Slip on lose power? Exhaust flapper valve just for noise? - Honda CBR1000 Forum : 1000RR.net
 
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post #1 of 9 Old 08-14-2019, 09:37 AM Thread Starter
Alice
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Slip on lose power? Exhaust flapper valve just for noise?

I want to install a slip on exhaust on my new 2018 cbr1000rr. I have done some searching and it seems like a short pipe will lose low end torque. That's important for me because I ride on the street and need smooth power from the low end. What about a slip on of similar length to the stock muffler? Will removing the exhaust flapper valve also make the low end suffer, or will it be the same as stock?. I want it for looks and sound, but not at expense of performance.
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post #2 of 9 Old 08-14-2019, 01:44 PM
child_of_fire
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It's my understanding that the flapper is more for noise abatement than it is for performance. As such a slip on will reduce back pressure and could certainly affect low end torque which is why a tune would be necessary. This way your gains will make up for any negligible loss you suffer.

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post #3 of 9 Old 08-14-2019, 04:04 PM
bored&stroked
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A slip on normally does nothing for performance in either direction. You don't need a tune after, and you won't feel a difference in power. Its just a noise and sound mod.
Removing the slip on and running a tip that ebay sells as a muffler, that's different. Also, toce and taylormade are known to loose power in older models from actually being more restrictive then stock.

'06 F4i: racetech front springs+valves, ohlins rear shock, steel brake lines, 'mura slipon, 87K miles
'08 600RR- steel brake lines, shorty brake lever. Stripped track bike.
'15 1000RR- Flapper mod, 08-11 gauge swap, hotbodies fender eliminator
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post #4 of 9 Old 08-14-2019, 04:41 PM Thread Starter
Alice
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Quote:
Originally Posted by bored&stroked View Post
A slip on normally does nothing for performance in either direction. You don't need a tune after, and you won't feel a difference in power. Its just a noise and sound mod.
Removing the slip on and running a tip that ebay sells as a muffler, that's different. Also, toce and taylormade are known to loose power in older models from actually being more restrictive then stock.
I would probably go for the Arrow Race Tech slip on, it looks about the same size as stock. Or maybe the Akrapovic slip on with the valve?

Are you sure that ditching the exhaust valve won't affect low end power? What about backpressure? (What is backpressure, incidentally?) Is the exhaust valve purely for noise limitation? Did you notice that Ducati uses an exhaust valve on the MotoGP bike?
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post #5 of 9 Old 08-15-2019, 05:42 AM
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The exhaust valve is for noise but also is critically important for efficient exhaust scavenging at lower engine speeds. From Honda's press release, the EXUP is used to decrease the effective diameter of the exhaust pipe and increase exhaust velocity. I don't know if that's true or not, but from my experience removing the EXUP valve disrupts idle quality and that is very difficult to be compensated for with fuel or ignition timing adjustments.

Imagine a garden hose. When there's a little trickle of water, water doesn't spray out very fast. Water is trickling out, not really a steady, constant, or even flow and it might even sputter (lope) a little. So you cover it with your thumb and now it squirts out faster in a continuous smooth stream. That's like an engine at low revs. Now imagine a garden hose hooked up to a fire hydrant. There's a huge gush of water coming out very fast and you don't need to cover it with your thumb to make it squirt out efficiently. Your thumb is the EXUP valve.

Taking out the EXUP valve does absolutely nothing to the high end torque or power because that's when the valve is open and not really doing anything. Low end is hard to tell from dyno's because most dyno graphs don't even report anything below 2-3k and certainly not at part throttle where the valve would actually make a difference.
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post #6 of 9 Old 08-15-2019, 11:12 AM
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Throw on either of the cans you like and enjoy the the sound, you wont notice anything else.

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post #7 of 9 Old 08-15-2019, 12:29 PM
benya
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Quote:
Originally Posted by 09_Blade View Post
The exhaust valve is for noise but also is critically important for efficient exhaust scavenging at lower engine speeds. From Honda's press release, the EXUP is used to decrease the effective diameter of the exhaust pipe and increase exhaust velocity. I don't know if that's true or not, but from my experience removing the EXUP valve disrupts idle quality and that is very difficult to be compensated for with fuel or ignition timing adjustments.

Imagine a garden hose. When there's a little trickle of water, water doesn't spray out very fast. Water is trickling out, not really a steady, constant, or even flow and it might even sputter (lope) a little. So you cover it with your thumb and now it squirts out faster in a continuous smooth stream. That's like an engine at low revs. Now imagine a garden hose hooked up to a fire hydrant. There's a huge gush of water coming out very fast and you don't need to cover it with your thumb to make it squirt out efficiently. Your thumb is the EXUP valve.

Taking out the EXUP valve does absolutely nothing to the high end torque or power because that's when the valve is open and not really doing anything. Low end is hard to tell from dyno's because most dyno graphs don't even report anything below 2-3k and certainly not at part throttle where the valve would actually make a difference.
This is a great analogy. Notice the Akrapovic street legal slip on has two pipe outlets switched by the valve. A garden hose sized, and a fire hose sized.
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post #8 of 9 Old 08-16-2019, 08:04 PM
TedEbear
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Quote:
Originally Posted by bored&stroked View Post
A slip on normally does nothing for performance in either direction. You don't need a tune after, and you won't feel a difference in power. Its just a noise and sound mod.
Removing the slip on and running a tip that ebay sells as a muffler, that's different. Also, toce and taylormade are known to loose power in older models from actually being more restrictive then stock.
That wasn't the case with mine. I put a Taylormade on my '08 and it tests at 160 hp on the dyno.
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post #9 of 9 Old 08-20-2019, 07:30 AM
benya
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The Aprilia V4 opens the exhaust valve permanently when the race map is loaded. I understand the CBR1000RR is an inline 4, and a V4 naturally makes more low end torque. Maybe the Aprilia can get away with losing a bit of bottom end? Maybe the race map compensates with higher etv openings down low? Or maybe that valve really is just for noise? That seems to be the consensus on the Aprilia forum.
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