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Discussion Starter · #1 ·
I'm starting to research how to do this, and could use a little guidance. So forgive the dumb questions....

Is there a definitive answer as to whether a 2:1 or 2:1:2 is best? I don't follow the logic that it must go back to 2 rather than using a bigger collector.

Would a crossflow muffler work, assuming short equal length primaries? If not, why not?

How do you 'tune' an exhaust?

I'm looking to build a lightweight exhaust for an 1100 Evo lump whilst giving a decent power/torque bump. Current thinking is an underbelly exit [single or dual] or a single under seat. Running a lot of pipe back and then adding 2 x cans isn't something I want to do unless there's a compelling argument to go with it.
 

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you have two exhaust ports quite some distance apart. if you want a system that connects the two together at some point, that defines your header style and length. the std headers from 90's models with the stamped crossover work great if you want to join them.

i would run a collected 2 - 2 if outright overall performance is the aim. the long single pipe section that a 999 full system or 1098 style system has does hurt the midrange. plus all the underseat sbk systems are really too long.

but the thing that dictates the most what you make is how you want it to look. with the exhaust ports so far apart, the usual theory stuff kind of goes out the window.

kaemna run a lot of individual pipe per cylinder systems on their hot 2v race bikes - check them out.
 

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Discussion Starter · #3 ·
That's partly the problem, looks. I want my form cake and eat it with function toppings.

I either want it tucked right up in the tail so that it can't be seen - like a tzr250 3ma - or hidden in the belly pan a la Panigale. I can't decide. Belly seems lighter which would swing it. Routing the primaries the same as a monster would allow a single collector to run under the belly where I was thinking I could maybe make something like the front exit 899 Pani Termis. In Ti it shouldn't weigh very much and should package well [evo lump, 848 frame, full fairings].

I'm prepared to fab it all myself if required and can use either monster or hyper primary routing. Just struggling to work out how you're supposed to tune exhaust length so the back pulses hit at the right time, and what the 'rules' are for not sapping power [the QD ex box seemed a reasonable solution until I saw a dyno plot!]. Once I've worked out lengths for each option, comparing them gives me a reasonable idea of which will weight the least.
 

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You can learn the general rules in books like "The scientific design of intake and exhaust systems" (I think that's the title anyway, I lost my copy years ago). You can make up spreadsheets to analyze the estimates of all the things that matter, and then you can figure out the optimium estimated design won't actually fit the bike. Then you make the design fit and if you're really touched you can go back and modify your estimates on the inputs to make the design that fits look better on the page...

The chances of being able to accurately develop the lengths without some pretty serious engine simulation software are low. The lengths are based on acoustics, which means the speed of sound is critical, and the speed of sound changes with temperature/density so unless you know those accurately you're just guessing at what's "right". And even if you do get everything right, that's only for one rpm. At some other rpm, all that work you did means the pulses are hurting you rather than helping.

Yeah, they were developing exhaust systems long before engine simulation software was around. They were also running engines on dynos to test the results.

Long winded point being... don't stress it to much. You can make more power on the intake side anyway.
 

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Just struggling to work out how you're supposed to tune exhaust length so the back pulses hit at the right time ...
If you mean exhaust pulses from Hor. cylinder, reaching (through the connector) the Vert. and from the Vert. reaching the Hor., at the "right" time (crankshaft °) , you can't.
Unless you have equal firing intervals, that is.

In your case, I would ditch the connector idea, build as big a silencer as possible with two separate compartments, calculate the primary's (I assume of 45mm diam.) length, and use at least 55mm diam. secondaries as equal length as space permits.

If you need a realistic simulator, use the freeware version of "Lotus Engine Simulation" @ https://www.lotusengineering.com/engineering-software/.

You need to input some engine parameters, and spend a few hours to learn to use it.
 

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Or you can ping Burns Stainless and they´ll do the calcs for you and even put a piping package together for you to build it.
Very nice to deal with and you can go back & forth on the design to optimise it for what suits you best in overall compromise...

That or get an electric bike if you don´t like exhausts... Me I LOVE the twin pipes on Ducatis especially if you high rise them - it´s almost a trademark!
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Discussion Starter · #7 ·
On a non SSSA i would agree in principle. Picture the same bike with a single arm though and twin side slung pipes don't work imvho.

On the 851/888 corse bikes it strikes me that there's ample room, with an SSSA, to tuck them under the seat.

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Long winded point being... don't stress it to much.
I think I am maybe getting ahead of myself in terms of aesthetics, I have been planning this build in my head for over a year now and maybe excited now the parts are coming together. Just the engineer in me [Aero / Energy] likes to be forewarned and readily armed. I'll do some reading and wait until I'm ready to fab to get the questions back out!
 

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I think I am maybe getting ahead of myself in terms of aesthetics, I have been planning this build in my head for over a year now and maybe excited now the parts are coming together. Just the engineer in me [Aero / Energy] likes to be forewarned and readily armed. I'll do some reading and wait until I'm ready to fab to get the questions back out!
I get it. I'm a retired engineer who worked in the exhaust industry for about 30 years. Degree is in aerospace, career was mostly in the auto industry. Around 20 years was spent developing mufflers for OEMs, but that job is virtually ALL based on sound, not performance. After the cats there's not much you can do with flow dynamics.

Anyway, someone mentioned scaveging from cylinder to cylinder. That's not the only way to get benefits from the flow dynamics. Any time there is a change in area in the exhaust system there is a reflection in the pressure wave - think two stroke expansion chambers or velocity stacks on intakes. But the more you get into it the more you're going to realize you don't know and will have to estimate. Without very detailed computer models, to the level that even the manufacturers struggle to achieve, you aren't going to be all that accurate. So use the general guidelines and make it look right to your eyes.

Computer models - Getting accurate, up to date computer models from OEMs that we could use for simulations was always a struggle. I can't count the number of times we were told the model we wanted didn't exist. It wasn't a secrecy thing - we could use black box models that didn't show specific details. The fact was, they just didn't exist.

Sure, you can get spreadsheets/software that will spit out numbers all day long, but they are all based on assumptions and without calibrating your models you're fooling yourself that the info is all that accurate. Even at a tier one supplier level, much of the computer simulations are done with the caveat that they show trends, not actual results. That was changing when I retired, but not a fast as some would lke to believe.

final ramble - the majority of the headaches in exhaust design came from making things fit where they needed to go, not how do we get more torque out of it.
 

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I used the program Pipemax to "model" the custom exhaust that i later fabricated for my multistrada 1200, then due to curiosity in optimizing cam timing, decided to try DynoSim6 which mostly agreed on exhaust lengths. Unfortunately (or maybe fortunately since it looks like you're also an engineer) they both require quite a bit of information to be accurate and as always with these things, garbage in = garbage out. I also contacted Burns on lengths and they corresponded pretty well to Pipemax. I was skeptical on Pipemax's choke recommendations and Burns was reluctant to give any. Based on this and what the aftermarket industry does on these things, i didn't use a real choke at the collector.

Due to packaging constraints, ended up with different length primaries which then spurred further, maybe backwards, development where i used the programs to figure out what RPM corresponded to those primary lengths and modified cam timing (slightly, and only after verifying P2V clearances) and modified the inlet tract lengths to match those rpms on their respective cylinder. Oh also i decided to match the exhaust port geometry (flat oval) and transisition to round where pipemax put the transitions for a stepped header. Havent had a chance to get it to the dyno yet so can't comment on how well it works. Also the engine is a Frankenstein high compression 1200 with 1098 cams so there wont really be a benchmark anyway...

Edit: Also went 2:1. Cant really comment on the other configurations but pipemax will give x pipe locations too.
 

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Hi,
There are some info here:
I have found the Monster 1000 Ducati Performance Spagetti system (Termignoni?) to give good result.
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