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Discussion Starter · #1 ·
How about the engines need for back pressure (not sure if that is the correct word here, since english is not my native language) in the exhaust system, when increasing the intake?

If one, for example, open up the end can diameter a bit for more "exhale", and also modifiy the intake to get more air/fuel into the combustion chamber, will this affect the balance as much as decreasing the power in lower register or is it negligible in the context for a 4 stroke bike engine?

I´m thinking of this vid for example, from Low and Mean, where he states not only more sound, but also a bit more power:
 

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Discussion Starter · #2 ·
"If one, for example, open up the end can diameter a bit for more "exhale", and also modifiy the intake to get more air/fuel into the combustion chamber, will this affect the balance as much as decreasing the power in lower register or is it negligible in the context for a 4 stroke bike engine? "

No engine gurus around to bring light about this?
 

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Administrator "Loose Nut" - From Houston, Texas
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If you just change exhaust to a free flow system normally rejetting is not needed as no extra fuel or air is being put in. When you change intake to a free flow system then you must increase the jet size to compensate for additional air being introduced.
 

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Discussion Starter · #4 ·
If you just change exhaust to a free flow system normally rejetting is not needed as no extra fuel or air is being put in. When you change intake to a free flow system then you must increase the jet size to compensate for additional air being introduced.
- Bolt have fuel injection, so it is Power Commander to tune this bike.
But the main question - will a airbox mod produce that much extra air that requires a engine tune?
On my ZX7R´s the jetting is required when changing the complete exhaust system, not only the end muffler.
 

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Typically, if you open the size of the exhaust you might gain some top end, peak hp but loose the bottom end torque. Is the main goal, sound or performance? Gearing may accomplish performance with keeping the tune problem free. Exhaust upgrades can accomplish sound with keep the tune problem free.

I may be to old and conservative....:cool:
 

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Discussion Starter · #7 ·
Typically, if you open the size of the exhaust you might gain some top end, peak hp but loose the bottom end torque. Is the main goal, sound or performance? Gearing may accomplish performance with keeping the tune problem free. Exhaust upgrades can accomplish sound with keep the tune problem free.

I may be to old and conservative....:cool:
- Yes the most common result, one gain here another loss there.
But the question still is how much/little can be done in the "airbox vs. exhaust"-area without affecting the balance enough to require PowerCommander tuning.

And my idea of a minor increase in the intake/airbox and small holes in the muffler is only performance wise, not the sound. I don´t like a noisy Bolt. (my CBR1000RR is noisy enough..)
 

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Discussion Starter · #8 ·
I now have replaced the original air filter with a Ramair filter (in the original airbox), and also made five 8 mm holes in the end of the muffler.
This - i hope - will equal the potential disturbance in airflow formula and still give the bike a liiiittle more aspiration : )
I also replaced the retro looking round headlight with a rectangular, slightly more aggressive one.
Vehicle Automotive lighting Automotive tire Hood Motor vehicle
Peripheral Hood Input device Automotive lighting Automotive design


..and will change rear position lights with:
Automotive parking light Automotive lighting Product Natural material Electric blue
 

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Discussion Starter · #18 ·
Tuned ECU and the performance muffler installed.
Bike is clearly faster and harder pulling machine 🤩
I think it got appx 10 kg´s lighter, due to the replaced stock muffler with its heavy mount.

But..that "muffler", it is almost an open tube without any sound absorbing tissue within, so the modest growling from before is now replaced with a earbraking roaring. Too much! Waking the neighbours if i start the bike in the early morning for work.
 

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I am late to the party here. The only thing I would add is that it really doesn’t matter much what you do with the can. Aftermarket mufflers will provide a different tone to your liking and are freer flowing for small gains.

Headers however are usually tuned to a specific engine. This is to try to make the exhaust pulses travel down the exhaust pipes in a manner that times it so the pressure wave from one exhaust cycle has left and a slight low pressure area at the exhaust port is present when the exhaust valve opens for the next cycle. This is exhaust scavenging. It provides faster evacuation of the exhaust gasses and also partially pulls new fuel/air mix into the cylinder while the valves are over lapped. Good after market headers do this well - others may not.
 

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Tuned ECU and the performance muffler installed.
Bike is clearly faster and harder pulling machine 🤩
I think it got appx 10 kg´s lighter, due to the replaced stock muffler with its heavy mount.

But..that "muffler", it is almost an open tube without any sound absorbing tissue within, so the modest growling from before is now replaced with a earbraking roaring. Too much! Waking the neighbours if i start the bike in the early morning for work.
It's all about give and take .. get this , lose that ... Ain't that the $hits ...
 
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