Air flow through hood scoop

[Anthony]

You can also build a custom air cleaner with air cleaner foam. I don't know how it flows compared to a good conventional filter, but you can shape the filter in any shape you want..

This is my "prototype"

[mr0077]

To confirm the above comments on the effect of the little Stelling and Hellings air cleaners, I ran two back-to-back chassis dyno runs with and without the standard 1 3/4" x 9" paper elements and with the air cleaner bases on the carbs. I got 397.47 HP/431.92 LB-FT with the filters and 406.15 HP/441.19 LB-FT with the filters off the motor. No difference below 3200 rpm, then a consistent difference above that all the way to 6000 rpm...maybe that was where the secondaries opened?

Like ItBites said above, the 7.82 HP/8.34 LB-FT increases works out to 2.181.98% increases...it all adds up, but that's not enough for me to notice or make it worth running without filters...

Now the cold air induction angle...I like that part, but the scoop? IMHO it's more for style than function.

[Lew Ledyard]

Ken:

You mentioned "air filters" (i.e. plural). Are you running dual carbs? If so, wouldn't the loss be twice as much with a single carb?

[Commander]

another perspective on the issue

Scoop effect

[Ant]

Morris,

Great work very impressive as you have gone the extra mile to make sure the FE gets everything it needs! I will be doing a similar base shortly. I am 373 cuin running similar rpms, K&N tech advised me that the filter I have flows 923.16 CFM @ 1.5" (h20.)

I could run an X stream on top, or make up a foam insert, if I go to a 2" drop, that will give me 2 - 1/4" above the carb flange (MAX) to allow for an X stream, but I am not running a block under the carb, which helps to allow for the air/fuel to turn in the manifold, so I dont know what is more important say a compromise using a 1/4" to 1/2" four hole block and an X Stream on what I have, the X stream may give some benefit with a bit less gap!

Another issue I have tried to find out is " how minimal the gap above the carb needs to be, taking into consideration I can cut my air tubes down on my Pro 950 carb to a bit over half, doing a 45 angle on them, as they are quite long and straight at present, that might give me a little. All this is with a BIG 3.5" scoop on the hood!

[mr0077]

Lew, you're right, I am running dual quads. I agree that a single 9" on a single quad would cause more restriction for the (more or less) same air flow my motor would use. I ran a `4" x 3" element when I had a single four bbl on it.

Actually, two 9" filters have more surface area than the factory-style oval with the same height filter element (1 3/4")...

[Lew Ledyard]

To me, that is the best reason to run a dual quad set-up.

As far as air through the scoop goes, there might be more air coming out of the scoop than going in. Whenever I drive my car and there is some moisture out (wet roads, light ran, etc.), there is a water droplet pattern going out of the scoop. I guess that this indicates that air from the radiator inlet is escaping through the hood scoop.

[Morris]

Ant

Running foam in as a filter for a carb is dangerous......as we found out ..... when it's cold or cooler and it back fires....... the foam will go up in smoke.....

So the extreme top would be the top of choice.......

We are running a 1/2" insulator under the carb.....and the 4 hole kind because the linkage of a dominator is in the middle of the holes and we would not want it to drop in to the intake manifold....

The minimum gap between the carb air horn and the top of the air filter is dependant on the shape of the base of the air cleaner housing ...... just like the boundry layer of air on the outside of the body..... it will follow the shape of the air cleaner base into the throat of the carb.....

And we have a large hood scoop facing backwards to evacuate the air pressure under the hood..... large.....

Morris

[pequa joe]

Not scientific but:
After tightening the screws on my 750 DP front accel. pump, because of a slight drip, Placed a paper towel(the folded type from a despenser) under the front fuel bowl to make sure no other problems (Vic Jr. manifold). The following week in haste for an early morning cruise forgot to remove it. Sixty miles later at speeds, opened the hood, paper towel still there. I'm running a 9" K&N so it's not like anything was shrouding the towel. My opinion the scoop does nothing, good thing I guess, don't know what would have happened if it landed on the headers.
Joe

[Aussie Mike]

I just fitted an Edelbrock Victor Manifold to my motor and a 1000CFM 4bbl Throttle body. I picked up this oval air cleaner from Summit Racing that I reckon might work OK. It's an airflow top style but it's narrow enough that it will fit through the scoop opening (after a bit of surgery on the hood).

The air cleaner is about 12" long and 8" or 9" wide with a 2" high element.



Here's the hood scoop opening and you can see where I've got to widen it a bit.



Cheers

[Anthony]

Originally Posted by Morris

Running foam in as a filter for a carb is dangerous......as we found out ..... when it's cold or cooler and it back fires....... the foam will go up in smoke.....

So the extreme top would be the top of choice.......

Did you have a wire mesh screen inside of the foam?, as this is supposed to prevent the foam going up in flames.

[Morris]

Anthony

We did have a mesh on both sides of the foam....... and it was gone in a second or two......

Even a extreme top can burn with a back fire and then a flame or two..... we did that as well........

That is why you have a wing nut on top of the air cleaner......so you can get it off fast and extinguish the fire.......

Only when you are using big componets.....like Victor and Dominator.....combined with cool weather and no choke...need lots of gas....... do we have to be extra careful...... during the summer ....no issues.....

Morris

[What'saCobra?]

Ditto here, Anthony.

i would add that if you run slightly colder plugs, flame-outs can even happen in the summer, if you are a little careless and let the plugs get a little too fouled or use too much accel pump before hot starting.

The use of nominal foam is just simply a fire hazard in any semi-serious application. You can live with it, from time to time, but you get flame burns on the hood interior which is a PIA to clean-up nicely.

And it is a little embarassing to have the smoke and strange start-up noises
at a show or on a nice quiet street.

No-choke carbs are, as Morris indicates, the worse-case offenders. But, i like them for their nice flow characteristics and live in the South year-round. Morris knows of which he speaks.

Of course, they remind me of the old Webers on the race cars, that used to belch and flame a whole lot. Real loud. The IDA"s were not particularly easy to start even when warm.

i still prefer that bark and smoke of a Pratt & Whitney (lthough they cut-out inverted), rather than the fuel-injected Lycoming, as nice as they are in aerobatic utility.

It's just old time religion...

[Ant]

Morris,

Thanks, I can see the benefits of the reverse scoop, and being wider than my JBL styled scoop, if I went to a scoop like yours, then I could go to a 16" filter, but I will stick to my 14" x 3.5" K&N, as mentioned I dont think it will need anymore than 925cfm, and I wont be oiling this race filter. I like the look of your scoop, but I would like to like my car to be like it was in the 1960's, but these big forward facing scoops are ugly!

I guess I can just run a mesh in place of the filter element for extreme events, but crap is still going to enter the engine!

Aussis Mike,

Nice job you are doing there!!!

[DocDirk]

This has been an interesting post to be sure! I've seen some hood air scoops which are open on the rear side as well as the front, mostly larger ones customized to accommodate a larger engine setup. I've wondered whether the flow of air thru the scoop would have a chance of setting up a vacuum effect at some speed, potentially robbing the air intake? It's been said to me as well that such a scoop is used to aid in reduction of engine and engine compartment temperatures. Anybody have experience or an opinion?

Thanks!

Dirk

[CHANMADD]

I have always used an Edelbrock 1000 cfm foam filter,I have burned the foam once due to a backfire but that only happens if the motor is out of tune.My scoop runs the air directly into the top of the filter and appears to have some ram effect .My motor does sit further back than normal so that my carb is right at the back of the scoop.

[Bill Wells]

I have the traditional hood scoops on my SPF, GT 350 clone and 57 TBird and am always amazed at how little water gets into the engine bay when driving at highway speeds in torrential rain . There is always water on the front lower frame rails and lower inside fender shields etc, as well as on top of the radiator shroud/surround- most of that is from the tires .

Interesting is that there is very little water, or water spots, on top of the engine, valve covers or air filter lid . It is almost like there is a blockout plate on the hood scoop opening or a natural created air dam . Go figure , as with the scoops I would expect monumental amounts of water . Bill

[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! The smart thing is to run the scoop reversed, with the opening near the windscreen where the pressure is higher. Doesn't matter what the original Cobra team guys did..those guys made a lot of mistakes but didn't change simply because it "looked" right. Peter Brock

[mr0077]

Badger, you're probably right (about the front of the scoop being a relative low pressure area - the base of the windshield is definitely a relative high pressure area), 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.

[Badger]

77..you're right, these are all good points, but the fact remains that the position of the scoop on the hood is still in a "transitional area" where the pressure is not positive enough to really make a performance difference. Sealing the underside will help, but simply reversing the position of the scoop on the hood makes a big difference, as the intake will now reside in a positive pressure area. As far as tuft testing goes... I did all that on the first Daytona Coupe (not exactly the same issue here) but was astounded to learn that the air intake at the base of the windscreen had created so much pressure that the incoming air was actually pushing the sealant foam away from the edges of the turkey pan! (I'd already determined, on the roadsters, that the air intake was in the wrong place, so I put the intake on the coupes back at the base of the 'screen) This "discovery" was important because if we hadn't learned this at the first test the engine probably would have leaned out at high speed and burned the pistons! The simple solution, as can be seen in early test photos of CSX 2287, was simply to drill a few holes in the front of the "blister" . The pressure was still so great that fuel dye from carb "standoff" can be seen flowing from the front holes! The fun thing in "reversing" the hood scoops on a roadster these days is going to a modern Cobra meet and having all the so called "experts" thinking you were so dumb in assembling your "kit" that you mounted the hood scoop "backwards" :0) Peter Brock