Drilling Carb Rain Hats

[valveandpiston]

Hi all,

I was chatting with a friend while looking at my engine yesterday. My engine has PMO carbs with a rain hat/filter set up. He mentioned that rain hats/filters rob ~10hp vs. just a mesh filter on top of the trumpet. We were brainstorming ideas to mitigate the hp loss and thought about drilling holes into the angled part of the rain hat to reduce air resistance.

I'm wondering if it will actually make a difference and also if there will be risk of rain/water getting sucked into the motor. If the latter is a concern and there are real gains, I could drill holes into only the part of the rain hat that is covered by the engine compartment and leave the part that is exposed under the grill solid.

Does anyone have thoughts or experience doing that?

Thanks,
Hootie

[bkreigsr]

10 HP by drilling a few holes in a portion of the hat?
Not to mention the faster lap times due to the reduced overall weight.
Sign me up.
Bill K

[VFR750]

I’ve heard that too from a noted engine builder.

I made a set of fiberglass tops which don’t have the drooped portion. Just the top. Keeps the rain out

I think the reasoning is the air has to go up and in, and the velocity stacks are at the upper end of the hat where it is the narrowest. Maybe it impacts flow?

Very hard to prove the benefit without some data, but generally It makes some sense.

[valveandpiston]

Originally Posted by bkreigsr

10 HP by drilling a few holes in a portion of the hat?
Not to mention the faster lap times due to the reduced overall weight.
Sign me up.
Bill K

It's obvious that you won't get the entire 10hp, but drilling holes for a few hp seems like a no brainer?

[H-viken]

I'd love to see some side by side dyne numbers on this before i buy in to it. Bigger chance it's the filter robbing HP if you compare with mesh only.

[GaryR]

After being shown the nice fine SAND the K&N free-flow filters lets inside throttle bodies of a 911 I knew right then I would go ahead and accept the limitations of a good clean paper element filter. If you think anything you can do regarding the air intake will increase you by 10 HP I have some nice land I would love to sell you...