modifying an exhaust can-- can it be done?

[3imo]

I have a used F1 cobra can.  I want to mount it as shown above.

one catch though, I want to cut the can, remove about 10%-20% off the top and reweld it.  I want to leave the top flat so it will not stick out as much.

does anyone know what the ramifications of such a mod are?  what things I need to take into consideration?

I've read over an over about how you must rejett if you upgrade your exhaust.  Is there someway to measure the output of a custom exhaust to determine what type of rejett is necessary, if any?

Another thing  why is a motorcycle different in this way. i haven't heard of adjusting the carbs on a car to tune the exhaust.  except on race cars. on regular cars I thought the rule of thumb was let her breathe as best as possible.

[My Name Is Dave]

What bike is that? Do you photochop that? It looks like a heavily-modified GS, made to look like Spider Man and without a rear shock.

Dave

[3imo]

its a photoshop I found floating around the internet, I have no clue of it's origin.
I love the seat and I'm gonna shoot for that look.  not the front fairing though.  for the front I'm going with dual streetfighter lights.
but thats all in the future. 
for now I need to start designing the exhaust.

[My Name Is Dave]

That tail is pretty badass. I'm not sure how you're planning on making that, but it should be sweet.

I have no useful information about the can, so I'm done yapping. Good luck on the project!

[budget speed demon]

no welding required. the end caps on some cans are rivited on. basically all you have to do it drill out the rivets, remove the end cap, cut down the can (and any interior bafolding) then drill your new holes on the shotend can and re-rivet your end cap on. easy as pie. I know you can do this with some yosh cans, and I ass-u-me that it will work on just about any can that has riveted on end caps.

[LimaXray]

My guess is the only thing messing with the can will do is change the sound of the exhaust.  If you make its volume smaller, it will be louder. 

Performance wise, by shortening the exhaust tubing when you put the can there, you'll reduce exhaust restrictions, and you may lose some low end power but gain some top end.   

[Cal Amari]

I think some people are confusing what you want to accomplish; the previous replies seem to suggest making the can SHORTER, but I think you want to reduce the DIAMETER... you might want to clarify that for us, just in case...

My guess is that Suzuki uses that same basic can on other four-stroke models not sold in the US; restricting the exhaust flow too much could increase backpressure in the exhaust stream to an unacceptable level, but others will have to advise you on the specifics.

Have you considered notching the can, instead of simply making one side flat? I'm talking about cutting out a section the entire length of the can, then sealing the opening with a plate in the shape of a "V" (probably 90 degrees). From an end view, the exhaust would look like a pie with a piece missing. I think doing that would allow you to tuck the exhaust within an inch of the lower frame rail, which might allow more ground clearance than simply making one side flat.

To help you visualize this, get a cardboard tube from a roll of papertowels, and push it lengthwise up against the frame rail. It should dent well enough to give you an idea of what I'm suggesting.

Now we need to hear from you to clarify things for us; let me know if you think notching the can will do the trick...

[Wrecent_Wryder]

[6

[budget speed demon]

I donno, I don't really like the rear end on that thing, it's a little too skinny. It's not substantial enough.

[3imo]

I have a used F1 cobra can.  I want to mount it as shown above.

one catch though, I want to cut the can, remove about 10%-20% off the top and reweld it.  I want to leave the top flat so it will not stick out as much.

does anyone know what the ramifications of such a mod are?  what things I need to take into consideration?

I've read over an over about how you must rejett if you upgrade your exhaust.  Is there someway to measure the output of a custom exhaust to determine what type of rejett is necessary, if any?

Another thing  why is a motorcycle different in this way. i haven't heard of adjusting the carbs on a car to tune the exhaust.  except on race cars. on regular cars I thought the rule of thumb was let her breathe as best as possible.

lets discuss the seat another day. 

to clarify, I am not using a stock can. it is an F1 Cobra slip-on, that was on
the 01' GS I bought wrecked. --> http://gstwins.com/gsboard/index.php?topic=24409.0

it does not have rivets. it is welded all the way around. and I doubt notching will work (please explain)

I want to mount it as the picture shows but it sticks out to low.   I want to slice the top off making it FLAT on top.
**mental image - flat tire)
so it will not stick out below the bike too much.

how will doing this affect the bike in regards to the questions I posted on the original post.

[3imo]

[LimaXray]

The exhaust note will change, it will be louder

As for rejetting, my guess would be start where everyone else starts for a slip on exhaust, but you will probably need to go a little richer

Why do cars not need a rejet with mods? I don't think that's entirely true.  An new can or filter on the GS probably has a greater impact on its volumetric efficiency then the same mods would on a car.  Why?  A car has a lot more plumbing then a motorcycle so such changes make less of an impact.  This is just a guess.  In any case, any mods greater then a new air filter or exhaust to a car using speed density EFI needs to have its fuel tables remapped because it depends on the volumetric efficiency.  I'd guess a carb'd engine would be the same. 

[3imo]

The exhaust note will change, it will be louder

As for rejetting, my guess would be start where everyone else starts for a slip on exhaust, but you will probably need to go a little richer

I don't care about the sound. I'd prefer somethin quiet - but thats besides the point.

Please explain what you mean by "where everyone else starts" .

  I was thinking LEANER but I know I am lacking in the knowledge dept. for exhaust systems.

My guess was that cutting  the exhaust would make it smaller, and cut air flow volume.

How does one determine the proper dynojet stage for a custom shaped muffler .

I recall a thread about not rjetting you bike will F**k it up. If I do this to this can and install a stage 3 dynojet will i be ok or is that overboard?

**I guess I could call the dynojet company and ask**
I

[RVertigo]

Why not just get an oval can?

[LimaXray]

I know nothing about carbs but from what I've read, I would buy the jets by themselves and screw the kit.  Do a search for rejet and see what everyone else is using for a slip on and use that as your starting point. 

The can allows the exhaust gasses to expand before going to the atmosphere.  The bigger the volume, the lower the pressure and the slower the gasses, a thus less noise.  (The same idea applies to sound suppressors for guns  )  By chopping off the top of the can, you are not adding any restrictions, you are only giving the exhaust gasses less volume to expand to.  This means higher pressure, faster flow of exhaust gasses, and louder exhaust.  This combined with the shorter exhaust plumbing will probably reduce restrictions, meaning you'll need more fuel.  The big problem to some people with reducing exhaust restrictions is it reduces back pressure which in turn negativly impacts low end performance.  On the other hand, you'll have a stronger top end, which leads me to want to say you should get slightly larger mains and use the same pilots.  But like I said, I know nothing about carbs...

[3imo]

Why not just get an oval can?

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

or to be exact,  LACK there of.

I already have scratched up F1 cobra can, that I can experiment with.  

[3imo]

I know nothing about carbs but from what I've read, I would buy the jets by themselves and screw the kit.  Do a search for rejet and see what everyone else is using for a slip on and use that as your starting point. 

The can allows the exhaust gasses to expand before going to the atmosphere.  The bigger the volume, the lower the pressure and the slower the gasses, a thus less noise.  (The same idea applies to sound suppressors for guns  )  By chopping off the top of the can, you are not adding any restrictions, you are only giving the exhaust gasses less volume to expand to.  This means higher pressure, faster flow of exhaust gasses, and louder exhaust.  This combined with the shorter exhaust plumbing will probably reduce restrictions, meaning you'll need more fuel.  The big problem to some people with reducing exhaust restrictions is it reduces back pressure which in turn negativly impacts low end performance.  On the other hand, you'll have a stronger top end, which leads me to want to say you should get slightly larger mains and use the same pilots.  But like I said, I know nothing about carbs...

THAT, Ladies and Gentlemen, is the type of answer I was looking for. BRAVO  LX, BRAVO!!!!!

now Can anyone Back him up?  It sounds good to me. but I dunno. thats the issue.  Anyone?  I'd hate to f**k up the engine just cause I wanna cool lookin bike.

ah..the price we SQUIDS pay....when will we learn.

[galahs]

The bigger the volume of the can does not mean in all cases the exhaust gases will be slowed down. The more volume of the can the larger the volume of space for the sound waves to be dissipated in (not gass flow).

On straight throuh muffler designs especially this is not the case (most sports cans are this type).

The body of the can is actually stuffed with tight weave fibreglass so the volume of the can is not a direct relation to gass flow.

I have seen tests on a cars straight through mufflers that flows at 94% and it has a large muffler body yet is a very quiet muffler (the size of the muffler achieves this).

A drop of pressure will only occur if it's a cheapo muffler that doesn't use a high density fibreglass packing.


The design of the muffler will make more of a difference. The perforated tube that runs down the centre of the muffler needs to have clean cut holes and by as smooth as possible. A straight through muffler is also prefered if your going to be cutting it.

It is a different story for dog leg mufflers though.

The volume of the can, on "centre expansion chamber" mufflers do reduce gas flow. (Our stock GS muffler is this type) The centre chamber is also located based on wave pulse tuning so cutting and shortening one of these could have some negative effects sound wise.



The only other problem I can see with having the muffler mounted where it is on that pic (closer to the exhaust port) is that shortening the exhausts primary pipes (the length before the collectors) can have an effect on top end performance.

[3imo]

will it damage the engine?

[galahs]

nope.

Just may not produce optimum flow at higher revs.