Mad Scientist Lab test - Boost Bottle

[Steve Best]

Does Honda use boost bottles on their range of internal combustion engines...

Yes Honda does actually Fabian, This log type intake is a "Helmholtz resonator" where the volume of the intake acts the same as the boost bottle.

The early 90s Ford Crown Vic Police engines had a plastic "boost bottle" plenum that worked very well:

In the Motor cycle and 2 Stroke world it was Yamaha who was known for boost bottle technology with their IT250, RD350, Banshee, TTR250 and DT200 motors.
They called it YEIS "Yamaha Energy Induction System". Remove it and you removed mid range power.

I owned a DT200 and rode IT250 and RZ350 where we experimented with blocking off the boost bottle. Here is the boost bottle on the TTR250 4 stroke, part #21:

Here it is in a DT engine (carb removed)

And here the stock YEIS in a modified DT:

All plenum type intakes run on this same "Helmholtz resonator" principal:

NASCAR racers figured how to build huge plenums to get by the carb restrictor rules:

If you have a look, I even have a boost bottle thread where I experimented with boost bottle size and effect on my Grubee bike engine:

The clear tube is the boost bottle. By moving and re-clamping the copper plunger, I can vary the volume of the bottle chamber.

What did I find?
Boost bottle volume had a large effect on power at all ranges. I could vary from tractor like low rpm power to very peaky top end power slightly more than without the bottle. What volume worked best? It depended on where you want the power and varied in a sinusoidal wave with length so that multiples of length worked as well as their fraction. In other words, you would have to experiment with volume for best effect. Likewise, hose length had a huge effect too, as did hose diameter. Small hoses were ineffective.

Why am I not using one and why to many manufacturers not use one? The effect can be built into good design and/or the additional parts, complication, potential leaks or cost is not worth the return. Same effect can be had with using a specific size and length intake hose and filter or filter box. If you build one, look for a hose to it that is nearly the same size as your intake tube, ie somewhere like 12mm-19mm.

I respect both of your (Jag and Fab) experience and opinions, and that this is often a "belief" topic like oil and mix ratios.

I say test it thoroughly before passing judgement. I know what I have done and seen, not what I have heard the crowds repeat.

Steve

 

[gary55]

You guys sure know how to get someone laughing. Reading through this puts Seth Macfarlane to shame. "Fools and fantasies" now that's some good stuff. I can't wait to see the approach to Steve's as usual unarguable facts. I'll take fools and fantasies for 500.

 

[Deleted member 12676]

http://www.hpibajaforum.com/forum/showthread.php?s=7cd6e233e2316aa19a917222db104028&t=27403
boost bottle on a 22.5cc two stroke dyno results

Engine specs (it’s without a reed valve):
http://www.davesmotors.com/chung-ya...22-214812-122-214803-122214812-122214803.html

TSR has software for calculating boost bottle dimensions.

also read: http://www.2-stroke-porting.com/Boost_Bottle.html

 

[Deleted member 12676]

some positive reports on the internet:

"I installed the bottle and so far I have buried the needle on my speedo over 45!! Never did that before. and it’ll turn a constant 35 uphill. Not too bad"

"I ran one on my brand new 1980 YZ125 and it helped with pulling off the low end out of corners. Back in the day the kit was a huge pain in the ass to install but it did work as advertised. When people say they don't work its usually because they had a piece of s**t system installed and not a good design. It should be noted that proper tuning, compression, and porting take away the need for a boost bottle, but don't ever tell me they don't work. "

"I have seen improved throttle response, smoother idle, and more midrange power"

I think what they do on a reed valved engine and on a piston port intake engine are different. On a reed valved engine one way they serve to aid low RPM power is by increasing the crankcase volume so that the crankcase compression ratio is lowered which benefits low RPM power at the expense of high RPM power. On a piston port intake engine they serve to absorb and give back pressure. When the piston closes the intake port there is a pressure created by the sudden stopping of the fuel/air flow from the carb. Some of that pressure enters the boost bottle and then exits back (hopefully at the time the port is opening). Its rate of entry depends on the inner diameter and length of the connecting tubing. Skinnier and longer presents more resistance to flow. So fat tubing creates less resistance and so allows filling and emptying of the bottle to happen faster which raises the RPM at which the bottle is beneficial. So although skinny tubing presents more resistance it may be essential for benefiting low RPM power. As to the size of the boost bottle I don’t think it should be proportional to the cylinder size but to the volume of the intake tract from piston face to the intake side of the carburetor. It is that flow and volume that the bottle is reacting to, not to the engine size. Of course that volume is usually bigger with bigger engines so there would be some relation.

 

[Deleted member 12676]

Looking again at that dyno graph I think it is bogus. No mod in the world will cause a horsepower graph to come to a perfect triangular peak.
But I still believe that a boost bottle can benefit a piston port intake engine. These china girl engines already have a low crankcase compression ratio so I can't see it helping one of these engines with a reed valve. If I were to make one it would be of adjustable volume so I could experiment with its volume till I liked the result. And if the result was that it took too much away from top RPM power no matter what the bottles volume was then I'd redesign it for a bigger connecting tubing. (larger diameter)

 

[Deleted member 12676]

If it's acting as a resonator then it is in essence a Helmholtz Resonator and it has a narrow bandwidth of RPM during which it "gives back" the fuel/air charge (at the right time) it received from the pressure created when the intake flow was stopped by the piston skirt closing the port. I figured out a test case and it worked from 2730 RPM to 3390 RPM which is only a band of 660 RPM. It turns out that the volume of the canister is dependent on the volume of the connecting tubing. The more volume the tubing has the bigger the canister has to be. I figured that for tubing with 6mm inner diameter 5 inches long the canister insides have to be 3 inches diameter and 3.8 inches long. The only situation I can think of that this would be of sufficient benefit is to tune it to work to boost the intake in the RPM range just below the pipe powerband when there's normally a dip in power (due to the baffle wave working against the intake charge transferring up into the cylinder).

 

[Deleted member 12676]

To keep the size down I had to design it to use it's second negative half of its sine wave.
I will make another design using its first negative half and then limit its size by designing it to work at the top of the powerband, like an expansion chamber does.

 

[Deleted member 12676]

Now this is much better;
using the first negative half of the pressure oscillation we get
a 1350 RPM powerband from 5430 to 6780.
connecting tubing 6" long of 1/4"ID
canister 3.9" long of 1.5" ID

(or tubing 8" long of 3/8" ID and canister 6.5" long of 1.5" ID)

I think since this is a resonator that it's important the connecting passageway to it has a smooth interior that is free from "steps" at the tubing connections. Just like the header of an exhaust pipe you don't want anything that creates interference patterns that would obstruct the flow.

 

[Deleted member 12676]

It's powerband probably is wider than 1350 but tapering off in power above and below that range.
It's hard to fully know just with mathematical calculations and assumptions.
Consider that a typical expansion chamber has a 2000 RPM powerband.

 

[Fabian]

A boost bottle is a misnomer for what can only be a device (at very best) to improve idle quality. Other than that, it's a waste of time and money. Helmholtz resonators are primarily used to attenuate induction noise in automotive applications, and serve no purpose as a "power boost" device.