|
Large
Plenum/Short Runner Intake Design
Below is outlined my effort at a low cost
large plenum, short runner intake. The
effort was based on seeing results on
Rennlist by user Corleone. His intake
approach (along with other mods) resulted in
the ability to keep making power with an 8V
well pask 7,000 rpm.
This style intake proved to be a very
effective solution especially considering
the large stroke (95mm) of my 3.1L Hybrid
Stroker motor. The approach has a
significant impact on mid range power but it
also opens of the top end.
Some questioned the center feed to the
plenum but flow bench testing showed the
runners to flow within a few percent of each
other and now after several years of use, it
has been proven to be a great solution.
Materials:
Plenum -
http://www.rossmachineracing.com/halfround.html
Plenum End Caps -
http://www.rossmachineracing.com/halfendcap.html
Bellmouths
-
http://www.rossmachineracing.com/175vstack.html
Runners -
http://www.sharpeproducts.com/store/bent-90-stainless-steel-steel-aluminum-pipe-tube-elbows
This graph is interesting (see below). The
Figure below illustrates the effect of
intake pipe length on the volumetric
efficiency at different engine speeds for a
naturally aspirated spark ignition racing
engine [Smith 1972]. Notice the dramatic
drop off in VE at high RPM with longer
runners. The shorter the runner the less
dynamic charging you get in the mid-range.
The dynamic charging due to resonance can be
significant, on the order of 2-4 psi at the
valve. The longer the runner, the more
dramatic the drop off in VE. The idea behind
the short runner design is you give up
something like 10% VE in mid-range (I have
some to spare ) and get 20% gain (or more)
up top. |
