Ideal intake runner termination design...

[edjza80]

Just been reading a few articles, in particular:

Wave reflections from duct terminations
A. Selamet and Z. L. Ji

and

The acoustics of racing engine intake systems
M.F. Harrisona,*, A. Dunkleyb

now ive typically designed my intake runners to terminate (either within an airbox, or atmosphere) with a (relatively) small radiused bellmouth - for the obvious reason that the loss coefficient of the bellmouth provides better net flow capability.

however, reading about the acoustic boundary of a bellmouth (being possibly the worst re: low reflection coefficient) im concerned that by and large an effective bellmouth cacels out any acoustic tuning advantage i design into my intake runners.

harrisions article suggests that acoustic tuning is reasonably weak and contributes only in the lower rpm band, ineria ram being responsible for the majority of higher engine VE increases.

have i just dudded myself out of all the hours i spend calculating harmonic intake lengths??

discuss

cheers
ed

 

[edjza80]

and secondly, and something i have not found much to read about myself, what would the effect of the introduction of a pulse plate overlying the bellmouth be?

 

[AboveRedline]

My experience (geez about 20 years now) has been that a constant area runner with a flow path which is fairly close to perpendicular from the plenum using a corner radius of about r/D=.15 or greater tunes in better @ 3500-4500 rpm than a tapered runner on the same engine. We always thought of this as better wave reflection properties.

 

[edjza80]

yeah, ive tended to go with larger r/D to improve the loss coefficient and improve flow capability. an example of my bellmouths can be seen below:

http://www.v-eight.com/images/Images_Forum/ITB_Manifold_Aug5.jpg

but with further reading, perhaps such a lareg bell is a bad idea for acoustic tuning?

given the drop in reflection coefficient, would this bellmouth see losses in tuned performance, just have a significantly louder intake noise, or both?

cheers
ed

 

[edjza80]

and is there a role for pulse plates or some other technique to improve wave reflections at this boundary?