'82 650 Exhaust Replacement

Help!! I did a horrible sin and threw my exhaust away!! Ok it wasn't like that completely, it was all dented and I pulled it off and am now looking for some aftermarket/performance type exhaust. Anyone have any ideas? I am looking for something that sounds badass and looks the part. Should I just have a system custom built by my local exhaust mech? Buy stock and reinstall? I still have the headers on, those are still in good shape.

I just got my bike a week ago and am new to the site. Any help would be much appreciated!

 

Stock exhaust flows well. Doing a 4:1 is also a thing. My bike came with one from the early 80's.
I'd look on e-bay for stock. I hear Mac makes a decent 4:1

 

Make custom made 4in1

 

@dkavanagh is right, the stock flows well and doesn't start messing with jetting. And from what I've read by searching this site, doesn't sound all too much fun.

That being said, my exhaust was shot behind the collector box, so I have it currently switch out to HD sportster pipes which perform well AFAIK and haven't forced me to make any changes. Do you still have to the collector or is that gone as well?

 

I prefer the look of the stock 4 in 2 to anything else I have seen. My xj700n came with a shiny new 4 in 1 and I am putting the old 4 in 2 back on. Depends on your budget too.

 

I have the headers and thats it, up until they turn aft. What about custom 4 to 4? I found this build, what are your thoughts? Would this require any rejetting? Don't hate me, but I am not a big fan of the MAC 4 to 1 or the original exhaust design.....I just don't like they look. But I will put them on if thats all I can do.

 

A 4-4 will need rejetting. The collector box performs a job that helps to get exhaust gasses out of the combustion chamber. It's not as critical as on a 2-stroke, but it does help with power development.

Looks don't help a machine go (usually).

 

As @k-moe said, 4-4 will require rejetting. If you are looking at doing pods as the image you posted has done, then you would be looking at rejetting anyways though. FYI, many people on here recommend keeping the stock airbox as pods seem to cause quite a bit of aggravation. But hey its your bike so do with it what you please!

 

I too like the look of 4 into 2 better than 4 -1 but I went with 4 - 4 straight exhaust.
My bike always ran rich, dark sooty plugs. Since I added a foam UNI filter and the striaght exhaust the plugs are much closer to the clean whitish colour they are supposed to be. I like the look and the sound.
One unexpected benefit was the oil filter is now much easier to reach and replace.


https://www.flickr.com/photos/giarc_dranrab/albums/72157619563031532

 

K-Moe you make me feel bad for wanting to do things to my bike. But I understand where you are coming from and what you mean. Craig B, glad to hear that the straight 4 to 4 is working for you. What kind of mufflers/collectors did you use? I see the exhaust tape, are those pipes connected underneath or just close together that it was easy to tape them both at once?

 

No mufflers. Straight pipe. No collector.
The shop I was working for at the time had an exhaust bender so i fabricated them myself.
Wrapped what I could indivigually but in some spots it was easier to wrap both at the same time.
Forget what diameter the pipe was but it fit just nice over the stock head pipes.

 

Awesome, that must sound pretty sweet. Picture says 2005, still runs good after all those years with that exhaust?

 

Runs the same as the day the pic was taken.

 

Go ahead and do things to your bike, just be smart about what you do and have realistic expectations of the results. There's nothing worse than pouring time, money, and sweat into a project and having it turn out to be less than you expected.

 

I don't know what you're talking about -- my new gas tank trim makes my bike go so much better around the ladies.

 

it is easier to get bike running right with stock setup first, then go to what ever mods you want. it eliminates problems that you may run into and getting a better diagnosis of any issues that arise from the mods..
stock exhaust every thing stock then ride this summer. do your mods this winter and you will have something first hand to compare it to.

my clymer book came with a list of performance mods to do to a 550 a 4 step program. most of the add ons are no longer available.
started with exhaust , then cams, then carbs (nonCV) then pods.
then continued to drag strip mods , struts and wheelie bar for full throttle starts off the line.

 

I have a theory to why it might work without the collector pipe. The diameter of your straight pipes might add enough back pressure to the system that the engine runs close to what it did to before you did it. If you did headers to 3 inch pipes/mufflers with no baffle then the exhaust will flow like a $2 [Let's keep it clean]. Le sigh

@SpectrumFighter if you do go to straight pipes it would be interesting if you compare the ride some how. Maybe documenting what the spark plugs look like pre and post exhaust changes.

 

chacal posted a lengthy write up on the yamaha exhaust system. I will see if i can find it

read it in this thread

4:1 Exhaust vs 4:2

 

Thats a nice read. However a lot of that is an educated guess. A good guess at that. I don't want to sound like some of the other people here and throw out fancy words or try to kill ideas that conflicts with my own ideology. SO in the spirit of having a proper discussion on the topic here are my thoughts...

After I read the article it made me question things more about sharing the exhaust back pressure. While the firing order/frequency definitely add's to the pressure build up I would think it would be a balance of exhaust flow + pressure. When you drop down to a smaller diameter pipe it will increase the air speed and flow and can potentially solve the pressure problem. Keeping the exhaust pipes separate and independent could help the problem as well.

Another theory....If cylinder 1 fires and lets say the back pressure is rated at 3 and when #2 fires it doubles it and is now rated a 6. How is the exhaust pressure mixing with cylinder 2? The yics system? If so then just block it so all exhaust pressure stays within each cylinder. Blocking the yics ports will stop all compression and gases from mixing. Also if everything is connected through yics then why isnt cylinder 2 and 3 sharing back pressure. In other words the theory of sharing exhaust pressure pre collector pipe seems wonky. I would think the collector pipe tries to fix a problem that is created by the yics system. Block the yics and potentially you can use any exhaust you want.

This is my theory. Don't take it as a fact or an alternative facts.

vagina

 

Back pressure: The myth and why it's wrong.

"One of the most misunderstood concepts in exhaust theory is back pressure. People talk about it with no real understanding of what it is and what it's consequences are."

Link to a good article regarding exhaust. I have built many a custom exhaust in my proffessional career but this article explains much more simply than I could here.

Put simply an exhaust on a 4 stroke engine should have zero backpressure. Any pressure build up reduces the engines efficiency.

http://www.gomog.com/allmorgan/exhaustbackpressure.html

 

The exhaust system begins with 4 little equally-timed exhaust ports. What happens prior to combustion (YICS) has little to do with this. Something smells fishy, oh never mind.

 

I actually read that article the other day. Good read. What i know from experience all vechicles need to have exhaust move at a certain speed to be efficent. Correct?

When you have a system like we have the cross pipe or collection pipes creates a specific flow rate that balances the exhaust flow. Am i wrong? Doing so it creates pressure in the pipe that goes out the end of the exhaust. Since air does have a mass it creates a negative pressure that goes against the outward flow. Think of blowing through a small straw vs big straw. This negative flow of back pressure is in all exhaust systems. The more twists and turns it has the more pressire build up it creates. If our bike are meant not to have backpressure then the collector pipe is moot. Running straight 4 to 4 exhaust would be best.

 

Personally I think we need to stop using the term backpressure. The term confuses many.

Each exhaust pulse creates a negative or (area of low pressure) behind it.
When a header or tuned exhaust manifold is used that negative area actually helps pull the next pulse through.

On a bike with a common collector to be honest I think all it does is allow the exhaust to be convientally divided into two tailpies.

 

I like to provoke conversation anyway i can. While i respect the wisdom and expertise this site brings. I also think some of it needs to be taken with a grain of salt. OEM parts are great, aftermarket are even better cause they are cheaper. Only if they fit. Mechanically i cant argue, chaps here can school me on piston sizes, temp ratings, shim calculations even fork replacements. When it comes to thinking out side the box and trying new things... i'll be the first to raise my hand. If a part i bought off ebay that was meant for another bike for $20 doesnt fit or work out, hey.. i tried something new. Questioning something silly like exhaust, or how to make pods work... i can do it all day.

Now to play devils advocate, if removing the collector screws with high and low pressure ratio, which it possibly does. Is that the reason why they say to rejet to allow a larger combustion to compensate? This is what i am picturing in my head.. the exhaust values open to let out dirty oxygen reduced air. Since the pressure in the exhaust is out of wack it cant escape fast enough, some of it gets traps back in the combustion chamber, next spark comes and the combustion its not as strong and makes you run lean. When you rejet and colortune you are basically compensating for that. Since i am running pods and rejeted i cant test your theory on the collector. Me personally, i think the right diameter straight pipe is the key. High/low pressure/back pressure its all about the flow.

 

Don't get me started on the antiquated YICS system. talk about conspiracy theory. Rothschild level.

 

Here's my example of aftermarket exhaust. Akrapovic slip-on on 4 in 1. I did however have to make angled adaptor/coupler. There was about 7 degrees angle between 4in1 and slip on. Coupler kinda bridge them out. Sounds badass revving above 6000 rpm and up, it's not obnoxiously loud idling but it has that distinct deep growl.


Some sound test video here

 

@

What did you use for the 4 in 1 part of your exhaust? The Mac? Some of my ring nuts are epoxied up from the previous owner. Would I need to rejet after this? I've seen your youtube videos before and I have all sorts of questions for you! Thanks in advance.

 

The YICS system is on the intake side, and does not see any exhaust gasses (aside from the very small amount that may occasionally not be scavanged from the cylinder.
The purpose of the collector is to use the exhaust pulses to help remove additional exhaust gasses from the cylinder than can be removed by the piston alone. The same result can be achieved with a well-designed 4-1 manifold.

 

although mine is a 750, I'll throw in my 2cents. Not sure what the differences are betwen 650 and 750. Never rejetted my carbs and have had no problems after 5 yrs of riding...

 

So, Bohemian.....I thought you sold that awhile back------whatcha riding now?

 

That is a amazing bike!

 

Thanks Reuben the build thread is here
Nope Hogfiddles, VooDoo is still casting her spell on me I was thinking about selling it when we sold our house in November of 2015. We moved in to our new home in December, and I'm getting ready to break ground for a pole barn, but after looking at the cost of concrete I may need to thin the herd to pay for a floor Got VooDoo and my 01 750 Honda ACE, plus my 82 CB900 I was starting mods on when we moved.

 

You can opt to pour part of the floor now, and the rest later. A neighbor in Oregon did that and it turned out well. After a few years you couldn't tell that the two halves had been poured three years apart.

 

Hey @Leo Chevalier come to my Desert military thread and ask me anything you'd like to know. Better keep this thread for one bike.