A little backpressure is a good thing . . .

[geospencer]

I have had two beautiful days to try out my new Termignoni 2 into 1 exhaust system. Since the baffle is relatively easy to take out and put back in I decide to try it both ways. This was an unscientific seat-of-the-pants evaluation but it was conclusive for me.

And my conclusion is . . .

Well, in another post Don (DUCeditor) reminded us that a little backpressure is a good thing and I am here to say that he is right.

With the baffle out my RPMs dropped to low at idle and I felt a hesitation when I accelerated up through the gears.

With the baffle in the RPMs don’t drop, there is no hesitation in any gear and I am able to use more of the power band. (I’m not sure if that makes and sense. With the baffle out I had to downshift a lot to keep the engine “pulling”. With the baffle in I do not have to downshift so often.)

You might experience something different but I am keeping my baffle in. (My neighbors will be happy. )

[MajorSoftie]

What you have basically described is that you need to adjust your idle if you run without baffles.

The dyno runs shown on this site show that there is much more power in the mid-range torque with the baffles out, along with somewhat higher peak power.


On the other hand, if you're happy with the baffles in, hey, it's your bike, and there's nothing wrong with making the neighbors happy. You still get a little more power than with the heavier stock cans.

[bongoboyla]

Originally Posted by geospencer

I have had two beautiful days to try out my new Termignoni 2 into 1 exhaust system. Since the baffle is relatively easy to take out and put back in I decide to try it both ways. This was an unscientific seat-of-the-pants evaluation but it was conclusive for me.

And my conclusion is . . .

Well, in another post Don (DUCeditor) reminded us that a little backpressure is a good thing and I am here to say that he is right.

With the baffle out my RPMs dropped to low at idle and I felt a hesitation when I accelerated up through the gears.

With the baffle in the RPMs don’t drop, there is no hesitation in any gear and I am able to use more of the power band. (I’m not sure if that makes and sense. With the baffle out I had to downshift a lot to keep the engine “pulling”. With the baffle in I do not have to downshift so often.)

You might experience something different but I am keeping my baffle in. (My neighbors will be happy. )

That's because from the factory the Termi ECU is tuned to work with the backpressure provided by the baffles.

If you pulled the baffles out and took it to the dealer for a tune, the bike would run like a top. At which point, re-installing the baffles would result in a poorly running bike due to the extra backpressure they provide; backpressure that the ECU would then not be tuned for.

[Motomonster]

It's true, well set-up Termis sans baffles easily outperforms a baffles in set up. The baffles in will smooth out engine performance which is great for cruising and kicking back. Without them, you have more of the engine on/off effect which helps the bike perform in the twisties.

Plus, the acceleration is much better. Baffles in is kinda sluggish in comparison.

[geospencer]

I see what you mean and agree. I am sure that the bike was tuned to run with the baffle in. Since I am not going racing . . . and since I have neighbors . . . I think I will be happy with the baffle in. But it is good to know that the extra power is there if I want to tune for it. Thanks for the explanation.

One reason that I will leave the baffle in is that some of the places where I ride are starting to crack down on loud mufflers.

One other thing that I can't prove . . . my seat-of-the-pants feel tells me that the bike runs better with the Termignoni 2 into 1 system than it did with the Termignoni 2 into 2 exhaust system. (It's probably that I just want to feel that way since I have invested in both now. )

[bongoboyla]

Again, a bike needs to be tuned if ANY modifications to intake or exhaust are made. These motors are very sensetive to airflow mass and backpressure. Tuning has a significant impact on throttle response, smoothness and idle.

Once you find what makes you happy, invest $99 in a tune. It's a whole different bike.

[redbcgraygt]

They used to tell me it's better for your engine to have a certain amount of back pressure, but I dont know how true that is.

[MajorSoftie]

Originally Posted by redbcgraygt

They used to tell me it's better for your engine to have a certain amount of back pressure, but I dont know how true that is.

Sort of true but not exactly. Any engine that has been designed to run with some back-pressure will never run as well with absolutely none. It's not just tuning, it's cam profile and duration, port volume, valve size, combustion chamber shape, etc..

On the other hand, I'm sure you've seen the exhausts on Top-Fuel Dragsters. They produce absolute highest horsepower per liter of any motor, but they have been designed to run their best with no back-pressure.

[bongoboyla]

Keep in mind that with the bends and joints in the system, there is always going to be a little back-pressure. The only way to have none is to remove the system altogether.

[duc-n-cover]

Exhaust Theory
There are two major areas of the complete exhaust system that are typically tuned for enhanced performance; the exhaust manifold .or header and the rear muffler(s). The exhaust manifold’s length, tubing diameter and the manner in which each cylinder is linked to the other is critical when attempting to maximize an engine’s power output. The manifold configuration can be manipulated in order to generate maximum power at low, middle or high rpm, changing the shape of the power curve accordingly. Naturally some compromise must be accepted when tuning an exhaust manifold for a street-car as the goal is typically to ensure balanced power output at low, middle and high rpm. This is in contrast to a race-engine where the exhaust manifold can be tuned specifically for maximum performance at high rpm.

After the exhaust manifold or header, optimum performance comes from making the balance of the exhaust system as short and large as possible. This approach will result in greater engine efficiency for maximum power, as well as minimizing the weight of the system. Probably the best example of an optimized, no-compromise exhaust system would be that of an F1 racecar. If you have ever had the opportunity to hear an F1 exhaust note, I think you will agree that it is best described as deafening. Clearly an exhaust system that even approached such a volume level in a performance street-car would draw far too much of the wrong sort of attention. Therefore, a modern street-car exhaust represents a number of performance compromises in order to achieve an acceptable exhaust volume, as well as meeting emissions standards.

In order to accommodate the various components and baffling necessary for a street-car, the exhaust system becomes longer and the flow of gasses more circuitous as noise and emissions standards are addressed. Each bend in the exhaust tubing, catalytic converter, resonator and so forth introduces restrictions to the exhaust flow, particularly at higher rpm where flow is most critical. Exhaust flow can actually reach hundreds of miles per hour when the engine is producing maximum power, which results in power robbing friction along the exhaust tubing
walls, particularly when the gasses must change direction. This friction results in increased backpressure that can be quantified with a pressure gauge. In addition to the friction issue, a tube or opening that is too small will result in extra backpressure as well. This backpressure restricts the amount of gasses that can be passed through the engine, resulting in a reduction of peak power.

I’m fairly certain that many of you have been exposed to a “bench racing legend” that would have you believe that increased backpressure will improve low rpm power and that low backpressure will increase high rpm output. Nothing could be further from the truth. An exhaust system is sized for maximum flow at wide-open-throttle and peak rpm. All exhaust systems are “oversized” for lower engine speeds (rpm), as backpressure is so insignificant that it can’t even be measured. Less back-pressure always results in more power at higher rpm, with no negative effect on lower engine speed performance. The amount of power that can be extracted from an
engine at a given rpm as a result of exhaust design is really limited by the exhaust manifold or header. After the header, less backpressure is always better.

The real challenge when tuning a street-car exhaust is to increase flow without making the system so loud as it becomes unacceptable or even illegal. It is also important to understand that vehicle manufacturers must meet more stringent maximum volume requirements than aftermarket manufacturers.

BMW’s current M-cars feature a distinctive quad exhaust tip design, punctuating the cars’ high performance image. This approach is very logical when applied to a “V” engine configuration because there are natural dual exhaust outputs with this engine design, as indicated in the following diagram. It should be noted, however, that packaging issues will certainly effect whether or not a dual muffler approach is feasible for a given BMW model, such as in the case of the 540 where a single muffler is employed as there is no space available for a second
muffler.