Cowl with vent holes

[douglong]

Is there a reason to have all the vent holes in the cowl? Even the side scoop doesn't make any sense.

 

[Timbo Whalen]

View attachment 319866
Is there a reason to have all the vent holes in the cowl? Even the side scoop doesn't make any sense.

As much fresh air to the carb as possible.

Based on a displacement of .45 cubic inches (7.5cc) and a max rpm potential of 28K, volumetric efficiency (VE) of 0.8, you're looking at a little over 3 CFM of air requirement. So, yes, give that V5 as much air as you can.

We played with a 'ram air' duct on an outrigger powered by an NR46DD and it needed more fuel, noticeably, above 45-50 mph. We finally had to drill spray bar and orifices in mixture block to get enough fuel at WOT.

 

[Mike Hughes]

It takes 3 thing to make fire. Fuel, spark, and oxygen. You close those off and the fire will burn off the oxygen quickly.
Mike

 

[Wasted wages]

When cowlings weren't so small and tight in the older days, I played with an old .67 Cobra cowl that I built some reverse ducts and drain holes in the inside of the cowl.

It was pretty effective in keeping water spray
from flaming out the motor when running through a roostertail... today's tubs are so narrow and tight there's no way to build ducts inside the cowls...