re rejetting carbs in article jburney hydra nodc noaa gov jburney hydra nodc noaa gov jeff burney writes if we are only talking about stroke i think i can understand exhaust pulse affect in a stroke the intake valve is closed on the exhaust stroke and the gas is pushed out by the cyclinder i guess there is some gas compression that may affect the amount pushed out but the limiting factor seems to be the header pipe and not the canister meaning would gases so far down the line the canister really have an effect on the exhaust stroke do the gases really compress that much for discussion purposes i will ignore dynamic effects like pulses in the exhaust pipe and try to paint a useful mental picture unless an engine is supercharged the pressure available to force air into the intake tract is atmospheric at the time the intake valve is opened the pressure differential available to move air is only the difference between the combustion chamber pressure left over after the exhaust stroke and atmospheric as the piston decends on the intake stroke combustion chamber pressure is decreased allowing atmospheric pressure to move more air into the intake tract at no time does the pressure ever become negative or even approach a good vacuum at the time of the exhaust valve closing the pressure in the combustion chamber is essentially the pressure of the exhaust system up to the first major flow restriction the muffler note that the volume of gas that must flow through the exhaust is much larger than the volume that must flow through the intake because of the temperature difference and the products of combustion in the last years the japanese manufacturers have started paying attention to exhaust and intake tuning in pursuit of almighty horsepower at this point in time on high performance bikes substitution of an aftermarket free flow air filter will have almost zero affect on performance because the stock intake system flows very well anyway substitution of an aftermarket exhaust system will make very little difference unless in general the new exhaust system is much louder than the stocker on older bikes exhaust back pressure was the dominating factor if free flowing air filters were substituted very little difference was noted unless a free flowing exhaust system was installed as well in general an engine can be visualized as an air pump at any given rpm anything that will cause the engine to pump more air be it on the intake or exhaust side will cause it to produce more horsepower pumping more air will require recalibration rejetting of the carburetor dave tharp dod you can t wear out davet interceptor cds tek com mra an indian scout k s indian chief ahrma or its brother the chief r s tr b ama they re built like rocks r velorex nsu max to take the knocks bmw r compulsive it s the harleys that my employer has no idea joiner give you grief
