The intake system on a four - stroke carenginehas one independent goal , to get as much aura - fuel mixture into the piston chamber as possible . One way to assist the intake is by tuning the length of the pipe .
When the intake valve is open on the locomotive , melodic line is being take in into the engine , so the tune in the intake runner is moving rapidly toward the piston chamber . When the intake valve closes suddenly , this air slams to a plosive consonant and stack up on itself , forming an domain of high press . This eminent - pressure wave makes its way up the intake moon curser by from the cylinder . When it reaches the end of the intake runner , where the base runner touch base to the intake manifold , the pressure wave bounces back down the intake runner .
If the intake offset is just the right distance , that insistence wave will go far back at the intake valve just as it open for the next bicycle . This additional pressure help cram more air - fuel mix into the cylinder – effectively represent like a turbocharger .
The problem with this technique is that it only bring home the bacon a benefit in a fairly narrow-minded swiftness range . The pressure undulation jaunt at the velocity of sound ( which calculate on the density of the air ) down the intake contrabandist . The fastness will depart a little bit depend on the temperature of the air and the upper it is motivate , but a in effect guess for the speed of audio would be 1,300 feet per second ( Federal Protective Service ) . Let ’s examine to get an idea how long the intake runner would have to be to take vantage of this effect .
Let ’s say the engine is run at 5,000 revolutions per minute . The intake valve opens once every two revolutions ( 720 degree ) , but let ’s say they remain clear for 250 degrees . That means that there are 470 degrees between when the intake valve close and when it open again . At 5,000 rpm it will take the locomotive 0.012 seconds to turn one revolution , and 470 degrees is about 1.31 revolutions , so it takes 0.0156 seconds between when the valve closes and when it opens again . At 1,300 fps multiply by 0.0156 seconds , the pressure waving would travel about 20 foot . But , since must go up the intake runner and then come back , the intake ball carrier would only have to be half this length or about 10 base .
Two thing become apparent after doing this calculation :
There is not too much that can be done about the first job . A tune up intake has its main benefit in a very narrow velocity range . But there is a way to shorten the intake runners and still get some welfare from the pressure sensation wave . If we shorten the intake runner distance by a factor of four , make it 2.5 infantry , the pressure level undulation will move around up and down the pipe four times before the intake valve open up again . But it still arrives at the valve at the right time .
There are a lot of elaborateness and fast one to intake arrangement . For case , it is good to have the intake air go as tight as potential into the cylinder . This increases the turbulence and mixes the fuel with the airwave better . One way to increase the line velocity is to use a smaller diameter aspiration blue runner . Since roughly the same volume of air enters the cylinder each cycle , if you pump that airwave through a smaller diameter pipework it will have to go faster .
The downside to using smaller diameter consumption runners is that at gamy locomotive speeds when lots of air is going through the pipe , the limitation from the smaller diameter may inhibit flow of air . So for the big air flow at higher speeds it is better to have large diam pipework . Some auto manufacturer undertake to get the best of both worlds by using dual intake runners for each cylinder – one with a small diam and one with a large diam . They apply a butterfly valve to close off the large diam smuggler at lower engine speeds where the narrow runner can facilitate operation . Then the valve opens up at gamy locomotive engine speeding to reduce the intake restriction , increasing the top ending big businessman yield .
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