leo_black_label, I know what you mean. I hear that **** all the time.. 'powerloss..' 'no backpressure..' etc. I think its mostly BS. until I see some dyno charts, I'm stickin to it. I had my stock F3 at the strip just ****ing around. Ran it a few times. unbolted the factory can and ran my best time of the night.. not sure if it was the weight loss of the can or it actually gained a pony or 2... take it FWIW

 

thanks for some ACTUAL FACTUALS, kinyeddi!!
you ran straight pipes and the effect was at least even w. if not bettr than with the mufflr.!

people worry about weight enuf to buy carbon cowlings (actually often heavier than the stock plastic) and then never think about the several lbs. (couple/few Kiloz) of their cans?
i was really surprised how heavy mine was . thats not actually a big concern for me.
i just was surprised iz all...

 

In the original post, I recorded that on my phone which doesnt do it justice at all. My father's got a HD Dynaglide, upped to 1550cc with screaming eagle pipes. With the shorty on the CBR, although not as deep and ballsy as the HD the CBR is louder/more obnoxious.

As for power loss I did lose a bit in the low end. Instead of its perky nippy response it was a fair bit duller. But when I got into the fun zone around ~9k rpm the bike took off.

What mods are you planning for your pipe? I chopped up a old spare one I got from a breakers so I can easily swap back for quiet commuting. One thing Ill say is if you go down the shorty route is get a decent set of ear plugs!

 

You're going to lose power when, all else remaining equal, you reduce the back pressure. You can choose to believe it or not, but it's a simple fact that is very easily illustrated.

Our bikes are designed to run based on a certain amount of air flow going into and out of the engines. When you modify that air flow -- high flow air fliters, drilling holes in the air box, chopping the exhaust, putting on an aftermarket exhaust system -- it changes the way your bike breathes and changes the optimal A/F ratio on your bike. The carb's/EFI system on your bike is pre-set to work optimally with the stock can/filter/ram air/air box. When your bike is allowed to breathe more on either end, that optimal A/F ratio shifts.

This is why you need to rejet or re-map your EFI system when you put on an exhaust system or get a high flow filter/slip-on. Pretty much every company that sells these components even note this in their products' documentation.

You can choose not to believe it, but it only makes you ignorant and hard-headed. (keeping in mind that you may not notice the marginal power loss just from shortening your can) The fact remains that it does affect your performance negatively, even if only a small amount.

 

This is ignorant "science". It could have been the weight loss. Maybe your carbs/EFI are out of tune for your setup and this actually brought you closer to correct.

More likely than anything, you just had better launches, as this is the single most effective thing you can do to improve times at the strip.

 

Geez guys-
dont go away mad...
I KNOW that the backpressure is an important aspect of the combustion stroke cycle!!
all I wuz tryin to clarify is WHERE that back pressure could come from in a straight pipe w. no constraints to the exit flow.
It seems like thered have to be a cone or stepdown in the can to force the exhaust through a smaller aperature- i think its called "tuned exhaust" when you build it like this, but i cant find enough info yet to really understand.
the longer straight pipe would be harder to shove air through at first-but once the flow was established wouldnt it be the same - cause its all moving one direction like a sifon? seriously im not trying to discount ANY of the opinions/facts thet anybody here is willing to share! Im trying to keep a conversation going so i can absorb as much info as possible and build a better exhaust for my f4!
(if no spec. changes, at least lighter when i make it in carbon!)
Thanks for the Help all!

 

Who's mad?

I was just replying to you and yeddi and wanted to dispel any illusions of power gains with his "proof" from the strip. You were taking them as "actual facts" and I wanted to clarify that there are too many unknowns from his story to draw any conclusions.

I can't tell you much with specifics, and you may need an engineer in order to get the kind of details you're looking for. Short of happening on some secret research from one of the Jap companies, you're probably going to need to just either stick with some kind of typical setup, accept some power loss, or do your own kind of trial and error research.

I believe part of the backpressure, which I understand is the main thing the muffler is contributing beside the obvious sound deadening, comes just from the length of the pipe. So a header, midpipe, muffler setup is going to have more back pressure than just a header that dumps right under the bike kind of like you're toying with. After that, back pressure is surely created from the holes in the muffler which give a level of friction against the air moving through and also with some extra back pressure added from the packing. I'd think a step-down like you're talking about would probably increase back pressure, but you may end up with other adverse effects. Again, you'd probably have to do some of your own testing if you really want to know.

This all, of course, is totally based on intuition and just based on what I know of how it works.

 

thanks chuckbear- i was just thinkin about that still and i think youre right abot the holes inside creating friction- thats what i was missing- (one of many things)
and its only cause im ignorant that i may be oversensitive about it- haha
btw- did you see this fighter that was all custom scratch build and the aluminum exhaust instead of being holes adound the pipe leading out - the pipe is actually bridged all through by smaller pipes across its diameters layed out in a spiral? it would be like the rifling in a gunbarrel and the backpressure would be a controlled effect of the layout and the exhaust would come out spinning! i wonder if it looks like its spinning as the emgine runs? sorry that was a bad explanation. theres a link on here somewhere ill try to find it.

 

ok! i found the link to this AMAZING build slideshow- its worth watching wethr you like the style of the bike or not- the work that went into it and the photos are beautifull!
check out the exhaust design - ive never seen anything like this-

http://www.flickr.com/photos/qmoto/s...39350990/show/

itll only take a coupla minutes and it opened up whole worlds conceptually for me of what a fella with some powertoolz can do if hes inspired.

 

Damn, thats a bad *** cbr!