exhaust theory

[brad black]

the problem with any theory on these engines is that the reality of getting the headers where you want them and looking how you want them to will dictate much of the system.  on an in line engine with ports lined up next to each other you can play with lots of stuff.  when they're a couple of feet apart and wrapped around an engine it gets harder.

no one has done any real testing either, so you'll never find the answers you are looking for unless you do it.

there is one graph i've done for something like this.  on my sport 1100i guzzi i made a full system (note to selve - next time, buy staintune) which was mild steel tube 45mm-ish od (1 3/4 with 1/16 wall i'd guess with 1 7/8 slip joints) headers into an X cross over under the gearbox about 75mm long and 50mm-ish (2") out of that into two long hindle TL1000S mufflers.  photo -> http://www.moto-one.com.au/performance/pics/sport1100.jpg  a seriously good looking bike in the (as it was then) 748 yellow.

anyway, i made it so the pipes out of the cross over were maybe 150mm or so long and then the muffler entry pipes slipped on to them - just under the footrest.  one day i made a cap for one of the out pipes and dynod it with one muffler removed and the pipe blocked.  it lost midrange mainly.  on the road it felt like it had lost midrange, but it felt like it was going to lift the front wheel on its own at the top end.  which it never did before (believe me, being long and heavy).  graph here - http://www.moto-one.com.au/performance/graphs/sp11g212.gif  it needed more midrange fuel for both these runs, but the difference was about the same overall and the tests were done back before i had good dyno technique anyway.

there's a few guys playing with the aprilia headers on the af1 forum on the bikes that have 2-1.  generally, going to a 2-2 on an early rsv or tuono will get you the 2-1 midrange hole filled and the same top end.  like a 999 or 1098, where the midrange hole seems related to the single pipe from collector to muffler spilt compared to a 998 with the same engine.  maybe the aprilia issue is the collector pipe diameter - it's big.  dunno.  i guess they tested and got what they could when they developed the bike.

http://www.apriliaforum.com/forums/showthread.php?t=142449&highlight=header
http://www.apriliaforum.com/forums/showthread.php?t=141552

might be off interest also.

[Rickoz]

Though this one needed a Bump 

[sbrguy]

so that is why crossover pipes are there to create a vacuum, that makes sense now.

[truckinduc]

well Im back. 

Ive decided on a 2-1-2 with no mufflers

Ill be building it soon

[ScottRNelson]

I have no evidence to back this up, but I think one of the big reasons most Ducatis have two exhaust cans is to meet noise emissions requirements.  You can buy a 2 into 1 exhaust for the Hypermotard from Ducati Performance.  In fact, their 2 into 1 into 2 on that bike is really one can in the tail with two outlets.  More volume to reduce noise.

[truckinduc]

Ya ive thought about that. 

I believe the tubing size - length and collector design is more important than 2-1-2 or 2-1

Ill be doing 2-1-2 for routing purposes, but the dual outlets will only be 4 or 5 inches after the single tube

[scott_araujo]

I have no evidence to back this up, but I think one of the big reasons most Ducatis have two exhaust cans is to meet noise emissions requirements.  You can buy a 2 into 1 exhaust for the Hypermotard from Ducati Performance.  In fact, their 2 into 1 into 2 on that bike is really one can in the tail with two outlets.  More volume to reduce noise.

Yup.  OEM single cans tend to be really huge on large displacement bikes, there's a lot of exhaust gas to move.  They get a little awkward.  Two smaller cans can be easier to mount and look better.

Scott

[truckinduc]

Plans have changed again.  New system will be full Ti 2-1 with under engine muffler.

[hackers2r]

I am still awaiting any opinions on 2-2 vs 2-1/2-1-2.  Any discussion would be greatly appreciated. 

[Langanobob]

Plans have changed again.  New system will be full Ti 2-1 with under engine muffler.

Can you post pictures of progress as you go?  (this coming from a guy who never posts pictures of anything  )

[truckinduc]

Yes I will. But the exhaust will be built after the swingarm and rear suspension.

So right now its alot of Ti tube sitting there.

[truckinduc]

ok. well its been long enough. Im finally back on this project.

The usable Ti tubing I have is 1.434" ID, very close to stock, and 1.685" ID.  Im wondering If I step up the diameter at a certain length from the valve if it will have any advantages.

Lots of newer bikes are using stepped exhaust now.  Anyone seen anything like this on a 2v Duc motor?

[monster monkey]

Another factor is back pressure. When certain motors perform better with a specific amount of exhaust back pressure. The "smart" guys in Italy do all the calculations so that our bikes meet the "standards" over here, yet maintain their ducati performance.

Once they get here, we get rid of the exhaust for a little extra HP because the "man" can't stop us!! 

FYI, I'm using the quotations gratuitously.......

I'm an auto tech, and have had the opportunity to "play" with different combinations of intake, exhaust, cams, etc... and a free flow exhaust isn't always the best

my .02

[Raux]

met a drag race bike builder once.

i asked him about pipes once. 2-2 2-1-2 2-1 etc.

he said all his bikes are 2-2 but basically straight pipes
the length is the key for him.

put a pipe on the bike longer than you think you need it following your route. put shoe polish on it from about 12-inches. back
where the shoe polish stops burning off, that's the length you need. no more no less.
but that's with straight pipes.

but my idea is that is should be the location of the cross over. and no i haven't tested the theory yet.

[scott_araujo]

met a drag race bike builder once.

i asked him about pipes once. 2-2 2-1-2 2-1 etc.

he said all his bikes are 2-2 but basically straight pipes
the length is the key for him.

put a pipe on the bike longer than you think you need it following your route. put shoe polish on it from about 12-inches. back
where the shoe polish stops burning off, that's the length you need. no more no less.
but that's with straight pipes.

but my idea is that is should be the location of the cross over. and no i haven't tested the theory yet.

Also, drag machine engines basically run in a very narrow RPM range where they need to make power.  The exhaust is tuned for that RPM.  Most other engines need to make power and torque at varying speeds, the exhaust is tuned to a compromise for many engine speeds.  That's why some more sophisticated engines have a variable valve in the exhaust, it allows you to vary the back pressure for different conditions.

Scott