Cowl modification

[Teal]

Hello, I am considering cutting off the round inlet/snorkel on the bottom of my cowl and reducing my exit air size at the back of my cowl as I am running a alternative engine and dont need the carb inlet below and have more than sufficient cooling. Does anyone know what speed gains are made with this airframe and a removed carb snorkel?

[andoman]

You may get a specific response, but I’m betting there are few data points on speed gains that would account for just the drag reduction.
I doubt the speed gain would be measurable.
I believe your justification for the work involved will end up being aesthetics.
-The unused intake is blocked off, yes?

[dlomheim]

Originally Posted by Teal

... I am running a alternative engine...

Which alternative engine are you running with?

Doug

RV-9A Mazda 13B/ FWF

[Teal]

Yamaha sidewinder

[Teal]

The inlet is not covered. currently it is feeding oil cooler

[Teal]

I read somewhere that significant speed gains were made by using the injected engine and removing the snorkel.

[koupster]

Originally Posted by Teal

I read somewhere that significant speed gains were made by using the injected engine and removing the snorkel.

Feeding your injection/carb intake from the round inlet on the bottom of the cowl can increase power and speed by increasing available manifold pressure because of the ram rise in pressure provided by that forward facing inlet.

My understanding of the term snorkel as applied to RV's is taking air from the front of one of the two upper air intakes and feeding it down to the injection/carb intake.

[RVbySDI]

Originally Posted by koupster

Feeding your injection/carb intake from the round inlet on the bottom of the cowl can increase power and speed by increasing available manifold pressure because of the ram rise in pressure provided by that forward facing inlet.

My understanding of the term snorkel as applied to RV's is taking air from the front of one of the two upper air intakes and feeding it down to the injection/carb intake.

This is a “snorkel”:
https://store.vansaircraft.com/va-13...-va-132-2.html

This protrusion on the bottom of the cowl, below the prop, in this picture of an RV7 is a “snout”:
https://www.vansaircraft.com/rv-7/#image-gallery-4

[Teal]

My engine pulls air from one of the main air inlets. Then the turbo charger compresses and sends to the intercooler

[Toobuilder]

after the first few posts I was going to chime in and tell you that removing the pitot style scoop on the bottom of the cowl in favor of the snorkle in the the cooling inlet will actually cost you speed due to the loss of MAP. I just did this mod to my Rocket in the hopes that the loss of MAP would be offset by lower airframe drag. It was not to be. Looks like the pitot is going back on.

That said, your MAP is not dependant on a ram rise because of the turbo so the pitot scoop is not contibuting anything but drag (but it isnt much). I would not expect to see much, if any, gains in speed with the removal of the scoop. Airflow management and cooling exit size, sure.