Air flow through hood scoop

[Bill Wells]

Badger , not to hijack the thread, but most importantly - How is your recovery coming along ? Bill

[Ant]

I have modified my JBL hood scoop and made it even higher, to suit my Ram SC, and its on more of a slope which lessens the front height! Will post a picture soon.

I guess that the front facing scoops dont work that well, but they might if you can get the air away from them or exhaust as the aeroplanes, GT40 Radiator vents etc. I am building a car of the 1960's and thats what they did, I looked at a reverse scoop and I dont think it will do, but I think a nice scoop tray around the carb, that doesnt seal that well around its base will help separate the under hood pressure and my carb should have adequate air!

Jac Mac suggested to block the front off and try and take air from the rear of hood, while still retaining the original look, but I still have that ugly scoop. In the UK, with the race cobra some have the air filter protruding out of the top of the scoop!

[Lew Ledyard]

Originally Posted by Badger

Lew Ledyard is the brightest guy on this thread. Peter Brock

My wife would so beg to differ.

[Anthony]

Originally Posted by Badger

Lew Ledyard is the brightest guy on this thread. The front of the scoop is a LOW pressure area! Air exits the front of the scoop!

Originally Posted by mr0077

but someone should do a "tuft" test to check that out (tape 1 or 2 inch long pieces of yarn or string onto the leading edge of the scoop and watch it while driving to see which way air was going at the scoop). Obviously having a turkey pan with a hood seal would affect the results due to engine air flow, and I suspect that there are a whole lot of other variables that could affect it...whether the cooling fan was on, is the radiator sealed to the body, is the radiator upright, etc.

With my car, you can see streaks of oil on the underneath side of the scoop going foreward, out the front of the scoop. My take on it is that the air coming through the radiator opening (after warming up) pressurizes the engine compartment, of which a portion exits out the scoop. So, if you nail the throttle, if you don't have a good seal on your turkey pan, not only are you getting low pressure air, but it is warm air as well, both decreasing engine HP. If you seal the turket pan to the scoop, at least you will get cooler air.

[mr0077]

Badger, that's some very cool background on the coupe testing/development, thanks for the info...I didn't realize you had tuft-tested and got those results...
On the Cobra, I would bet that AT BEST the air coming over the hood to the scoop has no positive pressure, and may actually have a lower pressure than the carb inlet area below it. If I get the time I may do a little tuft-testing to see what mine does, but if anyone beats me to it, please post here to let us know what they find. And I guess different configurations (different kit brands and intake setups) may get slight to large differences in results (sort of a "Your results may vary" kind of thing).
Like you said, just cause it looks cool or "looks right" doesn't mean it works right :-)

[Ant]

Cranky,

Are there any picts of Don the FEz Durners ERA with the oversize scoop?
You are on the money with your post, bigger is better. Did Don use a forward facing scoop or reverse?
I have modified my one as mentioned but being taller, and all the posts here guys have noticed vapour etc exiting the front, so I have a big useless bumblebee, bird catcher, I am thinking the original look can take a walk!

Originally Posted by RACER X #99

Todd,
If your just street cruising then what you have is probably good enough.
If you want to get serious and make some of the HP that your engine is capable of than you have to dump the turkey pan and modify a drop base 14" filter with at least a 3" element.

One time famous BB FE racer Don the FEz Durner even went so far as to have a custom built oversize scoop to house his 14 X 4" filter for his ERA Cobra. This could be one of the reasons he was so fast on the track. He knew how to make his engine breathe.

It really is funny when guys go thru all the expense to install two four barrel carbs on their Big Blocks and then choke them off with those tiny little Stellings filters.

FYI take a look at the filters the Nascar guys use on their 358CI engines.

Cranky

[G.R.]

With all this discussion of the airflow or lack there of through the hood scoops does anyone know why the 289 comp cars almost always have a drilled aluminum plate at the front of the scoop? I really never noticed the difference in air flow until I was tuning my Webers, at idle with the hood up I could get the engine idiling at about 900-1000 rpm...then I drove it and needed to adjust one of the carbs, leaveing the engine idling, now at about 700 rpm, as soon as I opened the hood the idle increased about 200 rpm. And I don't have a "drilled plate" in front of my scoop. I never really experienced a difference in idle when I was running a 4-bbl...hood open or closed...with the Webers there is a big difference.

Just curious as to why this was done an the early comp cars? Especially if an open scoop reduces airflow...one partially blocked would seem to reduce it more.

[Badger]

Thanks for asking Bill. The broken leg is healing well, but not fast enough! :0) Also with all the hardware "installed" I can't get through the metal detectors at the airport without causing the alarms to go off! I can hobble around now without crutches, but doubt I could scramble away fast enough from another errant race car! Badger

[G.R.]

Glad you are healing up so well Pete.

[Badger]

The reason the "oversize" hood scoop on that ERA racer of Don's worked better than the stock scoop is that the raised profile was getting above the slower moving boundary layer and allowing the air flowing over the hood to enter the scoop. Same reason Prostock drag racers run those hellaishly high forced induction scoops. Works good for the quarter mile, but not exactly the best solution for a road racer. Badger

[David Kirkham]

Badger,

Glad to see you are up and "hobbling" around! Better than the alternative of pushing daisies.

This thread reminds me of a joke my guys played on me. A couple of years ago, my guys got together on one of the SEMA cars and put the hood scoop on backwards. You work long, long, hard nights to get a SEMA car done and you loose track of time and your mind starts playing tricks on you. The stress is unbelievable. We had a zillion hours in the car and it had to be PERFECT!

Anyway, they were wondering how long it was going to take me to realize what was going on with the hood scoop backwards. Finally, when I saw it, I thought the guys just set the hood scoop on backwards just to lay it down somewhere--until I looked really closely at the hood scoop. I almost died--the hood scoop was riveted in! It would have taken hours to fix all the 21 holes in the hood and the scoop and we were already pushing the dead line.

Anyway after I had a heart attack, everyone started laughing. They had taken the shanks out of the rivets and placed them back in the holes so the hood scoop only appeared to be riveted on. They had even lined up two holes somehow and actually riveted the hood scoop on backwards in those two holes to make the effect complete. I think I aged 2 years that night.

As you can see, Kirkham Motorsports is actually a pretty cool place to work. They got me good--fair and square...of course, I did get them back!

David

ps. Peter, nice to see you on the boards! Get well soon! Anyway, you have to come by and try our new Rush. The car is phenomenal to drive. It is like driving a full sized go cart. We had it up at Miller's track last week. Everyone who drove it just giggled. It will run circles around a Cobra.

[Michael C Henry]

My thing with inline dual four is I have a tunnel wedge intake wich makes it high. Even the standard S&H elements have to be trimmed down in height. I feel the air filters are the restricion and when going full tilt the resulting vacum causes the mixture to go to the way rich side. Any better filtering would nessitate taller elements bringing the air filters up through and above the original plane of the hood .. At this point a scoop would more of another hood for covering the air cleaner. In a normal car these engines sit inclined with the rear lower and the carb sit somewhat level. In a Cobra the engine sits almost level which causes the carb to be inclined with the rear being higher than front. What I'm looking for is a scoop that looks appropriate and is as high in the rear as the front with respect to the hood surface. not a wedge blending to the rear of the hood. Large enough to get a Cobra style air cleaner with an adequet heigth element . So far cowl induction scoop[, the replica of the twin supercharged cars scoop , and one of those areo pro stock scoop are the choices.

[Ant]

Richard,

With Case 2, maybe using a large style tray semi sealed around hood scoop, with some exhaust capabilities/relief ducts off rear of tray, but I guess with the turkey pan there is a pressure build up affecting the air path? I read on Cobra Mustangs they fit a similar forward facing intake sealed system, with a relief valve exhaust that helps flow through!?!?

This seems to be a lot of work and nowadays they seem to have this problem solved by keep the air intake totally separate with eg 4" tubing and relocation of air filters in front of the radiator and you have your cold air system!

[Bernica]

I have CSX 4250. Just aquired it last week. All Shelby, including the stroked 582ci all-aluminum Shelby motor. Set up and has done road race (Willow Springs, Sears Point, Laguna Seca etc).
No hole in the hood at all and have a turkey pan w/ a race prepped 750 Holley. The guy I bought it from says Shelby doesn't cut to hood. It has a 1" AF that fits in the turkey pan. Kind of wondering what they are thinking? Any thoughts??? Has anyone cut their hood on a CSX4000???

[Rick Parker]

With the low hood clearance and relatively this air filters that all the 427 FE folks seem to be stuck with, the best thing to do would be remove the choke housing on the Holley and radius all incoming corners. There is a reason you don't see a choke housing on a Race Carb....air flow.

[Double Venom]

Sorry to come in so late on this, but we did do as much testing without a tunnel as we could. (2000 ?) The difference was amazing. We did use the yarn tufts, video taped at 30-50-70 and 100mph. Tufts were installed in the very front of the "Naca Duct" much like a Viper uses and on top of the Naca Duct. Tufts were installed in the very front of the rearward facing scoop, along the top and at the very back. Just for giggles we installed tufts about 4" apart on the lower windshield, the middle of the windshield and of course at the top.
What we found was amazing and good info. The tufts in front of the Naca Duct actually were sucked inward while the top tufts almost didn't move. The tufts at the rear of the scoop actually got totally sucked into the engine comparment ALONG with the tufts at the lower windshield area. The middle windshield tufts couldn't makle up there minds to go up or down into the intake. The upper tufts finally went up. The reduction of air pressure on the windshield was amazing in itself.

Bottom line, want more air into the intake with positive pressure and not a vaccum, turn the scoop around and no need to raise it higher.

Maybe the Kirkham group had something going there
DV

[Michael C Henry]

This information would have helped Shelby 40 years ago.. But he probably would argue that wouldn't have made any difference or that the technology would have not remained a secrete for long. There are resons for departing from some of the traditional body arrangements. My car is a replica and WA registertraion says KitV first . A cowl induction scoop would help my situation. Now to find a cowl scoop that would look appropriate on a Cobra hood. I'm up to bonding but a new layup seems intimidating. I'd Like to get all this done before getting car repainted. I know a change is neccessary and a scoop would be step to an end. Do you remember reading anewbie asking what you do once the Cobra replica is finished?
How or what did you come up with the rear edge ? Did the rear of the scoop follow the windsheid or end at the hood line edge or does the top extend over and open on sides.? What is the optimum shape?

[Double Venom]

Michael,
If you didn't know, it is a CR's Cobra. All I did was cut out the original scoop, turn it around and fiinished it from there.
DV

[Ant]

I have decided to bypass an original looking forward scoop and have a rear facing scoop, due to my scoop being quite high. Will be going to the hood edge which is about 6-7" away from the windscreen. The windscreen is going to be the original but am making a small 9" high polycarbonate screen that goes right across, so not sure on the air effect in that area, but for looks its 1000% better!

I think 6-7" is okay from the rear of scoop to screen to pick up air. To my way of thinking unless its an original scoop anything larger than that is just plain ugly.

Another bigger issue is the air filter, and I cant see the point in oval and small air filters, the oval dropped filters restrict in the side entry to carb, I have now a proper 14" setup, which makes the scoop a bit wider, and just have room for a 4" high air filter which has >2.5" above the carb flange!

[a427sc]

Ant Compare my ERA w/ large scoop (in front) vs a Contemporary (99's) behind.