More Belly Exhaust discussion...

[Jonny]

So i've been rolling this around in my head and if it goes poorly, I'll just pick up a 900rr header and call it a day. I'm somewhat on the fence about how to proceed though. I hope I descrive this clearly...

I like the idea of a belly exhaust can...if I can pull it off clean, but figured I could do it with a twist in one of 2 ways.

1. Cut it from the last joint right before it bends up into the tail, basically where a mid pipe would start. Then use a piece of 4in exhaust pipe crushed down, sealed on one end and slid over the end to bounce the exhaust back up to the front towards the headers with 2 1-1.5in pipes running inside the 4in pipe forcing the exhaust back towards the back of the bike and out a couple concave cone shapped openings on either corner to direct the exhaust around the back tire. Basically it would just look like the headers dissapear into an oaval with 2 outlets at the back, but inside, the exhaust would take it's normal rout before being directed back to the front and then out the tubes to the front. (is that confusing...it makes sense in my head. same design as the stock muffler without a partitian.)

2. would be the same, except I'd cut after the header joins into 2 pipes and use 2 legs up the middle for a little cleaner path inside the "can". Egh...maybe if I drew a picture...


_______________________________________
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ <<out this way]
I then>>>______________________________]____________
I <<Header exits here_________________________________ Header 2-1
I <<Header exits here_________________________________ Header 2-1
I_then>>> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ]
___________________________<<out this way]

If that helps any...

What do y'all think? Basically the tubes on the inside replicate the path the exhaust takes from the mid pipe out to the muffler, while bouncing around the sound waves helps cut down on volume...in theory. I'm thining I could maybe swiss cheese the inside end of the 2 legs and wrap with fiberglass to make a modified glass pack.

Should be compact, retain low end torque, cancel out some of the sound and if I paint it high temp black, should blend in and look pretty mean...or gay...guess we'll see!

Thoughts??

-Jonny

[Jonny]

Sorta like this: http://static.ddmcdn.com/gif/muffler-cutopen.jpg but imagine another outlet on the opposit side and they don't stick out. I'll angle them so they point outward just a touch.

-Jonny

[g00gl3it]

The stock headers for these bikes (I'm including the 900rr header as it's essentially the same engine/design) were made and ENGINEERED specifically for the engine. The way they bend, the length, diameter, everything.

Do what you please, but if you mess with more than what's stock, you're asking for some REALLY funky issues with how your bike runs.

Any increase or decrease of the backpressure (if you lengthen the pipes, you'll increase backpressure as volume builds up in the pipes - it takes longer for the gas to reach the exit and it will slow down towards the end, causing pressure) is going to mess with the engine. The pistons will lose energy on the exhaust stroke because gases stuck in the headers want to push back on the piston.

Somebody correct me if I'm wrong.

For the heck of it, I say do it, just to see what happens, but have a 900rr header and appropriate can on hand to put on as the finishing touch.

[Jonny]

I figure, if I cut after the tuned part of the header where it "Y"s together before the up bend, my mid range should remain intact. After that, it's not much different than a race glass pack, so long as I get about 18" of travel and keep the diameter around 1.25" for the "legs". I know it drops to less than 1" inside the stock cans, so I'm not real worried about overdoing the back pressure, but cancelling out enough sound. I'm thinking that the down and back may help with that. We shall see!

-Jonny

[nd4spdbh]

i say do it! always liked (and i hate to admit it) the buell belly exhaust!

your idea is pretty sound... pretty much 2 U turns then out each side... i dont see any major issues with backpressure or running problems so long as your not going down to like a 1/2in hole.

[BBB2]

I agree with g00gl3it, headers are engineered with purpose. I would find the cheapest header I could find and experiment away. But like we already discussed, motorcycle exhaust aren't cheap and finding one might be a huge challenge. And for the right price, only to be trashed in the end. I'm not trying to discourage you from being creative, just be prepared with plan B.

[AllanB]

Go for your life. Stick to the same header diameter (ID) and length in your design. Heres my design, feel free to use it!
The headers (custom) wrap around the crankcase and meet behind the engine going into a genuine belly pan muffler.

One day I'll make it!

[Pvster]

dude allen, that'd be sweet!

[nd4spdbh]

i like OP's idea, it seems a lil more slim to keep ground clearance, and honestly where hes planning on rerouting the exhaust any change is going to net almost no change in motor performance bad or good... as the header part is done.

[Jonny]

Ok, I did some reading this weekend regarding back pressure, mid pipe and muffler design. Also, looking at the stock cans leads me to believe, back pressure is less of a concern than originally thought. My original plan was like this: http://www.aa1car.com/library/perfor...er_cutaway.jpg only with the single pipe after the 2nd Y splitting back into 2 pipes, doubling back and then to the rear of the bike again like 2 squished "S"s stuck together.

The stock can chamber design as the exhaust looping around, except where people, myself included, had removed the baffle, allowing a straight exit. I didn't cut them up, but that's what it appears to equate to...

My major concern is more with sound reduction as a shorter exhaust path with less restriction should increase velocity. Now I'm starting to think, cutting after the first 2 primaries and 2nd set of primaries are "Y"d together and then having dual pipes "X" in the middle with perferations and housed in fiberglass would offer the best of both worlds. Improved flow and sound deadening, like this: http://www.ssrfanatic.com/forum/atta...53_cutaway.jpg Eliminating the "x" in the middle in favor of a partitianed chamber may sound pretty good too, but would offer a little more back pressure...I'm undecided at the moment.

Overall casing design has to lend itself to a belly pan or I'll just bail on the whole thing. I just got a '98 900RR header and mid pipe in perfect condition for $70 shipped, so...I have an out if it goes ugly on me...

-Jonny

[HeliMech]

I say go for it!

I think allans design would work well, maybe use a 600rr under tail muffler? Small enough and cheaply sourced.

[honda ng gingsa]

Originally Posted by AllanB

Go for your life. Stick to the same header diameter (ID) and length in your design. Heres my design, feel free to use it!
The headers (custom) wrap around the crankcase and meet behind the engine going into a genuine belly pan muffler.

One day I'll make it!

Tats a great sketch Allan! There was a belly exhaust mod done on a niner with a VFR single swing-arm floating around the forum somewhere that might be helpful.

Here:
My 91929VF800

[Jonny]

Originally Posted by honda ng gingsa

Tats a great sketch Allan! There was a belly exhaust mod done on a niner with a VFR single swing-arm floating around the forum somewhere that might be helpful.

Here:
My 91929VF800

Yeah, that's the thread that got me thinking about it. My plan, obviously, is NOT to have the pipes pointed directly at the back tire, but down and to the sides.
Also, I won't be doing a 4-1 header as that can have a more severe sound wave reverb much lessened by the 4-2-1(maybe even a 4-2 with an H in the middle or X at the muffler.
I'm still thinking this one out a bit. I'll make a model out of cardboard or something similar before hand so I can stand back and look at it...

-Jonny

[Jonny]

I bailed on the idea for now. I just don't have the free time. My 900rr exhaust should be here soon and I just ordered a DanMoto JISU. That should keep me happy for a while.

-Jonny

[BBB2]

Did you contact Dan Moto directly to get the right diameter muffler to fit a 900RR header? I am debating a shorter Dan Moto for mine if I can get the right diameter inundate a shorter can.

[Jonny]

No, I got the one for the R1 and I'll just nip the end off the mid pipe and weld it up, or I may see if I can just build the mid pipe the rest of the way and keep the 919 header. I'm debating that still. I know the 900rr is a little bigger, but don't know what that'll do to the power curve. I've just seen most guys do it to accomodate a side pipe.

I think if I cut the 90deg bend, rotate it 90ish and angle it, I can keep the cat, etc and retain much of the mid range I like.

I have yet to see any side by side dyno graphs though...stock vs 900rr...

-Jonny