Nice!
Carlos you are a great source, and go to guy for effective cooling improvements.
Carlos you are a great source, and go to guy for effective cooling improvements.
My new heat extractor hood
- Thread starter pkwest
- Start date
Thanks jimmy, i was wondering when you would come and visit us again.
Yea, to say I've been out of the loop for a while would be a massive understatement.
--> http://www.svtperformance.com/forums/road-side-pub-17/647626-feels-so-good-alive-home.html
sweet, nice job!
Thanks for the link jimmy .... i had no idea and rarely go to that forum. Glad you are back.:beer:
If anyone is interested in getting a hood to modify, I have an 03/04 hood for sale.
http://www.svtperformance.com/forums/interior-exterior-parts-260/645855-fs-03-04-oem-cobra-hood.html
http://www.svtperformance.com/forums/interior-exterior-parts-260/645855-fs-03-04-oem-cobra-hood.html
Back from the dead here for an inquiry. I understand the raised edges should improve the performance of the extractor, but I'm curious if a simple gurney on the leading edge of the stock vents would be beneficial. I have the stock hood vents on order from Tousley and I'm planning on doing some modification for track use. My plan is to completely remove all the grill/slats and add a rounded gurney using the material from the removed cover/flap and a 2-part resin.
Yes a gurney flap would help. The problem is look where the air would be extracted from, mostly above the radiator. It would be more effective if it was able to get the air past the radiator.
I've been investigating the '95/'00 R degas bottle for this very reason. They seem to be readily available, I'm just not sure I want the headache of mounting the smaller reservoir plus a catch can. It's a daily driver and I'm not out there to compete. However, the fun factor will go up if I can run more of the year (Summer months).
Tuft string test 2004 Cobra hood vents
Some interesting observations during tuft testing: first, the tufts on the stock vent (driver side) remained attached and smooth everywhere I put tufts. The 1" tall gurney in the first pic is more or less perpendicular to air flow. The strings attached to the leading edge of the gurney actually were flowing down and into the heat extractor vent. The air was quite turbulent. I didn’t put any tufts far enough back to see if the air re-attached to the hood as on the stock side for this first round. Back to the drawing board.
The second test, I cut half of the gurney down to 1/2”. The turbulence really wasn’t reduced. The tufts were all over the place.
Third test I bent the gurney back 45 degrees (pic 2). The tufts on the leading edge of the gurney now had laminar flow characteristics, but all the other "downstream" strings showed extreme turbulent flow especially on the 1” tall side.
Fourth test I cut serrations across the entire gurney (pic 3). The tufts on the leading edge of the gurney were still showing laminar flow. The “downstream” strings on the ½” side were attached, while the “downstream” strings on the 1” side stilled showed significant turbulence. The ½” gurney, bent back 45*, and serrated showed extremely similar characteristics to the stock vents side. So close in fact, that I couldn’t tell a difference in tuft movement or angle. Essentially, no improvement in my eyes.
I initially thought that the gurney would increase the height of the “canopy” of low pressure. After witnessing the turbulence, I’m now more concerned that any leading edge obstruction will do more harm to the laminar flow over the hood. So the question I have for you guys with modified hoods (Carlos’ design(s), Tiger racing) or even better, guys with experience or training in aerodynamics, is this: what should the tufts look like on and around an efficient heat extractor?
Some interesting observations during tuft testing: first, the tufts on the stock vent (driver side) remained attached and smooth everywhere I put tufts. The 1" tall gurney in the first pic is more or less perpendicular to air flow. The strings attached to the leading edge of the gurney actually were flowing down and into the heat extractor vent. The air was quite turbulent. I didn’t put any tufts far enough back to see if the air re-attached to the hood as on the stock side for this first round. Back to the drawing board.
The second test, I cut half of the gurney down to 1/2”. The turbulence really wasn’t reduced. The tufts were all over the place.
Third test I bent the gurney back 45 degrees (pic 2). The tufts on the leading edge of the gurney now had laminar flow characteristics, but all the other "downstream" strings showed extreme turbulent flow especially on the 1” tall side.
Fourth test I cut serrations across the entire gurney (pic 3). The tufts on the leading edge of the gurney were still showing laminar flow. The “downstream” strings on the ½” side were attached, while the “downstream” strings on the 1” side stilled showed significant turbulence. The ½” gurney, bent back 45*, and serrated showed extremely similar characteristics to the stock vents side. So close in fact, that I couldn’t tell a difference in tuft movement or angle. Essentially, no improvement in my eyes.
I initially thought that the gurney would increase the height of the “canopy” of low pressure. After witnessing the turbulence, I’m now more concerned that any leading edge obstruction will do more harm to the laminar flow over the hood. So the question I have for you guys with modified hoods (Carlos’ design(s), Tiger racing) or even better, guys with experience or training in aerodynamics, is this: what should the tufts look like on and around an efficient heat extractor?
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Now this is real world testing, thanks mu22stang. Even though i did not do this testing i modded my hood similar to the one below. I figured if the jaguar race team used this design then it would be good for us also.
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Nice test. Ive wanted to do this with tufts tapped to the underside of the hood then go for a drive and see if they come up through the vents or stay out of sight. Kinda hard to do on a non street legal car.
I dug this up on youtube awhile back. It shows the tiger racing hood in action.
Boss 302S Wind Tunnel Testing - YouTube
I'm thinking if a Gurney flap drops the air pressure more under hood, it doesn't really matter how messed up the air flow up top is.
If the pressure drop increases more air goes through the rad.
The flow up top is helpful but is not the main objective, it's all about more air through the rad.
If the pressure drop increases more air goes through the rad.
The flow up top is helpful but is not the main objective, it's all about more air through the rad.
I see it two ways, and with my lack of aerodynamic knowledge, I can't say which is better or if my hypotheses are even right. Either:
The smooth, low pressure, laminar flow of the boundary layer flowing over the recessed hood vent that "sucks" the pressure from the engine bay is more efficient...
or...
The large hole punched in the air by the gurney, despite the disruption of the smooth, laminar flow of the boundary layer, is more efficient.
The Tiger racing hood has a slight raised lip around the entire border of the recessed vents. Per the information I've followed from Carlos and his conversations with Paul Brown, turbulent flow over this area may not be good for extraction. Hence the 40* louvers added to Carlos' design, similar to Tiger Racing's unit. It's interesting that the Tiger racing hood's leading opening is similar in size to the stock Terminator hood vent opening. All others are narrower. I’m not necessarily concerned about the drag penalty, especially if cooling is improved.
I’m going to try some other designs this weekend: A slotted gurney (drilled holes), a rounded gurney (zero height at the edge, 1/2” to 1” at the center), a ramped face (concave) and a curved face (convex). I’ll try to get my wife to take some video with the iphone.
I suppose the only way to test the cooling improvement is to compare ECT's, but my next track day probably won't be until the beginning of May.
The smooth, low pressure, laminar flow of the boundary layer flowing over the recessed hood vent that "sucks" the pressure from the engine bay is more efficient...
or...
The large hole punched in the air by the gurney, despite the disruption of the smooth, laminar flow of the boundary layer, is more efficient.
The Tiger racing hood has a slight raised lip around the entire border of the recessed vents. Per the information I've followed from Carlos and his conversations with Paul Brown, turbulent flow over this area may not be good for extraction. Hence the 40* louvers added to Carlos' design, similar to Tiger Racing's unit. It's interesting that the Tiger racing hood's leading opening is similar in size to the stock Terminator hood vent opening. All others are narrower. I’m not necessarily concerned about the drag penalty, especially if cooling is improved.
I’m going to try some other designs this weekend: A slotted gurney (drilled holes), a rounded gurney (zero height at the edge, 1/2” to 1” at the center), a ramped face (concave) and a curved face (convex). I’ll try to get my wife to take some video with the iphone.
I suppose the only way to test the cooling improvement is to compare ECT's, but my next track day probably won't be until the beginning of May.
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Do you have a way of testing air pressure at different locations?
Regardless what the tuff's test proves cooling is the true test. Both hoods designs (Tiger racing and mine) do work in getting heat out of the engine compartment. With your testing you may find a more aero way to get the air out. I for one will be waiting for the results. Thamks for taking the time.
I'm glad to do it! I've been contemplating how to do this for a while. Finally figuring out the fabrication of the gurney was what set the fire for me. If it turns out that the best way to maximize a stock hoods is to pop out the vents, so be it. Hopefully these test will answer that question.
I think I'll add a simple manometer test to collect some more direct data. I'll place one end in the center of the vent and the other in the interior, using only reference lines for the level change. Using two different diameter tubes may help. I may also place a separate line about 2" below the hood vent mounting surface to see the engine bay pressure changes.
I have an Aeroforce gauge so I'll try to get some ECT info, but on track data will once again be the true test. The gauge should help in another way too. I can see IAT1's. Theoretically, the quicker these recover from a heat soaked, stop light engine bay, the faster the engine bay evacuation.
I think I'll add a simple manometer test to collect some more direct data. I'll place one end in the center of the vent and the other in the interior, using only reference lines for the level change. Using two different diameter tubes may help. I may also place a separate line about 2" below the hood vent mounting surface to see the engine bay pressure changes.
I have an Aeroforce gauge so I'll try to get some ECT info, but on track data will once again be the true test. The gauge should help in another way too. I can see IAT1's. Theoretically, the quicker these recover from a heat soaked, stop light engine bay, the faster the engine bay evacuation.
Great work. I'm following with intense interest.
As some of you might recall, after boxing my radiator and putting in a massive oil cooler in the drivers fender, I solved my heat problems... only to create an aerodynamic problem at 160+ (front-end lift). I'm stuck in the 140 mph class (110-168 range) in ORR until that is solved. I'm not wanting to throw money at the problem until I have a reasonable chance that the money will help.
So... I'm hoping that the hood testing will help us arrive at a reasonable solution to reduce front-end lift.
As some of you might recall, after boxing my radiator and putting in a massive oil cooler in the drivers fender, I solved my heat problems... only to create an aerodynamic problem at 160+ (front-end lift). I'm stuck in the 140 mph class (110-168 range) in ORR until that is solved. I'm not wanting to throw money at the problem until I have a reasonable chance that the money will help.
So... I'm hoping that the hood testing will help us arrive at a reasonable solution to reduce front-end lift.
If it were my car I would block off the upper grille opening and cover the headlights/front lip of the hood with a large piece of helo tape, vent the fenders and install an air dam with small splitter.
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