YICS Redux

What is the benefit and/or liability regarding YICS in terms of MPG and power?

I have read it was part of the emissions requirements in the 82 bikes and that is why it's there. There's always folklore as to why something like YICS is present but with the YICS chamber plugged while riding do you get better MPG? More power? Less MPG? Less power? No change in MPG and power?

It'd be nice to see results of Dyno tests on this and to hear from those who compared MPG before & after they plugged the YICS and operated it that way.

 

Most people only block YICS to sync the carbs.

Yamaha claimed it improved both fuel economy and power because the swirling of the incoming mixture promotes more efficient combustion.

The concept works; a lot of other manufacturers soon implemented similar ideas, like Suzuki's "TSCC" (twin-swirl combustion chamber) that I believe they still use.

 

Yeah, I guess the full yics eliminator is a really popular idea on xs11.com forums.

I think if it ain't broke - don't fix it, but to each their own.

 

The XS/XJ1100 is such a monster mill to begin with I don't know how much difference it made in those motors.

When the 550 Seca came out, CYCLE magazine (IIRC) said it made more power than any 650 they'd ever strapped on the dyno and everyone said it had "750 punch in a middleweight package." Compared to otherwise equal non-YICS motors of the era, it was certainly a step up.

I think it makes a bigger difference in the smaller displacment motors because of the size of the YICS passages relative to the size of the intake ports.

 

It is indeed a monster mill even though today there are much bigger monsters out there. It provides a linear acceleration, not so much of the "XJ power curve" it just has guts from the beginning. If I treat it like I was on a 1/4 mile track, the pull I feel in all the gears and throughout the RPMs is pretty much consistent with a bit more pull at the top end. On the Maxim-X the power is between 6,000 - 10,000 RPM and the pull there is far more than the XJ1100 offers. Between idle & 6K, the XJ1100 has far more acceleration than the X has.

It depends on the rider but the XJ1100 is much more predictable power wise, has huge consistent acceleration and is a serious joy on intermediate & long hauls.

Give me the X on a back road race every time.

I'm keeping both as long as I can still ride them.

That said, I'm always wondering what a company like Yamaha has to do mechanically to meet selling/EPA requirements of a major buyer like the USA and what "liability" if any to the engine performance resulted from those changes. In this case, was YICS a forced change that resulted in loss of power/MPG or was it ingenuity to give more power/MPG? I have no idea, just curious.

The official spin to anything will always be it was innovation to improve XYZ so I'd believe real life A>B reports more than the literature.

Gary