I watched that recently myself.
Yes very well explained for the layman.

Not sure there's that many reputable people left that really think they work is there?
There's plenty on the pocket bike forum I use that do.

[2TInstitute]

https://www.youtube.com/watch?v=E35g6AXw3bY

I don't mean to scratch an old scab but the above is an interesting article. The speaker is a bit hard to take at times when he goes off on a tangent but he knows what he's talking about with engineering and physics and is very precise with his use of words during explanation.

Ciao, enjoy

His two stroke knowledge is at best firmly rooted in the 70's.

On a DT 200 we tested with and without a boost bottle it made a big difference in 1 area ......fuel economy the DT did about 10 or 15ks more before hitting reserve. Made not one iota difference to performance.

[AusMecham]

I watched that recently myself.
Yes very well explained for the layman.

It is, albiet hit and miss.
Matt is an engineer not a mechanic.

Like most they use basic physics and engineering principles to reverse engineer how engines work, however any seasoned mechanic knows that often fails because not everything about engines is intuitive, particularly 2 strokes.

Which is why YouTube is full of engineers and sundry all explaining how 2 stroke expansion chambers work and none of them get it right. Only parts of it right but its clear they dont have a full understanding.
But if you didn't have some experience building them you would not know otherwise and be merely impressed by the words they use that makes it sound as if they are qualified on the topic

They are prone to not readings manuals and OEM procedures, more likely to read a sales brochure for numbers.

Engineering explained is another one, often part wrong part right.
Matt sometimes relies in EE's explanations which to me is fairly obvious when he carries over the same flaw in explanations from EE.

But they are entertaining and YouTube is all about entertainment not factual correctness.
As to disseminating flawed mechanics theory on a grand scale, well, is anyone watching really going to be using the information in a meaningful way, probably not so there is no real harm in it.

As for boost bottles.
He got that one a bit wrong and relied too much on Yamaha sales brochures.

[hybrid]

So you're a believer then?
I'm still yet to see anyone prove their worth, other than replacing the balance pipe on a twin if yours had one and has gone missing. Although many say the boost bottle should have a divider in the middle anyway, which would also preclude it from being useful as a balance pipe.

[James W.]

It has to be taken into account whether it is a single cylinder engine or a multi.

& with the multi, is each cylinder kept functionally independent/discrete..
or are certain functions 'ganged' like inlet/exhaust manifolds, with possible pulse overlap synergy?

Even the RD/RZ using an inlet balance pipe - allowed each cyl to breathe from both carbs,
& flowed enough - to enable a size drop to 26mm carbs from 28mm, as used on the air-cooled engines.

AFAIR, stock Yamaha factory 3cyl snow & watercraft 2T engines..
also used a combination balance pipe/boost bottle - inlet plenum set up.

[BRG1200]

So it sounds as though they don't do any harm, and may make a tiny increase in fuel economy.

Putting a plate in the bottle to divide between cylinders makes it sound as though a bottle for each cylinder is logical (how did Yamaha arrange this on aforementioned other motors?)

With regard to the balance pipe, picking up on comment about "sharing" the carbs, wondering how influential the width of the balance pipe diameter might be now?

Would it be detrimental or beneficial to have, say, a balance pipe, and then individual boost bottles on each inlet?

This is all curiosity, as I'm sure other elements are far more important.

[James W.]

www.totallyamaha.com/snowmobiles/aaTECH ... nstall.htm

RZ balance pipe increased in diameter/volume over original RDLC.

With a multi-cylinder engine, the idea of running a linked 'plenum' set-up VS an individual B-B per cyl,
may be about utilizing the timed pressure pulse phases in sync, space saving, or both..

I guess a back-to-back test - of each set-up - would show any signficant difference, if any..

[AusMecham]

All it does is improve low speed carburation, for a city ride it could help with economy, slightly..
Nothing to do with Helmoltz resonance or compression and expansion waves.

The RD LC350 had a balance tune, same deal.
In the 80's I welded new intakes on an LC 350, stuffed YZ, manifolds, 6 petal reed blocks and carbs on and ported it t o TZ G spec timing for road racing, cross over header TZ chambers and shaved the head down, no balance tube, does nothing at higher engine speeds.

[James W.]

Yeah, always variables.. esp' with reeds flappin' away..

I agree that discrete cylinder tuning makes most top-end power,
- though cross-over pipes on multis - do work, down low..

[Joonya]

I watched that recently myself.
Yes very well explained for the layman.

It is, albiet hit and miss.
Matt is an engineer not a mechanic.

As for boost bottles.
He got that one a bit wrong and relied too much on Yamaha sales brochures.

Hey AusMechem. You say he got it a bit wrong in the video but don't tell us how. I would be genuinely interested in knowing where he got it wrong. I'm not having a go at you, just looking for more detailed info. Cheers

[AusMecham]

Hey AusMechem. You say he got it a bit wrong in the video but don't tell us how. I would be genuinely interested in knowing where he got it wrong. I'm not having a go at you, just looking for more detailed info. Cheers

Where do I start.
For one thing, Intake lengths are not designed to be tuned to one particular RPM in 2 strokes, not since the invention of indoor plumbing at least.

In 2 strokes intake length is simpler.
Get the carb as close to the crankcase as physically possible, the gains from doing that will be over a fair RPM range to peak and far outweigh any benefit from tuning the intake length like you would in a 4 stroke.

Likewise for reed intakes there was a time we used equations to calulate reed dimensions but by the late 80s it was discovered fitting the largerst reed with the most petals you can physically stuff in there provides greater gains.

Boost bottles are simply to aid low speed carburation.
Likewise balance tubes on twins.
Neither of which do anything at high speed in the power band.

[Joonya]

I watched the video again. Twice

He does not talk about the distance from carbie to crankcase. He is talking about the entire intake length from the airbox to the crankcase. And weather it is tuned or not, there simply will a frequency (rpm) where it works best and others where resonance will be an issue.

And I can't find where he mentions calculating read dimensions. Maybe I missed it. Could you tell me the time index in the video where he mentions this?

[mboddy]

Likewise for reed intakes there was a time we used equations to calulate reed dimensions but by the late 80s it was discovered fitting the largerst reed with the most petals you can physically stuff in there provides greater gains

Do you have anything to support this claim?

I can see big reed blocks on TZ Yamahas.
But RS250 GP Hondas ran the same small six petal reeds as the RS125, NSR250 and CR125 even after 2000.
And the 2000s YZ125 used the same size petals and a very similar size reed block as the CR125.

I haven't seen anything that discusses why the difference in the Yamaha and Honda approach.

[Joonya]

Hey AusMechem.

Just want you to know I wasn't trying to set you up or anything. I was genuinely interested in any better information you may have had re boost bottles. Problem is, when I saw what you said, I didn't think it really stood up.