Interactive exhaust valve

[The Spaceman_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.

Do the Gixxers also have the secondary butterflies that are on the DL (VStrom) bikes?

I never ceased to be amazed at the endless threads on Stromtrooper and other sites from guys who removed the secondary throttle system "for more power" and then spent endless hours and money trying to get the power delivery back to something close to stock. All that for perhaps 3-4 HP, and that only at WOT?

[rboe]

Considering how flat a stock USA CB1100's torque curve is already I'm a bit surprised some markets use the exhaust valve. Can we get someone with that valve to post a dyno run so we can see what it brings to the table?

[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.

Do the Gixxers also have the secondary butterflies that are on the DL (VStrom) bikes?

I never ceased to be amazed at the endless threads on Stromtrooper and other sites from guys who removed the secondary throttle system "for more power" and then spent endless hours and money trying to get the power delivery back to something close to stock. All that for perhaps 3-4 HP, and that only at WOT?

Yeah, they do. The 750 has two power modes, one mimics the 600's powerband pretty closely and limits the peak power and torque. The other is full power.

For racing the exhaust valve should be tossed of course, because we're always in the top third of the powerband (almost always) but for street and track day use, the exhaust valve really helps smooth power delivery and maintain good, usable torque.
Here's some confirmation from an Aussie reviewer that the Interactive Exhaust Valve does increase low-end:

[url=http://motorcycleparadise.blogspot.com/2013/01/honda-cb1100-long-term-review-and-info.html]Be aware if you change the exhaust it will soften the lower rpm drive a little.The factory muffler has a interactive valve. I had to quieten my 4 to 4 down just to make it something to live with but in doing so my lower rpm response firmed back up and I was lucky to find the sweet spot where it is now.

[VTR1000F_imp]

Something new learned from this thread. My EU bike is valve-less.

[Red Mist_imp]

Can anyone find and post a dyno run of the IEV-equipped bike?

[AzBob_imp]

My CBR has the same thing. If you remove the servo, the bike yells at you (i.e. it goes into limp-home mode). The one on the CBR is there simply for noise abatement at low RPM's, not for torque curve tuning; there isn't any real difference in power with or without the servo/value on the CBR.

[Tortuga_imp]

I've just checked. My bike also has a jet-pack booster and nitro thruster bars installed.

..and to think I was excited about it being WHITE!!?!!

[Red Mist_imp]

My CBR has the same thing. If you remove the servo, the bike yells at you (i.e. it goes into limp-home mode). The one on the CBR is there simply for noise abatement at low RPM's, not for torque curve tuning; there isn't any real difference in power with or without the servo/value on the CBR.

Take a look at the actual test procedure and regulations; low RPM noise is not at issue here. Bikes over 676cc are tested at 55% of maximum RPM, at heavy throttle (aggressive acceleration just shy of wheel-slip or front-end lift). So your CBR1000 is going to be tested at 7150 RPM, with a maximum allowable dB rating of 80 dB. The IEV is not going to be involved with sound abatement, it's there to provide a very flat powerband. The Federal Government has just the one testing procedure for noise, [url=http://www.ecfr.gov/cgi-bin/text-idx?SID=05817b167977b31f19ba4aab4aa93b2b&node=40:26.0.1.2.11.5.17.26.13&rgn=div9]here, and one standard for sound restriction, [url=http://www.ecfr.gov/cgi-bin/text-idx?SID=05817b167977b31f19ba4aab4aa93b2b&node=40:26.0.1.2.11.5.17.3&rgn=div8]here, both offered for our perusal after installing that Staintune.

Another quick point is airbox noise is equally important here. My GSX-R 750, for example, has a very raucous airbox in stock condition; it's known for that feature and most magazine testers mention it. The exhaust note is whisper-quiet but the wide-open airbox lets it breathe very well so it makes very good power while keeping things civil at around 8K. It does have the IEV as was mentioned in another post.

[Pterodactyl_imp]

Can anyone find and post a dyno run of the IEV-equipped bike?

I can't provide one cause I've changed to Staintune. When the OEM was on I put the IEV (thanks, you've given me another acronym to put in the quiver) to open and ran the engine. There was no real difference, to the ear at least, in sound level. Without a dyno a torque comparison is difficult. I am still struggling with Honda fitting these to Aussie '10 models and then dispensing with them if they were effective. The valve doesn't seem to be associated with emission control so why? Next visit to the dealer I will have a chat with the service manager. Maybe he can shine some light on the subject.

If any of the other Aussies on this forum get their CB dynoed then they may pass it on. However most would probably get the dyno done after mods and compare to the book figures, I guess.

Cheers

[rboe]

I had a 2000 Moto Guzzi Quota; when I bought it it had a Super Trapp can, a popular mod for that bike. For reasons I can't recall I had it dyno'd at about 55hp. 55hp for a 1100 bike!

Naturally I thought something was amiss which lead to some fun stuff. In the mean time a fellow Quota owner that is a marine engineer said he never understood why the Super Trapp was popular as it did not have the volume to handle the big motor. This is a smart guy with lots of experience so I bought a used factory stock can, dyno'd it again, finding I had gained almost twelve horse power. By going back to the stock muffler. Sounded better too.