Inexpensive performance gain?

[Zackninja]

All,

Would love to hear from our tech / mechanical / engineering brain trust on this.

Attached is a photo of the stock Kawa EX300 exhaust. I had a very similar configuration on an Italian bike. It would seem to me that the 6 inch or so, cross flow pipe (the one connecting the 2 pipes together) may be hindering the exhaust flow and thus, leading to a loss of performance and economy.

Asked the dealer about this and a salesperson said it was needed for back pressure. As mentioned earlier, I had this on an Italian bike, I cut the member off and sealed both ends. This resulted in a substantial gain overall, the bike seemed to "breathe" much better and yes, mpg, top speed and launch times all improved.

I am skeptical about doing this simply because if there was a gain to be had, why wouldn't the factory have done it....?

My question is has anyone tried this and what would be the risk to do so?

p.s. As I look at most performance exhausts for this bike, they do not have this "cross flow pipe" in their design.

Thanks in advance for your thoughts.

[allanoue]

@kbryant ?

[micoulisninja]

Theory says:

from: http://www.rbracing-rsr.com/exhausttech.htm

When the exhaust valve opens there will be an instantaneous positive rise in pressure in the exhaust. Following this mass of expanding gas will be a negative pressure (vacuum) which helps evacuate the spent gases from the combustion chamber. If we have a 2-1 system this positive pulse will “hit” the collector causing a vacuum signal in the other primary tube..
Another way to look at it is that we have a soda straw...at one end is 15 psi and the other end is a vacuum. In this case the 15 psi is sitting outside your throttle body or carburetor and the vacuum is in your exhaust pipe. It is clear that having a low pressure event on the ass end of things can help the equation. Internal combustion engines are just air pumps and they need help.
The faster sonic (exhaust gas) wave acts in the same manner sending a signal down the exhaust pipe which, in the case of a 2-1 system, will cause a reflection back up the primary tubes as it enters the collector. These reflections can help your engine breathe by creating a lower pressure at the exhaust valve.With all these waves bouncing around the matter of their timing is really the million dollar question. Unfortunately this gets terribly complicated as header diameters, primary tube length and shape, collector design, tailpipe design, exhaust temperature, and a dozen or so other variables all get their shot at changing things. There are some general guidelines however, mostly based on exper-ience and exper-iment of manufacter...

Two-into-one pipes exhaust, if properly engineered, can increase efficiency through the "pulse effect" as both cylinders are feeding into one exhaust doubling the pulses thus increasing extraction effectiveness. The exhaust should travel uninterupted through the header portion of the pipe to the muffler section. There the pulses are doubled in the single resonator increasing extraction efficiency.

In fact many aftermarket systems have crosspipes too, mostly for keeping that pulse effect enough for low-mid rpm range (doesn't help much at the top end but does not sacrifice much power too) since widening the headers reduces exhaust gas velocity therefore the scavenging effect too, so that crossflow pipe remains at a certain distance from the exh valve to keep high pulse effect levels...

On the other hand, if how the system makes the engine sound is not an issue and low-mid range performance is not the TUNED engine's performance priority, it is better to prefer straight piped (Totsudo) or non-crossflow piped exhaust systems...
Basically it depends on what the tuner is looking for...
For example if an engine has been tuned only by re-jetting but looking for top end performance (without extreme mods that will help top end, such as bigger valves, wilder cams, higher comp, extra cc, bigger carbs etc) most people would prefer a non-crossflow system to give them that "punch" missing at the top end...
An engine with more mods that has enhanced flow and breathing capacities (always comparing to stock) could (and probably would) prefer an exhaust system with pipes big enough but also with a crossflow pipe to help preserve some mid-range torque and acceptable low-end...

Of course there are many other factors taken into consideration such as fuel consumtion (crossflow is claimed to keep good mpg rating and always a factory choice on small capacity inline 2 engines), firing order etc but it gets far too scientific for me beyond that...

Now V-2s are a whole different story(thinking you mean a Ducati or Aprilia by "Italian")... even among V-2 with different configuration angle... 45*, 60*, 90*(L), 180*(boxer) etc are each one a whole different story from one another mostly because of firing gaps creating different pulse effects...

As far as back pressure is concerned....

Backpressure does not increase horsepower.

An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work". Usually this comes from someone who is not a tuner or someone who is faced with a situation where he does not have the tools or means to adjust things. Anything you do in the exhaust will change the flows, the pressures, or velocities somewhat. The correct scenario is that the exhaust has to be properly designed and then you optimize the jetting, ecu data inputs, camshafts, port dimensions, valve sizes and the like. The exhaust has to be designed for the intended use.


Your engine has 15 psi (1 Bar) of atmospheric pressure sitting at the inlet and another 15 psi lurking at the end of the tailpipe. The inlet stroke creates a pressure differential and the atmosphere goes rushing inward. The exhaust valve opens and there is a pressure rise in the tube followed by a strong vacuum signal as the gases head down the pipe.

Logical extremes are often used to illustrate a point. For those who argue that backpressure can be a help they might say, from an extreme position, "Let's throw away the exhaust system so we have no backpressure at all". They would then conclude that the motor would run like crap and tehy are right. But that's only because they haven't gotten rid of backpressure, they simply have introduced 15 psi at the exhaust port and have given up any inertia, gas speeds or vacuum signals that exist in a primary tube.

The vacuum signal or low pressure that follows an exhaust event can be used to help scavenge the cylinder during overlap when both exhaust and inlet valves are open. Conversely, during this overlap period, the increase in backpressure can cause these burnt gases to re-enter the combustion chamber and contaminate the inlet charge. Result...loss of power.

The proper way to look at exhausts is to view them as a way to maintain the highest velocity that will not impede flow. As velocity increases the pressure drops and the engine can become more efficient. There is no "one answer".

[Country Joe]

Zack,
There you have it, a very well stated technical explanation of some of the intricacies of exhaust system design. Some aftermarket 4 into 1 headers have indeed had crossover pipes connecting pairs of pipes, but the added cost was not usually worth the gains to be had. Trust me, you are not likely going to find any benefit in cutting off and capping that crossover pipe. You might find miniscule gains on the top end at the expense of your mid range.

Joe

[sharky nrk]

^^^ can't say it much better than that, but the cliff notes of above it that a lot of exhaust use a link or cross pipe for scavenging effects on the other cylinder/cylinder banks. Some exhaust manufacturers incorporate this into the design, other's do not. It depends on the configuration and design of the piping. It may or may not help/hurt performance to remove the link pipe on the stock unit. Most likely if it gains anything it will be at the expense of performance elsewhere in the curve.

*edit* LOL Joe posted just a bit before I did *edit*

[kbryant]

Hi Zach - Welcome to the forum. In the simpliest form, the primary function in this particular case is that the cross-over allows smoother sound and reduction in decibels. In most (not all) motorcycle examples, that's why "cross-over" tubes are added. It allows the OEMs to reach the 80 dbA limit, while running a less restrictive muffler and/or without some kind of exhaust valve. Nothing more, nothing less. Twins are notorious for being difficult to pass sound legal limits. I can remember many years ago when designing aftermarket exhaust for Harley-Davidson Motor Company - the primary reason they changed to adding cross-over "balance tubes", was to meet the 80 dbA sound legal limits. It was the first time a manufacture truly admitted why the tube needed to be added. There are of course other ways to address it, but that would be simply through restriction in the muffler, which would lower the power level. The "cross-over" addressed the issue nicely and they were able to reduce sound levels 2 - 3 dbA (which is a huge amount), without the power loss. But it is a delicate balance of the positioning and/or size of the cross-over tube. This takes R&D to come up with the best positioning and diameter. Many times the actual "hole" that the tube is covering, is much smaller than the tube itself. Anyway, a lot more to it, but that is the basic reasoning behind the cross-over. The "surprise" you would get by removing that cross-over on your OEM headpipe, would be primarily sound; possibly a little better throttle response.

micoulisninja - That is a very well put statement. But when you post something like that, you should at least give credit to the people who actually wrote the paper and/or the brunt of it; and I would assume we both know who that is. Plagiarizing is not cool. Having been the in industry almost 40 years, we pretty much all know one another and/or seen most things before. Perhaps this was simply an oversight.

[micoulisninja]

Originally Posted by kbryant

micoulisninja - That is a very well put statement. But when you post something like that, you should at least give credit to the people who actually wrote the paper and/or the brunt of it; and I would assume we both know who that is. Plagiarizing is not cool. Having been the in industry almost 40 years, we pretty much all know one another and/or seen most things before. Perhaps this was simply an oversight.

The information I provided above is definetely not the distilment of my knowledge.... I just read and study as much as possible and simply know where to refresh my memory for that. It was indeed a mistake to omit to give the credit to those who deserve it and have the generosity to provide such vital and educational information to all of us for free. People whose work I admire and look up to.
Anyone interested can read in detail and examples given here:

http://www.rbracing-rsr.com/exhausttech.htm

I am sorry if I have offended you or anyone else by unintentionally taking credit from anyone for merely copying and summarizing some of my favourite articles on the web...

[kbryant]

Originally Posted by micoulisninja

The information I provided above is definetely not the distilment of my knowledge.... I just read and study as much as possible and simply know where to refresh my memory for that. It was indeed a mistake to omit to give the credit to those who deserve it and have the generosity to provide such vital and educational information to all of us for free. People whose work I admire and look up to.
Anyone interested can read in detail and examples given here:

http://www.rbracing-rsr.com/exhausttech.htm

I am sorry if I have offended you or anyone else by unintentionally taking credit from anyone for merely copying and summarizing some of my favourite articles on the web...

No offense taken and most definitely not my intention to insinuate such. Henceforth, my last statement of "Perhaps this was simply an oversight".

[micoulisninja]

Originally Posted by kbryant

No offense taken and most definitely not my intention to insinuate such. Henceforth, my last statement of "Perhaps this was simply an oversight".

Thank you Kerry !!

[LNasty]

The awesomely good natured people on this forum makes me want to hug kittens

[Alex]

Be gentle!

[kbryant]

And that is the primary reason as to why I solely support this site when it comes to the 250/300 crowd. Pretty much back to the beginning. Good stuff!

[LNasty]

Originally Posted by Alex

Be gentle!

"Of mice and Men" comes to mind

[fast1075]

How about "X" pipes? How do they work? What about the capped stubby pipes that seem to be there for no reason on some OEM exhaust? Straight cut pipe, or 45 degree slash?

Who's on first? What's on second? Can you really find the ideal collector length using a heat sensitive crayon? What's the deal with reversion harmonics?

I miss my 2 strokes.

[sharky nrk]

Originally Posted by fast1075

How about "X" pipes? How do they work? What about the capped stubby pipes that seem to be there for no reason on some OEM exhaust? Straight cut pipe, or 45 degree slash?

Who's on first? What's on second? Can you really find the ideal collector length using a heat sensitive crayon? What's the deal with reversion harmonics?

I miss my 2 strokes.

X and H pipes are pretty much the same concept and are also known as a crossover pipe, each system works by balancing the exhaust pulses from either side—or cylinder - or cylinder bank

Straight from Flowmaster

"Is an "X" pipe better than and "H" pipe?

Not necessarily. Flowmaster has performed extensive dyno testing of traditional “H” pipes and various “X” pipe designs and has found that in most typical street applications, there are no clear benefits of one over the other. “X” pipes have become a buzz word in the world of performance exhaust, and are now produced in a wide variety of styles and designs. Some types perform well, and some others can be quite bad due to the excessive turbulence generated in the merge area. Unlike anything else available, Flowmasters Scavenger X-Pipe design features patented D-port technology to maximize the communication surface area between the two banks of cylinders, and maintain the exhaust pulse velocity for peak scavenging. In terms of sound, an X-pipe will generally provide a smoother, higher pitched tone than that of a traditional “H” crossover pipe. In some specialized race applications such as small cubic inch engines and /or restricted (small bore) carburetors, we have found that an “X” pipe can respond well over an “H” pipe. As with all race applications, there is no substitute for time on the dyno, developing the engine package as a system."

[fast1075]

Years ago, there was a guy that ran a GPZ-550 in IDBA. I forget the class exactly, it was a Modified, I think. Dern fast little bugger.

At any rate, Murray built a custom "X" exhaust for it. That pipe made 6 more HP than any other pipe, plus it made the engine sound like it was turning a gajillon rpm. (It was in fact being turned to near 13,000).

That thing would make your ears bleed. ALMOST as loud as the Denco Triple/Triple (Three 750 Kawi triples in one chassis).

[kbryant]

Originally Posted by fast1075

Years ago, there was a guy that ran a GPZ-550 in IDBA. I forget the class exactly, it was a Modified, I think. Dern fast little bugger.

At any rate, Murray built a custom "X" exhaust for it. That pipe made 6 more HP than any other pipe, plus it made the engine sound like it was turning a gajillon rpm. (It was in fact being turned to near 13,000).

That thing would make your ears bleed. ALMOST as loud as the Denco Triple/Triple (Three 750 Kawi triples in one chassis).

Harry - Murray definitely had hero status back in the day (and still does to some of us). "X" pipes and "H" pipes are very different concepts when it comes to motorcycle exhaust design. If you had a CB750 SOHC or Z1 in the early 70's, you wanted a Murray because it was the best. And your reference to Denco is an obvious sign of your "age group" Both Dennis Murray and Dennis Dean were pioneers in our industry, along with George Kerker, Darryl Bassani and Pops Yoshimura. That's really where it all started for me. I was able to tutor under both Pops and Darryl in the mid-70's. I was driving down to SoCal from the Bay Area at least 2 or 3x a month in those days.

That being said, please correct your sig line about Kenny's ride at Indy as it's bugging me. - The TZ750 Miler was never a "short track bike". Back then it was either 250 or 360 two strokes only on the Short Tracks. That was an awesome ride even by today's standards. Kenny get's all the credit, but actually I think Mark Brelsford won a regional mile (Stockton) on an H2 before Kenny's historic win (although Kenny's was of course a GNC event), when everybody was going crazy about a 750 two stroke road race engine being used at a mile event. Ok probably dating myself too much here. Most of this stuff may have occurred prior to many forum members being born yet!

[garth285]

just for information.... NONE of the full systems for the ninja 300 have that crossover pipe.... might be worth it to find a used on on ebay cheap ($75 shipped) do the modification and do back to back testing.... a dyno would be the best thing to see if it makes a difference obviously...

Just my 2 cents!

[kbryant]

Originally Posted by garth285

just for information.... NONE of the full systems for the ninja 300 have that crossover pipe.... might be worth it to find a used on on ebay cheap ($75 shipped) do the modification and do back to back testing.... a dyno would be the best thing to see if it makes a difference obviously...

Just my 2 cents!

Well actually.... I believe Two Brothers does in fact have a cross-over in their headpipe. For their own particular reasons and/or logic.

[garth285]

Originally Posted by kbryant

Well actually.... I believe Two Brothers does in fact have a cross-over in their headpipe. For their own particular reasons and/or logic.

I stand corrected!

I wouldn't ever run Two Bros though anyways... never liked their quality

[fast1075]

I purposely used short track because most people instantly recognize the term. Only us old farts may recognize Grand Nationals.

I was so out of touch on short track, that when I went to see the races at Daytona in March, the bikes were just hotted up dirt bikes.

I was envisioning XR-750s crossed up throwing great spouts of clay in my face.

At the AIM show last October, on display at the K&N exhibit were two replicas of the bike that Kenny rode. Complete in every detail right down to the first gen Lectrons.

Tinkering is fun, but the most fun was my old job back in the 70's when I worked for Honda. TTD (Test to Destruction). What can possibly be more fun that taking a new bike and beating it till it dies and get paid to do it!

Speaking of Kawi triples, ever hear of Bill Baxter? He was THE MAN with the H2 drag bikes. In IDBA he held so many records it was unreal. He built an engine that made so much power that not even Paul Gast could build parts to handle it. So he sectioned off the transmission and built a unitized transmission that used Suzuki Pro Stock transmission parts.

Now days, I just keep my baby ninja running well, and turn the occasional screw on my buddy's Top Gas bike. That thing is a hoot to ride. If you turn off all the timers and the throttle stop, set the nitrous delay to zero, and give it a build rate of 2 seconds, it will (with my ancient 145 pound ass on it) run 7.80's at 188. And as many hot laps as I have had, it still makes my knees quiver after I get it hauled back down. Oh, and it does have an old Murray pipe that used to be on one of Bob Carpenter's old Pro Stock bikes.

[kbryant]

Good stuff.