Interactive exhaust valve

[The Spaceman_imp]

Thanks Ptero.

I'm surprised, but glad to have learned something new about our bikes. Manufactures usually try to build a single product they can sell everywhere. That's why we'll see almost all foreign bikes come with ABS, even though there's no requirement for it here.

[Pterodactyl_imp]

No worries Spaceman, one of the many good reasons we are here.

Cheers

[Red Mist_imp]

I wish my bike had this. All the Yamahas I've had were fitted with EXUP and they are able to retain excellent, flat torque curves, whilst meeting emissions regulations, by using this feature. My GSX-R 750 has this also and has very good low end and midrange.

There is all kinds of science involved with this kind of valve; it costs more money to include but it is a performance-enhancing feature. It's not there to cut noise or anything else.

My FZ8 doesn't have this and it exhibits the typical "flat spot" on the dyno we get with an inline four. A lot of I4's with a race pipe, which is always tuned for top end, really "come on the pipe" with a kick which makes the bike feel quite a bit faster than it really is. We don't need top end for street riding, low-end and mids are what it's all about.

The flat spot is caused by the Heimholtz resonance, which is basically two pressure waves fighting each other in the midrange. By varying the exhaust back pressure, this is eliminated and greatly helps airflow through the engine. This lets us maintain top-end power whilst preserving driveability. Racebikes don't use this because they rarely get that low in the powerband.

[url=http://en.wikipedia.org/wiki/EXUP]Power Valves explained

A little footnote to this, many of the guys/gals on one of the other forums I visit, Gixxer.com, are busy tearing out the power valve and yanking cables and heaving parts into the trash bin. They might just as well have bought a GSX-R 600 because they've just removed most of what makes the 750 great: its low end and mid-range power.

[The Spaceman_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

[Tortuga_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

There isn't. But there is a CB with one. Mine. UK velvet valve-monkey equipped!

[Pterodactyl_imp]

G'day Red Mist, thanks for that. Your post, and the link to Wiki, is very informative. It is interesting that the '10 models released in Oz are fitted with this valve but all US models are not. Why not? Cost, maybe, or ADR requirements. Any other ideas?

My OEM pipe had suffered an ugly case of gravel rash therefore I fitted my Staintune primarily for cosmetic reasons. After reading your post it would appear that despite a claimed power increase, and a significant weight decrease, there may be a penalty in low to mid end torque. When I am back in the saddle I will surely find out.

Apart from the muffler exchange "Last Blast" is undergoing other cosmetic surgery. I have re-painted sections of the frame and am in the process of removing gravel rash from the RH engine casing and re-painting. Masking-up is not easy with only one arm fully active

[/img]
Rash polished out and etch primer applied

There is a little rash on the muffler heat shield so will replace that. Then all beautiful again!

Once again, thanks Red Mist.

Cheers [/i]

[Red Mist_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!

[Tortuga_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine.

[Red Mist_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine. Smart aleck.

[Tortuga_imp]

Not to knock EXUP or Yamaha RM, but if there's a Yammie with a flatter, more perfect torque curve than the CB's, I'd like to see it.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine. Smart aleck.

But of course, our CB1100 with a proper exhaust power valve would simply retain its fabulous low-end and midrange, but have a more ferocious top end!
Like mine. Smart aleck.
Love you too buddy, love you too!