Exhaust Primary Length Calculation

[rjwoods77]

I searched the previous posts and didnt really find any clear answer on this. I have a burns 2 to 1 collector. When adding up my runner lengths do i include the pipes all the way up to their convergence point(collector tube instant center if you will)and the distance from mount flange to valve. I assume the answer is yes but was wondering if my assumption ws correct.

[rjwoods77]

I searched the previous posts and didnt really find any clear answer on this. I have a burns 2 to 1 collector. When adding up my runner lengths do i include the pipes all the way up to their convergence point(collector tube instant center if you will)and the distance from mount flange to valve. I assume the answer is yes but was wondering if my assumption ws correct.

[KU_Racing]

if you are doing the calculations for the exhaust harmonics, use you should include the length of the tube all the way up until the diameter starts to change. In other words, if you are using a slip-on collector, the geometry of the tube starts to change as soon as it ends and the collector starts to smooth the two streams into one. As soon as the geometry changes, the harmonice reflections will start.

[rjwoods77]

Our collector is a slip fit but the size of the tube after the flare/bulge is the same size as our primary so that gives me about another 3 inches before the fishmouh on the inside happens which is what you are saying as a section change. Correct? There will be a slight groove where the primary tube beds itself against the radius of the flare/bulge since they cant meet up perfect. Is this the spot or is what I said the first time correct?

[Buckingham]

That's like asking how much castor to run. It depends on your target HP curve. Its also a decision that is a balance beam between pipe losses (fluids) and wave timing. Freshman 1-D wave physics and Junior Mech Eng 1-D pipe flow can give you a good ballpark of each end of your balance beam. It is up to you to pick (test) where the pivot on that beam lies.

[rjwoods77]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by dhaidinger:
That's like asking how much castor to run. It depends on your target HP curve. Its also a decision that is a balance beam between pipe losses (fluids) and wave timing. Freshman 1-D wave physics and Junior Mech Eng 1-D pipe flow can give you a good ballpark of each end of your balance beam. It is up to you to pick (test) where the pivot on that beam lies. </div></BLOCKQUOTE>


I didnt ask how long to make them. I found myself about 5 inches short of the target length and got to wondering about how much the port length and collector lengths count if the do at all. I wont be short if that is counted as effective length. Stick to what I asked and not what you feel like hearing when you read something. I think that would be 3rd grade 1-Dimensional english Donavan.

[KU_Racing]

i see what you are saying about the geometry of your collector- I am used to hand fabbed collectors using up-sized tubing with no flaring- when that style is used, the geometry change is directly at the end of the runner. With the style you are talking about, you want to include any part of the collector that is the same I.D. as your runner tubing. In other words, measure the length of your runner seperate from the collector, then on the outsid of the collector, measure the length from the end of the flare (where the runner ends when it is inserted) to where the tube starts to curve (first change in geometry) and add that to your runner length.

[rjwoods77]

Plus port length? Actually that brings up the other side of things. Would this count for intake port for the intake manifold as well. I assume the gas doesnt know what it is flowing through as long as it has smooth transitions. Thank you for the response by the way.

[KU_Racing]

yes, plus port length it the transition from port to manifold is smooth.