Muffler questions!

[The Doctor]

Ok! So I'm revuilding a 71 cl450 and I want to make a customs set of pipes for it but I couple of questions raised!

When do you have to rejet? or how do you know to rejet you carbs when changing mufflers?

and

What is the performance difference between a 4 to 2 and a 2to 1 and a 4 to 1 etc??

thanks!!

[pvo22]

I don't know the answer to all your questions but might be able to help you a little as I'm planning on building a set of custom pipes for my 84' Nightawk 700.

You can check your plugs to see how lean your bike is running. If your plugs are black then the bike is too rich, if the plugs are white then the bike is too lean. You want plugs that look a nice creamy color. Also since the bike has several different jets that all correspond to different throttle positions you may want to check the plugs at those different positions to make sure your not starving the bike of fuel at a certain rpm. For example you would want to check the bike while at full throttle to see if the bike is getting enough fuel from the main jet. I believe the bike will also back fire if running too lean.

Depending on what kind of exhaust you put on will probably be the deciding factor as to whether you have to rejet or not. If you don't put a muffler on and run straight pipes I'm guessing your bike will run leaner because there will be no back pressure anymore. If you are going to use a muffler there will be a better chance you won't need to rejet. It depends on how much back pressure your muffler gives you.

I haven't built my exhaust yet but I bought a universal Supertrapp muffler that comes with discs that can be inserted or taken out to help with tuning the back pressure. Basically the more discs the more back pressure and vice versa. You may want to look into something like this.

I don't know what the performance differences are between 4-2, 2-1 and 4-1 if there are any. I'm going to make a set of 4-1s in hopes of achieving a better sound. I will also drop some weight since I have 4-2s on right now.

The other question that I have thought about is does the length of the pipes have any impact? I haven't got a definitive answer from anyone but I think it does. When I build my exhaust I am going to try to keep all 4 pipes that connect into the one the same length because I believe the pipe length factors into back pressure too. I don't want one or two cylinders having more back pressure than the other two (this I believe would cause those cylinders to run richer than the others). I have one carburetor for each cylinder though so I think I can tune so that all the cylinders run equal regardless of a slight difference in back pressure.

Also you will probably want to bend the pipes at fairly similar angles because I think the amount the pipes are bent affects back pressure as well.

[The Doctor]

Cool! Thanks for the response! Look what I found, is an utility to help you calculate the exhaust lenght to maximize performance. It might help you out too!
http://www.nightrider.com/biketech/calc ... length.htm

Keep me updated on your pipes build!

[pvo22]

Thanks for the link. I will have to figure out what the opening point is of my exhaust valves.

I will keep you posted on my build but it will be awhile before I get around to doing it. I still have to finish this semester of college up first. Then I can go home and get the bike out and do some work.

Also let me know how your pipes turn out.

[The Doctor]

I'll keep you post it. I got a lot of stuff to finish on this bike before I get to play with the pipes. It's a full rebuild and with school and work is hard to find a lot of time for it but I just finished the Engine just needs to be polished.

If you want to take a look at the rebuild go to http://motozin.spaces.live.com

[pvo22]

I had time this weekend to cut up my exhaust. It took me all of Friday and Saturday to get them put together but I like the way they turned out. They sound really nice, much better than stock. All I have left to do is rejet and paint my pipes.



Where to start?



That should look nice





The 4-1 cone was a pain



But I made it



1 down 3 to go



1 left



All done







And Installed!

[mydlyfkryzis]

Ok! So I'm revuilding a 71 cl450 and I want to make a customs set of pipes for it but I couple of questions raised!

When do you have to rejet? or how do you know to rejet you carbs when changing mufflers?

and

What is the performance difference between a 4 to 2 and a 2to 1 and a 4 to 1 etc??

thanks!!

Since the CL450 is a 2 cylinder engine, your choice is either 2 into 1, 1 pipe out of each cylinder goes into its own single muffler, or a 2 into 1 setup, where the 1 pipe out of each cylinder merges into one pipe and a single muffler.

Performance issues depend on many factors. The length of the pipe, how much back pressure, valve timing of the engine, the type and length of the bends in the pipe. 2 into 2 systems sometimes use a connecting pipe so the 2 mufflers are shared. This can increase or decrease back pressure depending on the design, and depending on what is needed.

I personally have put on a 2 into one system on my CB360t. the performance gain was not just better "exhausting" but a serious weight reduction over the stock system. OEM systems use double wall pipes and heavy contruction in the muffler. the aftermarket type are usually single wall (which discolors with heat) and much lighter muffler construction. You may save as nuch as 30 or 40 pounds depending on the original system. The lighter the weight, the faster the motorcycle, given similar engine tuning.

Exhaust designs usually cause a leaner fuel/air ration because of better exhaust scaveging, bit not always.