Exhaust pipe diameters

I had the pleasure of owning an FZR 1000 EXUP and it certainly did everything written on the tin, the exup was, is a fantastic road bike, pulled like a train from anywhere in the rev range and was good for 175mph top end, (well thats what was shown on the speedo). So good, I managed to get myself banned with it!!
I've often wondered if one of the serial fettlers on here would ever hash up a similar device and give it a try. It's right there in Hobots territory.

Fitting Exup to my 2 into 1 exhaust on the Seeley would not be difficult. The only thing is I believe two factors affect the position of the butterfly valve - the revs and the throttle position. So it would probably need to be programmed along with the ignition system. Without a dyno which gives precise torque readings we would effectively be working blind. There would be a major advantage if it could be made to work. I have been progressively increasing the overall gearing on my bike as I have increased torque. I am getting faster near the ends of the straights while maintaining my acceleration out of corners.

brxpb said:

I had the pleasure of owning an FZR 1000 EXUP and it certainly did everything

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There is the minor matter that the Fizzers had 5 valve heads short stroke motors and rather downdraft carbs to go with theirs exups though...

What makes me wonder is that top end power was never a problem with Japanese four cylinder superbikes. The ones with the Exup might have been set up to deliver more top end power and use the Exup to stifle the motor when bottom end is needed.

Generally speaking, a megaphone emphasises the power band and a restricted exhaust is easier to live with, so the bike is easier to ride faster.

There is no suggestion that exup was ever used on Yams racing bikes anytime ?

Nor YPVS on any of the TZs ?

Marketing acronyms for streetbikes ....

Rohan said:

There is no suggestion that exup was ever used on Yams racing bikes anytime ?

Nor YPVS on any of the TZs ?

Marketing acronyms for streetbikes ....

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1991 AMA championship, Vance and Hines OWO1.
Castrol 6 hour, FZR1000
Daytona 200
British superbike championships
16 world superbike wins
Much Isle of of Man success 400, 750 & 1000, all ExUP bikes!
That is bum information you're peddling there Rohan!

Their not race bikes though, they are street bikes gone racing. !

Do we know for sure that the exup was still fitted to them ??

brxpb said:

1991 AMA championship, Vance and Hines OWO1.

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"Yoshimura made a special pipe for me"

Not sure if this was current, or later...

So lets name all the classes of racing that aren't "street bikes gone racing", I'll start: motogp.

Why do they have homologation rules then?

brxpb said:

So lets name all the classes of racing that aren't "street bikes gone racing", I'll start: motogp.

Why do they have homologation rules then?

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In the old days of yore GP racing meant unrestricted –but within a few short parameters – and became VERY expensive for manufactures to complete. Most manufactures have quit this modern day spectacle at one time or another due to cost.
Modern Moto GP racing still has restrictions on types of engines, there are no longer any two strokes for example and in the top flight class 4 cylinders maximum.
There are restrictions on weight, types of bodywork, (the outright ban on dustbin fairings is a safely example) and at the moment the tea tray on the front of these bikes is up for discussion and maybe banned outright.
Overall, it is much the same in Formula 1- except like Motor GP they keep changing the rules to confuse people :!: :shock:

Yes my appologies to Rohan, two of your statements seemed to set me off all defensive, you seemed to be dismissive of the exup concept, where as Yamaha saw fit to run with it for 10 years or so, it worked perfectly as designed to beef up low and mid torque, brilliant for road use, which isn't here or there on a race bike, I would hope Eddie Lawson wasn't languishing around the tacho anywhere other than trying to break the needle against the stop when he was riding them, yes I agree with the marketing acronyms, but most people buy into the acronym, but there is working science behind most of them, vtec comes to mind, the other point that they were road bikes gone racing, whereas most classes of racing are just that, we didn't start with Peter Williams and the John Player Norton, most factories are ploughing more money into the road bikes gone racing than motogp, due to the old addage, win on Sunday sell on Monday.

Homologation - "the OWOl has little in common with the popular FZ750 roadster"

Moto3 has some exotica in the engine depts too, not sure you can buy a street version of them ?
Durned expensive some of them too.

You couldn't ever buy a street version of a dohc manx.
Nothing Nortons sold for street use had any magnesium in it.

ALL the GP racers for quite some years.
Not many TZ750 road bikes about.
(Some privately converted ones maybe).
RZ350 wasn't really the same as a TZ.
MV Augusta race bikes and street bikes were barely related.
Gilera 4 cylinders.
Rhondine 4 cylinders.
Guzzi V8
Laverda V6


Its not that I have anything against exup - would love to see a dyno chart with and without it though.
But for serious racing, the 1st thing in the bin would be an obstruction in the exhaust system !!

That Castrol 6 Hour win would HAVE to have it fitted.
The bikes are scrutineered after the race, and HAVE to be showroom standard.
Bikes have been disqualified for any minor infringements, inc race 'winners'.
But the tracks they used were fairly short, so exup in the low rpm registers could be an advantage.
Or maybe they won despite having exup fitted....

We diverge from Commando pipe diams, muchly.

I suggest the pipe diameter is important for bikes being raced on short tight circuits. It is all very well to have a powerful bike with an extremely pronounced power band on a large circuit with mainly sweeping bends, however most of the circuits I have raced on have not been like that. I think it is more difficult to make a bike fitted with large diameter pipes tractable than one fitted with small diameter ones. Perhaps the Exup allows the superbikes to be set up for the very pronounced power band, yet remain tractable when the low part of the power band is needed ?
My recently deceased friend always had the extremist approach, - that you use the highest compression with methanol fuel, the hottest cams and the open exhaust fitted with megaphones. He learned a hard lesson in 1956 when he came down Conrod Straight at Bathurst too fast and facing Murray's Corner he found it difficult to decide whether to veer right into the escape road or left around the corner - the angles were the same. He chose left and got around. He got as far as Skyline Corner on the top of Mount Panorama where the bike bounced him off the Armco fence - broke an arm and a leg. I ended up with the bike ten years later and it taught me almost everything I know about racing - the hard way.

I agree with Rohan. The Exup butterfly valve in the has to stifle the motor. I cannot buy this stuff about it changing the wavelength - it probably changes the amplitude of the wave, making the power transitions less pronounced.

I might fit it to my Seeley for the noise factor alone. I think that if I ever race it again, I might get raided by the guys with the noise meter. If it was partly shut at low throttle openings it could be good.

I know for a fact that the performance of a modern 4=cylinder, short-stroke DOHC motorcycle engine is pretty much unchanged by the addition of a free-flowing aftermarket exhaust system. The factory engineers have it down to a science, and the only gain is sound, less weight and looks. Used to be they could gain 5-10 bhp by opening up the pipes. Not any more. So while things like the EXUP valve may have an effect on lowering decibels, I think the purpose is smoother power throughout the rev range.

sixth picture at this link shows the exup valve on dovisiosos ducati. And yes the factory 2 strokes used exhaust valves of all kinds for many years

http://www.superbikeplanet.com/image/ar ... gp16-2016/

He 'exhaust valve' on a two stroke alters the port timing which is equivalent to changing the valve timing on a four-stroke motor. Back when four cylinder bikes became available to the average guy there was the CR750 Honda. It had proper race cams and four megaphone exhaust pipes and it took a hero to ride it well. These days the competitive 750 Hondas in Australian historic racing have 4 into 1 exhaust pipes, milder cams and they are bored out to over 1000cc and run methanol. They are still 'point and squirt' bikes, however they don't try to kill the rider. I know one guy who has raced both configurations. When he made his comeback, he found the modern version was much easier - NO ANXIETY.
I have a friend who is the most competitive privateer in current Australian Superbikes. I was in his workshop and the top was off one of the Fireblades. The cams had been welded up and reground, so I asked him what the cams were suited to. He said 'we change the cams to suit the circuit'.
When you change the exhaust, optimising it involves the cams.
With Exup, my suspicion is that it allows much more extreme cam timings, so power is increased right across the rev range. However the Exup keeps the power delivery at low revs SANE.
In the 70s, the guys were using Yoshimura cams in their four cylinder bikes - they were pretty mild. In 1978, I was involved in timing a set of Italian (Termignoni ?) cams in a ZIR Kawasaki. It was the fastest bike in it's class at Bathurst that year. Particularly when my mate left the screw out which held the baffle into the silencer and it fell out as the bike left the start line. We copped a license suspension for that. The rider was Craig Hemsworth. He is the father of those two actors of the same name.

With my own bike, I've found that substantially advancing the cam combined with the 2 into 1 exhaust and methanol fuel, the torque which is delivered is massive. So I have been progressively increasing the overall gearing. The main problem is the noise - I dare not start the bike at home. The power delivery is extremely strong and smooth. An Exup valve might not be all bad if it opened fully at full throttle and closed at low throttle openings.

http://www.superbikeplanet.com/image/ar ... 16/013.htm