"Exhaust" Vs Pipes - Kawasaki Ninja 250R Forum
 
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post #1 of 7 (permalink) Old 08-16-2009, 02:35 PM Thread Starter
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"Exhaust" Vs Pipes

My 09 is my first streetbike, I have finished the initial mods I wanted, now to address the exhaust. Here is my question, I've seen all sorts of exhausts out there, from wild to mild. I really like the look of the Hot Bodies megaphone for the ZX6, but I presume it wouldn't work??? Looks like the ZX6 has the "muffler" under the bike so it wouldn't be running straight pipes like if I put the "pipe" on my bike.

That said, why couldn't I run "straight pipes" much like a chopper? Would it hurt the bike?? I presume it has something to do with the backpressure but am not 100% sure since this is my first street bike. Being a car guy, I know running open headers isn't a big thing (or bad for it).... And I already know it will probably be loud as hell, but I'm not really concerned with being "to loud"... Loud pipes save lives right???

Since all you guys and gals are the coolest I've met, what say you before I start banging away at some metal stock I have and trying to fab up a cool "exhaust"???? I'd like to know if "straight pipes" would be OK on the bike and not ruin anything... I will have you know I barely have 100 miles on it so far since it's been so rainy here after I bought it and not sure if that matters (I have awesome timing, been a drought all summer, I get my bike and it's been raining sometime everyday since) THANKS RAIN GODS!!!!

Thanks everyone I REALLY appreciate it!!!

Shifty
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post #2 of 7 (permalink) Old 08-16-2009, 06:34 PM
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Its not about back pressure. Back pressure is restriction. It is about scavenging.
Scavenging is about inertia. The exhaust charge is accelerating out of the cylinder, and into the exhaust. After the exhaust valve closes, the exhaust is still racing down the header and toward the tail pipe. At a certain point during its journey, the exhaust charge starts to pull a vacuum on the header and immediate exhaust pipe. This is the ideal time for the exhaust valve to open again. The vacuum from the previous stroke should help "suck" the cylinder free of exhaust(remember, we are talking about engines here).
The same goes for intake manifolds, except the opposite. Instead of a vacuum being formed, a mixture of compressed(at least more than atmospheric pressure) air/fuel form right at the head, ready for the intake valve to open. RPM is critical for these events to line up.
The length and diameter of exhaust and intake manifolds determine the RPM of optimum efficacy.
Late 90s Ford engines (the 4.2LV6 in the F-Series trucks comes to mind) actually used a butterfly in the intake manifold to effectively double the length of the intake manifold runners to make the engine perform better across the powerband. The 4.2L engine ended up being junk, but the theory makes sense.

All I am getting at is... be careful of exhaust mods. You may actually free up restriction, but reduce overall power. Almost all of these after market exhaust systems have been developed by PHDs and dyno tested. I think you would be much better off buying an off the shelf exhaust system.
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post #3 of 7 (permalink) Old 08-17-2009, 07:32 AM
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Quote:
Originally Posted by Shifty418 View Post
I'm not really concerned with being "to loud"... Loud pipes save lives right???
Not really.

Quote:
Originally Posted by Kenny View Post
All I am getting at is... be careful of exhaust mods. You may actually free up restriction, but reduce overall power. Almost all of these after market exhaust systems have been developed by PHDs and dyno tested. I think you would be much better off buying an off the shelf exhaust system.
I agree.
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post #4 of 7 (permalink) Old 08-17-2009, 02:44 PM Thread Starter
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Thanks!

Thanks much folks... Makes sense, perhaps my "loud pipes" comment was a little too sarcastic, see alot of that sticker around town on the country boys with boat exhaust on their trucks.

Anyways, I think I'm going to go the shorty exhaust route for starters and see how it goes, I'm big into the DIY scene and looks pretty straightforward. I'll let you know how it goes!!!

Thanks again for thanks again for the input folks!!!

Shifty
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post #5 of 7 (permalink) Old 08-18-2009, 10:05 AM
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Yeah, it's thrown around quite a bit here too, and it doesn't help in trashing the myth to pieces.

Anyway, post up pictures when you are done. A video with the before/after sounds would be cool too.
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post #6 of 7 (permalink) Old 08-18-2009, 12:12 PM Thread Starter
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HA HA! Now you're getting technical on me! I can't even post a pic let alone a video on here

Forum idiot <<<<<<<<<<<<<<<<<<<<
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post #7 of 7 (permalink) Old 08-19-2009, 07:08 AM
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No worries, we'll walk you through it
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