71 Demon Twin Hood Scoop Hole diameter?

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Demonx2

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Does anyone know the actual diameter of the functional air hole in each of the twin scoops on a 71 Demon? I've seen various sizes listed...approx. 4", 4", 4-1/6" and even 4-1/8". Does anyone know the true diameter these holes were from the factory?

Thx!!!
 
I did mine 4-inch and the rubber seals worked perfect!!!
 
They were 4-1/8".

And when I drilled mine to 4 1/8" the rubber seals from DMT also worked perfectly.
 
Agree..I'm sure mine were 4 1/8 after cleaning and deburring... easy task....

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Depending on where you get your scoop seals, I would suggest cutting some "practice" holes, of various sizes, on some scrap material. I bought my scoop seals from DMT and cut 4 1/8" holes.
 
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Agree..I'm sure mine were 4 1/8 after cleaning and deburring... easy task....

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You know, now that I think back on it you make a good point. If it's important to you that the holes are really 4 1/8" you might want to go a little smaller on the hole saw. Cutting a hole in sheet metal with a hole saw that large isn't exactly a precision operation. Using a 4-1/16" hole saw would probably be a better bet than starting with 4 1/8", leaving a little extra to clean things up afterward.

I did use a 4-1/8" hole saw myself, and the DMT seals do fit just fine. But I'd be willing to bet the holes in my hood are probably a smidge larger than the 4 1/8" hole saw I used.

Depending on where you get your scoop seals, I would suggest cutting some "practice" holes on some scrap material. I bought my scoop seals from DMT and cut 4 1/8" holes.

Yes, this too. With a hole saw that large you want to go slow, with a lower RPM. Some hole saws are better than others, and all of them will tend to walk around a little. So a practice hole or two wouldn't be a terrible idea at all.
 
Thx to all of you for your expertise. It sounds like 4-1/8" is the correct size. I likewise got my seals from DMT so they should work out well. The holes in my hood were enlarged 40+ years ago and are being corrected back to the stock size hence my question. Thx again to all and FABO!!
 
if you can put a piece of wood on the backside of the hood for the pilot to go through, that will reduce run out when cutting your holes.
 
does anyone have the hole location relative to the hood scoop? I have been wanting to add the holes but how far back within the scoop do you go back? Also, where can i find the insert you are all talking about? does it have a "filter"?
 
The bottom of the hood will have a semi-circular cutout in the bracing. That will show you where the hole goes.
 
The holes are actually pretty far forward near the opening of the scoop. This picture shows some of the landmarks on the under structure of the hood.
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The holes are actually pretty far forward near the opening of the scoop. This picture shows some of the landmarks on the under structure of the hood.
View attachment 1715564703
Thank you guys! this really helps a lot. I checked mine and the scoops are off centered from the holes, this assuming that the holes would line up in the centerline of the scoops. I agree that the holes are closer to the inlet that I would have thought. The scoops are tapered down towards the back and would have thought you get more of a ram air effect if the hole was towards the back of the scoop (or the scoop closer to the front of the hood). Was the thought intended to have the air directed towards the valve cover/header area or does the insert direct the air to the intake?
 
This is not a ram air setup, just fresh air. Ram air would be plumbed straight into the air cleaner.
 
Thank you guys! this really helps a lot. I checked mine and the scoops are off centered from the holes, this assuming that the holes would line up in the centerline of the scoops. I agree that the holes are closer to the inlet that I would have thought. The scoops are tapered down towards the back and would have thought you get more of a ram air effect if the hole was towards the back of the scoop (or the scoop closer to the front of the hood). Was the thought intended to have the air directed towards the valve cover/header area or does the insert direct the air to the intake?

The holes aren’t centered, they’re actually very close to the inside edge of the scoops, more toward the center of the hood.

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The scoops aren’t tall enough for any ram air effect. They’d be completely in the boundary layer of air going over the hood. They’re probably more effective at venting hot air out of the engine compartment then they are at bringing outside air in.
 
If this is your first time with this a couple hints - take your time, you don't want to warp the hood when cutting the holes. When you install the seals, the thick side goes up (see post #15 picture) to keep water from running onto the engine in the rain. It helps if you use just a little sealer on the outside of the hood to make that seal really do the job. Good luck - it sure changes the character of the car!
 
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