Under Engine-Exit Exhaust

[Toast]

I'm wondering if my current Arrow undertail exhaust is the ideal solution for my '03 600RR race bike. Reasons being:
-It seems a waste to have that much weight as far from the bike's CoG as possible; and more importantly to me
-It passes worryingly close to the shock resevoir, which I do not want to be heated up and suffer a loss of damping

I was thinking about getting a custom under-engine exit exhaust to solve both of those problems. However, someone who used to tune bikes on dyno's told me that with such a short exhaust the bike would become very difficult to tune, and likely lose a lot of its mid-range power.

Is this the case? Has anyone tried such an exhaust out on a bike that doesn't normally have one?

[Cajun]

as i aware as a in some lame terms, if not designed for a stubby, you will result in lost of back pressure, which in turn lack of hp,

in theory you can tune the pipe & bike, for certian rpm range, so for track would be possible but trying to tune it for the whole rpm range be a big mission.

[nodrog]

isnt the undertail where the factory pipe was anyway? i'm sure the guys at honda would have put alot of time and research into the pipe weight versus COG etc, and designed the rest of the bike accordingly so i wouldnt worry about too much about the COG.

But a short under engine exhaust would be cool, but they are definitly harder to tune due to lack of back pressure etc, when i fitted the racefit mega to my GSXR it spent all day on the dyno, and the guy actually said that short pipes are a pain in the arse to tune verses the other more standard designed pipes.

[imdying]

will result in lots of back pressure

due to lack of back pressureWay to confuse him guys :niceone:

[Cajun]

Way to confuse him guys :niceone:

sorry mine was spelling mistake

edit, it says lost, and i didn't even correct it

[Toast]

isnt the undertail where the factory pipe was anyway? i'm sure the guys at honda would have put alot of time and research into the pipe weight versus COG etc, and designed the rest of the bike accordingly so i wouldnt worry about too much about the COG.

But a short under engine exhaust would be cool, but they are definitly harder to tune due to lack of back pressure etc, when i fitted the racefit mega to my GSXR it spent all day on the dyno, and the guy actually said that short pipes are a pain in the arse to tune verses the other more standard designed pipes.

Correct, under the seat is where the pipe is on the stock bike. Keep in mind that Honda also had noise and emissions regs to contend with which would have influenced their decision on the pipe's length and location. My main concern is the fact that it passes right next to the shock resevoir. I've got that part of the pipe wrapped with some cloth that's supposed to stop heat transfer, but it's still pretty hot to the touch.

Can an experienced exhaust builder not affect the back pressure on a short pipe by putting a small S-bend in there, or modifying the diameter of the pipe at certain points, or something clever that I don't understand like that?

[Cajun]

anything is possible toast, but might take alot of time which means $$$ to do it correctly.

Have you tread looking at other methods of keeping pipe colder, can't you get that hpc paint stuff on that might help keep it cooler, double, or triple wrap it

[Pwalo]

Can an experienced exhaust builder not affect the back pressure on a short pipe by putting a small S-bend in there, or modifying the diameter of the pipe at certain points, or something clever that I don't understand like that?

I'm pretty sure that they could, but do you want a lump like they have under the Buells, or the later GSXRs?

Not too sure that it would be the cheapest idea either.

[Toast]

anything is possible toast, but might take alot of time which means $$$ to do it correctly.

Have you tread looking at other methods of keeping pipe colder, can't you get that hpc paint stuff on that might help keep it cooler, double, or triple wrap it

What's HPC paint? Where can you get it?

I've got it double-wrapped now. Problem is that if the wrapping gets any thicker it will be rubbing on the shock resevoir.

[nodrog]

Correct, under the seat is where the pipe is on the stock bike. Keep in mind that Honda also had noise and emissions regs to contend with which would have influenced their decision on the pipe's length and location. My main concern is the fact that it passes right next to the shock resevoir. I've got that part of the pipe wrapped with some cloth that's supposed to stop heat transfer, but it's still pretty hot to the touch.

Can an experienced exhaust builder not affect the back pressure on a short pipe by putting a small S-bend in there, or modifying the diameter of the pipe at certain points, or something clever that I don't understand like that?

another option could be to replace the shock with an aftermarket option that has a remote resevoir.

as far as i know the supersport Hondas still run the underseat pipe, so it cant be all that bad. :yes:

http://cms.tenkateracingproducts.com/index.php these guys will have all the answers you need.

[Mental Trousers]

It's possible that you can make the pipe go under the engine then do a U turn into a muffler (also under the engine) that exits near the front of the bike rather than the rear. That might give you enough length while still having a muffler (a rather tiny one though).

[Pancakes]

Isn't the undertail exhaust to make the person behind's draughting less efficient? I thought this is why SuperSport bikes did this v.s lower cans more inside the wheelbase? So it doesn't make you faster it makes the person a foot behind you at 200K's slower or use more gas or be less able to slingshot past. (Or the other riders don't like breathing exhaust gas?)

[speedpro]

There will be an optimim header length. The end of the header doesn't need to be the start of the muffler. The end of the header could be well inside the muffler. It would make it a bit trickier to get good gas flow. R6s have a big muffler under the engine with just a little short exit pipe. As far as a lot of things like where the exhausts are, my own cynical view is that it is mostly marketing driven, and that applies to supersport class bikes as well.

[AllanB]

Its probably more fashion than anything else, just like the single side swingarms on the Dukes and Speed/Street triples.

My hornet has the undertails and I too notice that the pipes split in front and either side of the shock - obviously heating it up a bit and the remote damper is above the left muffler.

Most of the high pipe Duke reviews complain of seat heat. Such is fashion.

But I digress - Don't know about your ride but on mine the pipes going to each muffler are very narrow - I've seen a couple of single pipe designs for the Hornet and they use a larger pipe from the main join (4-1 bit) to the single. What I am saying here is if you desire a lower pipe by using a larger diameter mid pipe your muffler may be tucked in closer.

Attached is a Speed Triple single low pipe as an example.

[DEATH_INC.]

Yep, it'll work, but it's gonna take a shiteload of figuring out to get it to fit, without being so low it'll scrape round turns....
The most important part of the exhaust is the four header pipes,before they join into 1 or 2, these affect power more than any other part. On a four > two > one system, the secondary two pipes also have a fairly large effect.
The jury's still out on back pressure, good vs bad. back pressure increases the wave strength in the pipe, but also costs hp to push it out. Only the dyno can tell if you have the right balance.....
I've seen a test on a V8 racecar where they experimented with it, and anytime they introduced any backpressure it lost power.....we also experimented with a vance and hines system on a GSXR1100, which came with different sized restrictors that fitted behind the headers, again it lost power with any one of them fitted.
You also cannot argue the fact that a really free flowing bike engine is a bitch to tune....

[mogiman]

one of those shorties like the gp bikes or the ones that the gsxrs use ,off the lastest models that sit by the swing arm that would keep your cog lower take weight away from the rear and also keep heat away from your shock and you still have the ground clearence and would prob be a lot easier to tune!!!

[imdying]

There will be an optimim header length. The end of the header doesn't need to be the start of the muffler.Not even that easy :D Look at the 999, asymmetrical exhaust system... I think the 999 powered Vyrus is something like 700mm long for the back header, and nearly 2m for the front one.

[Toast]

Cheers for the input, people.

I just read the Sports Production rules though, and it seems that 'The location, appearance and profile of the silencer must remain as original', so that puts that plan to rest.

It also says, unfortunately, that 'Wrapping of the exhaust system is not allowed', so it looks like I'll be doing the HPC coating thing come Nationals time.

[Gremlin]

I looked at the idea for my road bike when deciding on a new muffler... thought a full under engine custom system would be neat.

Problem was pipe length... either you do a full loop under the engine for length (and I had no room for that) or you run a box similar to the gixxers, underneath the engine (I say similar, coz you don't want the cat and shit). In the end, for me, the time and effort involved, coupled with the unpredictable outcome didn't make it worth it.

Got an expensive small side pipe, and had it tuned up... Never looked back :love:

[HDTboy]

Cheers for the input, people.

I just read the Sports Production rules though, and it seems that 'The location, appearance and profile of the silencer must remain as original', so that puts that plan to rest.

It also says, unfortunately, that 'Wrapping of the exhaust system is not allowed', so it looks like I'll be doing the HPC coating thing come Nationals time.
I'm glad I completely read the thread, cause I was going to point that out.
If you're looking at a new exhaust system, why not go Ti? the Leo Vince on Chris's bike runs cold enough to touch most of the time
Titanium pipe and carbon muffler, runs cold as, and nice and light. Don't ask what it cost though

[cowpoos]

I'm glad I completely read the thread, cause I was going to point that out.
If you're looking at a new exhaust system, why not go Ti? the Leo Vince on Chris's bike runs cold enough to touch most of the time
Titanium pipe and carbon muffler, runs cold as, and nice and light. Don't ask what it cost though
what did it cost?

[Toast]

I
If you're looking at a new exhaust system, why not go Ti?
Don't ask what it cost though

And that's all that needs to be said :)

I spoke to the guy from HPC. He said that their regular coating will give a 20% reduction in radiant heat (much greater reduction of internal exhaust heat, apparently), and their 'Extreme' coating will give about a 60% reduction in radiant heat.

I'm thinking go for the Extreme stuff where it passes the shock, and the other coating for the rest of the exhaust.

Supposedly the cooler exhaust temps means greater rate of flow for exhaust gases, so that'll probably do something to the fuelling? Another learning experience coming up...

[vifferman]

Isn't the undertail exhaust to make the person behind's draughting less efficient?
Apparently, having the exhaust umm... exhausting into the slipstream reduces drag noticeably. Although I couldn't see how on a bike with a fairly unaerodynamic lump sitting on it a small thing like that really figured.

What'd HPC quote you for the coating, Mr Toast? I could do with the headers and cat coated (they're a bit crappy looking). And they're one of the few things I haven't modded yet....:rolleyes:

[Toast]

The price list for the standard coating is:

Motorcycle / Jetski / Kart
Exhaust System
HiPerCoat ™ Exhaust Coating (up to 700°C)
Exhaust Pipe Price
Exhaust Pipe $19/ft
Single w/Muffler $123
2 into 1 w/Muffler $145
3 into 1 w/muffler $200
4 into 1 w/muffler $245
2 into 1 no muffler $78
3 into 1 no muffler $139
4 into 1 no muffler $178
Dirt Bike 2 into 1 no muffler $49
Muffler $73
Muffler less outer case $50
Two Stroke
Expansion Chamber $89
Exhaust colour options: HiPerCoat Polished, HiPerCoat Satin, Semi Gloss Black, Cast Iron Grey
Used, Rusted or zinc pacifated parts will need a chemical strip:
Single Pipe $17 Chrome stripping service available POA
2 into 1 $23 Chrome Strip is essential for parts to be HiPerCoat Polished
3 into 1 $34
4 into 1 $39
Dirt Bike 2 into 1 $17
Expansion chamber $28

The Extreme coating was a fair bit more expensive, about 2.5 times I think.

[Pancakes]

...................Supposedly the cooler exhaust temps means greater rate of flow for exhaust gases, so that'll probably do something to the fuelling? Another learning experience coming up...

Air has viscousity and weight like fluid so for gasses fluid dynamics still apply, think, cold air = cold honey and warm air = warm honey and now you'll see why the same volume of hotter air will be easier to force out of the exhaust constrictions than colder air.

(don't ask me to build an exaust that works but I can tune loudspeakers quite nicely:cool:)


Apparently, having the exhaust umm... exhausting into the slipstream reduces drag noticeably. Although I couldn't see how on a bike with a fairly unaerodynamic lump sitting on it a small thing like that really figured.

What'd HPC quote you for the coating, Mr Toast? I could do with the headers and cat coated (they're a bit crappy looking). And they're one of the few things I haven't modded yet....:rolleyes:

Yeah I thought that too, how much of a difference can it make but I guess for SUperBikes its not HOW MUCH difference but ANY difference and the mod will get the nod.

[Maido]

I had an 04, 05 and now have an 07 CBR600, That I have raced at nats for the last however long, I never had trouble with the shock over heating.
Keep in mind it should only really get hot in there when the bike is idling before or after a race when there is no air moving past. I realise there will be a small low pressure area beneith the rear cowl but I don't really think it is enough to cause the shock to overheat.
As said earlier Ten Kate seem to be able to set record laps throughout the race which is usually a good indicator that is works ok.
As far a weight goes and keeping a low COG, the heaviest bit of that exhaust system is the headers (stainless) and they are quite low, the only bit of that system that is Ti is the muffler housing so it probably evens out the weight distribution.
We also ran the full HRC with arrow system on the 04 and 05.
Also you are bang on the money as far as keeping to the original configuration and looks as far as rules are concerned.


I was thinking about getting a custom under-engine exit exhaust to solve both of those problems. However, someone who used to tune bikes on dyno's told me that with such a short exhaust the bike would become very difficult to tune, and likely lose a lot of its mid-range power.


Realistically with the current NZ rules the only thing the Honda has engine wise above the other brands is a fat mid range, they don't share a peaky high HP that the other 600's have, so losing that would definately put you at a disadvantage.

As far as exhaust systems go, we dynoed that system against 2 other 600SP Hondas that were running the larger diameter Arata exhaust, which also feature nice tapered headers (one was Haydens BWH bike) and they were all within about 1HP and 1Nm torque and all had the same shaped curve.(meaning I should be able to ride as fast as Hayden, now why is it that I can't!!)

The thing we picked the most performance in with the 04 was the cam timing, I would suggest you look at that if you already haven't. (The 05 was pretty close to where we wanted it from std)

If you need to know anything racing wise about them just give us a PM, cos there isn't many being raced in NZ, it is hard to get info on them.