I was wondering if any of you Gurus could explain how an aftermarketexhaust affects the air/fuel mixture. Is it related to back-pressure?
Specifically want to understand how you end up with a lean/rich condition from a part that is downstream of combustion. I'm guessing it has to do with air velocity....?

Thanks in advance for the education....

 

I'd actuallybe curious about that too.

 

Just like you said GC. it's the extra air velocity that leans out the fuel mixture. to compensate, you would need to re-jet your carbs, or reprogram your ECM if you have FI.

 

Without back pressure, the velocity is normally increased. Less scavenging is happening for the other cylinders as well. So more fuel needs to be pumped into the engine to reach your a/f mixture.

 

The problem with changing your exhaust is that it drastically upsets the delicate balance of hydrodynamics, back-pressure, and carefully shaped interior of the airbox, carburetors, and intake tracts that KHI spent more time and money than we public-road privateers will ever have, in perfecting. We civilians (and aftermarket exhaust companies) simply don't have access to the testing equipment, PhD's, and empirical knowledge that KHI does. And Dynos are sloppy measuring tools that can easily be manipulated to overcome any post-purchase ambivalence.) I've spent many months, read many books, and spent many thousands of dollars, but I'm still basically one of the lucky chimpanzees who gets to enjoy the rocket-ship ride.
A crotchity (but fast) old fugger once said to me: "Back in the 60's and 70's, we tried everything, including filterless air-horns of varying lengths, polished intake tracts (ha!), and megaphone exhausts to get an advantage over each other on the track. What we ultimately learned is that Mr. Kawasaki knows a lot more than Mr. K and Mr. N know about making a motorcycle go fast."
If you want a faster bike, don't destroy the machine you currently ride and cherish; buy a faster bike.

About the best evidence of this is Don Canet placing 17th in the 600-pro-class of the Daytona-200 (the same race that had Colin Edwards, Miguel DuHamel, etc.) on a STOCK Yamaha R6. [:-]

But it's your bike.
-CCinC

 

nice post carlsbad, interesting for me to read, I was interested in a cheap 2-1 I found, but after that I think I will save my hard earned cash

 

Yup thanks all for the info. I'm not gonna part with my slip-on's but I do at least have an idea of the effects. Time to do some reading......

 

I also wondered about this, good post. I was looking into the muzzy's for this spring and know I'll probably need to re-jet, but knowing the physics always makes me want to grab my wrench.

 

Good luck in your reads and understanding.