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Exup and exhaust cam timing

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Exup and exhaust cam timing

Postby acotrel » Thu Apr 06, 2017 4:04 pm

I have a question about Exup. Does anyone here have experience with it on modern bikes ? I'd be interested to know whether the exhaust cam timing on models of bikes fitted with Exup is very different from when the motor does not have Exup. I cannot understand how it increases bottom end, if it is a standing wave effect. One comment I've read was about the much lower noise levels when it is fitted. When I built the 850 motor, I advanced the cam by 12 degrees and got huge torque, however even with the 2 into 1 exhaust, the noise levels are horrendous. Another person on this forum corroborated that this happens when the 850 cam is advanced. Perhaps the modern bikes use more advance on their exhaust cam and use the Exup valve to control the noise ? I was told by one competent tuner that the modern bikes are faster when the Exup valve has been ditched.
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Re: Exup and exhaust cam timing

Postby Rohan » Thu Apr 06, 2017 4:24 pm

acotrel wrote: I cannot understand how it increases bottom end, if it is a standing wave effect.


As has been said here before, more than a few times, its NOT a standing wave, its a PULSED WAVE.

pulse-pulse-pulse-pulse-pulse.
This explains a lot, that a standing wave cannot.

And, if the purpose of exup is to improve torque low down in the rpm register, for road riding,
then ditching it and keeping the throttle pegged wide open could indeed "be faster".

Dunno what this has to do with Commandos though, LAB will shortly move it...
Its not like Commandos are gutless revboxes either, that they'd need anything like exup....

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Re: Exup and exhaust cam timing

Postby Fast Eddie » Thu Apr 06, 2017 6:54 pm

acotrel wrote: I was told by one competent tuner that the modern bikes are faster when the Exup valve has been ditched.


I think you'll find that's because they are primarily fitted to such modern bikes in order to reduce noise at lower RPMs, where they are noise tested, then they open up at higher RPMs.

Some cars, like Aston Martins, have them for the same reasons too.

My BMW R nine T had one, but it doesn't any more!
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Re: Exup and exhaust cam timing

Postby Rohan » Thu Apr 06, 2017 8:10 pm

Exup was all the rage in MotoGP at some point - at least the Ducs had it.
Was this for noise ??, or more torque low down in the rpm register.
Some of the other marques too ?

Sometimes with electrically variable inlet trumpet lengths, so they were chasing something.

Quite a number of strokers (bluesmokes) had it too, with expansion chambers,
so noise can't been solely the purpose for them either . ??

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Re: Exup and exhaust cam timing

Postby Fast Eddie » Thu Apr 06, 2017 9:17 pm

Rohan wrote:Exup was all the rage in MotoGP at some point - at least the Ducs had it.
Was this for noise ??, or more torque low down in the rpm register.
Some of the other marques too ?

Sometimes with electrically variable inlet trumpet lengths, so they were chasing something.

Quite a number of strokers (bluesmokes) had it too, with expansion chambers,
so noise can't been solely the purpose for them either . ??


Maybe in the MOTO GP world, but along with who knows what other goodies?

Alan's comment was, I believe, with regards to modern commercially available motorcycles, and that is what I was answering.
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Re: Exup and exhaust cam timing

Postby Rohan » Fri Apr 07, 2017 3:11 pm

So, here we are over in motorcycle related...

You and I both know that Alan doesn't ride road motorcycles,
and never talks anything but racing motorcycles. !
But I take your point.

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Re: Exup and exhaust cam timing

Postby acotrel » Fri Apr 07, 2017 5:03 pm

This matter is also relevant to road motorcycles. When you set up your cam timing, do you OPTIMISE it by moving the timing backwards and forwards to see where it operates best for your purposes ? I am always suspicious of motorcycle manufacturers. Would anyone really claim that Pa Norton did not move the cam timing in the Commando back a bit from best, to comply with the noise laws ? If Exup achieves noise reduction rather than anything else, it might help the situation where you want performance from your road bike without getting booked for noise pollution. i.e. move the cam forwards and fit Exup ? Fitting a throttle-operated butterfly valve into the pipe after the collector on a 2 into 1 exhaust would be a soda.
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Re: Exup and exhaust cam timing

Postby Fast Eddie » Fri Apr 07, 2017 5:54 pm

acotrel wrote:This matter is also relevant to road motorcycles. When you set up your cam timing, do you OPTIMISE it by moving the timing backwards and forwards to see where it operates best for your purposes ? I am always suspicious of motorcycle manufacturers. Would anyone really claim that Pa Norton did not move the cam timing in the Commando back a bit from best, to comply with the noise laws ? If Exup achieves noise reduction rather than anything else, it might help the situation where you want performance from your road bike without getting booked for noise pollution. i.e. move the cam forwards and fit Exup ? Fitting a throttle-operated butterfly valve into the pipe after the collector on a 2 into 1 exhaust would be a soda.


Alan, go on eBay, you can by a butterfly exhaust valve for next to nowt cos' folks take 'em off their new sports bikes! You can then play with it to your hearts content. If you were in UK I'd send you mine for free...!
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Re: Exup and exhaust cam timing

Postby Rohan » Fri Apr 07, 2017 10:25 pm

And we look forward to the dyno charts showing progress. !

Heck, we still haven't seen hide nor hare of any factory dyno charts showing that the
balance pipe in the 850 zorsts does anything....

P.S. Most motorcyclists rely on making a quick getaway, not a quiet exit ??
A lost cause already....

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Re: Exup and exhaust cam timing

Postby acotrel » Mon Apr 10, 2017 4:27 am

Pulse or standing wave ?
I don't believe Exup works to produce more torque by shortening the pipe length. I suggest it's more likely that the cam timing changes the torque characteristic and the Exup valve is used to control the noise.

https://www.youtube.com/watch?v=jSLw01C9Pv8&t=224s

Actually Eddie, I've got a couple of butterfly valves and I am going to try fitting a throttle cable -controlled Exup to my 2 into 1 pipe, that is when I get rich enough to go out and have another bit of practice. As far as the dyno is concerned - what is the benchmark for torque output on an 850 commando engine ? Should I do a before and after ? - the before was 25 years ago. How many dynos give accurate or even repeatable torque readings while the motor is spinning up ?
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Re: Exup and exhaust cam timing

Postby Rohan » Mon Apr 10, 2017 4:47 pm

It CAN'T be a standing wave - for approx 3/4 of the time ( for a single cylinder breathing down its own pipe) there is NO FLOW happening. How can a 'standing wave' survive coitus interruptus in those conditions ?

As for the rest, you'd have to try some repeated dyno runs wih and without the exup valve to see.
We've had this discussion before, you obviously have never been near a dyno, they are repeatable.
The local bikeclub here had a dyno-on-a-trailer turn up to a bike show, and offer free runs to all comers.
The shootout between a 955i and a ZZR1100 was a highlight - obviously some time back now.
Those things had some serious mumbo, the very short intervals between gearchanges spinning that huge flywheel weight told you that just by ear, without even seeing the printouts. The Beemer Harley old Duc etc were somewhat leisurely by comparison...
I have video of this even, although a bit rough and ready (handheld) not suitable for uploading.

I cannot imagine that MotoGP WSBK bikes would be using exup valves to reduce noise at lower rpms.
In conjunction with electrically variable length intake trumpets, whats more....

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Re: Exup and exhaust cam timing

Postby acotrel » Wed Apr 12, 2017 1:59 pm

I have always found it difficult to imagine how flow happens when there is a standing wave. I understand it happens by mass transfer, however in my reasoning each pulse must move down one every time there is a firing in a single cylinder motor and pop out the end of the pipe. However if you think about how a tsunami works, it is all about energy.

About the dyno. Have you seen the videos of John Renwick's dyno ?
https://www.youtube.com/watch?v=Zw6hhAm ... H2-U7DWD-W
They show a bit about calibration. I doubt that midrange power can be measured with enough sensitivity to give meaningful results. I suggest that most guys are only interested in the ultimate horsepower figure. What I am talking about is how fast the motor will spin up as it comes up through the gears under load with that heavy crank. I usually see about 1000 RPM drop in revs on every up-change. If I can get it to drop less than that I would increase the overall gearing to give the bike more legs at the end of the straights. The top end of the horsepower curve is not a measure of that, it is where the peak of the torque curve is that matters .

As far I am concerned, the Exup thing is only about controlling the noise so my bike would be legal at historic race meetings, which I rarely attend . Changing the cam timing has already given me sufficient torque to be competitive.
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Re: Exup and exhaust cam timing

Postby Rohan » Wed Apr 12, 2017 2:44 pm

acotrel wrote:I have always found it difficult to imagine how flow happens when there is a standing wave. I understand it happens by mass transfer, however in my reasoning each pulse must move down one every time there is a firing in a single cylinder motor and pop out the end of the pipe. However if you think about how a tsunami works, it is all about energy.


Of course there is no standing wave with a PULSED flow, how can there be !
Good that ye have finally twigged....
Its all about pulse tuning.

acotrel wrote: I doubt that midrange power can be measured with enough sensitivity to give meaningful results.


How little do ye know....

The computer measures the acceleration of the heavy roller ALL THROUGH THE REV RANGE,
so midrange torque/hp calculations are just as valid as in the low range or top end rpms numbers.

As said, even without the 'puter you can HEAR when a bike has a lot of mumbo, and just zips through the gearchanges instead of labouring. The puter spits out drawn graphs of the torque and hp curves, whats more.
Compare that to a braked dyno, where the operator writes numbers on a sheet of paper and then hand draws the graphs to suit the numbers. (OK so fancier brake dynos may have a 'puter too these days...).

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Re: Exup and exhaust cam timing

Postby acotrel » Thu Apr 13, 2017 3:11 pm

The horsepower figure which comes off inertia dynamometers is usually adjusted with a fiddle-factor which relates it to the specified figure for the Yamaha Vmax - the bench-mark. So probably the only way the figures can mean anything to a tuner, is if they use the dyno as a comparative tool between sessions. This relies on the calibration of the dyno remaining constant between sessions. There is a dyno about 70 Km away from my home. Should I take my bike there and rely on someone who is probably an opportunistic incompetent ? Once when I was racing my Triumph, one of these idiots offered to rebuild the motor for me. I felt like strangling him. Nearly every 650 Triumph in Australian historic racing has disintegrated and disappeared - simply due to idiots such as that. - In simple terms - THEY DO NOT KNOW ! The common mistake is to set the motor up to rev. high and use low gearing. The result is often that the back gets pulled out of the crank-cases.
What you have been saying is OK in theory, however you forget the human factor.
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Re: Exup and exhaust cam timing

Postby Rohan » Fri Apr 14, 2017 1:23 am

acotrel wrote:The horsepower figure which comes off inertia dynamometers is usually adjusted with a fiddle-factor which relates it to the specified figure for the Yamaha Vmax - the bench-mark.


Since when ?

Roller dynos have been around for eons before the V-Max,
going back to very simple versions.
Pre computers even.

So, if you always use the same dyno, no problemo.
And as said above, you can hear when the gearchanges are quickfire,
something with serious mumbo is mumbo-ing !!

Building Triumphs is entirely a different ball game to dyno runs....

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