Some feedback about jetting. I've been running about 4000 km's with the Laser 4-2-1 system now. Yesterday I checked the plugs and they are correctly colored, exactly as the "normal" example in the Haynes manual. I also have a KN-filter. With the stock downpipes and dual aftermarket mufflers, the bike runned on the rich side according to the plug colour. The bike had Dyno Jet needles already when I got it and the needles where set to mid position at that time.

So, I will not change the stock jetting which is #122. From examples I've got, people has only went up a few numbers in jet size after changing the exhaust. The reason my bike is not running lean is probably that I've rised the needle two steps, thats quite a lot. When the needles where raised that much, I had to grind off about 2 mm on the top of needles beacuse they bottomed in the holder and could not move sideways as they must not to carve the main jet pipe.

I've got a tremendous midrange pull after exhaust change, so the power is defintivly there, and it easily revs above 11 k even if that's meaningless since power falls off after 10+ k. The bike almost feels as strong as my GSX R1000 with about 170 hp (on the crank) when I have a passenger on that bike, without passenger the difference is of course hughe. The only reason I would go up a few steps in main jet on the CBR would be if the bike was runned on max rpm for extended periods but that will not happen. There is almost always a faster gear to put in if one need to go fast, and running for extended periods at top speed and full wind load at 255 km/h on #6 is not actual on this bike the way I use it.

 

Some update. I've installed the dB-killer (included in kit) since a few days to reduce the very high and long-term annoying sound level. It first it felt OK to have a sound like a fighter Jet, but in the long run and the way the bike is used for commuting mostly, the volume was far to high. The dB-killer from Laser was said to only reduce the noise by about 3 dB (about what the human ear can recognize as a change), maybe that’s right if one measures the noise level over the whole frequency spectrum. But the sound reduction feels quite more than 3 dB since the short insert tube kills the most intense noise transients effectively. The sound level appears to have been reduced by 50% to my ears. The engine still pulls very strong also with the reduced sound level, I would have to measure 1/4 mile and top speed very accurate if I would like figures, but I won't since the feel in the pants is the same and I prefer the more bearable sound. I guess it now sounds quite above a stock system even though I haven’t heard such since the bike was equipped with aftermarket mufflers when I got it.

 

Seems like we all want the same thing, an aftermarket pipe that sounds good but not too loud or expensive. I've read tons of info today and can't reach a verdict. Anyone?

 

Well, well, well, MR. Flying pig.
Yes we want it all but you can't have your cake and eat it too.

The 4-1 systems work by a high pressure traveling through the exhaust pipe when the exhaust valve opens. Since you can't have a high pressure w/o a low, it stands to reason that the low pressure follows the high. Think of a train yard where the high pressure is represented by a boxcar. If the tracks are setup correctly a boxcar passes through the intersection where the 4 tracks merge into one. That boxcar has a low pressure behind it drawing the next boxcar, so on and so on. That's why 4-1 systems look like spaghetti. They are tuned.

Due to this "sucking" action a free boost is created (delta P is higher) however low to mid RPM suffers as there is some leakage when the valves overlap. This condition worsens with aftermarket cams that are designed for high RPM. There is more overlap and the leaked fuel/air mixture ignites in the exhaust port causing a clog. To fix this problem the idle is turned up much higher to clear the ports. Bikes with 4-1 systems tend to be peaky and jumpy in city driving. With a system that has some backpressure, low to mid RPM is fine but you don't get the gains of a 4-1 system at 6,500 RPM and up.

I chose a Two Brothers slip-on. It installs in 1/2 hour, you keep the center stand, and you get increase in low and mid RPM where most of the riding is done. There is some increase in high RPM power. You get a deep crisp sounding idle and midrange. It is hard to tell with a helmet on but it sound to me that the sound level is the same as stock at highway speeds with normal throttle. I am very happy with my choice.

You must first decide what RPM you will be using your system at.
The Vance and Hines 4-1, I hear is a good system for track and drag racing, but very loud.

I hope this info helps you.