Modded Boost Bottle

[cannonball2]

OK all you 2stroke gurus heres a question.

Take a boost bottle(or just about any container) and basically make it a catch can(vented to the atmosphere) and add a check valve in the connecting hose so that the intake vents the rich positive pulse into the can but closes otherwise. Seems like the rich mixture would migrate to the catch can and not contaminate the intake system. It would close on the negative impulse drawing in theory fresh intake charge hopefully doing away with the rich mixture 4stroking normally found on engine over run and low speed running.
I cant imagine that the actual build up in the can would really need emptying except rarely to clean the accumulated oil as the fuel would evaporate(not for use in Califorina-lol)

In theory this eliminates the need to have the boost bottle system tuned for the intake tract. The check valve system would not offer the incoming pulse that the boost bottle theoretically does, but would possibly eliminate the over rich low speed condition due to back pulsing, which should improve low speed running.

 

[maniac57]

Nope. No free lunches.
What a properly tuned "boost bottle" WILL do is smooth out intake charge column pulsations which can have a beneficial effect on low end torque and throttle response.
It all depends on the engine what it wants. Some will show no effects. Some will show good effect.
Mostly it's a bling part unless it's on a high-strung, race ported beat with radical port timing and a light switch powerband.
But you are correct about it being tuned to the intake tract. I'm pretty sure there's a formula for intake volume and timing you can use to get in the ballpark, but I wouldn't know where to find it.
At least that is my experience.

 

[cannonball2]

Im not sold on or wanting to go the boost bottle route. I know people say great things about them and just as many don't. Seems a boost bottle is a try at getting around a properly tuned intake tract. Or in fact the perfectly tuned tract may be impractical due to size. I think I grasp that the tuned intake works exactly as an expansion chamber does for the exhaust, returning a pulse at the right time in a given rpm range to counteract reversion. This is especially needed at lower piston speeds. The product of reversion is deposited fuel at the carbs intake, just where it doesn't need to be. We have all seen the oil that accumulates there.

Im looking for a way to lessen the by-products of reversion. On the surface the check/bleed system seems logical whether it will work or not who knows. My thinking is it will lessen/dispose of some of the reversions pulse particularly at low throttle plate openings hopefully being bled off before it reaches the carb.
Its a simple matter to make it, I already have a check valve on the way. Its a shot in the dark as to sizing and opening rates. Just have to see. Might get lucky!

 

[maniac57]

Use as big a nipple as you can fit into the intake, all the ones I remember that worked had large plumbing.

 

[snorks]

I have often thought about using a grease gun or a large syringe from a livestock / horse supply shop.
Connect the manifold to the grease gun /syringe.
Use an accurate tach.
Start motor and rev until it comes onto the pipe.
Note RPM.
Pull or push the grease gun / syringe to adjust the volume.
Pay attention to the tach to note any power gain.
If there is, turn engine off and measure volume of greasegun /syringe.
Make a pretty bottle using the measured volume.
Connect the new bottle to inlet pipe using a ball valve so you can close off the bottleduring normal or sedate riding or if the bottle affects the bottom end.

Make sense? Or is this just fantasy?
Cheers
Simon

 

[cannonball2]

Snorks...like your thinkin man!! That sounds like a good method. If you could come up with a variable displacement bottle then it could be tuned for different power bands/porting/ pipes etc. Maybe you could valve and switch two bottles for different ranges. Im no expert on boost bottles but your plan sounds like a good approach to see what the real scoop is.

M57 I agree on the large size being the way to go with the check valve. I probably bought too small with 1/4". I just didn't want to open the intake enough to get a 3/8 plumbed, wouldn't be much metal left for the fitting.
I may be ok as the pulse doesn't have to compress as in the boost bottle only dissipate and only at lower rpms. The pulse would probably happen so fast at higher rpms that the valve may make no difference, that is fine. Im only after improving low end rideability with a stock engine, not improving overall performance, though if the entire range improved I wouldn't complain. Heck might do nothing, but will have less than $10 and very little time invested. That's how we learn.

 

[snorks]

Do reeds reduce (to some extent) the pulsing of the intake charge?
Reeds operate on more of a vacume/demand basis (softer opening and closing)as opposed to piston porting, with the piston abruptly interupting gas flow?

Cheers
Simon

 

[cannonball2]

Reeds eliminate the intake reversion(pulse) and I imagine respond almost immediately to the change in direction of the flow.

 

[snorks]

So there is no tuned inlet tract length for motors with reeds? Ive always thought rotary disc valves were superior to reeds.....just trying to think why exactly.....
I have also often thought that so called boost boottles have a very small diameter connecting hose? I would nave thought the opening should be bigger.

Cheers
Simon

 

[maniac57]

Well even though I generally think bottles are a waste of time, I HAVE seen a few good results in my day, some where a bottle made a HUGE difference, so I cannot tell you it WON'T work. Just depends on your particular setup.
Experiment and try everything you can think up. Only way to know if you like it.
But remember, failure is ALWAYS an option with a chinadoll.
Lol!

 

[maniac57]

So there is no tuned inlet tract length for motors with reeds? Ive always thought rotary disc valves were superior to reeds.....just trying to think why exactly.....
I have also often thought that so called boost boottles have a very small diameter connecting hose? I would nave thought the opening should be bigger.

Cheers
Simon

The reason disc valves were so much more powerful was that a disc allowed MUCH longer intake duration which makes for better transfer flow from a higher pressure charge in the cases. Also allows better control over intake timing and more aggressive port timing.
Remember the sick Rotax case induction disc valves? Those engines had almost TWICE the power of the same displacement if piston ported. But they were EXTREMELY violent and had a BRUTAL hit which was harder to ride fast.
Only the very best riders could use the hit to actually go faster. most just flipped over backwards or lost traction.
While I LOVED my Can Am's, even I have to admit, it was NOT fun to ride really hard....you really had to be assertive and think ahead. When that power hit, you better be pointed in the right direction, 'cause you were going that way RIGHT NOW!!
Plus it's damned hard to steer with the front wheel in the air all the time....

 

[cannonball2]

Ok finally got the check valve from the snow bound north. Had already modded the intake so it only took a bout 10min to get the system up and working.
Works just as I hoped it would. Its effective in the first half of the throttle. Runs very similar to a reed motor. The valve dumps the pulse headed up the intake to the carb. This eliminates the over rich condition of fuel reversion and contamination of the air filter. You can feel the pulse exiting the valve.
The idle is much improved, is smoother and will idle at a lower rpm. Tractability is greatly improved. This bike wasn't very happy below 12mph. Now it will ease along fully at 6/8 mph.
Throttle response is better from down low as its not over rich from excess fuel.
Probably the only effect it will have on the top end is maybe a bit better running as the air filter should stay less gas saturated. I have cleaned the filter and carb throat area to see if oil accumulates there again.
If you look at the pics of the tube and valve you will see the red tint of the oil that has exited, the gas has evaporated. I will eventually run a very small catch can.
So far Im pleased!

 

[maniac57]

Ok finally got the check valve from the snow bound north. Had already modded the intake so it only took a bout 10min to get the system up and working.
Works just as I hoped it would. Its effective in the first half of the throttle. Runs very similar to a reed motor. The valve dumps the pulse headed up the intake to the carb. This eliminates the over rich condition of fuel reversion and contamination of the air filter. You can feel the pulse exiting the valve.
The idle is much improved, is smoother and will idle at a lower rpm. Tractability is greatly improved. This bike wasn't very happy below 12mph. Now it will ease along fully at 6/8 mph.
Throttle response is better from down low as its not over rich from excess fuel.
Probably the only effect it will have on the top end is maybe a bit better running as the air filter should stay less gas saturated. I have cleaned the filter and carb throat area to see if oil accumulates there again.
If you look at the pics of the tube and valve you will see the red tint of the oil that has exited, the gas has evaporated. I will eventually run a very small catch can.
So far Im pleased!

So you notice a change? Very interesting. I basically tuned out at "boost bottle" and had no idea you intended to do this.
I would never have imagined it doing much.
Learn something here every day.

 

[cannonball2]

Most definitely a change. I guess the title was misleading. I was thinking of using the boost bottle but venting it to the atmosphere and using it as a catch can. The idea behind this thinking was to dump the out going pulse, (half the phase of a boost bottle). This returns nothing, which I feel is better for low end. Also there is no need to worry about bottle displacement. I rode the bike a bit after the above post and feel its ride ability is greatly improved over a broader range than I first thought. If I poked around riding slow(trail riding), or idled awhile then the engine had to clear of accumulated fuel, which took several seconds before it would run clean. Now its basically immediate. This means the acceleration is better from the bottom until it tops. No more power or top speed, just smoother operation.
I don't know if this is the "big deal" for all engines. Mine is basically stock, cant say about a highly tuned engine. Someone give it a try. I suspect like a lot of other mods it will have little or no effect on a poorly tuned/jetted engine. But I bet if one has spent a lot of time setting up and jetting an engine and its running pretty well this will add improvement. I will do it to all my engines.

Heres all one needs: A tapped intake with a nipple(mine is tapped midway), a check valve, needs to be Vynar which is fuel/oil proof and a short length of tube to connect it together. I used 1/4" which seems fine, wouldn't go smaller.

 

[Davezilla]

So basically yours is more of a dump valve so the return pulse just goes out instead of being stored and re entered... Good thinking there and if you could use a larger line and check valve it would probably increase low speed rideability even more. I'm thinking you could probably use an automotive exhaust check valve found on some models for pulling in fresh air to feed the catayletic converters or to pull a vacuum off the valve covers as a crank case ventilation system, these check valves are usually 5/8" to 3/4" at the openings and with the right adapter you could run up to a 3/8" or even 1/2"tube off your intake into the larger check valve that could be located under the engine out of sight, or behind the seat post tube out of the way. You would have to weld a tube to your intake manifold's underside that's as large as possible and angle it so the reverse pulse would go into the check valve tube instead of back to the carb, then at the other side of the check valve you could fab up a catch can to catch any fuel/oil that may accumulate.
I doubt it would add any power anywhere, but it would smooth out the lower rpm range and maybe offer up a small amount of part throttle torque once the carb is tuned for this mod. From what you're doing, this mod seems like it would want the largest diameter tube possible at the intake and to the check valve which would also need to be as close to the intake as possible to prevent top end loss, but if done right, at high rpm, the engine would never know that system was in place.

 

[cannonball2]

I agree bigger is better-lol. The little 1/4 was an easy way to test proof of concept and made enough of a difference to think maybe a 3/8-1/2 might be adequate. The advantage to the valves you are referring to is the diaphragm size would probably be more sensitive. The little valves opening pressure is .5lb/in/sq.
This idea was more of a mechanical approach than the concept of intake resonance. Just basically get rid of the excess fuel, a product of the untuned resonance.
I felt the middle of the common upswept steel intake was the proper place to intercept the pulse. Seemed to have guessed right. I noticed many of the CNCed intakes have the port right at the head. I think port placement has some effect.
Just this small valve has made enough of a noticeable difference to make the idea worthy of further development. I may go a bit larger, but will probably leave it to others to run with it.

Have fun!

 

[Davezilla]

Placement and the angle which the reversion is going into the check valve will both affect the way it dumps off the reverse pulse, if you can fab up an intake with the reversion port at a really tight angle to the intake tract it'll be more effective, pretty much as close to parallel as possible and at least 1/2 the intake tube diameter. the more sensative the check valve the better as well since at part throttle this opening would be the path of least resistance and at full throttle and at low rpm the carb will become the path of least resistance, but if the tube is big enough it can bleed off a considerable amount of the reverse pulse if the hole is on a straight run before a bend headed toward the carb. this could be easily fabbed up on a steel intake that can be welded on, but easier to cut and work if made out of aluminum, either sand cast using another intake as the model for a mold, or just getting an aluminum intake and using some alumaloy brazing rods to braze in the dump tube outlet.
Just a little more fuel for thought... My business has picked up at the shop exponentially in the last 3 weeks so I don't have the experimenting time I had just a month ago but I know you can get it sorted out and working.

 

[cannonball2]

That's why I used the steel angled intake you can silver solder to it. I can only visualize flow and that's not always what happens hence smoke chambers and such. I may have done better with the nipple closer to the bottom, but felt by the midpoint the flow had attached itself to the lower tube wall where the outlet would be right in the flow. Certainly a bigger outlet would be better, looks like 1/2" is probably max before having to fab an intake. Im thinking an outlet at the beginning of the upsweep and parallel to the carbs mounting tube. This is a straight shot right out of the intake port.. Its a simple matter to cut tubing to fit at an angle and solder it there. The angle created there will make a very large opening in the intake. However it may affect intake flow creating turbulence and such or maybe that helps atomize, who knows?

 

[KCvale]

Spiffy.
Certainly cheaper than an intake reed.

Maybe not so useful on a long offset Z intake as they tend to tame the back pulse, but neat for stock short intakes.

 

[Davezilla]

That bend right before the carb might be the best place on the top of the intake because the reverse pulse would go straight into the check valve if using one of those stock intakes that have the bend to keep the carb level, it may even be possible to use a smaller diameter nipple in that location and still be effective...
pretty much at any bend before the carb would work so it could even be effective on those longer Z intakes since the reverse pulse would want to go in a straight line more than it would want to make that turn toward the carb.
I'm not a fan of the boost bottle hype but I can see where this would make part throttle performance and rideability more pleasant, maybe even some better part throttle torque or responsiveness could be gained once refined.