Yeah, I read it. Until I see more concrete proof, I still hold firm that my little free resistor mod gave me what I needed (as have others who have done it). From what I've seen, with my own use and also following Dr Steve's build, the servo resistor and Graves plug do the same job. I have yet to see someone that's taken one of those plug n play units apart to see exactly what's involved.

My point exactly. Simple. If it's simple, then there can't possibly be anything more than what's been done with the resistor. It does the same job the resistor does, just costs a helluva lot more.

I'll preface this post by saying I am no expert, and the only way to know for sure if the EXUP motor feedsback into the ECU and changes anything with fuel curve, would be to do a back to back dyno run( actual dyno..not butt dyno) with the resistor in and with the motor itself in.

This is my theory, based on what I think I know.

1. The Yamaha EXUP system, both on this bike and others, serves a two fold function. One is to lower exhaust noise at idle, and the second, and more important, is to increase torque at lower RPM. These motors, and the inline four design they are based off of, do not typically make a lot of power down low in the RPM range. Not a big deal when you have four cylinders firing. Bigger deal when you only have one cylinder.

2. Based on looking at the wiring diagrams, I think the "other" wires do not feed back into the ECU..but instead get further input FROM the ECU/ other sensors. The wires going to the motor, are also tied into the speed sensor and throttle position sensor. Being that you need the valve closed at lower RPM to make more torque, and more open at higher RPM to make more HP, it would make sense to have these sensors feed into the control of the motor. Almost like a PLC loop system.

3. Japanese do not typically make things more complicated than they need to be. Germans and British do enough of that.

4. CEL's are usually thrown when a sensor is not working. The ECU's only get the idea that something is not working, when it does not get the resistance back to the ECU. Only one set of wires is needed for that. Thus, why a resistor is only needed to connect two pins.

Conclusion: Based on what I mention above, I personally feel there is no difference between the resistor cheap fix and the Graves unit. My guess is that if someone smashed the graves unit, it would just be either one resistor, or a couple, still doing the same thing , and just tricking the ECU into thinking the motor was still there working, in place.

Doug, there's a huge debate over what the EXUP does.

Many will side with the camp that it's ONLY an emissions and noise device.

It there was any power benefit at any place in the powerband why wouldn't race teams and aftermarket pipe manufacturers include such a device in their products?

Why wouldn't Honda and all the other companies utilize something of that nature?

I don't say you're wrong - just that there's wiggle room for much debate regarding the EXUP and what it does.

Which further complicates the idea that the Graves unit provides any performance advantage at all.

Racing is not apples to apples comparison, since they are never interested in the lower part of the RPM range, to put around at low speed. High speed, high power, high RPM is typically what they are interested in.


Not that Wiki knows all, but makes sense to me:

http://en.wikipedia.org/wiki/Four-stroke_power_valve_system

As I said....it's a debate.......

yep...I saw that. Thanks.

Here is that link I posted, incase you missed it.

http://en.wikipedia.org/wiki/Four-stroke_power_valve_system

Guilty as charged. Sorry about that! To top it off I called the crotch rocket a firebird when it's actually called a fireblade.

LOL..it's all good.

>"Good pickup with Yami making NO POWER CLAIMS with Graves mod.

If we conclude from this that Graves vs Servo has no performance difference. And if we conclude resister vs Servo has no performance difference (based on multiple butt dynos) than that means TwilightZone has picked a correct internet handle to go by."

Hmmm... Notice that I said that the peak power was the same. When the ECU bypass with the resistor comes on, yes it really comes on.
But I feel the power feed is changed in the low to mid-range of the power band. I guess other people could try the servo hooked up (or resistor plug) and resistor. Report back. Try it yourself... see what happens.

Only way for sure is if somebody finds out the ECU and mods... or do multiple dyno tests and examine the low to mid rage of the power band.

The EXUP valve is the absolute last part of the chain of events that happens in the intake, combustion, exhaust equation.

Why would the electronic brain that controls air-fuel mixtures and combustion and what-not care what happens at the EXUP valve?

By that time everything that could happen regarding combustion has already happened.

Get the price of what you're buying up a bit and shipping will look a lot better. 3 of the 6P090 Female Half connectors and shipping is now showing $4.37.