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High Performance Bicycle Engine Tips and Motorized Race Bicycles We all want our bicycle engines to push our bikes faster. Get exclusive engine modification tips and suggestions from us. Also check out some of our racing members builds

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  #1  
Old 02-27-2015, 07:13 AM
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cannonball2 cannonball2 is offline
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Default Modded Boost Bottle

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.

Last edited by cannonball2; 02-27-2015 at 07:21 AM. Reason: Forgot what the he** I was talking about.
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  #2  
Old 02-27-2015, 05:05 PM
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maniac57 maniac57 is offline
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Default Re: Modded Boost Bottle

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.
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  #3  
Old 02-27-2015, 08:48 PM
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cannonball2 cannonball2 is offline
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Default Re: Modded Boost Bottle

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!
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Old 02-27-2015, 10:03 PM
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maniac57 maniac57 is offline
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Default Re: Modded Boost Bottle

Use as big a nipple as you can fit into the intake, all the ones I remember that worked had large plumbing.
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  #5  
Old 02-28-2015, 12:53 AM
snorks snorks is offline
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Default Re: Modded Boost Bottle

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
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Old 02-28-2015, 07:26 AM
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cannonball2 cannonball2 is offline
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Default Re: Modded Boost Bottle

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.
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Old 02-28-2015, 12:50 PM
snorks snorks is offline
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Default Re: Modded Boost Bottle

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
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  #8  
Old 02-28-2015, 02:32 PM
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cannonball2 cannonball2 is offline
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Default Re: Modded Boost Bottle

Reeds eliminate the intake reversion(pulse) and I imagine respond almost immediately to the change in direction of the flow.
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  #9  
Old 02-28-2015, 02:55 PM
snorks snorks is offline
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Default Re: Modded Boost Bottle

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
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  #10  
Old 03-01-2015, 02:54 PM
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maniac57 maniac57 is offline
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Default Re: Modded Boost Bottle

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!
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