Performance

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How much performance improvement can I expect by purchasing an Akrapovic exhaust system?

Simply stating the final maximum horsepower rating is not enough; when we speak of increased power we also have to take the torque curve into account. Only by comparing both the power and torque curves can we form an accurate picture of the performance of a modified exhaust system in comparison to the stock system. When reading power and torque curves it is also important to take into account the nature of the increase (sharp, smooth) as well as the distribution of the increase over the rpm range of the engine. This is different for every model of bike as well as each line in the Akrapovic exhaust systems rang.

The increase can be read in the segment where the motor reaches its peak power and torque output at certain rpms, which are not necessarily the motor's highest. It is also not necessary that the maximum power and torque readings for the modified system appear at the same rpms as the stock system's maximum output. (This is a good indicator of the contribution of the modified exhaust system, i.e. the increase of the range of the motor with the use of the modified system, and at the same time it shows the character of the modified system.) We can also read for maximum increased power, i.e. the greatest difference in the power output of the modified vs. the stock system.

The performance improvement of Akrapovic exhaust systems varies. The power increase for the Racing line is explosive and concentrated in the upper end of the rpm curve. Some models offer maximum increased power in the lower and middle sections, while still others smoothly enhance and increase the stock power curve throughout the entire rpm range. One characteristic common to all Akrapovic exhaust systems is a tendency to smooth out unpleasant fluctuations in stock power curves.

As already mentioned, the increase in power depends on the type of exhaust system and the type of motorcycle. The set-up of the stock bike also has to be taken into account, especially with regard to legal regulations (power restrictions etc.) for the specific market for which the bike was produced.

Several parameters affect the measurement of the performance of the engine of an individual motorcycle:

• immediate environmental factors (air temperature, atmospheric pressure, humidity, intake air velocity),
• state of the motorcycle (engine temp., condition of the rear tire, chain or shaft drive),
• type of measuring equipment,
• percentage error which appeared in the building of the engine.

In addition to all this, you have to be able to maintain the same conditions for quite some time, which is unfortunately impossible. Because of this, various correction factors are employed to compensate for different influences, but none of them is capable of properly calculating all of the changes which occur during the measuring period. It makes no sense to compare two diagrams measured on two different dynos. Only a difference measured on the same bike on the same dyno under the same conditions counts.

We must emphasize that we have not taken into account the use of special engine parts for improving the engine's power output in combination with our exhaust systems. All of our measurements were made using stock factory engine set-ups (with certain exceptions).

Since the measurements of Akrapovic exhaust systems were obtained using stock engines and compared with those of stock exhaust systems, the quality of the stock exhaust systems is also an important factor in the final results of our measurements.

For the majority of our exhaust systems we offer a dynograph which shows performance improvement in comparison with the stock exhaust system. The exception is the Evolution line, which was developed and tested on Superbike and Supersport factory machines. The flagship of the Akrapovic range, offering only the highest performance.

Is the sound of the carbon outer sleeve muffler different from the titanium outer sleeve muffler? Is there any influence on performance?

No, neither the sound nor the performance is affected. The choice is purely aesthetic.

Can the performance of a 4-stroke motorcycle engine be improved by installing an aftermarket exhaust system? What happens when you do? How does changing the configuration of the exhaust system affect engine response?

The shape and length of the tubes is extremely important for ensuring the optimal flow of exhaust gases. The object is to create the best possible and fastest flow of exhaust gases away from the cylinders. Conical tubes are most often the best for this. Recently we have been using hydroforming technology for certain motorcycles and exhaust systems, which allows us to produce special D-type header tubes. D-shaped, conical and appropriately bent tubes allow us to achieve the optimal shapes in places where exhaust gas turbulence is at its highest level and causes the greatest amount of interference.

Clear evidence for the effect of tube length on engine performance can be found in the recent trend of mounting motorcycle exhaust systems under the seat. On some motorcycles with inline four cylinder engines, under-the-seat exhaust systems have a negative influence on engine power. In some cases the power is decreased due to the excessive tube length dictated by the design of the system. The design in question is better suited to V engines. The trend of using such configurations comes from MotoGP, but on ordinary bikes it has for the most part only a visual effect. Another negative effect of such mounting systems is overheating due to insufficient cooling under the seat. This mounting style also affects the motorcycle’s center of gravity, since the muffler is mounted higher than usual.

In addition to the shape and dimensions (diameter and length), for single and twin cylinder engines the shape of the outlet cap is also important. The length, diameter and final angle of the outlet tube also have to be taken into consideration. These parameters also have a major effect on the sound of these types of engines. In conformance with the regulations on exhaust system noise levels for both competition and street use, we also produce special outlet caps with noise dampers installed.

We should also mention the relation between the exhaust system and the engine settings as electronics, ignition, injection, carburetors. The Slip-On, Bolt-On, Racing, Evolution and all Street Legal lines are designed to function properly using the stock carburetor or electronic fuel injection settings. This means that no changes to the stock settings are necessary in order to use Akrapovic exhaust systems. Also, all of the performance specifications which we measure and list for each exhaust system model are based on stock settings. We assume full responsibility for the accuracy of these specifications. However, we also believe that it is possible to improve the original settings when our exhaust systems are used.

Of course, the market for tuning kits is extremely large, covering practically every motorcycle component. Tuning of the exhaust system includes the carburetor and EFI settings in addition to aftermarket components. There is a huge demand for this particular combination.

For more information see the answer to the question I bought an Akrapovic exhaust system. Do I have to rejet the bike? Which jet kit do you recommend for use with your exhaust system?