Compact underbelly exhaust

[Babelfish]

Please note the technical terminology I use to describe the type of exhaust I am interested in....indicating I am on the VERY first steps of understanding the concept of the ikle exhaust systems some of the new bikes are coming out with such as the er-6n kwakka et al.

My question to can buffs, is what is the concept of the compact little units they put on the new bikes and on some race bikes where its a really short header, and a snubby can that sits on the underbelly of the bike? Buell do the same thing, but doesn't this screw with ground clearance? Can the pipes still be tuned at that length? Or do they have to snake them a bit to get the length? And wouldnt that create more resistance to the flow of exhaust gasses?

The reason I ask is to find out whether its possible on my vtr, as right or wrong I quite like the look of them.

Appreciate anyones input on the matter.

[Skunk]

My non-expert 10 cents worth. The headers are tuned to suit and the engine postioned to suit the underbelly can and handling requirements. Doing it to a VTR could be a bit difficult and would have to compromise something. Don't think it can't be done though.

Edit: I think you'll run into real issues with clearance thinking about how 'pointed' and low the cases are on the VTR...

[Cajun]

always something like these

often called high mount exhausts

[Babelfish]

Yeah nice, and I do like the under tail solutions too but I havent seen a underbelly jobbie on a vitter yet....and probably for good reason as skunk points out.

I'm happy with the 2 bros (more than happy when the parking block I am in sounds like a tree full of cicadas when I come in and go out again), but if it can be done, the underbelly exhaust would be pretty trick.

[Crisis management]

I don't know a lot about this but.....the primary pipes tuned length is designed to reflect the exhaust pulse to assist in scavenging the exhaust gasses at particular revs, the higher the revs, the longer the pipe length (roughly).
Buell assist this on the new XB12 with an exhaust valve in the "muffler" that opens & closes to change the mid range torque curve, similar to Yamaha's EXUP valve.

Short answer, unless you get really tricky with an exhaust valve, you will have to sacrifice some top end power by using shorter primaries to get the exhaust to fit.
So its possible to do it but expect the engine output to change somewhat, probably not a biggie unless you are commonly riding in the top 20% of the rev range.

[davereid]

ER6F/N etc have a catalytic converter stuffed in that can. Rumour Control has it that the Vance & Hines aftermarket pipe produces a very noticeable increase in power. Mines on order.. let you know !

[Babelfish]

Yeah, figured the power would take a hit, but then I own a vitter so power isnt my main tent pitcher. Good info though thanks. I did find this mod that a guy did on his VFR. I am keen at some point to stick a VFR800 single sided swing arm on the vitter, but even without it, this could work in theory:

http://www.vfrdiscussion.com/forum/i...9&#entry218679

[dangerous]

My question to can buffs, is what is the concept of the compact little units they put on the new bikes and on some race bikes where its a really short header, and a snubby can that sits on the underbelly of the bike? Buell do the same thing, but doesn't this screw with ground clearance? Can the pipes still be tuned at that length? Or do they have to snake them a bit to get the length? And wouldnt that create more resistance to the flow of exhaust gasses?

Its funny... but years n years ago, like back in the days of the Manx Norton etc, a short header and megaphone was the in thing for performance... then came the mufler and 'race can'
Now if we use the RCV11 or even the latest GSXR 600, you will notice the short stumpy pipework... well this is the return of the megaphone... its were the hp hides.

Like the two stroker chamber it is about harmonics and sound waves n shit (bit beyond me) but at the end of the day it has done the full circute, hell it wasnt that long ago that the longer the pipe the more top end you got.

IMO... your VTR, I'd wind the headers around as much as possible then dump the megaphones out under the engine but most likley they will have to poke up a tad.

EG: my bucket CB125 twin, to maximize the hp, a matamatical measurment is made up to obtain the corect length of each cone and the entry and exit diameter.

make sence... thought not

ps: the japs on there rd bikes also use a muffler box to keep the pipes quiter.

Buell assist this on the new XB12 with an exhaust valve in the "muffler" that opens & closes to change the mid range torque curveShort answer, unless you get really tricky with an exhaust valve,

Not quite true, yes the std buell can does have a restricter butterfly in the can, but the race can does not and with the moded ECU it hauls an extra 10hp. and more top end.
So, Id say buell cover this with having long winding headers, and retuning the timing/fuel mix to suit.

[Mental Trousers]

I don't know a lot about this but.....the primary pipes tuned length is designed to reflect the exhaust pulse to assist in scavenging the exhaust gasses at particular revs, the higher the revs, the shorter the pipe length (roughly).

The pulse travels back up the header pipe at approx the speed of sound. It takes longer to travel up a longer pipe. If the pressure pulse assists scavenging every exhaust stroke then the longer the pipe, the slower the engine has to spin to stay in sync.

If you increase the overall length of the exhaust system you can raise the back pressure which changes the speed the pulse travels at. This is not the same as getting tuning the length of the header pipe.

Under engine exhausts are usually put there because it helps centralize and lower the exhaust systems mass (mufflers are farken heavy) and to keep the hot exhaust system away from the rear shock (heat degrades shock performance). It also looks farken cool from a marketing perspective.

[Babelfish]

Good shit Dangerous, thats some good info and more stuff for me to check on. Biggest hassle will prob be the rear cyclinder...but where theres a will theres a way....or a dead person...

[Babelfish]

Mental trousers, its the lower slung mass that interests me as much as the aesthetics. Sounds like once I have the overall look sorted out, I'm going to need to get some help decided on pipe length n shizzle.

[TonyB]

I've been looking at doing something similar to the Monster. Proposed F3 rules may kill this idea- haven't looked into it properly yet.... Gav?.

I like the idea of 'mass centralisation' as Eric Buell calls it, ie the weight of the can is down low and right under the engine. The Monsters cans are big, heavy, they stick out miles more than they need to, and with the standard suspension they drag on the ground before you ever get near the edge of the tyre (have hopefully fixed that with some decent springs). High/ underseat pipes look cool, but I've heard many complaints of roasted nuts, plus they put the weight of the cans up about as high as it can go. However, if I want to get them out of the way it may be the only option. I guess a downside of under engine cans is if you have to take an off track excursion- I can imagine them being grounded and crushed pretty easily.

The Harley engines Buells use lend themselves to under engine cans because its fairly easy to keep the headers the same length, whereas with an 'L' twin like a Ducati or VTR one cylinder is down low and the other is up high- kinda tricky to keep the lengths the same. I will be watching this thread closely... unless of course I forget

[dangerous]

The Harley engines Buells use lend themselves to under engine cans because its fairly easy to keep the headers the same length, whereas with an 'L' twin like a Ducati or VTR one cylinder is down low and the other is up high- kinda tricky to keep the lengths the same.

Its not that tricky Tony, take a look at a SV or VTR... even better look at the congestion of pipes on a VFR single sided swing arm, amazing pipage there.

[Babelfish]

So am I right in thinking the twist and turns dont effect the pulse too much...that the length is the important thing? Looking at some of the pipes they stick on the buells, or the play about they did with the vfr, it seems twists are ok?

[Mental Trousers]

Bends aren't ideal but are necessary. They do tend to mess with the tuning of the pipe though.

The ideal (for tuning headers) is totally straight pipes. One technique used to find the right length is to calculate the length (the pressure pulse moves at almost the speed of sound and exhaust gas expansion rate is known etc) and add a bit extra for errors, cut a piece of pipe to that length, put it on, test, then cut a bit off, test ...... repeat until you get the best power at the desired rpm. You can then make up a pipe with bends to suit using the best length from the testing.
Of course, that requires a dyno!!
Otherwise, the OEM pipes are a good place to start for the right length.