Install a Hoodscoop

HOW TO INSTALL A HOODSCOOP

Racing pioneer, inventor, and world-class horn dog Smokey Yunick (read his autobiography "Best Damn Garage in Town" if you don't believe the horn dog part) proved that every 10-degree reduction in inlet-air temperature has the potential of increasing engine output by 1 percent. While this may not seem like much, let's crunch the numbers and take a second look.

It all starts with realizing that even though the ambient air temperature--the air you breathe in the driver seat--may be a comfortable 80 degrees F, the engine-compartment air temperature beneath an unvented hood is well in excess of 180 degrees F thanks to the heat radiated by the engine, exhaust headers, manifolds, and cooling system. That's a 100-degree difference in the air temperature above and below the skin of the hood.

What if you broke through the hood and took advantage of that cooler outside ambient air temperature? By Smokey's account, you'd reduce inlet-air temperature by 100 degrees and see a 10 percent increase in horsepower. So, in theory if you're making 400 hp breathing underhood air, you'd get 440 with outside air thanks to its greater density. Is it free horsepower? Yes and no. Yes, in that we don't have to lay a finger on the engine to see gains. No in that there is always an aerodynamic penalty (increased drag) any time appendages sprout from the vehicle surface. Regardless, the scoop's aerodynamic drag is less than the power increase, so it's a worthwhile trade-off.

As with everything we do to our cars, there's a form and function balance that must be respected. There are few things tackier than seedy off-kilter hoodscoops and butchered sheetmetal that look like the work of a pre-Sharon Ozzy wielding a rotary axe. In this how-to, we'll explore some tricks to help you cut the hood and mount the scoop so it looks professional.

For this story we're installing a reproduction '68 Hemi Dart fiberglass scoop on the CC Rambler. Its massive dustpan design grabs the maximum gulp of cold air. Several outfits make these scoops today. The darker one is from Kramer Automotive Specialties ($195). The lighter one is from Unlimited Products ($60).
For this story we're installing a reproduction '68 Hemi Dart fiberglass scoop on the CC Ra
A quick pass with an abrasive scuffing pad roughs up the paint so the temporary locating marks stick instead of smudging away. In situations where the paint is show quality, a little extra care will be needed to avoid collateral damage during the scoop installation.
A quick pass with an abrasive scuffing pad roughs up the paint so the temporary locating m
With the hood removed, pull a pair of strings across the length and width of the engine bay so they intersect exactly over the carburetor air-cleaner stud. Use masking tape to secure the lightly stretched strings to the body. An extra-long carb stud or a length of all-thread screwed into the carburetor prevents guesswork and incorrectly placed holes.
With the hood removed, pull a pair of strings across the length and width of the engine ba

Mark one end of each string to record its location before unsticking the tape and pulling it out of the way so the hood can be set back in place. This operation can also be done with the hood still bolted to its hinges.
Mark one end of each string to record its location before unsticking the tape and pulling
With the extra-long carb stud removed and the hood back on the car, re-stretch the strings and stick the loose ends back over the marked locations. You now have an exact X-ray view of where the carburetor stud is positioned.
With the extra-long carb stud removed and the hood back on the car, re-stretch the strings
Mark the intersection with a paint pen like this white grout marker. It dries fast and doesn't smudge but is easily removed with mild chemicals or polishing compound.
Mark the intersection with a paint pen like this white grout marker. It dries fast and doe

Drill a single 38-inch hole where the strings intersect, then use a bolt to center your air-cleaner lid over the hole. Use the grout pen to draw a circle around the lid that is 1 inch greater than the diameter of the lid. The extra inch provides clearance for hood opening and closing. If Doug was content with a single four-barrel on his Rambler, the next step would be cutting this circle out of the hood using the jigsaw. Then we'd either stack a pair of filter elements to get them up into the cool air stream. Or we could make a pan-type air-cleaner base with a foam ring sealing it to the underside of the hood. This would isolate the carburetor inlet from hot engine-compartment air and take full advantage of the ram-air effect at speed. But not us . . . we're going the tunnel-ram route.
Drill a single 38-inch hole where the strings intersect, then use a bolt to center your ai
With the tunnel-ram in place, we pull the strings again to create a virtual box around the manifold, carburetors, linkage, and fuel lines. Allow at least 1 inch of space to clear moving parts and to provide an adequate swing-arc as the hood is raised and lowered on its hinges.
With the tunnel-ram in place, we pull the strings again to create a virtual box around the

After removing the intake manifold and reinstalling the hood, the strings are repositioned and the grid clearly spells out where the hood needs to be cut for tunnel-ram clearance.
After removing the intake manifold and reinstalling the hood, the strings are repositioned
Mark the corners where the strings intersect with the grout marker, then draw a perimeter outline of the cut zone using a straight edge to connect the dots. Note the difference in the markings for the single-four barrel hole and the tunnel-ram hole.
Mark the corners where the strings intersect with the grout marker, then draw a perimeter
With the hood off the car, the cutting begins. A variable-speed jigsaw makes it easier to control the cut and follow the painted lines. The proper blade for cutting thin-gauge sheetmetal like the Rambler's hood has 36 teeth per inch. Coarser blades will yield jagged edges.
With the hood off the car, the cutting begins. A variable-speed jigsaw makes it easier to

The first trial fit of the hood shows that all measurements are correct and the carburetors, fuel lines, and linkage have ample clearance. Now we can move on to mounting that groovy hemi scoop.
The first trial fit of the hood shows that all measurements are correct and the carburetor
Thanks to a central character line running down the Rambler hood--and a similar feature on the scoop, centering the scoop on the hood can be done almost entirely by eye. A tape measure is used to ensure equal distance and symmetry between the edges of the scoop and hood. Once the scoop is centered, the grout marker is used to draw an outline.
Thanks to a central character line running down the Rambler hood--and a similar feature on
The outline also has tangential indicating lines that correspond to lines drawn on the scoop for exact mock-up placement during the fastener drilling operation.
The outline also has tangential indicating lines that correspond to lines drawn on the sco

The Unibit will be used to drill a series of 316-inch fastener holes in the scoop and hood. But this is where things get tricky and require some planning.
The Unibit will be used to drill a series of 316-inch fastener holes in the scoop and hood
Because of the maze of stiffening braces running beneath the hood skin, don't make the mistake of assuming that the fastener pattern that works for the scoop will work for the hood. Unless you are prepared to remove it entirely (and suffer a floppy steel hood) the bracing calls the shots as to where the fasteners can go. Here is the eventual pattern of 11 rivet holes we arrived at.
Because of the maze of stiffening braces running beneath the hood skin, don't make the mis
Here's another shot of the final fastener pattern as indicated by the temporarily placed raw rivets. To transfer this pattern to the hoodscoop, remove the rivet guides, precisely align the scoop with the pre-drawn painted outline, and tape it securely in place. Mark the scoop for drilling by poking the grout marker through the holes in the hood from below. This will transfer the fastener pattern to the bottom side of the hoodscoop flange. Now drill 316-inch holes through the white dots on the scoop flange with the Unibit.
Here's another shot of the final fastener pattern as indicated by the temporarily placed r

Going for the rough and tumble look of a back-alley street racer, we're content to blast everything with a simple coat of flat black. Remember to coat the area that'll be covered by the scoop prior to scoop installation, because access will be nil afterward.
Going for the rough and tumble look of a back-alley street racer, we're content to blast e
Though nuts and bolts can be used, we chose aluminum 316-inch rivets because they're more sanitary, they won't loosen, and they won't rust if they get wet. Be sure to use flat washers whenever riveting fiberglass. They distribute the pinch load as the rivet is tightened to prevent cracked fiberglass and pull-through.
Though nuts and bolts can be used, we chose aluminum 316-inch rivets because they're more
From the beginning, we knew the rivet gun was too tall to be operated from inside the scoop. All rivets must be applied from beneath, thus the significance of working in harmony with the underhood bracing.
From the beginning, we knew the rivet gun was too tall to be operated from inside the scoo

Not only will the Rambler benefit from cool, dense intake air, the Hemi Dart scoop transforms the diminutive compact from meek to freak!
Not only will the Rambler benefit from cool, dense intake air, the Hemi Dart scoop transfo