Exhaust header design. Motorcycle content

Shift518 Automotive
1

I have headers to build for my Ducati project so i am doing my research.

Being 2 cylinders and a simple compact engine its far less complicated than a car engine. With understanding the ideas behind getting the vacuum pulse to hit the overlap and aid in scavenging the cylinder, there are some great calculators out that seem to help get you in the ball park for tubing diameters, lengths at given egt’s, but I cant seem to find a simple calculator that will help with the bends.

understanding that the bends, the merge angles, and other small variables impact the design I want to start with just the bends and how they theoretically add “length” to a design. I am not talking physical length, i am talking about pressure and velocity difference when the tubing hits an XXX deg bend with a CLR of X"s.

I know SW can help me flow a tube with bends and give me some numbers, but I dont have the time to sit infront of the computer and design something, yet.

My idea is to design each primary as close to symetric as i can. So if i have 400 degrees of 6" CLR bends and 25" of straight tube to make Primary A, i try to do the same thing for primary B (if packaging allows under the bike), then hit a merger point at symetric points and put a single short muffler section on after that as straight as I can.

So what ever links, ideas, data, pictures, what ever you can come up with just blast them in here.

This is what I have sofar:

Length=204,000/(.85*redline) measured from Valve seat to (I think the merger point, cant confirm that yet)

140mb PDF for a book on tuning 4 stroke engines, lots of people suggest it for exhaust information.

http://hotfile.com/dl/96853340/4295ed4/Four_Stroke_Performance_Tuning_3rd_Ed_-_A_Graham_Bell.pdf

http://www.rbracing-rsr.com/exhausttech.htm

2

I am going to do something like this:

http://www.schubert-motorcycles.de/images/buell_xl/05.jpg

2 into 1, off the side of the bike, down under the oil pan, into a stainless muffler I will make from a 3X4" dia oval SS tube, with a 2.5" dia perforated tube in the center, stuffed with fiberglass muffler packing, slash cut off to the side infront of the swingarm.

3

y u no just dump pipes straight down?

4

nothing much to add, other than if you put the muffler under there, do yourself a favor and reinforce it enough that you can lift the bike with it. Buells like pictured have factory jack points under certain spots on the muffler.

The one you pictured i believe is a micron full exhaust for buell xb

5

:rockon Mod Powarz. Off topic replies, even from friends, will be moved.

6

They are now, and its god awefull loud:

/ Video

I want loud but not retarded loud. They have to be some sort of 2-1 design with a muffler to provide a bit of back pressure as not to burn up valves, which apparently the Ducati 2 cylinders like to do if they are simple straight pipes.

I gotcah. It wont be strong enough to pick the bike up, or large enough to balance it either, but I can make it compact enough that I can put a skid plate under/around it from 3/16th aluminum and bolt it to the frame, that would support it and protect it too.

But thats the idea, like the Buells, an under the motor muffler design for sure.

7

Buell did it for low cg. just so happens it looks spiffy too. :smiley:

8

Looks good, sounds like it really gobbles with the dumps. Make it sound like a ferrari that would be cool.

9

Yeah it sounds insane. Higher RPM it doesn’t sound like a shit harley actually. Idle sounds like an aggressive cam’d V8.

10

Ceramic muffler packing > stainless scrub packing > fiberglass packing. fiberglass is cheap but breaks down. Stainless is bulletproof, but is heavy. Ceramic fiber is the tits, but costs more.

Making the muffler strong enough to support jacking off it is crazy on a bike. You’d end up with a muffler that weights ten times what it should be just to do a job it shouldn’t have to(AKA buell). Make it light. Why weigh the bike down with unnecessary pounds.

While the layout may be simplistic in comparison to a car, you’re going to find tuning reversion on this bike far more finiky than your typical car stuff. Less # of cylinders = stronger wave pulse per cycle. Obviously your best bet is to get it as close as theoretically possible to the RPM range where you expect/want to make the power, but I wouldn’t try to make it 100% perfect as it’s going to be very difficult to do so. You’ll have to factor in the intake reversion, VE, etc. Honestly, find what ducati worked into their system and base your stuff off that. Ducati is VERY good with this, much like BMW is on their cars. They’re torque bikes, not high HP so keep that in mind.

Your concern about the bends is diving into fluid dynamics and is more complicated than it’s worth. Calculate the total length of the runner using the CLR and be done. On this bike we’re talking negligible differences between the two routes.

I like the project idea.

11

Pipe size calculator:

http://dairally.net/daihard/chas/MiscCalculators/DaiPipes.htm

Ducati 900 2V engine specs:

http://shift518.com/attachment.php?attachmentid=4533&stc=1&d=1323983380

And this is what I got from the calculator:

http://shift518.com/attachment.php?attachmentid=4535&stc=1&d=1323985752

http://shift518.com/attachment.php?attachmentid=4536&stc=1&d=1323985758

Notice I had to change the multiplier a little (.19) to get the stock TQ numbers to match. RPM’s are off it seems but who knows.

What I got out of this is I need 51mm (2") dia 32.7" long primaries.

12

Nice!!

… Still reading PDF. More from me later.

13

I like how it lists to included the ports as part of the dimensionality. Not something people take into account all the time.

Factor in about 1" of the primaries length to be parallel with the exhaust port exit angle before going into a bend. This is another important step that often overlooked, because they just don’t know about it or space constraints don’t allow.

There’s another way to make some more power over a standard header setup but requires some serious knowledge in the physics and principles behind tuned pipes. It’s a technique that is usually used by select custom fabricators building a setup for a very specific engine and tune, but when implemented in a proper way is proven to increase power on the motor it’s designed for. I can go into it in more detail here if you’d like me to, just would take a hefty post if I don’t cliff note it and I have to get back to putting insulation up in the shop ceiling.

14

I am headed to the shop tonight so I will take a measurement of the inside exhaust ports and pump them in the calc too.

Ditto on the 1" at least prior to the first bend. Luckily the way the engine sits there is loads of room before the first bend needs to be made.

I am not racing the bike, and I dont even want to ride it hard since we will have a lot of work into it and will be showing it as much as we can to muster up business. So the pipe doesnt have to be nutty specific to a rev range. Low-mid range is what I want. No need to rev it to 10K every shift.

Adam if you have the time some point and initiative to post what ever you have up your sleeve please feel free.

15

damn that bike your posted looks nasty.

i would just do a simple 2 to 1 to keep pressure constant. size, length, bends you have to decide what fits and what power. i see you want low/mid so i would get longest design plus change the timing.

either way im sure itll look good. nice work and nice work in other threads

16

Thanks homie. I cant wait to start putting it together. Right now the bike is a pile of parts, swing arm, and frame need to be blasted and powder coated, then the motor can go back in and I can start on the pipes. Sadly this will be a few weeks out.

17

always good to think ahead.

just a idea but you should try to design the muffler so it looks like the lower valance. or make the muffler and add some sheetmetal to look like a cow catcher off a train. i thnk that would look sweet but it would take some metal fab to get it right

18

He said jacking off. :rofl

Link me to some bad ass ceramic material, It cant be that expensive, since I only need a little bit.

RGR that on the bends, just measure the center line radius and make the length correct.

Well, if I use the calculator I get a 2" dia and 32" length. If I use the formulas on the PDF/book I get 1.65" and a 30" length. for aprox a 6500 RPM
happy point.

SO, i will measure what the stock pipes are and see where they lie and go from there.

19

Port inside dia is 1.5".

Valve to port exit is 3".

Stock tubing is 1.55".

Front primary is 21" long.

Rear primary is 17" long.

x pipe is 3" each side.

X pipe exit to canister inlet 15".

muffler to tip is 20".

20

after the collector or the X pipe in the stock system, does the “tail pipe” length matter? IE the “slip ons”.

or does all the tuning and exhaust science go on primary and/or up to the collector?