Air-Cooled Engine Exhaust

[RB]

I have an S2R (800cc), and am going to build a complete exhaust. I have done some research and have figured out that my primary headers need to be 1-5/8" diameter by 23" long in order to take advantage of scavenging. Every exhaust i have seen does not have identical length pipes for the Air-Cooled models (if you know of some that do this, please post a link). Why? The new 696 has stock exhaust that does exactly what i have described. Usually this exhaust idea is refered to as 'spaghetti', and are found on the aftermarket kits for the testesratta engined S4Rs.
So i am figuring that the average cost for a full system is roughly $1200, no labor charge. I am thinking i could have a system built to my specs for that price, one off and it would be properly configured according to my calculations (cam lift, duration, firing order...), right? I have a friend that does this sort of thing, so it would definitely be a project i would have to work closely with.

Why would this be a bad idea, or a waste of effort? Or do you have any suggestions for design?

RB

[mitt]

I think it would work.  A few people over the years have proposed such things, and some have made them, or had them made, and are surprised by the cost of custom exhaust.  It takes a lot of fiddling to get things lined up and bent correctly.

mitt

[DarkStaR]

I have an s2r800 with the spark mid-pipe and exhaust.  I measured the distance from the header to the exhaust tip and the length is with in a couple of inches.

The crossover pipe leading to the left exhaust can closely makes up the length of the longer vertical cylinder exhaust.  The only thing with this is the crossover is not equidistant from the cylinders.  Without a crossover, and with a bit of design tweaking, you may be able to use any of the (l+r) dual can non-shotgun style exhausts as a base for your design.

[RB]

thanks for the replyies.
I am aware it is a bunch of fiddling, i have been designing the exhaust for a month now in AutoCAD.

I have the Spark midpipe also, but not the full system. The only legnth that makes any difference in this exhaust idea is fromt the exhaust valve to the crossover, and as you point out, they are not the same with this configuration (Spark Midpipe).

Thanks,
RB

[DarkStaR]

Does your design require the crossover?

[RB]

Does your design require the crossover?

Yes, which is why the primary headers need to be equal length.

[DarkStaR]

Yes, which is why the primary headers need to be equal length.

Does your design call for the crossover to be a specific distance from the header?  If not, maybe you can design the crossover downstream.  For example, right before the cans.?

Also, will an H or Y crossover suffice, or is an X crossover necessary?

[RB]

Does your design call for the crossover to be a specific distance from the header?  If not, maybe you can design the crossover downstream.  For example, right before the cans.?

Also, will an H or Y crossover suffice, or is an X crossover necessary?

Yes the crossover needs to be at 23", to be most efficient. As for the crossover type. A 'Y' style would work,  and be the lightest design. The 'H' design would work, but simple flow dynamics indicate that an angled crossover is more efficient in its affects to create low pressure in the adjacent pipe aiding in the evacuation of exhuast gases. I will be using the 'X' style crossover so i can retain shotgun style exhaust. This is obviously for style points only, and that is the only place fashion will out weigh function. After the crossover it really doesn't matter what you do with the exhaust pipes, as long as you don't restrict the flow.

RB

[Norm]

I've been building custom exhaust sytems for years as well as testing some others. All my work has been with the 900 based motors in various displacements. While I understand the "benifits" of crossovers & equal length pipes & have a lot of experience with tuning big block Chevys, I find the 900 based Ducatis don't really care much. I never use xcross overs anymore & while some exhaust lengths are pretty close to even, some are 4-6 inches different. Standard exhaust theories just don't seem to apply to these motors. I would assume the 800 charactoristics are pretty close to the 900, but I have no FHI.

[RB]

Norm,
Glad to here from you ,and thanks for your input.
If i go the route you are suggesting, then this build will be cheaper and quicker then trying to shove a crossover in the mix. And i would assume the characteristics of the 800 is similar to the 900 as well. I have to question why other manufactuers are putting crossovers in their pipes then. I say that because they are not correct lengths to the crossover, and they cost more $$ to manufacture....so why do they do it? let me qualify my statements here,....i only know what i have read about exhaust building and have very little experience building an accurate and efficient system. I have cobbled exhaust together before, but with no regard to performance, just tone.

[brad black]

make the system to fit the physical contraints of what you have and put an X or (if you have to) open H cross over as close as you can to the heads.  in reality the closest is the same place the factory do in the older stamped header sets, but a muffler on each side makes that easier.  you have to turn them both out the right side.  i wouldn't Y them into a single pipe.

modify the above to make it look like you want it to.

with these engines theory tends to bend over for reality, mainly being style and practicality.

in my experience no cross over will hurt them from around 7,000 rpm upward, the extent might vary with pipe diameter.

[RB]

thanks for the info brad

[truckinduc]

im designing my exhaust too. After i build the rest of my bike. Would anyone like to offer why they dont like equal primary length, 2 into 1 designs?