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Discussion Starter #1 (Edited)
With advice of temporary Kiwi I built a full custom exhaust system designed to eliminate the dip in the torque curve around 5-6000RPM, this worked fantastically but since I was using the stock 51mm OD final pipe this limits the maximum horsepower, so I decided to upgrade the exhaust system again, the Dyno operator also believed that by bike was being held back on max power by the small pipe)

I based it on conventional thinking of 52BHP/square inch of pipe, however nearer the engine the gases are much hotter and thus expanded more and thus need more area

Based on this I calculated (not including hotter gasses at the exhaust ports) the max power per pipe

I used 39/44/51mm OD pipe originally, (1.5,1.75 and 2.0 inch OD pipe)

1.5 - 78 BHP per pipe (4 pipes) (total 312 BHP) - plenty of headroom
1.75 - 107 BHP per pipe (2 pipes) (total 214 BHP) - reaching the limit with the hotter gasses
2.0 - 147 BHP per pipe (1 pipe) (total 147 BHP) - At the limit

So I designed a new system - Fortunately on my existing system the secondaries and rear pipe were all held together by springs so was easy to remove parts and change them.

I kept the primaries at 1.5", secondaries upto 2.0" and end pipe silencer went up to 2.5"

1.5 - 78 BHP per pipe (4 pipes) (total 312 BHP) - plenty of headroom
2.0 - 147 BHP per pipe (2 pipes) (total 294 BHP)
2.0 - 269 BHP per pipe (1 pipe) (total 269 BHP)

I also made the end pipe longer to help smooth the bottom end (200mm longer) and did it in Titanium to save weight

I realise I will have slower gas velocities and this may affect scavenging of the cylinders but it seems to drive extremely well, slightly smoother at the very bottom end (maybe down to the longer pipe) and makes a great noise, even better than before and looks good IMHO.

TemporaryKiwi, I'd be interested in your thoughts - looking forward to the next Dyno trip



 

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hi paul, i agree the stock tailpipe is very small, it means exhaust gas exit speed is well over 300ft/second. but the 63mm /2.5" tailpipe drops that a long way, plus the 50mm secondary's also reduce gas speed considerably, it may deliver more high topend power, but id think at the expense of midrange to lower topend grunt.
ive made a new tapered exhaust system with headers starting at 41mm id, tapering to 36mm id at collecters, secondarys tapering from 45 id to 42mm id, tailpipe tapering from 56.5mm id to 55.25 id, the whole exhaust system is tapered to suit the heat at each and every portion, but also to provoke manufacture of vacume into next cylinders combustion chamber
 

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Discussion Starter #4
hi paul, i agree the stock tailpipe is very small, it means exhaust gas exit speed is well over 300ft/second. but the 63mm /2.5" tailpipe drops that a long way, plus the 50mm secondary's also reduce gas speed considerably, it may deliver more high topend power, but id think at the expense of midrange to lower topend grunt.
ive made a new tapered exhaust system with headers starting at 41mm id, tapering to 36mm id at collecters, secondarys tapering from 45 id to 42mm id, tailpipe tapering from 56.5mm id to 55.25 id, the whole exhaust system is tapered to suit the heat at each and every portion, but also to provoke manufacture of vacume into next cylinders combustion chamber
Thanks for the response.

From the butt dyno it doesn't feel as though I've lost any bottom end at all but will have to wait for the real dyno to find out for sure, if Ive lost or gained anything and where....

From the grin dyno its all positive ;)
 

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Discussion Starter #6
why is the pipe discoloring at those two areas? looks good Paul.
The entire end pipe and silencer are Titanium, Titanium is both lighter and stronger than stainless steel, because it is stronger the walls can be thinner as well making it even lighter. Another advantage is it is more corrosion resistant than stainless (being a Scuba Instructor i know this as every stainless knife will rust in salt water but Titanium doesn't at all). Pick up a titanium exhaust pipe and the weight difference is quite shocking.

When Titanium heats up (and it's thinner so heats more quickly) it produces an oxide which is blue, thus the blueing of the pipes, heating the pipes before bending them will cause blueing as will riding hard.

Many people like the look of blueing Titanium pipes, whether it's down to the actual look or just bragging rights to show you have titanium pipes I'm not sure....
 

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That is a beautiful exhaust!! And as usual pretty neat upgrades from you. Have a couple of questions :
- What did it cost to make it in Titanium vs Steel?
- Any plan to share the design or maybe sell these?
 

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Discussion Starter #8
That is a beautiful exhaust!! And as usual pretty neat upgrades from you. Have a couple of questions :
- What did it cost to make it in Titanium vs Steel?
- Any plan to share the design or maybe sell these?
I built the full stainless headers to my design, but the rear pipe and can in Titanium i purchased and modified and they don't do an alternative in stainless so don't know of the price difference, however the price was not excessive.

Someone else asked me about buying one, and I may well get them made and sell them but not until I've had it dynoed, I would also be more than happy to share the design at the same time :)
 

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up dated exhaust

Thanks for the response.

From the butt dyno it doesn't feel as though I've lost any bottom end at all but will have to wait for the real dyno to find out for sure, if Ive lost or gained anything and where....

From the grin dyno its all positive ;)
im not saying youll lose power in mid-topend, but you may not gain any there, probably will gain more topend power though
worked out your ex gas speeds roughly 159 ft/sec-37mm id headers, 188 ft/sec-48mm id secondrys, 250ft/sec-59mm id tailpipe, thats if your running 12500rpm max
 

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Discussion Starter #11
im not saying youll lose power in mid-topend, but you may not gain any there, probably will gain more topend power though
worked out your ex gas speeds roughly 159 ft/sec-37mm id headers, 188 ft/sec-48mm id secondrys, 250ft/sec-59mm id tailpipe, thats if your running 12500rpm max
Showing my lack of knowledge on this subject - I've been reading as much as I can and i get the idea and the reasoning that faster is better and bigger is better but you can't have both and that once the bore is too big the gas slows down too much to get any decent scavenging, but that too small restricts the gas too much....

But what I can't find out is what speed is too slow? what is a good speed - and its even more confusing when you combine imperial and metric... ;)
 

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i was fortunate to know someone who made extremely good exhaust systems when i was younger, his ideas i still replicate to this day, anyway he beleived around 300ft/second was as fast as was required for tailpipe exit speed, i ve found thru experimentation that the header speed can be alot lower on a 4-2-1, as long as the speeds increase into each section in a progressive amount, such as 180ft/sec followed by 240ft/sec, and then 280-300ft sec in final section.
so here is exhaust building 101 - craig smiths version, - the aim of an extracter exhaust is not just to provide a free flow escape path for the gases, but to utilise this force as a means to increase the low pressure zone in the combustion chamber, this then enabling more inlet charge to fill said chamber and boost power. namely by providing vacume on the next junctioned cylinder at a time when the inlet valve is opening, just as the ex valve is closing, i.e that being the overlap period of the cam timing.
the force used is the inertial weight of the gases moving down the exhaust tubes, this force is the amount of gases moving and the speed that they are moving, so if they are moving faster into each section, and each section has more volume, the said vacume force will be greater, then its a matter of getting it to effect that next cylinder at the correct time frame, hope that gives you'all something to ponder..
 
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