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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.


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.



Short Runner/Large Plenum Custom Intake
Pre-fabbed Components from Ross Machine Racing
Plenum Dimensions
Plenum Dimensions
Plenum Dimensions
Machine work complete - ready for tig welding
Bellmouths on the inside of the intake
Tacking the components
Welding completed
Completed Intake
Broke through to over 535 rwhp (over 20hp/psi) with the new intake


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