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Re: Hood scoop performance .. [Re: Neil] #2824646
09/24/20 03:27 PM
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polyspheric Offline
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Hood scoops are cosmetic


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Re: Hood scoop performance .. [Re: polyspheric] #2824664
09/24/20 04:09 PM
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Originally Posted by polyspheric
it was picking up SIGNIFICANTLY more air than the engine needed

That's what a supercharger does.


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.

Originally Posted by jcc

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?


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.


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Re: Hood scoop performance .. [Re: A39Coronet] #2824681
09/24/20 04:42 PM
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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.


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Re: Hood scoop performance .. [Re: A39Coronet] #2824683
09/24/20 04:49 PM
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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.


In theory, there is no difference between theory and practice. In practice, there is.
Re: Hood scoop performance .. [Re: polyspheric] #2824685
09/24/20 04:55 PM
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Originally Posted by polyspheric
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.


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.”


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Re: Hood scoop performance .. [Re: A39Coronet] #2824693
09/24/20 05:08 PM
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Originally Posted by A39Coronet
Originally Posted by polyspheric
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.


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.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Hood scoop performance .. [Re: madscientist] #2824705
09/24/20 05:36 PM
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Originally Posted by madscientist


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.


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Re: Hood scoop performance .. [Re: A39Coronet] #2824761
09/24/20 08:39 PM
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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.


If the results don't match the theory, change the theory.
Re: Hood scoop performance .. [Re: CMcAllister] #2824886
09/25/20 09:47 AM
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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.


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Re: Hood scoop performance .. [Re: bigdad] #2825021
09/25/20 02:25 PM
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Have fun!


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Re: Hood scoop performance .. [Re: A39Coronet] #2825029
09/25/20 02:36 PM
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Originally Posted by A39Coronet

Originally Posted by jcc

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?


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.


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.


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Re: Hood scoop performance .. [Re: jcc] #2825043
09/25/20 03:09 PM
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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

Last edited by 340man4ever; 09/25/20 03:11 PM.

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Re: Hood scoop performance .. [Re: 340man4ever] #2825103
09/25/20 05:55 PM
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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.

Last edited by cudaman1969; 09/25/20 05:57 PM.
Re: Hood scoop performance .. [Re: cudaman1969] #2825117
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Originally Posted by cudaman1969
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.


If the results don't match the theory, change the theory.
Re: Hood scoop performance .. [Re: jcc] #2825132
09/25/20 07:38 PM
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Originally Posted by jcc
Originally Posted by A39Coronet

Originally Posted by jcc

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?


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.


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.


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.

Last edited by A39Coronet; 09/25/20 07:41 PM.

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Re: Hood scoop performance .. [Re: A39Coronet] #2825640
09/27/20 12:10 PM
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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

Re: Hood scoop performance .. [Re: cudaman1969] #2825810
09/27/20 07:17 PM
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Originally Posted by cudaman1969
A friend raced a Corvette tube chassis car that 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
iagree
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 tsk down twocents
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 shock
They said aerodynamics really came into play above 150 MPH on most race cars work shruggy

Last edited by Cab_Burge; 09/27/20 07:18 PM.

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Re: Hood scoop performance .. [Re: Cab_Burge] #2825926
09/28/20 07:29 AM
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About 60% more, varies roughly by the cube of the speed.


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Re: Hood scoop performance .. [Re: polyspheric] #2825989
09/28/20 10:47 AM
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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.


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Re: Hood scoop performance .. [Re: cudaman1969] #2826048
09/28/20 01:03 PM
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Originally Posted by cudaman1969
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.
I still use a paper box.

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