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Open Scoop - What Difference does it make?


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That's to be expected. The question is what difference does it make? :headscratch:

 

Gentlemen,

 

Though I have not logged on here for a while as I have been quite busy moderating the Ford GT Forum, the enjoyment I get from driving my Shelby GT remains undiminished after several years of ownership. I came across the question above on a related thread and thought I would pass along some information. As on most automotive topics members post up endless amounts of speculation as to what they think might be occurring without any hard data to back it up. Such speculation is interesting and entertaining, but almost always worthless as actionable information. I had my own level of speculation during my involvement in the open hood scoop project for a couple years now. I wanted to answer the following questions.

 

1. Did air actually flow into the Shelby GT hood scoop when it's open or did air flow over the top and actually create a vacuum drawing air out of the hood?

 

2. What would the effect of an open hood scoop have on air pressure (barometric pressure) underneath the hood?

 

3. What would the effect of an open hood scoop have on air temperature underneath the hood? For those of us running superchargers (which suffer serious performance degradation when they get hot), a substantial reduction in temperature around the supercharger would clearly be beneficial.

 

With accurate measurements of the above I could calculate air density, which has a direct relationship to performance. In addition I wanted to measure the difference in effectiveness between a forward mounted scoop like the Super Snake's, the center mounted hood scoop like the Shelby GT, and a rearward facing scoop like Chevrolet's cowl induction. With the help of my son Charley Beck, we combined all of these into an award-winning science project that brought him great accolades at his prep school.

 

We utilized aircraft instruments supplied by Heath at Performance One Aviation. A sensitive altimeter allowed us to measure minute pressure changes at various locations under the hood, outside the car, and inside the scoop. A remote temperature probe allowed us to take precise temperature measurements at all these same locations. Measurements were taken with the car at rest, and at varying speeds up to 100 mph. My Shelby GT was utilized for measurements with the scoop open, and with it taped shut. In addition, a very thin vertical cardboard flap was affixed to the scoop opening and photographed at speed to demonstrate that air was indeed flowing in and not flowing out.

 

As the hood scoop on my Shelby GT is not movable, I utilize my Ford Taurus with one of my spare "Heath Scoops" securely taped in the three different locations while pressure and temperatures were recorded at various speeds.

 

I do not have in front of me our complete data logs, but here's the information in a nutshell.

 

The open hood scoop resulted in a temperature drop in the area of the supercharger of over 20° Fahrenheit at a speed of 60 mph. With the hood scoop closed the under hood area of the Shelby GT experiences a slight vacuum at speed. The air pressure actually drops when the car is in motion. The net reduction in air density was greater because of the temperature differential than pressure differential. The hotter air is, the less dense it becomes. The total reduction in air density, temperature and pressure combined, was over 5%. With the hood scoop open the under hood pressure was equal to or just slightly higher than outside ambient air pressure.

 

When photographed at speed from another vehicle, the thin cardboard flap mounted at the opening of my Shelby GT scoop folded back and clearly indicated a substantial quantity of air was indeed flowing in to the Shelby GT hood scoop.

 

Another interesting phenomenon was observed. As soon as my Shelby GT came to rest with the hood scoop closed at a stoplight, the under hood temperature near the supercharger skyrocketed by over 30°F in just 90 seconds. In my Ford Taurus the rise in temperature at a stoplight was almost as rapid. With the hood scoop open, the temperature rise after 90 seconds was only 18°F. Clearly, that open scoop gave very hot air a place to escape even when the car is at rest. FYI, that 30° jump in under hood temperature after 90 seconds result in an additional 5% decrease in air density!!

 

The forward mounted scoop (Supersnake) is indeed more effective than the center mounted scoop that our Shelby GT's use. The rear mounted Cowl Induction type scoop is slightly less effective than the center mounted scoop. In all cases however, measurements show the primary benefit of any hood scoop is a reduction in air temperature, which greatly exceeds the increase in air pressure through ram air effect.

 

I am not a supercharger expert and I cannot tell you precisely how much of a difference that air temperature surrounding it affects the operating temperature of a supercharger. Perhaps somebody more knowledgeable than me in this area can chime in here. What I can tell you is that allowing the supercharger of my Ford GT (before I went with twin turbos) to cool down for a full hour between runs at the Texas Mile resulted in substantially faster speeds.

 

The purpose of the intercooler on our superchargers is to lower the temperature of intake air to make it more dense. The colder the air, the more dense it is and the higher horsepower will be. At the Texas Mile that ended yesterday, early morning temperatures 20° cooler than midday temperatures resulted in morning top speeds as much as 10 miles an hour faster than midday top speeds.

 

Is an increase in air density of 5% and a reduction in under hood temperature of 20°, especially if you're running a supercharger, beneficial to your car's performance. The answer is yes. Is this small but measurable difference in performance worth the time and expense to open the hood scoop on your car? Only you can answer that question.

 

Aside from all that, when you see a Shelby GT with an open "Heath Scoop" mounted, you have to admit, they look cool!

 

All the best.

 

Chip

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Hi Chip. Good to see you over hear as well. I had on 08 GT500 and now have the 09 KR.

Neat project. I can confirm the heat generated by the supercharger in the 500 and the KR is huge!! The KR front hood opening and rear hood venting make a big difference.

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Wow excellent thread, Chip! I'm sure glad I had my Shelby scoop made functional when it was replaced under warranty. The looks alone are worth the upgrade, in my opinion. But having this info certainly helps to justify the time I spent making it functional. Thanks to you and your son for putting this amount of effort into testing the scoops.

On a side note, have you noticed an increase in front end lift or a floating feeling at very high speeds? Perhaps it's all in my head, but after opening the scoop up, I felt like the front of the car was lifting more on the road course. I recently added Super Snake heat extractors at the back of my hood to try to help counteract this effect. I haven't been able to test it out on the track yet though. If nothing else, it ought to help with underhood temps even more.

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On a side note, have you noticed an increase in front end lift or a floating feeling at very high speeds? Perhaps it's all in my head, but after opening the scoop up, I felt like the front of the car was lifting more on the road course.

 

I have no way to measure that. I have had my Shelby GT up to 145 MPH and I stopped there because my stock 2 piece drive shaft started to vibrate. Up to that point the car was rock solid and I had no hood shake. How fast is the high speed you are talking about?

 

Chip

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Two things:

 

1. Chip thanks for the info. I opened up my hoodscoop and love the look. I thought it had to have some effect on cooling the supercharger and now I know, and it is very cool.

 

2. Ken your signature is going to get me in trouble. My sister in law works for me and stepped into my office right as I scrolled down to your comments. The only thing she saw was the picture. Her comment "Oh Brother what are you looking at?" :o Now I have some explaining to do when I get home.

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Chip! GREAT to see you and GREAT info!

 

I guess I'll just say I'm not surprised by your findings, and THANKS SO MUCH for taking the time and effort to do them, but as a non-engine-techie I'm still wondering what that temp drop really means. So here is where I come from on this stuff, and I may be wrong, but I assume (and you know what they say about that) Ford has two goals in mind when they engineer a car. The first is to provide maximum performance while the second is to reduce liability and warranty repairs. On second thought maybe these are reversed! :hysterical:

 

So I am left to wonder why would Ford not, or any manufacturer would not, add such cooling hood scoops to their cars? It's pretty cheap. I mean is the lack of such cooling mean it's unnecessary?

 

I am a computer guy and the CPU of an average notebook runs about 140 degrees. If I decrease the temp to 120 it does nothing as far as performance goes and negligible in overall longevity or stability so if presented something to do that it would be rejected as having no real ROI.

 

Now, that said, we don't judge things on a "cool" factor so in the end it may just be that you either want an open scoop or it's not a compelling enough issue for you. Again I don't know enough to judge either way and just see it through my CPU lens.

 

Again GREAT info, GREAT to see you, and thanks for all that you've done for the cause over the years!

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Hey Chip! Nice of you to drop in!

 

For those that don't have one, the Heath/Beck scoop is a fine piece of hardware and now you have the proof that it works!

 

I admit, I always thought that there was very little benefit "at speed" because I haven't done any research to prove otherwise! What I DID know was the amount of heat that was escaping from the opening after shutdown was quite a bit as the heat waves were easily visible!

 

Nice to know that the benefit while underway is way better than nothing!

 

Now Chip, about those side scoops...is Heath working on anything?

 

Sam

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Chip! GREAT to see you and GREAT info!

 

I guess I'll just say I'm not surprised by your findings, and THANKS SO MUCH for taking the time and effort to do them, but as a non-engine-techie I'm still wondering what that temp drop really means. So here is where I come from on this stuff, and I may be wrong, but I assume (and you know what they say about that) Ford has two goals in mind when they engineer a car. The first is to provide maximum performance while the second is to reduce liability and warranty repairs. On second thought maybe these are reversed! :hysterical:

 

So I am left to wonder why would Ford not, or any manufacturer would not, add such cooling hood scoops to their cars? It's pretty cheap. I mean is the lack of such cooling mean it's unnecessary?

 

I am a computer guy and the CPU of an average notebook runs about 140 degrees. If I decrease the temp to 120 it does nothing as far as performance goes and negligible in overall longevity or stability so if presented something to do that it would be rejected as having no real ROI.

 

Now, that said, we don't judge things on a "cool" factor so in the end it may just be that you either want an open scoop or it's not a compelling enough issue for you. Again I don't know enough to judge either way and just see it through my CPU lens.

 

Again GREAT info, GREAT to see you, and thanks for all that you've done for the cause over the years!

 

 

dont doubt the chip, he made chuck norris what he is today lol

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So I am left to wonder why would Ford not, or any manufacturer would not, add such cooling hood scoops to their cars? It's pretty cheap. I mean is the lack of such cooling mean it's unnecessary?

 

I am a computer guy and the CPU of an average notebook runs about 140 degrees. If I decrease the temp to 120 it does nothing as far as performance goes and negligible in overall longevity or stability so if presented something to do that it would be rejected as having no real ROI.

 

Hi Jeff,

 

Because of my work with the Ford GT Forum over the last five years, I've been able to spend time at the track, in the bar, and at dinner with a number of Ford's top performance car engineers. One of my favorites is Jamal Hameedi (pictured with me below at Las Vegas International Speedway) who was the program manager for the Ford GT during its development and who attends all of our major functions. An engineer by trade, Jamal is currently Ford SVT Chief Nameplate Engineer. I was questioning him about the design of the GT500 KR hood and why it was so complicated, expensive, and different than the Super Snake hood. His answer reveals why simple hood scoops like the Heath Scoop on my Shelby GT would be unacceptable for Ford to utilize on mass-produced products like the Mustang.

 

Jamal told me that it is incredibly difficult to satisfy all of the requirements for vehicular design imposed by both government and the Ford Motor Company itself. Everything is a compromise and a trade off. For example, open intake systems produce more horsepower but cannot pass intake noise limit restrictions. Running an engine cooler produces more power but it also makes catalytic converters less effective resulting in engines that cannot pass emissions limits. Open free-flowing exhaust systems that do not require 180° exhaust turns produce more power because they are less restrictive, but again they fail noise limitations. A simple open hood scoop like mine reduces under hood temperatures but if an individual was using a high-pressure power washer and shot it directly into that scoop, it might be possible to damage under hood electrics. Therefore, the hood scoops of the GT500KR force air through a couple 90° bends that make the scoops less effective but manage water drainage. Compromise and trade-off. Almost every one of us has modified our cars with headers, freer flowing mufflers, different rear end ratios, larger wider wheels, and God knows what else. Almost all of these modifications have proven performance benefits so why don't manufactures use all of them? Because they can't. The cars would fail some test or government requirement imposed upon manufactures. So these items are left to the aftermarket that isn't burdened with such restrictions. Note that 95% of Harley-Davidson riders (including me) throw away the government mandated quiet mufflers the day the bike leaves the showroom and replace them with illegal mufflers marked "off road only". Harley knows that owners hate the stock mufflers but they have to build the motorcycles with them anyway.

 

I know that my Ford Racing shorty headers make my catalytic converters less effective, my Ford Racing straight through mufflers would fail new-car noise standards, my supercharger reduces fuel mileage, etc. etc. I don't care about those standards as much as I care about improving the performance of my car.

 

To say that Ford didn't incorporate a particular performance enhancement and therefore it's unnecessary is a true statement. Not a single one of the performance enhancements that I have added to my car is necessary for it to function as a car. The Ford Racing short shifter incorporated on the Shelby GT is unnecessary on the Mustang GT and equally unnecessary but still desirable on the Shelby GT. The Heath scoop is kind of like that.

 

Finally, I don't know much about computers but I do know they do not function as air pumps. The internal combustion engine is an air pump. The more air they pump, the more power they produce. With a wide open throttle fuel/air ratio set at 12 to 1, if you can increase air density by 10%, you can increase fuel volume in the intake charge by 10%, and the engine will produce 10% more horsepower. There is a direct correlation between air density and power potential. But again, there is that trade off. In this case a 10% reduction in fuel mileage. Want maximum mileage, or maximum power? Performance car enthusiasts normally choose the latter, everyday drivers would choose the former. A computers performance may not be affected much by ambient temperature or air density, but an automobile engines performance is affected.

 

I have been caught out in some driving rainstorms as have many other owners of the Heath scoop. Not a single one of us has had any trouble as a result of water entering that scoop. BUT, I believe Jamal when he tells me that if I shot my power washer directly through that scoop opening toward the firewall of my car, it might short something out. That's the type of thing Ford engineers need to worry about, but as an owner who will never do that, I don't worry about that. Let's make it go faster, handle better, and look cooler, government and environmental regulations be damned. My Harley sounds much better, and my Shelby GT hauls ass! Cheers.

 

Chip

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So Chip any advice on what to cut the hood with to spare the paint? I'm in you convinced me...

 

The opening is marked with a black felt pen (Sharpie). A small drill bit punches pilot holes 1/8 inch from each of the 4 corners. A 1/4 inch drill bit then opens the 4 corners with a nice radius. Use a fine rotary blade on a high powered Dremmel type tool to cut the rest of the opening.

 

I removed the hood insulation (see my pictures) and painted the bottom of my hood so it was as nice as the top but that's not really necessary. From the top you can't see the edges because they are covered by the scoop. The bare unpainted edges of the hood cut will not corrode because the hood is aluminum but you can touch the edges with touch up paint if you like.

 

Chip

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The opening is marked with a black felt pen (Sharpie). A small drill bit punches pilot holes 1/8 inch from each of the 4 corners. A 1/4 inch drill bit then opens the 4 corners with a nice radius. Use a fine rotary blade on a high powered Dremmel type tool to cut the rest of the opening.

 

I removed the hood insulation (see my pictures) and painted the bottom of my hood so it was as nice as the top but that's not really necessary. From the top you can't see the edges because they are covered by the scoop. The bare unpainted edges of the hood cut will not corrode because the hood is aluminum but you can touch the edges with touch up paint if you like.

 

Chip

 

 

 

Thanks Chip! Hope we meet some day in person, you are very nice to share your experiences...

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I have no way to measure that. I have had my Shelby GT up to 145 MPH and I stopped there because my stock 2 piece drive shaft started to vibrate. Up to that point the car was rock solid and I had no hood shake. How fast is the high speed you are talking about?

 

Chip

 

Anything over 130 mph has made me nervous since opening my hood up. I have no way of measuring it either, but I've only noticed it after cutting the hole.

 

Two things:

 

1. Chip thanks for the info. I opened up my hoodscoop and love the look. I thought it had to have some effect on cooling the supercharger and now I know, and it is very cool.

 

2. Ken your signature is going to get me in trouble. My sister in law works for me and stepped into my office right as I scrolled down to your comments. The only thing she saw was the picture. Her comment "Oh Brother what are you looking at?" :o Now I have some explaining to do when I get home.

 

Sorry buddy, I didn't realize my wife's legs would cause such a stir on TS! ;)

 

Howdy Chip, thank you. Glad to see you posting again my friend. I am taking my scoop off I might have to go cutting, what did you guys use to make the cut without screwing up the paint? Thanks!

 

Use a Dremel and a steady hand, my man. The hole that I cut is about half the size of Chip's FYI. I wasn't sure about cutting out the ribbed center support, so I left it alone for fear of weakening the hood too much.

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I have no way to measure that. I have had my Shelby GT up to 145 MPH and I stopped there because my stock 2 piece drive shaft started to vibrate. Up to that point the car was rock solid and I had no hood shake. How fast is the high speed you are talking about?

 

Chip

 

 

Regarding speed on the SGT.

 

Right after I got mine I took it on a spin to Cheyenne, WY. This was in February. When I left the house the temp was about 60 and still. By the time I got to the border the temp had dropped to about 30 and was spitting snow, and there was a very strong headwind straight out of the north. I had the speedo up to 90 and the hood started to flutter at the rear (by the windshield) - it was lifting up with main hood springs. I stopped for gas and a diet Coke and asked in the station what the wind speed was - their weather station stated 55 sustained with 65+ gusts. So I estimate the hood flutter started at about 145 equivalent. That has been confirmed by others as well. I also believe the front hood pins were actually function in this case.

 

On the trip to Vegas last year I had it up to 135 on an empty piece of I70 (just me an the 18-wheeler in front of me - he honked as I went by him after closing the gap from about a mile.) It still had plenty of more "go" left and no sign of any wind or driveshaft issues, but I ran out of runway. It was a little valley about two miles long with both ends of the highway and I started to see oncoming traffic so I let off after I passed the truck.

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I live near the utah border and I have access to long empty stretches of I-70. I have had my car to the electronic cut off on several occassions when it was stock. I did not have any issues with hood shake. Since opening the hood scoop I have been to 145 (4th gear) with it and still no issues. Not sure what the top speed is never been wot in 5th. Jail is not my idea of fun.

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Anything over 130 mph has made me nervous since opening my hood up. I have no way of measuring it either, but I've only noticed it after cutting the hole.

 

 

Sorry buddy, I didn't realize my wife's legs would cause such a stir on TS! ;)

 

 

Use a Dremel and a steady hand, my man. The hole that I cut is about half the size of Chip's FYI. I wasn't sure about cutting out the ribbed center support, so I left it alone for fear of weakening the hood too much.

 

 

just harassing you on your new photo.

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Two things:

 

1. Chip thanks for the info. I opened up my hoodscoop and love the look. I thought it had to have some effect on cooling the supercharger and now I know, and it is very cool.

 

2. Ken your signature is going to get me in trouble. My sister in law works for me and stepped into my office right as I scrolled down to your comments. The only thing she saw was the picture. Her comment "Oh Brother what are you looking at?" :o Now I have some explaining to do when I get home.

 

 

 

 

 

Here's what you tell her....................."why honey it was work related"

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For those of you that have opened up your hood-scoops were you able to use your stock hood-scoops to do this or did you have to get this "heath scoop"? I have had my scoop and hoodstripes replaced twice already and believe I have the most recent redesign of the scoop. I am not a fan of the cheap fake honeycomb and would like to eventually open the scoop up. Is the fake honeycomb used for supporting the structure or can it be easily take off to open the scoop?

 

08sgt1289

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For those of you that have opened up your hood-scoops were you able to use your stock hood-scoops to do this or did you have to get this "heath scoop"? I have had my scoop and hoodstripes replaced twice already and believe I have the most recent redesign of the scoop. I am not a fan of the cheap fake honeycomb and would like to eventually open the scoop up. Is the fake honeycomb used for supporting the structure or can it be easily take off to open the scoop?

 

08sgt1289

 

 

I am looking at my original OEM scoop and I don't think using it "open" would be a good idea. It seems sturdy enough, however you would have to not only remove the honeycomb piece, but also grind down a lot of support structure found behind it, then drill out all of the fake rivets. I think that once you got it remounted, the center of the scoop would sag from lack of support and besides that, you'd probably still have to deal with the curling/warping edges.

 

I've never seen the Shelby replacement scoop, so I can't speak about how it's made or if it can be opened up and used.

 

The Heath/Beck scoop was expensive and is shipped unfinished, but it truly is a nice piece of work. I'm very happy with mine!

 

I sent my old OEM scoop to Mr. Shelby and had it signed so now I have a very unique keepsake! (well, not totally unique, I think Andrew did the same with his!)

 

Sam

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