YEIS info

jaguar

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YEIS stands for Yamaha Energy Induction System and it first appeared on the YZs and ITs back in the 80's. It is a method to boost low RPM power by increasing the reed to carb volume. Theoretically it can be designed to boost power at high RPM also. Designing one for a high RPM boost depends on treating it as a Helmholtz Resonator so that it is pushing back its received intake charge between 180 and 360 degrees of crank rotation. I'm making a spreadsheet calculator for those interested in designing their own. But I first need to analyze Yamahas "boost bottles" by the dimensions of ones on any YZ or IT model. I have specs from one so far that holds 2 cups volume (470cc) and its resonant RPM is 6300 so that its range of most influence is basically the range below the pipe powerband when the returning baffle wave fights against the flow of the intake charge from the crankcase to the cylinder. In effect it may be eliminating the lag in power just before the engine gets "on the pipe".

So please anyone with a Yamaha with YEIS box let me know:
1. the box dimensions (or better yet pour in/out water and measure the volume)
2. the inner diameter of the connecting hose
3. the distance along the hose from intake manifold to YEIS box
 

Rich Rohrich

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Yamaha published an excellent paper on the subject : http://papers.sae.org/810923/

It's an interesting area to play with but the results at least in my experience have never really been worth the effort.
 

jaguar

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I have that research paper and I've included graphs and info from it on my YEIS page. It may just be a little help to trail and street riders but I guess I'm going to find out. Every little bit of improvement I can make to my 100cc is being done..
 

jaguar

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After reading their paper what I'd like to know when someone says they "tried it" is if they designed the boost bottle and tubing to resonate at the same RPM at which their bike has a power dip (for dirt bikes that is just below the pipe powerband). Doing that is essential for success. I doubt I would put it on a bike only used for motocross since they are meant to be operated within their powerband, not also below it like a trail bike.
 

Rich Rohrich

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Suzuki tried it out on Mark Barnett's bike at one point but it was never a commercial success. We sold a few through Eric's company Schelgor in the early 80s. One of it's failing was it tuned to too narrow an rpm range. In my opinion boost bottles suffer a similar fate to a large degree.

In my opinion a system that could be variable would be much more useful. If we were to design it today it would be significantly different. but you're always smarter in hindsight right? :)
 

jaguar

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That patent also targets the “flat spot” in engine horsepower. It says “The frequency of operation of this invention must match the frequency of the engine’s flat spot (hesitation in acceleration point). Each engine has a different frequency of operation and the present invention must be modified in length (tuned) to insure that its frequency of operation matches the frequency of operation of the engine.”

What I don’t like about it is this: “Another object of the present invention is to eliminate or greatly reduce this undesirable backflow of combustion mixture through the intake system without significantly increasing the volume of the intake manifold.”
I thought only pure piston port intakes had backflow and that reed valves stopped all but an incredibly small amount.
This patent says that boost bottles, because of the increase in manifold volume, cause “a detrimental effect on the engines performance which is very noticeable at high engine RPM”. If that is true then how did Yamaha get away with putting them on their motocross models in the 80’s?
 

Rich Rohrich

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Reeds have a significant amount of intake reversion, certainly much less than any piston port design, but it's still there.

Intake volumes, reed design, crankcase compression ratios are among the many compromises that an engine designer has to balance. Yamaha made a compromise in a certain area in the boost bottle days. The lack of boost bottles in production or the aftermarket should give you an idea of what engine designers generally think about the value of that particular compromise given the current understanding of engine design variables.
 

jaguar

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Well I tested with and without the boost bottle on my Suzuki AX100 (2 stroke, reed valve, expansion chamber) and found that it works just like the Yamaha people said it does.

boost bottle tuned to 4800 RPM (3800-5800 BB powerband) although I wanted it tuned to 5100 but couldn't due to space restrictions.
increased pilot jet from .6mm to .64mm hole diameter (I drill my jets instead of buying new ones)
lowered slide cutaway 1mm with JBWeld
AX100 gets “on the pipe” at 5900 RPM
Test area: short uphill with a light pole at the bottom of it and one near the top of it. Cruising at 50kph (4800RPM) till first pole and then opening the throttle.
before boost bottle: no acceleration from 4800 RPM going uphill
with boost bottle: acceleration from 4800 to 5900 RPM going uphill
 

Rich Rohrich

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For what it's worth. What we found during testing was introducing additional volumes and reflection redirections into the intake track can have a profound influence on the fuel curve. It was difficult for us to tell the difference between a device that was functional ( OR NOT) and a change in the FUEL CURVE that changed performance. When we were doing this work 30+ years ago we didn't have measurement equipment sophisticated enough to always be able to be certain of cause and effect relationships between device function and fuel curve changes.

I'm impressed that you're willing to put in the work to test the theories. It's interesting if sometimes frustrating work. Good luck with your testing. Thanks for sharing your results.
 

Rich Rohrich

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... and that's the rub. Without the data acquisition tools to very specifically measure transient air/fuel ratios and torque changes it can be tricky to distinguish what is really working and why. If you keep at it I think you'll find it's worth the effort, even if only to further your knowledge.
 
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