Air flow through hood scoop - Page 2

ItBites · #21 (**permalink**) 03-10-2004, 05:15 PM

By the way. Back on my first reply on this thread, I'd suggested the old tuft of yarn test around the scoop inlet area.

Is anyone going to try this? I'd really like to know what happens to the flow in this area.

I think speeds of 50, 100, 150, and 200 mph would give us enough data

Lew Ledyard · #22 (**permalink**) 03-10-2004, 08:48 PM

With regard to cooler air, someone (I think it was Thomas Kirkham) told me that the turkey pans reduce the temperature of the intake air by 40 degrees f.

aumoore · #23 (**permalink**) 03-10-2004, 11:46 PM

I have a 600 Vac secondary Holley on my 302 and am running a 9" Ford Motorsport round open element air cleaner. I started with the stock paper element that came with the air cleaner. Car ran great but I decided to use a K&N filter. The paper element was about 1.5" tall and I calculated that a 2-1/2" tall element would work. K&N had a 2-3/8 element that worked perfectly.

Did the K&N work? I say it probably added maybe 5-6HP which is barely enough to make any differance.

I did add a turkey pan later and it had more effect than the K&N.I would guess at least 10HP due to a cooler running carburator which heats the fuel less and gives denser fuel. Hence more HP. I think the pan helps direct the cooler air from the scoop directly to the carb and keeps some of the hot engine compartment air away from the intake of the carb.

It is a good idea to put a heat shield below the carb to protect it from the engine heat.

PnRCobra · #24 (**permalink**) 03-11-2004, 07:43 AM

You could always switch the manifold to an Edlebrock air gap. This will help keep the air between the manifold runners and the hot oil from the block. Another idea would be to use the X-treme K&N air filter top. It is almost like running with out an airfilter. I did both on mine which I gained more HP and torque in the 12% bracket.

Rich
Sweet as Kandyapple..................Faster than it's prey

Michael C Henry · #25 (**permalink**) 03-11-2004, 04:44 PM

I have the dual carbs. They use 8 1/2" air cleaners.They could use an extreme top or equivilent.They stop at 9".
The original scoop was an after thought when areodiamics was realy getting started.A lot of the builders have thought hard and come up with alterations. On the Shelby comp series they use a larger scoop that has some resembelance the original .I've seen a recreation fo what I was told was the twin suppercharger scoops .It was wider taller and came forward more.The cover car on Summit Racing is a car with a larger higher flow through design ,probably works as cowl induction at speed.The hood scoop was on the original 37 or so SC's.The street roadsters didn't come with scoops.but many were converted.
I'm not happy with my EM scoop. The tunnel wedge 2x4 makes even 1 3/4" tall Stelling and Helling's hit.The front edge under hood and rear at back.If I were in a position( Like going to paint)Change that scoop in order to get the air cleaners up into the flow.I'm still waiting for a couple of extreme tops for my two 8 1/2" cleaners

Richard Hudgins · #26 (**permalink**) 03-11-2004, 09:42 PM

Quote:

Originally posted by ItBites

By the way. Back on my first reply on this thread, I'd suggested the old tuft of yarn test around the scoop inlet area.

Is anyone going to try this? I'd really like to know what happens to the flow in this area.

I think speeds of 50, 100, 150, and 200 mph would give us enough data

Mr. Bites,

We have done tests on the scoop used on the JBL. It is a big ugly thing. Look here. JBL hood scoop

We did do a flow path test using oil drops to show patterns. (Please note: Oil paths are much easier to observe in real world testing than tuft testing.) Unfortunately. I do not have any photos of the results. Sorry, as photos would show the reality of what is going on with the flow.

There were a couple of test parameters that need explaining:

1. Open bottom (No “Turkey pan”)
2. Closed bottom (With turkey pan.)

The results of the test were as follows.

Case 1. Flow: The oil streams were consistent and did not divulge from the expected flow path. The pressure at the opening was (at 100 mph) 9 inches of water. ( .3251 psi) This was no doubt the internal pressure of the engine compartment. Temperature was 87f. Ambient was 71f.

Case 2. The oil streams were not consistent. Significant divergence was found at the annulus and evidence of stalling and boundary separation was apparent. The pressure at the opening was (at 100 mph) 11 inches of water. (.3974 psi) This was obviously due to flow separation and boundary layer effects due to closed annulus. Temperature was 73f. Ambient was 72f.

From these tests, it is obvious that the only real benefit is temperature. Ram air effect is negated by the flow properties and stalling of the flow at the annulus.

There are also a number of problems with boundary layer effects and the curvature of the front section. It would be quite easy to fix these problems, but then it would even less like a Cobra then the JBL does now.

Therefore, things were left as is.

Note: we did test the small scoop configuration as well. This unit provided no flow enhancement. It actually reduced pressure at the annulus. This was due to boundary layer effects. In other words, at 100 mph, the flow is over the unit due to thickness of the boundary layer, therefore giving a net reduction in pressure.

That’s all I know.

Edley Rondinone · #27 (**permalink**) 03-11-2004, 09:50 PM

I just hope my annulus never has "flow" problems!!! lol !!!

Excaliber · #28 (**permalink**) 03-12-2004, 01:11 AM

he he,,,,,,that was funny Edley.

Very informative Richard, I always appreciate your expert analysis of a problem!

Ernie

aumoore · #29 (**permalink**) 03-12-2004, 07:37 AM

Richard
Come on now Edley was just making a joke and it was actually kind of funny.

Now that I have said that could you translate that for us non-engineers?

Wayne Maybury · #30 (**permalink**) 03-12-2004, 08:25 AM

One thing I have often wondered about this subject of air filter size is the following. When a formula is used to calculate the required filter size, is it referring to the size of the opening, that is, the height times the circumference of the filter container OR is it referring to the actual surface area of the filter element which is much greater due to it's flutted shape?

Has anyone ever run their car on the 1/4 mile with and without the air filter? If so, did it make a difference?

Wayne

maxrpm · #31 (**permalink**) 03-12-2004, 09:21 AM

I picked up 1-2 tenths in et and approx 2-3mph by sealing the scoop to the carb. But figure in that I also upped the jetting 2 sizes at the same time in anticipation of more air. I put the air cleaner on for a pass & dropped 2mph, my air cleaner is the small round 9"x2". I'm in the process of fabricating a filter housing for installing a 9" xtreme flow K&N filter in there, I'm a firm believer in the K&N after experimenting with it in my modified Dodge Cummins dualie. I'm not thrilled about running no filter at the track.

flipper35 · #32 (**permalink**) 03-12-2004, 10:46 AM

Richard, I heard the Challenger T/A has its scoop up off the hood because of the boundry layer. It's modeled after the scoop on the belly of a P-51 for those that don't remember what they look like.

Even if the scoop were up in to the moving air, how much would it help due to ram air?

Sizzler · #33 (**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 · #34 (**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 · #35 (**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 · #36 (**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 · #37 (**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 · #38 (**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.....

Morris · #39 (**permalink**) 03-04-2007, 08:09 AM

And of course when it's installed we had to modify the Hood ....

But it all worked very good on the high end.....and when a FE is pulling 7000 rpm's...... it's using a lot of air.....

Anthony · #40 (**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.