All you ever wanted to know about your EXUP...and much, much more

[02R1FUN]

The Last Great Invention by Mike Armitage

Twenty years ago, Yamaha introduced a landmark technical innovation: the EXUP valve. And nothing has fundamentally moved the game on in quite the same way since.

Engine design is a compromise. Bore and stroke may decide a large part of an engine's character, but the fixed nature of the other components is equally relevant - camshaft profiles work best at specific engine speeds, as do the size and the shape of the inlet tracts, combustion chamber, valves and exhaust. Designing them for high revs and power can mean sacrifices lower in the rev range, and tuning for low rev torque makes things wheezy at the top end. There will also be compromises paid in emissions, economy and response away from the region where intake, cams and exhaust give optimum performance.
The ideal solution would be an engine with variable geometry. Unfortunately the theory is sound but the application is akward, which is why technology like variable valve timing has been tried but mostly rejected. Too much complication and cost, too little reward. Honda's VTEC switches between two and four valves per cylinder based on revs, but isn't really variable as valve lift and duration is unchanged. Yamaha's YCC-I system on the R6 and R1 alters inlet trumpet length but, with two preset positions, isn't exactly flexible. Of the attempts so far, there isn't a truly variable technology that has advanced bike design.
Except that is, for Yamaha's EXUP. A simple throttle valve located in the exhaust pipe, the concept has proved so successful that every major motorcycle manufacturer now fits them.

Tube Talk

Exhausts seemingly play a simple role, ferrying waste gas from the cylinder head to our lungs. But the difference they make to engine character and bike performance is far greater than their basic, inert appearrance suggests.
On a four-stoke engine, the exhaust valve opens and the rising piston pushes hot gas, crammed with residual combustion pressure and noise energy, into the exhaust. This creates a positive pressure wave, travelling down the header pipe to the collector. When it reaches this larger diameter section (or another tailored change of section or shape) the gas expands, slowing down and sending a negative wave back towards the cyclinder at the speed of sound. This reflect back and forth around three or four times (becoming weaker each time).
For a small amount of time when the exhaust valve is open, so is the inlet valve. This is overlap. Its necessary in high revving engines - the valve need to open a sufficient time to let useful amounts of gas past, and so exhaust closing gets later, inlet openings get earlier, and the overlap period increases as the designer targets higher revs. This causes problems. Valve timing wont be ideal at low revs, and gas flow can be compromised - waste gas can get back into the combustion chamber, taking up space and getting in the way of the next combustion cycle. Volumetric efficiency and torque suffer.
An exhausts pipe's pressure waves are useful here. The length and diameter of the header pipes is set so the returning negative wave reaches trhe cyclinder as overlap occures, ensuring everything flows in the correct direction by effectively sucking the waste gas out and starting to flow fresh charge into the combustion chamber. A couple of milliseconds later, just as the exhaust valve is closing, its useful for the pressure waves pinballing around the exhaust to appear in positive form. This pressure wall prevents the fresh intake of mixture short-circuiting directly into the exhaust.

Under Pressure

This is all well and good, except the pressure waves in the exhaust move at uniform speed regardless of revs. Short header pipes might supply the negative/positive double-hit of pressure at the cylinder at the ideal time on a high revving motor, but wont be right at lower speed. An exhaust working well at 10,000 rpm will also work, to a lesser degree at 5,000 rpm, in between - at 7,500 rpm - it'll be wrong. The pressure waves will be out of sync with engine, spoiling efficiency and causing a dip in the torque curve.
For a race bike this doesn't matter, most riders taking a few more horses at high revs in return for a few sacrifices (noise, lumpy midrange, gruff tickover). But its a problem on road bikes, especially when silencing causes further problems - any sudden restriction in the exhaust can reflect high pressure (or 'back pressure'), making the engine work harder to pump waste gas out, sapping power. So manufacturers use cunning techniques to optimize the torque curve. Staggered length headers. Tuned length secondary pipes. Links between the individual headers. Discrete tapers to create reflections over a wide rev range, almost like have variable length.
While these work to a lesser or greater extent, the compromise remains. We need genuinely variable geometry, but an exhaust assembled rather like a slide trombone would hardly be practical. So what we need is EXUP.

Throttled

Yamaha's idea wasnt completely new. Their YPVS (Yamaha Power Valve System) was introduced in the early '80s to tame their peaky RD two-strokes. The height of a two-stroke's exhaust port is the one thing to which there are most sensitive,so Yamaha devised a valve to lower and raise the port roof depending on revs. This allowed an exhaust designed for maximum power with the valve rasised (at high revs), while lowering the valve (altering the timing and time-area) gave better torque and flexibility at lower revs. It made an enormous difference in usability.
Four-strokes aren't as sensitive to a single alteration, but using a computer - basic by today's standards - a team lead by Kiyotaka Yamebe and Hideaki Ueda worked out pressure and flow in an FZR400's exhaust. They discovered a throttle valve located at the end of the collectors could be used to tailor the pressure waves, and the theory was supported by experiments on real bikes. Yamaha realized they could now effectively build a full race system then use the throttle valve, by now tantalizingly called EXUP (EXhaust Ultimate Powervalve), to tidy up any resulting dips or hollows in the shape of the torque curve.
First used on the Japanese market FZR400, Yamaha made big claims when the FZR1000R EXUP arrived in 1989: 10% more peak power than an engine without EXUP; low and midrange torque increased by 30 to 40%; a more stable tickover; and a quieter exhaust. Tests in California showed slightly increased C02 emissions (more fuel being burnt) but significantly reduced hydrocarbons (fuel burnt more efficiently).
Noise reduction were due to to the valve being active a lot of the time. A four-stroke's exhaust tune only really works at one speed (or harmonics of that speed), so EXUP operation wasn't an open and shut case. Literally. At around 3,000 rpm the EXUP opened to around 30%, by 5,000 rpm was open almost fully, but at 7,000 rpm only opened between 40% and 60%. From 8,500 rpm it progressively opened wide. Operation was by a servo-motor controlled by the bike's ECU, with a sensor monitoring pulley position and sending information back.

All round appeal

That was then, this is now. With indisputable benefits and advanced engine management, every major bike builder now employs throttle valves in their exhaust systems, and on all manner of machines - Kawasaki ZX-6R, Yamaha MT-01 and Suzuki M1800R all feature a widget up their chuff.
Designs have evolved. The original EXUP system used one valve running through all four side-by-side pipes at the end of the collector, rotated by a pulley and working like a guillotine. In 2000, Honda introduced the H-TEV (Honda Titanium Exhaust Valve) on the FireBlade, still using one valve but with the four headers arranged in pairs on top of each other, in a square layout. The valve was located in the upper pipes, and when closed it opened a hole through to the lower pair, restricting the total area and making use of the bottom pipes' tuned length, as well as the new length of the upper pipes. The 2002 R1 used a similar arrangement, but with a valve in each pair of pipes.
Today, valve location varies considerably. Kawasaki's ZX-6R and the current FireBlade hide them deep in the silencers, while Triumph's Daytona 675 nestles one in the secondary pipe, between the collector and the end-can, just after the catalytic converter.
'We didn't want the weight and bulk of the valve and its actuator at the back of the bike,' says Triumph's product manager, Simon Warbuton. 'This location is the best place for keeping the bike compact, putting mass where it will have the least impact on handling while still giving us the effect we wanted.'
And the desired effect has changed. With advanced injection and ignition systems, the role of the throttle valve is no longer about filling the midrange or chasing horsepower. 'On the 675 it has nothing to do with emissions or peak power.' continues Simon. 'There's a small effect on torque at lower engine speeds and it can improve driveability in some conditions, but it really helps on noise - a valve in the secondary pipe helps to take the edge off exhaust noise without compromising power.' They're corks bunging up pipes to keep them quiet.

The future

As regulations get tighter, the exhaust valve's popularity can only grow. Its a simple, effective technology for meeting noise restrictions, with the added, if small, benefit of being able to improve an engine's torque curve.
New technologies to achieve targets for both power and emissions can be combined with an exhaust valve for the best results. Influencing intake pressures by playing with the intakes and airbox produces similar effects on the torque curve as exhaust design; it's why Yamaha fir variable length inlets on the R6 and R1.
Tuning the intake to work at the same rpm as the exhaust will give the highest peak output but at the cost of deeper dips in the torque, but a slight mismatch gives a wider spread and helps fill the holes. So using two (or more) different systems on the same bike double the benefits - it's why Honda's exhaust valve has always been linked to a flap in the airbox and Suzuki's system works in conjunction with the ECU-managed secondary inlet throttle butterflies.
But while developments like variable inlets are welcome, Yamaha's original EXUP remains the most effective and most simple innovation. More engine performance, reduced emissions, less noise. Absolute genius.

[deadbanana0717]

with all this R and D put into the EXUP, why would anyone want to put a full exhaust on their R1's or new bikes for that matter?

[rorytsm]

Originally Posted by deadbanana0717

with all this R and D put into the EXUP, why would anyone want to put a full exhaust on their R1's or new bikes for that matter?

sound and power gains? oh, and weight loss?

[deadbanana0717]

Originally Posted by rorytsm

sound and power gains? oh, and weight loss?

sound, and weight loss... fair enough.

but the power gain is only on the upper end right?, as the previous post said. you cant win on both ends.

i guess your reply pretty much sums it up.

[Nordic Berserker]

Originally Posted by deadbanana0717

with all this R and D put into the EXUP, why would anyone want to put a full exhaust on their R1's or new bikes for that matter?

I have never dynoed my bike but running stock exhaust at 100mph it was right at 7k RPM's now with gutted cat and race baffles it's 6700RPM, so this tells me it has made power throughout the powerband.

Yamaha spends money on things in order to comply with government regulations, something that I don't give a damn about. Look at the new Ninja way down on power for this very reason.

[deadbanana0717]

Thanks Nordic for your input. I was trying to gather more information on my R1's Exhaust system. I bought a 98 R1 with a full two brothers exhaust, but noticed the diameter of the midpipe and the canister (where they attach) was 50-52mm in diameter. vs the stock 60mm diameter. Are there any theories to explain why narrowing the pipes would be advantageous to the bike? I thought the more air flow the better. I could only think of "back pressure" as an explanation. Got any input on this?

Originally Posted by Nordic Berserker

I have never dynoed my bike but running stock exhaust at 100mph it was right at 7k RPM's now with gutted cat and race baffles it's 6700RPM, so this tells me it has made power throughout the powerband.

Yamaha spends money on things in order to comply with government regulations, something that I don't give a damn about. Look at the new Ninja way down on power for this very reason.

[triplex76]

Originally Posted by Nordic Berserker

I have never dynoed my bike but running stock exhaust at 100mph it was right at 7k RPM's now with gutted cat and race baffles it's 6700RPM, so this tells me it has made power throughout the powerband.

Yamaha spends money on things in order to comply with government regulations, something that I don't give a damn about. Look at the new Ninja way down on power for this very reason.

what?
speed/rpm ratio CAN'T be altered from an exhaust...
the only way is changing primary or secondary transmission ratio.
however yamaha proved that there are different ways to achieve linear band results....crossplane is an answer.....that's why it doesn't need an exup....it's way more efficient than a classic inline over the range but there is a con...there is more fuel burnt so a worse fuel economy, beeing more efficient for a motor doesn't mean directly less gasoline needed.

[Nordic Berserker]

Originally Posted by triplex76

what?
speed/rpm ratio CAN'T be altered from an exhaust...
the only way is changing primary or secondary transmission ratio.
however yamaha proved that there are different ways to achieve linear band results....crossplane is an answer.....that's why it doesn't need an exup....it's way more efficient than a classic inline over the range but there is a con...there is more fuel burnt so a worse fuel economy, beeing more efficient for a motor doesn't mean directly less gasoline needed.

If your engine makes more HP per revolution you need less revolutions to propel the bike at a given speed.

It is noticeable, my shift light when I got the bike was programmed to 7k and right at 100 I would always hit the shift light, now as I said it's like 6700 or 6800 at 100, same tires, same road, same conditions, same driver.

[sss r1]

Originally Posted by Nordic Berserker

I have never dynoed my bike but running stock exhaust at 100mph it was right at 7k RPM's now with gutted cat and race baffles it's 6700RPM, so this tells me it has made power throughout the powerband.

[Nordic Berserker]

Originally Posted by sss r1

Explain to me where the logic is flawed, posting smiley faces doesn't refute anything I have said.

[Dbl_D718]

Originally Posted by Nordic Berserker

If your engine makes more HP per revolution you need less revolutions to propel the bike at a given speed.

Doesn't work that way, sorry. Engine RPM vs speed is gearing dependent, not power dependent.

[Nordic Berserker]

Originally Posted by Dbl_D718

Doesn't work that way, sorry. Engine RPM vs speed is gearing dependent, not power dependent.

I understand what your saying and as I said I have no dyno evidence to back up my HP gain claims. However 2-300 RPM at 100 is something I can't account for the only thing that changed on the bike was the exhaust.

I don't contend that if you had a 500HP bike that you would only be turning 1k revs at 100, however I think that it does play a small role only 2% or so in this case.

[deadbanana0717]

still wrapping my head around this discussion. i kinda see the reasoning behind "Engine RPM vs speed is gearing dependent, not power dependent." but for some reason i kinda see where nordics going at. i wish i could contribute to this discussion, but i dont know enough about bike specs, gearing ratios to throw in here.

[Blu916]

Originally Posted by Nordic Berserker

I understand what your saying and as I said I have no dyno evidence to back up my HP gain claims. However 2-300 RPM at 100 is something I can't account for the only thing that changed on the bike was the exhaust.

I don't contend that if you had a 500HP bike that you would only be turning 1k revs at 100, however I think that it does play a small role only 2% or so in this case.

Bro seriously, stop now, all you're going to do is make everyone laugh their ass off.

HP has nothing to do with the amount of Rev's it requires to move a bike. Have you ever done anything with your Sprockets? Changing Sprocket size is the ONLY way really to change what Gear correlates to whatever speed and RPM you're going. No matter how much HP your bike makes, even if it was a Turbo R1 with 300 HP, If your running stock gearing everything will be the same, if you go -1/+2 that will change it, but if you throw a turbo on that bike, it will stay the same. Also from my own personal experience, i know that as your chain stretches, or if you get a new chain, depending on what the bikes exact wheelbase is (as you move the rear wheel back to compensate for the chain), it can have a minor effect on RPM/Speed. But very little compared to actually changing Sprockets out.

We have a fixed drive-lines on our bikes, you're talking about it changing as if our bikes had torque converters like an automatic car/truck. Different levels of HP pushing on a TQ converter can change RPM as needed with the same speed being achieved. But even in those situations, once the TQ converter goes into full lockup (@ freeway speeds) the final drive ratio will always be the same, and as our bikes are setup a fixed drive-lines, they're always limited to whatever their final drive ratio is, based on whatever sprockets you're using and then each gear's ratio within the Transmission.

[bacchus40]

never road my 09 stock... broke it in w/ slip ons.. then dropped the y-pipe in..

so i cant add to current discussion as far as proving your theory Nordic.. but i can see it has some merit at least..
but yeah, i think FACTS prevail on this one... its all in the gearing..

ohh, and i got my 3/4 system for SOUND TONE, LESS WEIGHT, LOOKS, SEAT OF PANTS FEEL, well worth the cash..

[Twistgrip]

Originally Posted by Nordic Berserker

I understand what your saying and as I said I have no dyno evidence to back up my HP gain claims. However 2-300 RPM at 100 is something I can't account for the only thing that changed on the bike was the exhaust.

I don't contend that if you had a 500HP bike that you would only be turning 1k revs at 100, however I think that it does play a small role only 2% or so in this case.

If you are reading your rpm dif from a dyno chart it can either be the Wheel size that is difrent on the two runs, or the rev setting being out on the dyno

[Blu916]

Originally Posted by Twistgrip

If you are reading your rpm dif from a dyno chart it can either be the Wheel size that is difrent on the two runs, or the rev setting being out on the dyno

Doesn't sound like he's ran it on a dyno

[Twistgrip]

Originally Posted by Blu916

Doesn't sound like he's ran it on a dyno

In that case, he's bike must be driven by PRM

[Blu916]

[ss55539]

Originally Posted by Twistgrip

In that case, he's bike must be driven by PRM

the most valuable mod to date