There are many conflicting arguments about the head / extractor feature between 4-1 and 4-2-1. The most common thing I usually hear is "picking untuk 4-1 (couple), 4-2-1 plak untuk long (high speed)." I will not argue what is what, I just want to share what I think is the correct theory.

I think 4-2-1 is for low to mid rpm, which in general terms of collection or couple, meanwhile is 4-1 for high speeds. Then you say "Kalau Cam Tu kenapa Kereta drag racing Pakaya 4-1, Bukan nak Ker diaorang pickup?" An drag cars running in high speed, the shift to 7000 RPM and above, each quarter to drop the RPM 5000-6000 RPM, so that's why drag cars use 4-1. If you look at the track cars, they usually use 4-2-1 configuration, why is because they need a little mid RPM, they corner, going to brake, change the fifth gear to third speed of 1 GB, the speed decreases and a second full throttle back to Redline, all this is a 4 to 2 -1 characteristic.

For this example, I'll copy and paste some info I got from other sites to review for you and myself:

The first misconception that needs clarification is that a header against relieves pressure, but against a certain amount of pressure is needed for optimal performance. Just the opposite is true. A good head against not only relieves pressure, but goes further and creates a vacuum in the system. When the exhaust valve opens next cylinder, the vacuum in the system pulls the exhaust from the cylinder. This is what the term "scan" means.

The first consideration is the diameter of the tube proper. Many people think "Bigger is Better", but it is not. The smallest diameter that will flow enough air to handle the DC motor to your desired RPM redline should be used. This small diameter will generate speed (air speed) needed to "clean" at low speeds if a too small diameter is used the engine will pull hard at low revs, but at some point in the RPM top tube will not be able to airflow that the engine is pumping, and the engine will "sign" the beginning, not reaching its potential peak RPM This would require a larger size is the diameter of the tube.

The second consideration is the length of the tube proper. Length directly controls the power band in the RPM range. Tube lengths longer get the couple to a lower RPM range. Shorter tubes move the power band in a higher RPM range. Engines red line at 10,000 R.P.M. short tube lengths would need about 26 "long. The engines are couplers and the red line at 5500 RPM would need a tube length of 36". This is what is meant by the term "Tuned Length". The length of the tube is set to run the engine at a desired speed range.

The third consideration is the collector outlet diameter and length of extension. This is where major differences occur between four-cylinder engines and V-8 engines. The optimal situation is the four-cylinder because of its cooking cycle. Each degree of rotation of the crankshaft 180 there is an exhaust pulse entering the collector. It's the perfect time because, as a pulse leaves the collector, the exhaust valve is opening and following the vacuum created in the system pulls the exhaust from the cylinder. In this ideal bike 180 degrees to the diameter of collector output should be 20% larger than the diameter of the primary tube. (Example:. 1 3 / 4 "primary tubes need a 2" diameter collector output) The golden rule here is two tube sizes. This keeps the high speed scanning to increase, especially at low rpm Go to a larger diameter output will hurt the midrange and low rpm torque.

**Larger diameter moves peak torque at a higher rpm compared to a smaller diameter.**

The larger the diameter, the area most cross. Flow of exhaust gases must overcome the additional transverse tube area and therefore the flow moves more slowly. It takes the rpms to climb to a higher speed before the speed of 240 ft / sec (hence, peak torque) is reached. While increasing diameter offsets when 240 ft of torque / sec and the peak is reached at a higher rpm or later because it takes longer for the rate of flow of air to 240 ft. / sec.

In addition, a larger diameter will increase the number of actual peak torque (ie not just change the location of diameter, it also increases the couple).

**Longer tubes will create more torque at low rpms the torque peak.**

How do they do that?

Longer tubes will accelerate the rate of flow of air. The flow velocity of 240 ft / sec and a maximum torque occurs at a higher rpm compared to a shorter tube. Changing the length of the tube-head does not increase the value of peak torque as the diameter does. Instead of the term behavioral changes around the torque peak torque down the rev range.

If you imagine the torque vs rpm curve from a dyno to be like a seesaw: when, on a swing there is a point where the board to allow it to rock up and down. This is usually in the middle of the see saw and is also called the pivot. Our torque curve vs. rpm, peak torque imagine to be the pivot, even if this support does not have to be in the middle as the swing ... it can be moved. Change in length "rocks" of the torque curve of peak torque.

If you have a tube top over primary, the torque curve will "rock" so that the left side is higher than the right side. There is a higher torque at the earliest before the maximum torque RPM. There is less torque at rpms later, after a couple of points.

If you reduce the length of the primary tube, the torque curve will be the swing with the right side than left. So there is more torque at rpms later, after a couple of points.

Longer tubes will accelerate the rate of flow of air. The flow velocity of 240 ft / sec and a maximum torque occurs at a higher rpm compared to a shorter tube. Changing the length of the tube-head does not increase the value of peak torque as the diameter does. Instead of the term behavioral changes around the torque peak torque down the rev range.

If you imagine the torque vs rpm curve from a dyno to be like a seesaw: when, on a swing there is a point where the board to allow it to rock up and down. This is usually in the middle of the see saw and is also called the pivot. Our torque curve vs. rpm, peak torque imagine to be the pivot, even if this support does not have to be in the middle as the swing ... it can be moved. Change in length "rocks" of the torque curve of peak torque.

If you have a tube top over primary, the torque curve will "rock" so that the left side is higher than the right side. There is a higher torque at the earliest before the maximum torque RPM. There is less torque at rpms later, after a couple of points.

If you reduce the length of the primary tube, the torque curve will be the swing with the right side than left. So there is more torque at rpms later, after a couple of points.