Bro, i m dun really understand about when u say 421 is for hi rev n 41 is for low rev... mind to share more on that? coz from what i know is hks 4-4-1 extractor is also known as racing headers... n from my understanding, racing headers is meant for those constanly on hi rev to get the most hp...
coz i m using hks 4-2-1 now, and i am damn happy with the 2-3.5k rpm torque n response...
may be will try 4-4-1 n see how is the performance..
i dun know about extractor well..... plz shoot if wrong
I also hard to say... some said 4-1 is for accelerate, some said 4-1 is for high rev...
i used 4-1 extractor before... found that,... 4-1 respond better at low rpm than 4-2-1...
Anyway.. this is old timer thread..that had been discuss before...
http://www.zerotohundred.com/newforums/toyota/67829-4age-exhaust-experiment-report.html
Generally, the exhaust manifold is the part which collects the exhaust gasses from the respective cylinders of the engine to lead the flow of the collected exhaust gas to an exhaust pipe. In a 4-cylinder engine, usually four runners or pipes are used. In one type, the four runners are directly connected to a gas confluence part that is connected to the catalytic converter and leads to the exhaust pipe and muffler. In another type, the runners are connected in two pairs respectively to the gas confluence part.
The former type (in which the four runners are directly connected) is generally called 4-1 type. In this type first, second, third and fourth runners are connected to a gas confluence part with uniform spacing between the runners at the point they join the confluence part. The gas confluence part is provided with a sensor installation slot for installing an oxygen sensor.
While this type of manifold has a simple structure, the spacing between the runners is narrow where it joins the gas confluence part. As a result, the gas confluence part frequently cracks due to thermal stress, with the result that the overall life of such an exhaust manifold is decreased. An additional drawback exists in that exhaust gas interferences occur between the runners in accordance with the ignition sequence (first cylinder→third cylinder→fourth cylinder→second cylinder).
The second type of manifold (in which the four runners are connected to the gas confluence part in two pairs) is generally called 4-2-1 type. In this type the first and fourth runners are joined together in a Y-shape before being connected to the gas confluence part. Likewise, the second and third runners are joined together in a Y-shape before also being connected to the gas confluence part. As a result, only two passages, i.e., a passage which has been formed by the joining of the first and fourth runners, and another passage which has been formed by the joining of the second and third runners, are connected to the gas confluence part. The gas confluence part is also provided with a sensor installation slot for installing an oxygen sensor.
This 4-2-1 type exhaust manifold has an advantage that the flow of the exhaust gas is more efficient compared with the 4-1 type exhaust manifold. However, in this exhaust manifold, because the first runner and the fourth runner face toward each other, if the length of the first and fourth runners is too short, an exhaust gas interference cannot be avoided in accordance with the igniting sequence (first cylinder→third cylinder→fourth cylinder→second cylinder). As with the 4-1 type exhaust manifold, the spacing between the runners is narrow where they join the confluence part, again resulting in thermal stress cracks.
Further, the 4-2-1 type exhaust manifold is more complicated in its structure compared with the 4-1 type exhaust manifold. Consequently, the manufacture is more difficult and the weight greater
