With all of these manifold / plenum threads around, you think there'd be a bit of discussion as to why some are designed differently... guess not

At any rate, here's my Q (or topic for discussion):

What impact does runner length have on making horsepower or torque (seperate effect, IIRC)... i.e. so why does the Kinetix manifold have long runners while the SSR manifold has short runners?

I know there aren't many dynographs out there, but try to make a point on a theoretical basis... i.e. the long-runnered part would be better for FI due to increase in laminar flow allowing higher cylinder pressurization (and vice versa, n/a for the short-runnered part due to higher amount of turbulent flow and better fuel burn)


caveat: i am not a mechanical engineer, am asking for guidance

thanks in advance!

 

typically, longer runners will give more torque. sometimes, by adding length to the runners, you won't necessarily add torque, but you will shift it to a lower rpm in the power band. shorter runners are better for forced induction, because you are not worried about tuning the flow, or minimizing pressure drop...you just want to get the air into the motor. with forced induction, it is slightly less important to have a beautifully tuned intake manifold, because the flow is compressed, and the pressure will equalize between the runners. with an N/A motor, the runners need to have equal volume and velocity. this is done by reducing cross sectional area, as the runners break off, because the volume of flow is reducing.

i hope this helps,

Chad

 

helps, thanks

guess i'll just have to get as many different types of manifolds as i can to try them all out (and sell the lesser ones)

 

Let me add that the number of turns that the air must make make a difference, as each turn separates the fuel molecules, creating a.....non-constant intake charge as the heavier fuel molecules are thrown to the outer side of the "tunnel". With FI, it is less of an issue than with NA.

With that poorly phrased statement, I'll add that there are better solutions coming soon.............

 

can't wait

i just don't see why someone doesn't build an intake manifold with a front-side inlet to get rid of that ridiculous turn...

there wouldn't be as big a problem in FI engines due to the lower mean free path causing more resistance to fuel movements...

wait a sec... are the fuel rails below the manifold? so manifold shape should have nothing to do with fuel, just air volume delivered, flow characteristics, flow rate, etc... right?