What effects can too long exhaust pipe cause?

[youngmaavin]

Hi, everyone.

Hoping to get advice from some exhaust guru on here.

I fitted an arrow loop type exhaust on my R7.

Pipe was designed for mt07 and as a result I can't fix the slip on part with clamp in place due to different rearset desing.

That with combination of the loop in midpipe leaves zero space to make some kind of custom bracket there (you can see by the white blemish where the clamp was on mt07 previously).

The guy who fitted the exhaust suggested he can lengthen the midpipe upwards, like on Akrapovic version, then I can fix the slip on where passenger pegs mount. I would also like this solution since there would be less chance exhaust would rub on track.

However, since this version already has a loop in it  I'm afraid extending it will cause the total length to be too much.

I know about basic tradeoff of higher end power with long exhaust, but can extending this pipe even more cause me to lose too much power up top?

Edited April 21, 2023 by youngmaavin

[youngmaavin]

This is the akra pipe for reference, which sits higher and mounts to passenger pegs:

[youngmaavin]

Or this Graves version.

All these long pipes don't have a loop in them though

[klx678]

Really doesn't have any negative effects in damaging the bike.  It will only deal with performance.  From what bit I've picked up over the years, mainly through Hot Rod magazine,  it seems the longer tubes and collectors are used on smaller displacement engines and tend to broaden power with small sacrifices at the very top of the power range.   

Short isn't always better, which becomes obvious when companies start coiling the collector under the engine.  The only reason they do it is because of the current trend to have the cannister exiting just under the swing arm.  Otherwise they'd extend it the usual way. 

In a quick look there is a mix of the kinds of pipes used in MotoAmerica race bikes, indicating that they both can be utilized.  AFT flat track Yamahas are mainly running a long style 2-1 pipe from Graves, Vance-Hines, or other sources, occasionally running a 2-2 set up.  So really you probably aren't losing much at all if any.  

 

You could make an aluminum support using the two reservoir mount fasteners and space the heel plate out to clear it.  The can shouldn't be very heavy, so it may not be any problem to do so.  Otherwise a longer bracket from above like that Graves exhaust support might be possible.   Of course bending up an extension and trying it certainly couldn't hurt.

 

 

Edited April 21, 2023 by klx678

[youngmaavin]

7 hours ago, klx678 said:

You could make an aluminum support using the two reservoir mount fasteners and space the heel plate out to clear it.  The can shouldn't be very heavy, so it may not be any problem to do so.  Otherwise a longer bracket from above like that Graves exhaust support might be possible.   Of course bending up an extension and trying it certainly couldn't hurt.

 

 

My can is way too low at the moment to mount to reservoir or passenger pegs, bracket needed would be 40 cm i reckon.

It really isn't heavy, I just don't like that it shakes in the wind and on bumps, no need for heavy duty support for it.

[youngmaavin]

7 hours ago, klx678 said:

In a quick look there is a mix of the kinds of pipes used in MotoAmerica race bikes, indicating that they both can be utilized.  AFT flat track Yamahas are mainly running a long style 2-1 pipe from Graves, Vance-Hines, or other sources, occasionally running a 2-2 set up.  So really you probably aren't losing much at all if any.  

The longer exhausts don't have a loop in them at the bottom like mine has.

So my concern is if I lengthen the loop type exhaust, I'd end up with something longer, than any product on the market.

I would be combining both of these basically

[klx678]

The loop is a bit more restrictive than straight pipe in that application, but still is effectively making the pure length longer.   If the curves  were such a great issue you wouldn't see that loop or the automotive "bundle of snakes" they make to create equal length individual cylnder head pipes.   

Plus, you have the exhaust, what do you have to lose trying the upswept additional length.  Worst case scenario is you might lose a bit on top, not a real problem unless you're racing.  It actually might boost the mid range from 3500 up to near redline.

Another option is to cut out the loop and extend the straight pipe.  Seems kind of like a negative, but you could find out how long the straight pipes are on the other exhausts and make the new mid-pipe to equal out the length.  Here is Graves full exhaust, and it is long:

Here is the Delkevic system with the 18" can that I have on my 700

But the thing is the actual length isn't that hypercritical unless racing.  Picture just how long each pipe is on the Ducati 916 from the mid 90s

When it comes to the mounting strap, 40 cm isn't all that long.  As you see below, it wasn't uncommon for flat track bikes to have straps up to around  60 cm long supporting the silencer and exhaust.  This  is the Estensen Yamaha 700 flat tracker with the long mount strap supporting both pipes.  Wasn't at all unusual for any flat track bike to have long mounts.

Not at all uncommon and they held up no problem.   The twin exhaust was used on the half miles and short tracks, from what I saw, the 2-1 exhaust was used on the mile races and actually on a lot of the half miles too.   Those pipes took some pounding too.

 

 

Edited April 21, 2023 by klx678

[M. Hausknecht]

The most significant factors impacting exhaust system efficiency are: primary tube length and diameter; whether the primary tubes are joined together; and the style and dimensions of the collector. Secondary factors include the amount of back pressure created by the muffler (could be a primary factor if it is very high and the overall length of the exhaust system. The pressure waves that exit the exhaust port when the exhaust valves open are reflected partially back towards the combustion chamber whenever there is a change in diameter. So, there is a reflection at the collector, at the opening to the muffler, and then at the end of the system. Adding length to the system between the collector and the muffler, which is what you're thinking about, will tend to slightly boost power at lower rpms (the longer length takes more time for the pressure wave to travel back to the combustion chamber). My understanding is that Arrow added the loop, the extra length in the system, to reduce the the sound level of the system. I also believe the extra length tends to keep more heat in the engine, which needs to be dealt with by the cooling system. If you add still more length, a few inches, I would expect a very minor change to overall maximum power and heat.

[klx678]

Can't be much worse than a cat converter in there.   

I don't know about the added heat, the hotter the exhaust the higher the velocity going through the pipe.

I did some calculations years ago for my SR500 and got 1-5/8" dia x 33" long.  The flat track pipe I had was, oddly enough, 1-5/8" dia x 33" long... imagine that!   I did a similar thing for my KLX250 and for the 8600 rpm hp peak the exhaust was to be 1-3/8" x 21", if I figured 10,000 rpm it would have shortened by 2".   The head pipe for the KLX300 is about 21" long, not sure of the diameter though.  I do know the 250 pipe is no where near 1-3/8" dia.  The aftermarket head pipe i have is 1-3/8" x about 21".   Without a cam change I don't see any gain with the pipe calculated for the larger diameter, the cams would need to conform.  

Exhausts are really interesting, but as we see, quite complicated now.   There are the constant increasing diameter type head pipes and the stepped diameter pipes along with the ones with the chambers on them.   More going on there than I know or understand for sure.  

[shinyribs]

With an engine like the CP2 that makes good power everywhere and not a ton of horsepower at high rpm I think you'd find that exhaust length is not going to matter at all. Certainly not to the point of throwing the tune off, and most likely 100% unnoticeable. 

I'm not sure how much length you're talking about adding, but you can't even make it but do long due to the small size of a bike. 

 

I realize it's apples to oranges, but I had a drag car that filled up with smoke real bad during burnouts. Really messed with my concentration. I rerouted the exhaust to the back of the car in such away to help blow the smoke away. All in all, added nearly 10' of pipe between both sides. Time slips were unaffected and we were measuring down to the hundredths of a second. 

I'd say rock on, buddy.

 

[youngmaavin]

So, today we routed the exhaust up, as discussed here.

I personally am a fan of how it looks, I know short cans underneath the belly are all the rage now, but I like showcasing a nice carbon muffler.

More of an old school vibe.

Butt dyno wise, I don't notice any changes in power/dynamics.

The sound changed I think and there's also some more noticeable hissing on deceleration.

[shinyribs]

The hiss may just be the personality of the Arrow can and how they make their baffles. The Arrow X Kone on my bike sounded kinda hissy/puffy when I first got it. I started drilling extra holes ( whatever matched the existing hole sizes) in the removable baffle until it went away. It only increased the sound output a very, very little amount. I don't remember how many or where I drilled just added a couple at a time until the puff sound went away and it had a nice crisp sound to it. 

 

Upswept does look good! 

[klx678]

On 4/23/2023 at 11:31 AM, youngmaavin said:

So, today we routed the exhaust up, as discussed here.

I personally am a fan of how it looks, I know short cans underneath the belly are all the rage now, but I like showcasing a nice carbon muffler.

More of an old school vibe.

Butt dyno wise, I don't notice any changes in power/dynamics.

The sound changed I think and there's also some more noticeable hissing on deceleration.

I like it, different is good.  You won't see another one like it and that is kind of fun!

[youngmaavin]

Interestingly enough, after driving for a week with it, I feel like there's a noticeable power loss.

The bike is not tuned, but feels like it has less power at the top, top speed is noticeably lower.

I don't see/hear any obvious exhaust leaks.

I wonder what's up, because usually putting on a full system on this bike without a tune doesn't result in power loss, from what I gather.

[klx678]

You also might be experiencing self fulfilling prophecy.  You thought it would lose power and now you think it has lost power without any actual proof.   If you want to know for sure you would have run some sort of objective test of performance, like a quarter mile run or some kind of timed roll on.   Remove the extension pipe and put the muffler back where it was made to be, then do a roll on test somewhere with some method to time it, then put the extension pipe back on and go do the same test again.

I mention this because sometimes better power delivery can be deceiving.   Kevin Cameron, of Cycle World, wrote up a column on his experience with this.  He was working with his pro rider, Cliff Carr, trying to jet in one of his race bikes and using lap times to see how all went.   It wasn't going all that great though.   After one series of laps Carr came in.  Cameron asked him how it felt.  Carr said it felt slow, worse that the previous laps.  Cameron told him his lap times - 0.4 seconds quicker!    With the better jetting the bike was easier to ride and that made it seem slow.   Carr wasn't working as hard, making the bike seem slower, but the numbers don't lie. 

That can happen with any number of modifications.  Unless you actually have some kind of objective test you really don't know.   One situation that frequently can happen with aftermarket exhausts is when the pipe is lacking in midrange power, but provides a burst at high rpm.   The bike feels faster because of the boot in the tail at the high rpm.  It may actually be producting less power, but feels stronger because of that burst.   I remember a GSXR750 that one magazine did some hop up on, had a 3 hp gain at peak power, but actually lost a couple of horsepower below peak power in comparison to stock.   

Even works with suspension at times.   Back when riders had to do their own chassis modes to get long travel on off roaders I forward mounted the shocks on my TM125.  On one particular rough up hill I was hammering pretty hard, as hard as when it was stock position... thing was I was now running one gear higher going up the hill, 4th instead of 3rd, there was definitely a speed difference because it was easier to ride with the better suspension travel.

[youngmaavin]

1 hour ago, klx678 said:That can happen with any number of modifications.  Unless you actually have some kind of objective test you really don't know.   

All very interesting thoughts.

Well, for me the objective test was top speed, as I mentioned.

It’s around 10-15 kmh less now at the top of 6 gear.

Roll on power in lower gears doesn’t feel different enough to be certain of any difference. Certainly doesn’t feel faster.

[youngmaavin]

Hopefully I’ll get the bike on the dyno soon and before tuning it will see on the base run if it’s making at least stock power with this exhaust.

[youngmaavin]

Just to clarify, power loss I'm feeling is not from lengthening the exhaust, but from the stock one.

Without a map, with a stock exhaust top speed was noticeably higher.

[klx678]

On both the original and the modified exhaust or just on the modified one?  

I think you're doing the right thing getting it tested and possibly doing a reflash.

[balkor2]

On 5/7/2023 at 7:33 AM, klx678 said:

I think you're doing the right thing getting it tested and possibly doing a reflash.

And sharing your knowledge

 

Thank you

[klx678]

6 hours ago, balkor2 said:

And sharing your knowledge

 

Thank you

I have to be careful when sharing...   I don't have a whole lot.  

[Pursuvant]

On 5/1/2023 at 4:45 PM, youngmaavin said:

Hopefully I’ll get the bike on the dyno soon and before tuning it will see on the base run if it’s making at least stock power with this exhaust.

Perhaps the last experience with the dyno should be given consideration ?...

[youngmaavin]

On 5/7/2023 at 2:33 PM, klx678 said:

On both the original and the modified exhaust or just on the modified one?  

I think you're doing the right thing getting it tested and possibly doing a reflash.

Pretty sure both the original and modified one lost power at the top end in comparison to the stock exhaust.

[youngmaavin]

On 5/9/2023 at 2:42 AM, Pursuvant said:

Perhaps the last experience with the dyno should be given consideration ?...

Yeah, for sure, would be more oversight and a different tuner. Or maybe just a base dyno run with no flash to see the power and AFRs.