Why are performance exhausts upswept?

[-deuced-]

I've been wondering about this. It's not exactly a new design, Ducati has been doing it for years on some models. Norton Commandos had upswept exhausts. Even remember seeing it on the old Honda fours that had stock exhausts replaced with a 4 into 1, there was a kick up at the collector. Most of today's metric bikes have upswept exhausts. Is there a performance reason? Does gravity offer a bit of back pressure? Is it just for looks? Is it so the muffler runs level when the bike is up on the back wheel? If I bend my headers so my mufflers are upswept, will my hd go faster? I'm losing sleep over this.

[smokein]

clearance

[Ohio HD]

    The downward thrust gives better rear wheel traction...         

[rigidthumper]

 Import exhaust theory is put the intake in a high pressure area, and exhaust in a low pressure area. Ram air takes care of high pressure, and airflow should create a low pressure pocket at the exhaust outlet. Harleys are backwards- lo pressure at the intake, high at the exhaust   

[06roadglide]

If I bend my headers so my mufflers are upswept, will my hd go faster? I'm losing sleep over this.

I hope this is wrong or the people with baggers are gonna get ticked.

[14Frisco]

If I bend my headers so my mufflers are upswept, will my hd go faster?

Yes.  And please take before and after pics.

[04 SE Deuce]

deuced,  funny you question the upswept pipes,  I question the Harley exhaust that points at a slight angle toward the ground when being ridden.

Harley aftermarket exhaust companies tend to make pipes long, low and level to the ground kinda like afterbirth hang'n out of a mama cow that just birthed.  Both are about equally appealing to me.  I guess that is what the end user wants or at least a lot of company's interpretation.  I've mentioned this before,  a few years ago in a conversation with Paul Dean, (tech editor for Cycle World magazine and old guy that can flat ride),  he stated that the priorities for a Harley pipe and a sport bike pipe are almost reversed.  The Harley rider wants it to look and sound good, then maybe consider HP, and last is fitment/ground clearance.  Where as a sport/performance rider wants fitment/clearance, HP,  sound, then looks.   This isn't always the case obviously,  but basically true a lot of the time IMO. 

I couldn't run a lot of the popular aftermarket pipes for a softail.  A lot of them are needlessly low and fitment shows a lack of effort towards integrating the pipe to the bike and little regard for ground clearance.  Many of them are level with the ground on a stock ride height bike sans rider.  Add a rider,  passenger, lowered suspension and you have varying degrees of pointed at the ground when the bike is in motion...somebody else's idea of cool,  not mine.

If you notice the motorcycle manufactures try to fit/integrate the pipes to each bike model tucking them up and in to maintain as much ground clearance/lean angle as possible,  making the pipe look like it belongs and was made for the bike.  From a legal standpoint motorcycle manufacturers no doubt cover themselves by not crippling the lean angle and cornering ability of their bikes by making an exhaust system than hangs down off the bike.  The aftermarket tries to make one pipe fit as many bikes as possible (floorboards or pegs etc.) regardless of the shortcomings these "stick out" and "hang down" pipes create. The aftermarket seems perfectly content to make pipes that could double as a right side jiffy stand.

Other than a few odd creations,  leaning while cornering is unique to 2 wheelers and one of the most appealing aspects of riding a motorcycle IMO.  The first thing that drags when turning right on my Deuce (stock headpipes) is the footpeg...as it should be.   Rick

[IronMike113]

Volume is the key Item,Other than no scraping on pipe or pipes 

[Rags722]

Come on guys... You never stuck a hunk of tubing in a bucket of water, shot the air hose across the  top of the tube and watched as it drew the water out and sprayed it?  This isn't magic.  Same concept on performance bikes, speed of the air draws the exhaust out rather than using HP to push it out. 
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Anybody buying it???

[koko3052]

 
... finally got to use it!

[Ohio HD]

... finally got to use it!

Bill, that's for use in the AFR and Tuning Zone forum.     

[04 SE Deuce]

Come on guys... You never stuck a hunk of tubing in a bucket of water, shot the air hose across the  top of the tube and watched as it drew the water out and sprayed it?  This isn't magic.  Same concept on performance bikes, speed of the air draws the exhaust out rather than using HP to push it out. 
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Anybody buying it???

Ahhh no.  A lot of sport and roadrace bike have tips that re-angle the exit straight to the rear regardless of the angle of the pipe.  There's rigidthumper's low pressure theory.  Rags I knew you were kidding and looking for a nibble.  Rick

[calgary56]

Racing exhaust upswept so it doesn't create airflow turbulence, Harley exhaust straight out the back to kick up dust & dirt so the race bikes can't see well enough to pass

[JohnCA58]

... finally got to use it!

Bill, that's for use in the AFR and Tuning Zone forum.     

  They could use that over at the CVO forum, in the tuning section and a little of this   

[kd]

I recently read an exhaust article (who knows where??) that explained the reason track racers raised the pipes to the rear and actually tucked them into the low flow area created behind the bike on purpose. It actually created less drag and more high speed stability. 

[CndUltra88]

Did someone say ''NIPPLE"
Rob

[04 SE Deuce]

Did someone say ''NIPPLE"
Rob

  Fixed it just before seeing your reply.  Mades about as much sense either way.   Rick

[tomcat64]

Does gravity offer a bit of back pressure?

wow,, can you imagine how good these things would run on Jupiter!!!

[harleywood]

The main reason is cornering clearance from my sportbike days. Get the can up and out of the way.

[wavlovr1]

I can't believe no one got this... You can't upsweep Harley exhaust because the motor will fill up with rain water at the local bar and occasionally be used to snuff out a cigarette, spill a beer, or even worse be confused with a urinal....

[tomfiii]

Other than putting exhaust outlets at a preferred location these bikes don't have any mounting locations down low like a Harley!!!