Air flow through hood scoop - Page 3

Sizzler · #1 (**permalink**) 03-12-2004, 11:27 AM

I personally don't think much air at all gets in through the scoop, AT SPEED. Because of the boundary layer issues. AND, if it did, you wouldn't want it because the force of the air, again AT SPEED, would mess with the fuel entering the venturi, and not in a good way. That's why good ram air systems have built in baffles and shelter the venturi from the airstream. At lower speeds and idle, I really think the major benefit of the hood scoop, assuming it's open, is as a heat exhaust.

maxrpm · #2 (**permalink**) 03-12-2004, 11:54 AM

I also didn't think that the little opening on the scoop would really pull much air but back to back runs at the dragstrip proved me wrong. I was thinking that I would actually hinder performance by restricting the engine to scoop only air.

Ant · #3 (**permalink**) 03-04-2007, 03:41 AM

This is an area that I havent really sorted yet, and due to having a high hp Nascar based engine with an Edelbrock 2961 inlet, I have bonnet clearance issues, and am using what Richard calls an ugly scoop, plus I have had to modify it another 3/4" higher to give approx 2.25" clearance above carb, plus I will have to angle and cut the breather tubes down somewhat, and on my car the air cleaner is tilted down at the front, which looks about the same as the JBL!
I am going to have to make a dropped base of almost 1.75" for my 14" X 3.5"High, K&N race filter, my engine isnt running the large rpms of the Nascar engines but will still see between 7000-7500rpm, going by the K&N calculation formula I have 32.5cfm additional capacity for dirt etc!

With this air filter I will have about 1/4" clearance above the filter top, and have considered an X stream top for it, but K&N recommend 1" clearance above the carb, plus I have read where these top filter systems dont actually do much for HP, well I went to the motoracing yesterday and see these V8 Falcons etc with the X stream and air boxes integrated with the hood, but these were reverse cowl induction. So some Cobra owners maybe using the X stream with little improvement in power, due to being to close to the hood?

I might be better to make an airbox around the carb, and have filters elsewhere away from any heat sources, but thats going to get messy for maybe little gain......!?!?

Morris · #4 (**permalink**) 03-04-2007, 08:02 AM

Ant

We are using a Dominator Carb.....and had to build the air cleaner just for the Dominator..... Here's the base we made to get the proper air flow into the carb....

Morris · #5 (**permalink**) 03-04-2007, 08:05 AM

Then we built the top of the air cleaner to contain the filter and use the Extreme Flow top.

It has a 2" drop with a 4" Air cleaner it's also a 16" air filter.....

Morris · #6 (**permalink**) 03-04-2007, 08:07 AM

The Dominator will pass over 1000 CFM's...... so we paid special attention to how we built this air cleaner.....

Anthony · #7 (**permalink**) 03-04-2007, 08:24 AM

Quote:

Originally Posted by maxrpm

I also didn't think that the little opening on the scoop would really pull much air but back to back runs at the dragstrip proved me wrong. I was thinking that I would actually hinder performance by restricting the engine to scoop only air.

What someone could calculate is the scoop frontal opening area, and compare it to the total venturi area of the carburetor to get a ratio for comparison of air flow velocity, considfering you have a sealed system.

I don't think air via scoop is highly pressurized ( ram effect), but I think the main benefit for sealing the scoop to the carb is colder air, denser air, for more power.

David Kirkham · #8 (**permalink**) 05-07-2007, 07:41 PM

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.

Anthony · #9 (**permalink**) 03-04-2007, 08:39 AM

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 · #10 (**permalink**) 03-04-2007, 08:42 AM

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 2.18

1.98% 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 · #11 (**permalink**) 03-04-2007, 12:03 PM

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 · #12 (**permalink**) 03-04-2007, 12:42 PM

another perspective on the issue

Scoop effect

Ant · #13 (**permalink**) 03-04-2007, 01:05 PM

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!

Morris · #14 (**permalink**) 03-04-2007, 08:46 PM

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

Anthony · #15 (**permalink**) 03-05-2007, 04:24 PM

Quote:

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.

mr0077 · #16 (**permalink**) 03-04-2007, 02:02 PM

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 · #17 (**permalink**) 03-04-2007, 06:06 PM

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.

pequa joe · #18 (**permalink**) 03-05-2007, 01:44 PM

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 · #19 (**permalink**) 03-05-2007, 04:15 PM

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

Morris · #20 (**permalink**) 03-06-2007, 08:13 AM

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