Custom Fighters - Custom Streetfighter Motorcycle Forum banner
1 - 20 of 61 Posts

· Perpetual Project
3,717 Posts
Discussion Starter · #1 ·
Before you say the obvious, "So we don't piss off the cops!" read on...

Ok, so I was researching a bit of the science behind exhaust flow, headers, mufflers, ect. today.

From what I've gleaned, it leaves me with one question: WHY do we run with mufflers?!? ("we" being streetfighters). The only aparent benefit that I can find from mufflers is reducing sound, otherwise they just impede the flow of exhaust causing increased backpreasure causing decreased power.

I guess I was always under the false impresion that you NEEDED a muffler to keep some extra backpreasure in the system. But from what I read it seems like the headers and midpipe are the only parts that really control backpreasure to a significant amount, and even then, less backpreasure is better!

Now everything I read said that for the best performance you would want the smoothest flow-through system as possible, with as little restrictions as possible (i.e. baffles). -which of course I know because all the aftermaket exhaust systems are better flowing/less resistance systems- So, if you were to not at all be worried about sound, wouldn't it be best to just run straight pipes hypothetically speaking? For some reason I also always thought that taking the can off my bike and running it around would be a big killer for my engine performance... am I wrong here or what?

I'm not gunna loose my muffler and ride around going deaf and bringin in the cops from miles around, but it would be good to REALLY understand this stuff. So somebody clear this up for me here. Would it give you more power if you removed your muffler completely, or not?:confused:

· hack
735 Posts
doesnt it depend on how the system is designed to run? if you just take the muffler off it will run like crap, but you can adjust for it being gone??

1,865 Posts
dragsters run with no mufflers cause they run a super high rmps all the time. They rebuilt alot too. Since we don't run at 18000 rpms all the time, we need backpressure so we can deal with the low end curve of our motors.

Also Milage. Track what your gas milage is with the pipe for a week and then run a week with out a bike, Don't be surprised that your gas cunsumption goes up 25%.

· the mad doctor
3,416 Posts

If you ran an open exhaust, you can tune it to run "ok", but you'll lose all kinda of low/midrange power. it will SCREAM at high rpm though. same goes for the intake tract, you can put big huge carbs or whatnot on a bike, or leave the filters/airbox off and run open velocity stacks, but you need that little bit of restriction to have any kind of decent low/mid range power.

that's the whole reasoning behind intake flaps/exhaust valves. you get the slight restriction at lower rpms to boost power in that range, and the valve opens at a higher rpm to allow the better flow needed for the most power at high rpm.

· Senior Member
236 Posts
You can tune your bike to do all kinds of things. Mufflers are for sound suppression. You don't "need" them. The perfect exhaust would have no mufflers and no back pressure. The exhaust would have to be designed specifically for what is desired. In general, wide short pipes equal power at high RPM's and high horse power, narrow long pipes equal power at low RPM's and high torque. Same for the intake side. The entire exhaust and intake need to be tuned to each other for all this to work properly.
When a bike comes from the factory it is tuned to run with everything designed together. That is why if you get just a K&N or just take your mufflers off your bike runs like crap.

Bottom line: You have to tune intake, fuel, and exhaust to work together or you are wasting you time.

Let me know what you guys think.

· Function IS Form
19 Z900, 88 Kat11
17,636 Posts
I'm not even going to get into this whole bullshit backpressure thing. Backpressure isn't what makes your bike run like shit when you take the mufflers off, it's the lack of ability to compensate for the increased exhaust flow.

· The Soft Serve Enigma
16,791 Posts
Sev's a prick...I try to be a nice guy and let him use my pc and this is the thanks I get...You my friend, are a FUCKTARD. Get off my couch, and leave my coke in the fridge. Bitch.
1 - 20 of 61 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.