drilling a hole in the back of your scoop?

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Cudafever

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In my twin hood scoop thread someone said this:

every 8" you want to drill a 5/8 hole along the back of the pan to let dead air escape because otherwise you carb will be drawing from partially stagnant air thus eliminating the effectiveness of the scoop.

Anybody have an opinion or info on this subject?.......Or even a link to a theory of this subject?

I have seen big scoops with holes in the back of them......Assuming that they were for gauges like fuel pressure temp exc. Maybe they were not?............
 
I would think doing that will allow the air to just pass over more instead of directing the air flow to the carb, but it is just a 5/8" hole so it's not that large of a hole. Is your carb sealed to the hood? You see people mostly on import do holes I the rear bumper to decrease drag. Be interesting to see the ones that do the hole drilling if it does show benefit
 
"When I wuz a kid" (and that was a LONG time ago) "they," "the thems" did a test of hood scoops. "In general" the small scoops sitting low profile on the hood were not all that effective, in terms of ram air.
 
Not sure about the twin scoop, I had a six pack scoop on one of my darts, I did drill 2 holes in the back, but it was because it wanted to remove itself from the hood at speed. You could tape some string inside the scoop and stick a go pro under the hood, if the air was stagnant the string would just dangle.
 
Depending on the scoop, it may suffer from packing. Too much air enters a space and has nowhere to go. The scoop basically can't accept any more air. Cutting a hole in the rear allows air to flow through. It's a balancing act.
 
gtsdude said:
Not sure about the twin scoop, I had a six pack scoop on one of my darts, I did drill 2 holes in the back, but it was because it wanted to remove itself from the hood at speed. You could tape some string inside the scoop and stick a go pro under the hood, if the air was stagnant the string would just dangle.
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That is a great idea! but i have no go pro.......or a smartphone for that matter.
I need to drill a small hole in the base, for rain/moisture but if i could some reality to this.....
Yes i know, won't get much ram effect with these scoops. when and measured the opening. basicly 1.5" tall X 12" wide X2 scoops= area of 36"

So he must be talking about a square..ish carb pan. And for every 8 Inches you drill a 5/8 hole. Mine is a 22" round carb pan or base with a 16" air cleaner in the middle.

anybody seen holes drilled into a pro stock hood or carb pan(yah i know they don't use a scoop any more.
 
crackedback said:
Depending on the scoop, it may suffer from packing. Too much air enters a space and has nowhere to go. The scoop basically can't accept any more air. Cutting a hole in the rear allows air to flow through. It's a balancing act.
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Is there any proven math for this?
this is purely speculation here BUT
Thinking a little deeper from my statement above 1.5" tall X 12" wide X2 scoops= area of 36"....../ by 8= 4.5 So 4.5 5/8" holes in the back!?!
 
67Dart273 said:
"When I wuz a kid" (and that was a LONG time ago) "they," "the thems" did a test of hood scoops. "In general" the small scoops sitting low profile on the hood were not all that effective, in terms of ram air.
Click to expand...

That's because of the somewhat stagnant "boundary layer" of air right on the hood surface. Here's the theory:
Boundary Layer

The inlets of either the twin soop or the six-pack scoop are raised to be up above the boundary layer - and the Hemi Dart/Barracuda scoop is so danged tall the boundary layer theory doesn't apply.
One of earliest scoops to address the boundary layer was the "mailbox" scoop on the '69 Hurst SC/Ramblers.

1969_AMC_SCRambler_hood.jpg
 
justinp61 said:
Ask Thumper if it's bs.
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I wish thumper would educate me on this subject.

I understand boundary layer, weather it is on the surface of a hood or the walls of a syl port.
and my twin scoop hood has that issue for sure. But that's not the question I'm asking.
 
You 'd have to test this with either the strings or a smoke generator to see what the air is really doing.
A lot of theories would did with the first test.
 
If you want to run at a track,check the rule book. I think nhra dosent allow flow through hood scoops. Holes in the back of a scoop. Holes in a pan that seals a scoop to a carb might be okay.
 
Scoop must have one opening only in Professional categories, and Top Alcohol Dragster, Top Alcohol Funny Car, Comp, and Super Stock. All other
classes, multiple scoop openings permitted.

from rule book. You'd have to look at whatever class you ran to see if there is a restriction.
 
yeah sportsman bracket racing, don't think there will be a problem that way.
 
I'm fairly sure it would make the car .0000000000001 faster.
Same with cutting the stupid holes in the bumper.

Just makes it where they lost by .000000000001 less. :D

Besides, what car pulling 600+cfm of air is going to leave anything stagnant?
It only matters at WOT throttle and if there is anything in the intake system stagnant at WOT you're driving a Prius.
 
If the scoop has a large enough opening and is in the air stream resulting in more air than the engine can use it can cause turbulence in the scoop and actually pull gas out of the carb vents, not good for afr's. Holes in the back of the scoop or air pan give the air somewhere to go.
 
justinp61 said:
If the scoop has a large enough opening and is in the air stream resulting in more air than the engine can use it can cause turbulence in the scoop and actually pull gas out of the carb vents, not good for afr's. Holes in the back of the scoop or air pan give the air somewhere to go.
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exactly I did this on my square pan and the car picked up 2 tenths consistently at the big end and this is from to much air flow

1588-S.jpg
 
I had a pan in the car that was 22x26 an I had 4, 5/8 holes drilled along the back of the pan to dead air to escape into the engine bay
 
Cudafever said:
how many inches is the opening of your scoop?
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I have fuel inj. and a filter under a 6 pack scoop, and not worried about it at all. more worried about the scoop raising up at speed. do have 8 hood pins in it tho. people that tell you scoops not working unless they are tall ones are full of it. we had a 66-67 suoer stock scoop on the hemi back in the early days, and it raised the whole fiberglass hood up to where I could see the carbs. at a 128 mph. we did add some hood pins !
 
I would say it makes more sense that any speed increase (track time decrease) seen after drilling holes in the rear or deck under a scoop is simply due to a slight decrease in drag. The holes will allow potential air pressure build up to decrease, which will act to minimize any potential ram air effect. It is a balancing act to reduce drag while increasing performance gains. Certainly if the hood or scoop is deforming or lifting, there is probably more drag being created than I would expect would be offset by any performance increase.

"Dead air" means nothing. It is air under higher than atmospheric pressure, so it doesn't matter if it is stagnant.
 
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