Different length Exhausts

[muks]

Hi Guys,

Just after a bit of feedback. I broke the cardinal rule of exhaust building this weekend, I made different length exhausts. They are quite a bit different in length as the pics will show. I just wanted to know will I have trouble tuning this thing or will I be okay. I don't mind sacrificing a little performance for looks as long as I'm not battling to get it to run right, otherwise I'll have to rethink my strategy. Excuse the pics, I'm no Gordon Scott, and this is my first attempt having a go at making exhausts!

Any feedback welcome, what do you think of the exhausts? and the bike? This is my first go at building a bike, more of a car guy. I'm about to rebuild the engine and was thinking of just doing the top end, I don't know the history of the engine (never heard or seen it run) I should probably inspect the bottom end while I'm at it, I guess thats common sense but I'm reluctant as its all a little unknown to me. This site is amazing though and has been a wealth of knowledge, its certainly made it a lot easier.

Thanks Everyone

 

[hard_y_rd]

Me thinks the exhaust is O.K. Might rework that headlight and mount though.Kinda sitting out there in no mans land. Is that a one off hardtail. Otherwise bike looks good.

 

[muks]

Yup one off hardtail. Yeah the headlight is a little out there, excuse the pun, and not for everyone but I like it. Thanks for the feedback!

 

[jd750ace]

Pipe craftsmanship looks good. What diameter are they? They don't look like the left would be a great deal more restrictive, but the short length of the right might invite reversion.

 

[weaselbeak]

That headlight mount will most likely not hold up on an XS650, but it looks kinda cool.

 

[fredintoon]

Hi muks,
the XS650 engine was designed to run with back pressure and your open drains ain't got none so it'll be a bitch to tune right anyway.
What I'd try is to cuff a straight extension onto the short pipe so they're both the same length and see if it makes any difference.
BTW, love the headlight mount, looking weird is a good thing.

 

[Tomterrific]

Put a connective tube between the pipes at an equal length then jam some baffles into the ends or use mufflers.

I have to warn about having no rear fender. You have a chance of getting your butt stuck between the spinning tire and the seat. This happened to a fellow with a set-up like yours. It was not fun for him!

The headlight mount will break at the end attached to the fork. You can prevent this by triangulating the mount with a support going above the existing support.

Tom

 

[RatyXS]

^^ I like that idea also. It will help aid in scavenging.. Not a must but will help with some performance if thats what your after.. I would opt for a 45 deg kick out and down on those, would look even better but just my op.. Looks good, minus that way out light, again my op..

 

[muks]

That headlight mount will most likely not hold up on an XS650, but it looks kinda cool.

Thanks for the feedback weaselbeak. Definitely will have to reinforce the headlight bracket, don't want that sucker falling off, this is one thing I would never have thought off so thanks pointing that out.

Put a connective tube between the pipes at an equal length then jam some baffles into the ends or use mufflers.

I have to warn about having no rear fender. You have a chance of getting your butt stuck between the spinning tire and the seat. This happened to a fellow with a set-up like yours. It was not fun for him!

The headlight mount will break at the end attached to the fork. You can prevent this by triangulating the mount with a support going above the existing support.

Tom

Thanks Tom, as mentioned will stiffen up the headlight bracket. Was planning on running baffles but I think I may have to do as you suggested and put a connective tube in as well.

And I will be running both front and rear fenders, its a legal requirement here in NZ. That's the next job on the list actually.

Thanks for all the feedback guys

 

[650performance]

Check this link out. It may give you some insight.
http://downloads.650performance.com/XS650_750_engine_modiffication_guide_sample.pdf

 

[aldo5468]

Others please correct me if I'm wrong, but I've always believed that the most fundamental principle in designing/tuning multi-cylinder bikes was to get all (in our case, two) cylinders to work in the most evenly-balanced manner possible. Having different length exhaust pipes seems to invite different reversion characteristics - might pose quite a tuning challenge.

 

[TwoManyXS1Bs]

That's right. Otherwise, you're tuning two different single-cylinder engines that share a crankshaft...

 

[XSLeo]

What I might do is starting at the head going out to the first bend angle both pipes toward the center of the frame, between the front engine mount and the forward controls cross bar. After the pipes drop far enough down they will come close to touching, at this point you can bend them to the right then bend them back along the frame as you have them.
This will even up the length of the pipes.
May even improve the look.
Leo

 

[muks]

I'm going to put this out there purely for discussion purposes, now please please please don't flame me for this, I feel bad enough just posting it, I'm not saying I'm going to do this or anything, alright here goes;

Now, what if I made two baffles of different length. One long one and one short one, and put the long baffle in the short pipe and the short baffle in the long pipe to try to balance things out. Other than the bike sounding terrible, what would happen? Tune and run like shit?

 

[TwoManyXS1Bs]

Open exhaust pipes have a resonant frequency, similar to organ pipes and wind instruments. The timing and nature of this resonant frequency helps with scavenging at certain rpms, and hurts it at the 180°-out phase. If this resonance is sufficiently damped (what folks call backpressure), then these effects are mitigated. The wave-shape can also be modified to alter the influence.

Now, imagine that you're looking to tune a pipe organ, and there's two different length pipes that the organist wants to have the same sound. Sounds impossible, but, if the frequency is high enuff, they can match because of differing harmonics. Kinda like the way you can get multiple fixed frequencies from a fixed-length army bugle.

But, this is the challenge to engine builders, dealing with a variable rpm engine with a fixed-length exhaust.

I still remember that one biker, back in the early '70s, who showed up at the dragstrip with a trombone type sliding tailpipe concoction. I love this kind of experimentation. The bike itself was nothing special, and he was an unknown, just a guy who ran respectable times, then left. Haven't seen anything like that since...

 

[Tomterrific]

The connecting tube idea is to have each equal length pipes before the connector using both unequal lengths after. Since drag pipes most often have horrible restrictors jammed in the ends this will have the added bonus of each cylinder using both pipes. More flow and added volume. Nothing complicated, it is simple exhaust science found on the stock system and many others.

Tom