Hood scoop performance ..

Any data to back up any use .. or, just for looks

Depends on the scoop.

There is a lot of information on hood scoops that is out floating around. Most of it doesn't matter to the average bracket guy but if you're going faster than 150 mph it gets fairly critical. The shape of hood scoops in Pro Stock changed significantly over the years as they figured out what worked and what didn't.

When Warren Johnson was actively racing in PS, he was working with K&G on filters and scoops. The Pro Stock scoop of that time ate HP to make HP. Don't remember the numbers but it was something like it ate 35 to make 64. A velocity stack makes the most HP with its simpler technology. Straightens the air to give the carb a strong and consistent signal.

I thought this interesting
https://www.dragzine.com/tech-stori...p-speed-with-a-forward-facing-air-inlet/

As long as the carb is sealed to it, same ET...I switched from a cowl hood to a Six pack hood, same ET...Same MPH

Apologies for butting in on the OP but I don't think most 6 pak scoops are high enough to catch the clean air. We did pick up (slightly) by sealing the carb to the very large six pak scoop on ours though.
We've changed now to a flat hood and perspex scoop, now I'm a little worried about hi speed lean out (140+ terminals) to the point I've been considering using a boost referenced regulator and tapping a port into the scoop.
I have no real idea of what pressure will build up inside the scoop 'til I try it though

The night my 67 lost the scoop going through the lights, I had to run the rest of the evening without it. The car picked up significantly. Did some math, and with the hemi scoop sealed to the carb it was picking up SIGNIFICANTLY more air than the engine needed and the pan wouldn't let it escape. Ran the rest of the career without a carb pan. I think most people who have scoops actually hurt themselves with the opening size.

Being devils advocate here, but that says to me if you had jetted up, you would have gained some H/P, and this agrees with the info in the article I posted above.

Negative. The scoop was fiberglass and would pop up in the middle indicating it was full. It became a snow plow against incoming air, like trying to push an exercise ball down track at 125mph. The car picked up because it was less drag, not because it was fat and came into range with A/f.

You want to run the smallest scoop you can get away with to make sure there isn't negative, or excessively positive, pressure above the carb. Aerodynamics aren't our friends with these old bricks as it is.

OK, this all makes sense. I have some data logging on the car but won't find out until next year if the new scoop picks up some. But if it does, I'll now be wondering if it's through aero or H/P

it was picking up SIGNIFICANTLY more air than the engine needed

That's what a supercharger does.

There's the trade off.

I'm interested in any experience on the ET loss for a scoop without HP gain - I'm trying to decide whether to keep the 6 pack scoop on my Coronet with the change to a turbocharged engine. I love the way the car looks with the scoop vs flat hood, but if I'm giving up tenths of ET pushing air that I'm not going to be gaining anything from I might feel different.

Would a 6 pack scoop be much worse than a prostock scoop in how much disturbance to aero it causes?

I would guess it depends how high and how far forward they are placed. Most of the stock positioned ones ( 3" hi ? ) are apparently out of the clean air flow. I would think the difference would be negligible but I don't have any data to say one way or the other..

I am going to be testing this weekend to fugure out why my car picked up 3.8 mph by not running the hood, which is seperate from the scoop. The fastest pass was without an aircleaner or hood. I hope to test a couple of combos of aircleaners.

Not very scientific, but my results were interesting to me...
I had a six pack hood on my car years ago. Taller than the stock A12 scoops, but not real tall. It went a little over a tenth quicker and 1.5 mph faster w/ the carb sealed to the hood. It was trying to rip off the car at 120+ mph though.

I switched to the 5" cowl hood that was NOT sealed to the carb and the performance didn't change one bit. I expected it to slow a little not being sealed up, but it didn't. It gained weight too...the six pack was a lightweight lift-off hood and the cowl is a heavy bolt on.

Not clear to me in the above example how we know the "Pop up" was from over pressure underneath vs a low pressure above the scoop sucking it up?

Sealing the carb to the bottom of the hood does work. My brother ran his car without the sealing pan and it would blubber a little at the top end. Not bad, but you could tell something was amiss. Only when he installed the pan and foam to the bottom of the hood did it pull clean all the way thru.

the front of each car is so different that only a wind tunnel is really going to tell you what works I'd think. Cars with recessed grilles (E-bodies) have a ton of turbulence that builds up in front of the grill at speed. Guy here has a purple 70 Challenger with a glass hood and the front edge bows up a lot on the top end. Enough that I would be worried about the hood cracking eventually. How does a hood scoop function on a car like that where the air all around the nose is scrambled up?

There was an old tech paper in NHRA magazine on Pro Stock hood scoops and hp gains[1% I believe at 200 mph]

Hood scoops are cosmetic

Supercharger forces air into the intake, no amount of scoop is going to creat tangible boost in that way. Youre best bet is you're supplying ample air to the engine and not starving it.



Because it occured at the CASS, which I believe was around 42 MPH. No chance, based on the shape of the car, there was enough negative pressure to break the scoop tie downs. A 5" WO67 scoop has a significantly more in^2 than even a pro stock hood. Sealing that scoop to the pan made no sense to me.

no amount of scoop is going to creat tangible boost in that way

200 mph = 2 psi boost

I saw no remark w/r/t the longer a car is at high speed, the smaller the intake needs to be. Those big scoops are needed for 0-100, not after.

I have seen a 68 SS/AH scoop that was narrowed and the bottom half of the opening was blocked off. I didn't talk to him about what he was going after and if it helped but I think he may have been asked not to bring it back.

Like I said, no scoop is going to create tangible boost like a blower.

Per Warren Johnson:

“If you plug in the numbers, you’ll find an increase in inlet air pressure of .142 psi at 90 miles-per-hour. Standard atmospheric pressure is 14.7 psi, so this represents an increase of just under 1 percent. If the air/fuel ratio is adjusted to compensate for the increased pressure, there should be a corresponding 1-percent increase in horsepower. For a 1,200-horsepower Pro Stock engine, that’s a gain of 12 horsepower. Hood scoop pressurization increases dramatically at faster speeds: It’s 2 percent at approximately 130 miles-per-hour, and 3 percent at 158 miles-per-hour. At the magical 200 mile-per-hour mark, the theoretical pressure increase is .704 psi, or 4.8 percent. That equals 56 “free” horsepower.

“Unfortunately in racing, just as in life, there is no free lunch. The penalty you pay for this increase in inlet air pressure is the extra aerodynamic drag produced by the hood scoop. A hood scoop is inherently dirty in terms of its aerodynamics. You can minimize the penalty with proper radii and contours, but you can’t get rid of it. And because the scoop has to be large enough to enclose the carburetors and intake manifold, you don’t have much latitude to change its physical dimensions and frontal area.

“From all of my calculations, it’s a wash between the increased horsepower from the ram effect and the higher aerodynamic drag produced by the hood scoop. In other words, though we gain horsepower from the increased inlet pressure, we have to use all of that power just to push the hood scoop through the air.”

And sadly for WJ, his performance calculations didn’t equate to real life MPH gains. Still today, the MPH is not where it should be for a Pro Stock car factoring in the average gains across the last decade before the scoops were eliminated. Plus, the cars look stupid with that flat hood, and since they aren’t any faster, bring back the hood scoop AND carbs.

That's probably a sign the decade before the switch was focused on things not induction related but rather ring packs, suspension, and transmissions. I'd imagine those items are all but optimized at this point.

I get their reasons for the switch, those same reasons don't seem consistent with the rest of their program though. However that's another thread for another day.

Easy enough to put a pressure sensor in the scoop.

On just about anything carbureted, the carbs will be thru the hood. Something has to cover them. Why not make it a sealed scoop which will (should) improve performance. If the cowl rear opening type of scoop was effective, I'm sure they would have been in use by the people who had the budget to test such things..

Attention needs to be paid to internal construction to make sure it is pressurized with a minimum of turbulence.

On the 1965 Hemi Belvedere with a factory scoop it picked up two MPH placing the factory plate on the carbs sealing the carbs to the hood on the first pass with the plate. I know in 1972 John Petrie decided to copy his 65 car and put a cookie pan on his doms on the1972 Cuda and it picked up a few MPH and some ET. Next time out most people in Pro Stock started to copy him. The scoop was a Shoe box type old pro stock scoop. I would say some work and some do not. You have to experiment to see why some things work and some things do not.

Have fun!

The "CASS" reference is unclear to me also, and so you stating there was not enough low pressure above the hood/scoop to suck it upwards, but there was enough high pressure air inside the scoop to lift the hood up, the latter which I find nearly unbelievable.

I saw almost a tenth in the quarter mile on my high ten second big block Dart, 68 Hemi Dart scoop.....not sealed vs sealed....back to back passes....When I was engineering the seal set up for that scoop, my buddy assured me that I was wasting my time...He ate crow when it worked......Your results may vary....Test, Test, Test

My 64 Maxwedge ran almost the same with a stock hood as with a sealed Six Pac type. Don’t know why they worked but the rage at that time (70s) where newspaper boxes. They just worked, especially on tunnel rams, just cut carb holes and and long rod to hold them on. Prerunner to the Jimmy Durante nose.

They were simple with a minimum of fabrication, they were sealed and they were free.

Losing a scoop and a hood on two separate occasions renders it the opposite of unbelievable. Do the math, per the article, the scoop was too large and my car picked up without the carb sealed to the hood because the excess air captured by the scoop could escape instead of cause aerodynamic drag.

I'm not telling anyone what scoop to run, I'm sharing my experience. That car won the 2017 TriState Stock/Superstock championship without a carb pan, along with a bunch of Mopar event wins. It worked.

A friend raced a Corvette tube chassis car, light, would run 180 mph in the 1/4. Hood blew off and car became very squirmy on top end almost lost it, lucky the chute helped. Like was said aerodynamics plays big time at that mph

I use to live near El Mirage Dry Lake where Southern California timing Association ran their top end Bonneville type cars during the late fall, winter and early spring months, I went out to watch and ended up asking about what cars needed to go fast out there, I had a 1970 Dodge T/A at that time and I had thought about trying to set a record in stock with that car. The record was right at 175 MPH back then so I did the math on what tire RPM would be needed to run over 175 MPH with a set of 2.76 gears, I ended up not doing it due to the rule about having to have SCTA approve tires on any car going faster than 150.00 MPH back then and I could not buy new ones back then, only used from another racer
I was told by several old time racers that anyone could go 125 MPH in a lot of stock cars, some could go 150 MPH but it took twice the HP to run 175.00 MPH than it did to run 150.00 MPH
They said aerodynamics really came into play above 150 MPH on most race cars

About 60% more, varies roughly by the cube of the speed.

I have a couple cars that picked up 1 tenth in the 1/8 and 1.5 tenths in the 1/4 making an air pan and sealing it to the 440 six pack hood.

They run 10.50-11.20 range.

Definitely worth the effort.

I still use a paper box.

Yes there is an aerodynamic factor is every car and 150 MPH things begin to happen with a lot of cars. The 1965 SSBA car is stable at 154. Another friend SS 1968 Barracuda with a big aluminum hemi ran 830 and did not fully complete the pass under total power because the air was getting under the car and making the nose super light and scary at 170 mph. The Barracuda races Hemi Shoot outs and Cam AM so making it slower was a good thing. The sealing to the hood has to be tested with every car and motor combination. Might work might not the answer with be in the Time Ticket. There will be a lot of pressure on the hood so it better be bolted down right and a strong hood.

I am going to fabricate a scoop for my car and will post the results when I run it next weekend. I have been running hoodless with a uni filter so I suspect it will pick me up several hundredths.

Mocked one up in carboard today. To check left lane tree vision. If this works good I will fit a hood around it over the winter. Trying to get a 5.40 1/8 mile pass before year is out.

In an old issue of Mopar Collectors guide they did a feature on a white 68 hemi cuda race car and the owner cut about a 1" or so opening across the back of the hemi scoop to let some of the excess air escape. With it enclosed on all 3 sides the volume of air at the top end was pulling the hood scoop and hood apart at the front corners. For a real fast car this may be something to consider doing???

Here is the car that I'm talking about.

https://www.dragracecentral.com/DRCStory.asp?ID=22155

Edit, Thought about a clear perspex scoop ?

https://hosting.photobucket.com/alb...7-4E9C-BEBE-B959F4F7B9F3_zpso5trlzdf.jpg

My Dart has a six pack scoop on it, on the street I don't seal the carb to the hood and I run a air filter. At the strip I run it with no air filter, it's faster sealed to the hood than not.

IIRC Dom had some afr issues at high speed with his carb sealed to a six pack scoop, the general consensus was that air was stacking up or there was turbulence in the scoop. Drilling some holes in the back of the scoop fixed it.

it should always run better with a scoop sealed just got to play with jets

A few weeks back I posted results regarding my hood. I have a 68 roadrunner with six pack hood on it. Victor intake and 2" super sucker put the dominator vent tubes about 3/8" away from the underside of the hood. During test and tune we took the hood off and replaced it with a 4" K&N air filter with x stream top, 14" diameter. We gained three tenths from the previous run. My hood is not sealed to carb, but do pay attention to how close the carb is to the underside of the hood. I went 11.52 with the hood and 11.20 with air cleaner and without hood. +3mph

I am considering running a cowl hood like that setup to smooth airflow up into the scoop if my setup works. Although not as tall as that one.

There are a few posts about the perspex scoops on The Bullet, not many back to back tests but most claim 1 - 1.5 tenths and around 3 mph improvement.
https://www.yellowbullet.com/threads/lexan-carb-scoop.567887/
HTH's

kool

The velocity stacks looks like the best answer. The aerodynamic drag should probably be minimal. The carb and/or stack is in the wind and getting cooled down. As by design, it straightens the air giving stronger and consistent signal(s) to the carb. The motor, as an air pump, will suck all the air it needs and should keep up with the air speed. I imagine that each combo would like a different height. I'd avoid the K&N filter that are sold some stacks. I think that Thumper was thinking about the velocity stack during several of our conversations. As a cab guy, he's got to have more insight on this issue.

Have you tried the hood without the carb so close to it? My vent tubes are probably 3" from the roof of my scoop.

.

"Excess air!"
Where can I buy some of that?

Yes sir and cutting 5 tear drop holes in the rear made the afr's more stable and solved some siphoning issues w/the bowl vents as well......

It's right here in this thread, and free, but don't take to much it will blow you away.

Too hot also

I understand and agree with owners/builders reporting their own experiences.
What I find fault with is the idea that if these events actually occurred (and we take your word for it) that witnessing the event gives you some special insight as to exactly what caused the effects: causation vs. coincidence is perhaps the largest single fallacy in analysis.
Unfortunately, although I am not by nature a lazy person, there are simply too many non sequiturs, false conclusions, rationalizations, and "it stands to reason" assumptions for a comprehensive response.
Those who would enjoy reading my opinion can PM me.
Thanks.

Have you did some before/after testing on this?