TC88 you have a choice between the 1 3/4” and the 2” designs. We can sum this up in Twin Cam terms: 88”, 95”, and evenġ03' motors should use 1 3/4” primary tubes. Inch Big Twin do not need the same exhausts.D’OH!Īs to what tube size to choose aren’t very scientific but are based onĮxperience. The reason we do this is that an 883 Sportster and a 160 In both 1 3/4” and 2” as well as tapered Nitro Duals that open up fromĢ” to 2 1/2”. RB Racing makes two basic diameters of primary tubes.LSR 2-1 designs The rpm band up about 600 rpm for the same size engine. Simply put, an increase of of 1/4” in diameter will shift Tube size much larger than this “slightly larger” is no benefit Increase the flow on the “short” side or floor of the port. The “D-shape” flattens out the floor to the port to Larger that the exhaust port area which, in itself, will most likely be Highly negative pressure in the exhaust during the overlap period whenīoth inlet and exhaust valves are open, is the key to making power.ĭesign will influence this but, in regards to the primary tube size, we We want a lower pressure and a higher speed in the exhaust. BERNOULLI explained this mathematically for us a long, long, time ago. Pressure and, conversely, a higher speed is a lower pressure. For the expanding, hot gases a slower speed means a higher Things simple, this is summed up as “the larger the tube, the lower the Said the primary tube size is important to these gas speeds. Of a lot better that “The Mummy Returns” tape routine. Temperatures higher that if the exhaust was chromed and it looks a hell While this might seem to be logical, we do not Go to “ugly lengths” to wrap their exhausts in thermal blankets to keep Those really long fat pipes you see are decellerating the exhaust as To keep this simple, it just means cooler is slower. The mathematical solution is that this velocity variesĭirectly with the square root of the ratio of the absolute exhaust Loss of temperature as the exhaust travels down the exhaust will slow The speed of these gases will be determined by the diameter and shape of the primary tubes and the temperature of the exhaust. Secondly, the hot expanding gases head down the pipe atĪbout 300 feet per second (91 meters/second). A sonic wave heads down the pipe at about 1600 feet/second (about 487

Sportster cam change