Sorry for the thread resurrection, but I am also designing an intake tube and I don't think that OP's question was quite answered. He was asking about the relationship between intake tube diameter and engine performance. Either way I have some new questions that pertain to the same topic. For the sake of simplicity, let's assume the absence of an air filter and no modifications to the cylinder head (valves, ports, etc...).
1) Is this correct? (below)
hhn2002 said:
...
the intake track is only as strong as its bottle neck, generally speaking. so a 4ft long intake tube that's half 2.5in diameter and the other half 3in is a lot like a straight 2.5in diameter tube as far as maximum efficient airflow.
Doesn't the flow potential of a tube depend on both it's diameter and its length? Ergo, a 4'x2.5"dia tube would be more restrictive than a 2'x2.5"dia tube connected to a 2'x3"dia tube? Further, doesn't the nature of the transition between the two diameters have an impact as well?
2) What is the relationship between tube length and internal diameter in regard to its flow potential? For instance, If I have a 3" and a 6" straight tube how do I calculate their lengths in order to achieve equal air velocity and restrictive characteristics?
3)Given a constant air flow, say for instance 432.36CFM, through a tube via an infinitely powerful source of suction, a smaller diameter tube will facilitate a higher air velocity and conversely a larger diameter tube will have a lower air velocity. Obviously a naturally aspirated engine is far from an infinitely powerful anything so at what point does decreasing the diameter (or increasing tube length) stop increasing the air velocity and start restricting flow?
4) How do I determine the effects of bends in the tubes?
Thanks in advance for any insights you may have. I just joined this forum last night and so far I have read some extremely interesting things. (Hilsche vortex tube! WTF??!??!) Keep up the good work!