Straight pipe exhaust problems
- Thread starter eglintonw
- Start date
CALfeRacer
Fat man on a little bike
Adding length, baffles, and some baffling material are going to be the only ways to quiet it down, but if noise levels are an issue which is actually tested with a dB meter where you are, I doubt a few baffles are gonna be enough to be legal. Maybe look in to making a muffler which is of a slightly larger OD than your current pipe, and having a legit baffle and packing material in it.
HollywoodMX
Coast to Coast
Research loli pops. Keep in mind strait pipes are less performance.
High On Octane
Ton Up or Shut Up
Straight pipes are a joke. They are too loud, perform like crap, mess with the tuning, and further more, are illegal in all states. Not to mention they make the bike look incomplete.
High On Octane
Ton Up or Shut Up
I didn't realize you were down under. And everyone is entitled to opinions. If you prefer mean looks over actual performance, that's your choice. But be prepared to replace the exhaust valves in the future, straight pipes will burn them up.
crazypj
Split personality, I fake being smart
The title says it all.
Straight pipes are pretty crap for anything other than land speed record where motor is at max rpm.
If you want bike to perform at different rpm (like for instance, riding in the real world instead of fantasy island) you will need a real exhaust.
Anything you fit inside the pipes will lower the already low performance
Straight pipes are pretty crap for anything other than land speed record where motor is at max rpm.
If you want bike to perform at different rpm (like for instance, riding in the real world instead of fantasy island) you will need a real exhaust.
Anything you fit inside the pipes will lower the already low performance
CALfeRacer
Fat man on a little bike
Just curious for the sake of discussion... IF you were to make up a set of straight pipes that was a proper length how different would it be than putting a straight-through muffler (which I'm led to believe most of the aftermarket motorcycle ones are) of an appropriate length? Other than the obnoxious noise and illegality of course 
crazypj
Split personality, I fake being smart
The absorption type mufflers allow gas to expand before exiting so effective length changes depending on rpm, temp, packing material, etc. If packet too tight with 'rockwool' performance usually suffers (although max rpm power may improve)
A straight pipe works exceptionally well, over about a 500rpm range, varying the length can change where the 'benefit' will be but is usually a net loss.
I like to use the drag pipes on Harley Sportsters example (mainly because I've seen the dyno results and I can also remember some of the numbers ;D )
A stock 883 Evo Sportster makes around 43bhp. (yes, really, it does)
Fit drag pipes, it makes at best 37bhp but usually 35~36 bhp.
The pipes are a tuned length, problem is, the tuned length is around 2,500~3,000rpm higher than the engine is capable of turning.
With 'correct' cams, carb, induction system, the motor will produce closer to 100bhp (@9~9,500rpm)
A straight pipe works exceptionally well, over about a 500rpm range, varying the length can change where the 'benefit' will be but is usually a net loss.
I like to use the drag pipes on Harley Sportsters example (mainly because I've seen the dyno results and I can also remember some of the numbers ;D )
A stock 883 Evo Sportster makes around 43bhp. (yes, really, it does)
Fit drag pipes, it makes at best 37bhp but usually 35~36 bhp.
The pipes are a tuned length, problem is, the tuned length is around 2,500~3,000rpm higher than the engine is capable of turning.
With 'correct' cams, carb, induction system, the motor will produce closer to 100bhp (@9~9,500rpm)
CALfeRacer
Fat man on a little bike
So basically you get a peaky dyno curve, as opposed to something with a broad curve that doesn't peak as high. I watched a video yesterday where they were tuning a flat 6 turbo swapped subaru legacy (really cool build) and the ECU guy was talking about how they tune for broad power curve. Obviously this is engine management (VVT etc.) but concept seems to carry over.
Back to this example, if I'm understanding it right the ability for gas to expand within a muffler (absorption type) effectively increases the exhaust length, without physically increasing it. This brings it back in to the realm of hitting your peak HP at an attainable RPM, which you would have to have a MUCH longer straight pipe to achieve.
Sound right?? I've always been curious about the effects of exhaust length, muffler choice, etc. on an engine. Seems like too often short straight pipes are thought to be a performance boost. Hell, I used to think it was
Back to this example, if I'm understanding it right the ability for gas to expand within a muffler (absorption type) effectively increases the exhaust length, without physically increasing it. This brings it back in to the realm of hitting your peak HP at an attainable RPM, which you would have to have a MUCH longer straight pipe to achieve.
Sound right?? I've always been curious about the effects of exhaust length, muffler choice, etc. on an engine. Seems like too often short straight pipes are thought to be a performance boost. Hell, I used to think it was
High On Octane
Ton Up or Shut Up
No, not really. An expansion chamber helps mostly for scavenging exhaust gases from the cylinder itself. As pj mentioned, even pure race bikes don't run straight pipes. Not even on LSR bikes. A true race exhaust will be stepped in a few places, slowly increasing the size of the pipe, and then go into a free flowing muffler. I seriously think drag racing is the only auto sport that runs open headers. And they only get away with it because they operate at WOT for only a few seconds.
crazypj
Split personality, I fake being smart
The very first 'tuned length exhaust' was used in the 1860's on an industrial engine pumping out a mine.
It almost doubled power output to 12 BHP@200 rpm (yep two hundred revs)
Torque was up in the thousands of ft/lbs though (I'll have to find book to check actual numbers)
Pipe was over 100ft long ;D
It almost doubled power output to 12 BHP@200 rpm (yep two hundred revs)
Torque was up in the thousands of ft/lbs though (I'll have to find book to check actual numbers)
Pipe was over 100ft long ;D
High On Octane
Ton Up or Shut Up
FWIW It is also known as "wave length tuning".
stroker crazy
crazy as a fox
Sonreir posted a lot of very useful information on exhaust design in "Doing it Right" or "How to Build a Functional Café Racer":
http://www.dotheton.com/forum/index.php?topic=39814.60
Crazy
http://www.dotheton.com/forum/index.php?topic=39814.60
Crazy
CALfeRacer
Fat man on a little bike
I've read the whole thingstroker crazy said:
HollywoodMX
Coast to Coast
I disagree but that's fine. It's one of the more popular mods to quiet strait pipes coming from the number 1 users of strait pipes, the Harley boys. Countless threads out there with the success of queiting it down to some degree.hillsy said:
crazypj
Split personality, I fake being smart
When you use a pipe that is way too big diameter they kinda work a bit (HD using 1.75" or 2" pipes can afford to loose some 'flow')
Using stock double wall pipes, the inner will be sized closer to what the motor actually needs, restricting flow will cause a further power loss on top of the losses caused by incorrect exhaust length.
If you used a length of larger diameter pipe slipped over stock head pipes you could restrict it in various ways (including making baffles and absorption layer) to get a deeper sound that isn't totally obnoxious (in effect make a long thin silencer)
Using stock double wall pipes, the inner will be sized closer to what the motor actually needs, restricting flow will cause a further power loss on top of the losses caused by incorrect exhaust length.
If you used a length of larger diameter pipe slipped over stock head pipes you could restrict it in various ways (including making baffles and absorption layer) to get a deeper sound that isn't totally obnoxious (in effect make a long thin silencer)
CALfeRacer
Fat man on a little bike
The long thin silencer was what I was curious about and tried to get across in my first response. That way you could get the "look" but still have some sound reduction.
