EXUP… the very name can conjure up a machine all by itself – mainly Yamaha’s big-bore sportsbikes of 1989-1994, but it is actually a bit of techno-gubbins to do with a wide-range of Yamahas, large and small…
The first machine we Brits saw with an EXUP valve fitted was the 1989-on model of the Yamaha FZR1000. This machine in earlier FZR1000 guise was known by the name ‘Genesis’ from the name of the frame/motor/chassis symbiosis that Yamaha pioneered at the time, so it was reasonable that owners would differentiate between early and later model FZR1000s by stating they owned either a ‘Genesis’ or an ‘EXUP.’
So, over here at least that interesting little gizmo became the generic name for a line of big-bore motorcycles that (in the UK at least) lasted for around five years.
But, the FZR1000 wasn’t the first EXUP. Oh no. EXUP itself stands for EXhaust Ultimate Powervalve and it was first seen on the 1987 FZR400R, which wasn’t officially imported over here. The EXUP system was a four-stroke power valve system, placed in the bottom-end of the exhaust’s downpipes to fool the pipe into thinking it was the best ‘length’ for both mid-range and high-rpm operation.
You see, exhaust systems are a compromise. Just ask Akrapovic, who – during the 2002 World Superbike season – went through about a dozen different designs for the Castrol Honda VTR1000 SP2 race exhaust, each would suit different tracks where you may need more top-end power or more mid-range…
This is because one length/diameter works well at high RPM, one at lower RPM and without talking about ‘Helmhotz resonance’ or anything too confusing, it’s down to the back pressure in the pipe itself. If you can change the lengths of a pipe and therefore the pressure within, then you can optimise the performance of the exhaust over a wider spread of engine RPM.
But how do you do this? For Yamaha they devised a system that would open and close a series of valves in a section of exhaust. Operating this system were a series of butterfly valves which were opened and closed at the correct RPM by a servo motor controlled by the ECU. On a big litre-class machine, the valve is almost closed at very low RPM and fully open from around 6000rpm up to the top-end of the rev range.
The EXUP valve worked brilliantly and was used on a wide-range of Yamaha machines. Bikes such as the FZR250R and FZR400RRs used the valve – as small-capacity machines would get a useful mid-range hike from the system. The revvy FZR600R of 1989-1993 didn’t get EXUP in the UK and Europe, but did in the USA, as it helped fuel economy and therefore emissions which were notoriously stringent in states such as California – remember the old RD/RZ350 even had a catalyser in its exhaust for the US market back in the early 1980s…
Yamaha’s 600cc sports machines did eventually get the EXUP valve…but it took a while. The ‘foxeye’ FZR600R (4JH) didn’t have it, although 1993’s YZF750 similar-looking did: Yamaha claimed that the system wasn’t needed on the newer 599cc motor and that it would have added around £600 on top of the machine’s price new in 1994 of £6299…
Fast forward three years and in came the EXUP valve in 1999’s new Yamaha YZF-R6 as well as the previous year’s YZF-R1. Since then the system has been improved and refined and even been seen on the likes of Yamaha’s big cruisers and weird MT-01. When you ride a bike with EXUP you can almost feel a surge in the mid-range – which is very handy out on the road. And – as a good idea – it’s oft been copied.
The patent for Yamaha’s EXUP valve system ran out after about 10 years and this meant it could be taken apart, scrutinised and (of course) copied. Honda was one of the first with their H-TEV system, which ran on the 2000-year model CBR929RR and subsequent 954cc Blade.
According to the brochure blurb, the ‘Honda Titanium Exhaust Valve’ (H-TEV) ‘….provides the scavenging and related power benefits of a 360-degree exhaust collector design across low to mid-range engine speeds.’ Then, when the throttle is wound open, it switches to a 180-degree system. Yup, that means it’s pretty similar to the Yamaha system, and when married to Honda’s ‘H-VIX’ (Honda Variable Intake/Exhaust Control System) which uses a flap in the air-box to increase or decrease the volume of air getting to the (new for 2000) fuel injectors, you had a motor which was tractable and flexible. The H-TEV system was at the bottom of the downpipes, like the EXUP system. Updated H-TEV systems were also on later 1000cc Fireblades.
Suzuki also made a similar system: SET or Suzuki Exhaust Tuning system, which debuted on the 2001 GSX-R1000 K1. This was a little more complex than earlier systems, as it took readings from engine RPM, gear selection and throttle position before opening and closing the butterfly valves in the collector pipe. Since then more manufacturers have used their own version of the system, including Kawasaki on their street bikes and even on Triumph’s Daytona 675…
If this sounds like an unqualified success then you’d be right – but some people hate the EXUP valve. Racers, for one: they tend to use a bike at the very top-end of its rev-range and would trade a beefy bounce of torque low down for a few more bhp at the top-end any day. So, while Yamaha may have used the EXUP system a few times on the likes of the OW-01 and YZF750 racers, it was of little use as they were chasing power at 11,000, not 3000rpm. Also, on today’s bikes it’s thought that system helps more with emissions that as a low-rpm power boosting tool.
And it’s not been without its problems. Being sited so low down in the exhaust means that even with the benefit of a fairing the servo motors and cables get gummed up. Many owners reckon in the depths of winter you would do well to service the valves more often than the suggested 4000 and 6000 miles suggested by Yamaha themselves.
Whatever, the word EXUP and associated systems has become legend in classic biking…
