rsicard Posted July 12, 2013 Share Posted July 12, 2013 Jon: What would be a way to rid the hood of its lift potential? I proposed putting just enough of an upward angled air dam to the leading edge of the hood, to cancel the Bernoulli effect of the hood. Perhaps this would create a low pressure area behind such an air dam to create down force and it also would create DRAG. The way to reduce under-hood pressure is to restrict the amount of fresh air entering through a tunnel to the radiator. Then exhaust the under-hood hot air out through vented hinged inspection covers. Have also thought about putting electrical squirrel cage blower just beneath the vented inspection covers to SUCK the hot air out from underneath the hood. Your comments please. Thanks. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 12, 2013 Share Posted July 12, 2013 I don't think you can get around the fact that there will be low pressure on top of the hood. Your spoiler idea will create LOWER pressure on the hood, by spoiling the airflow. That's what a spoiler does, it makes high pressure in front of it and a low pressure wake behind it. You'd be creating low(er) pressure than would otherwise exist and allowing it to act on the hood's top surface. This is why you see the Gurney in front of a hood vent. It produces lower pressure and helps to suck the air out of the vent. With no vent, it's just going to be sucking on the hood. What we're after is a better pressure differential. If we can get lower pressure under the hood than on top, then we have downforce. Blocking off airflow and ducting air to the rad are no brainers. Rad exhaust duct is also a fairly easy one to do, and you see this on lots of ALMS cars, and we have a couple people here who have gone that route (74_5.0L_Z and blueovalz). Controlling the airflow through the radiator and into the engine is most of the battle. Above and beyond that we can try to lessen the pressure under the hood in any number of ways. We can do this by venting the hood, and letting the flow on top suck the pressure out from underneath. We could remove the fenderwells and shape the fenders to exhaust the underhood air out the front fenders like NASCAR does. Tony D just mentioned a stovepipe in one of the other aero threads. Put a tube right through the middle of the car and terminate it right where the license plate is. There is a nice low pressure wake right there, that would suck air out of the engine compartment to fill that low pressure area and probably reduce drag as well. Your idea of fans might work, but I wouldn't put them (or vents) on the inspection covers and call it a day. Venting the inspection covers isn't a bad idea, but the covers are too small to get the job done. If you're going to do a sucker car, do a SUCKER CAR!!! Thinking Chapparal 2J, gas powered fan motors, etc... Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 12, 2013 Share Posted July 12, 2013 Jon: Thanks for your comments. I screwed up thinking the upward air dam at the leading edge of the hood would work. You are correct about the effect of same. Don't know that I have the real estate for radiator exhaust ducts out the hood. Please expand on the NASCAR exhausting under-hood air out the front fenders. Is the space behind the front spinning tires a low pressure area? Don't know what Tony D stove pipe thing is. What was he exhausting where? If large round holes are cut into the side pockets below the inspection panels into the wheel-house area, is that an area of low pressure and would that exhaust the under-hood hot and higher pressure air? Does putting an air dam with splitter at the bottom within 2 inches of the road surface create DOWN force? Really appreciate your thoughts and comments. You keep me on the straight and narrow. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 12, 2013 Share Posted July 12, 2013 This will explain the NASCAR thing: http://www.circletrack.com/techarticles/ctrp_0707_stock_car_aero_downforce/viewall.html Tony's stovepipe thing was just a theoretical, although I'm sure land speed cars have probably done it for real too. He was literally talking about taking a tube and connecting it from the engine compartment to the back of the car; cutting a hole in the firewall and in the back of the car, and connecting them. Since there is a low pressure wake behind the car, this would suck air out of the engine compartment (and reduce the wake behind the car - useful for LSR). Yes, there is a low pressure area behind the tire on the Z, this was clearly shown by the first wind tunnel test. Cutting holes below the inspection covers and venting to the fenderwells would help. They did this in the last windtunnel too, and they put fender vents on the outside to help get the air out on the blue car and tested covering the vents vs leaving them open. Again, the vents and the holes were pretty small. If you have a caged front end, you should be able to cut much bigger holes, and putting them further forward (in front of the strut) might help a bit too. Airdam 2" off the ground by itself reduces drag and lift, but you're not going to get real downforce until you close up the grill and do some of the other things in addition. If you look at those NASCARs though, they DO make real downforce and they are not very complicated, they just have very low ground clearance, have a rad duct, and exhaust the underhood air out through the fenders. It would be interesting to see what Dan's car (74_5.0L_Z) would do in the tunnel, since he has no fenderwells and the rad ducting. I'd bet his car would be among the best of the ones on this site. Just needs a splitter and big ass wing to complete it. Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 13, 2013 Share Posted July 13, 2013 Am uncertain what the airflow under the hood is in front of the struts is. More certain about air flow at the rear of the engine compartment either out through the ventilated inspection covers and/or boring a large hole through the inner fender panel underneath the inspection cover. Also have given thought to mounting an electric squirrel cage blower inside the wheel well with the intake affixed to the large hole beneath the inspection panel. Then run an exhaust tube from the blower downward and rearward. Or, a stovepipe from the large hole on the inner fender to vents on the outer fender. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted July 13, 2013 Share Posted July 13, 2013 The air behind the radiator is stalled at about 15 miles per hour, according to the windtunnel operator. Mike Quote Link to comment Share on other sites More sharing options...
rsicard Posted July 14, 2013 Share Posted July 14, 2013 If the air behind the radiator was stalled, then likely there is not enough of a rear vent for the under-hood air. Jon: I have gone over the circletrack magazine article and have captured same. The closer the splitter is to the ground, the lesser amount ram air will go under the air-dam/splitter. That means less positive pressure underneath the vehicle therefore the lesser amount of upward pressure or lift. There needs to be a way to evacuate the air coming through the radiator and around the engine. Quote Link to comment Share on other sites More sharing options...
ZT-R Posted July 16, 2013 Share Posted July 16, 2013 How do you think this would on the white car would perform? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 17, 2013 Share Posted July 17, 2013 I'd wager the black one would do a lot better. Quote Link to comment Share on other sites More sharing options...
ZT-R Posted July 17, 2013 Share Posted July 17, 2013 Yea, maybe cause its slightly more forward, but not quite as clean. Quote Link to comment Share on other sites More sharing options...
Sideways Posted July 17, 2013 Share Posted July 17, 2013 Has anyone done any kind pressure tests on the hood of their Z to see where the most ideal place for vents is in the first place? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 17, 2013 Share Posted July 17, 2013 (edited) There was some talk about using a manometer to test the pressure on the hood, can't remember if anyone did it. The black car has "alligator teeth" louvers which will extract more air than the flush louvers, at the cost of more drag. http://auto-racing.speedtv.com/article/le-mans-the-aerodynamic-influence-of-louvers-on-prototypes/ Edited July 17, 2013 by JMortensen 1 Quote Link to comment Share on other sites More sharing options...
duragg Posted July 17, 2013 Share Posted July 17, 2013 (edited) Neat article Jon. I do think just simple observation and copying can get an operator quite far. I am new to Aero discussion (on cars) and after reading all the threads many times it seems on a stock s30: 1) Adding virtually any front airdam will reduce drag and lift. 2) Adding virtually any rear spoiler will reduce drag and lift. 3) Controlling (limiting & directing) airflow into the radiator will improve cooling and reduce drag. 4) Helping air escape underhood will reduce drag, help limit lift and improve cooling 5) Adding more aggressive front devices (splitter) requires careful attention to #3 & #4. 6) Devices randomly scooping air INTO the hood are not helpful. Edited July 17, 2013 by duragg Quote Link to comment Share on other sites More sharing options...
Sideways Posted July 18, 2013 Share Posted July 18, 2013 (edited) There was some talk about using a manometer to test the pressure on the hood, can't remember if anyone did it. Ive seen a bit of talk about it as well but sadly no results. It spurred my (amongst other things) to start gathering some tools to conduct my own testing (The most recent and probably most important to me was just a simple magnehelic gauge). One I make it back state side Ill be experimenting with as many things as I can and will be recording my results- Which I plan to share here. Mind you its not as detailed as a windtunnel testing, but it is far cheaper and more practical. I wont have the super-detailed "numbers" youd get in a tunnel (exact cds, actual measurements of lift/downforce, etc) but Ill be able to measure air speeds and pressures, which should give me (and us!) at least a moderately decent idea of whats working (or not working). Maybe I should drum up a thread with requests on things people would like to see tested. I plan to start this in december, so it gives plenty of time for some good ideas to get hashed out. Edited July 18, 2013 by Sideways Quote Link to comment Share on other sites More sharing options...
duragg Posted July 18, 2013 Share Posted July 18, 2013 (edited) I think there is a thread about the "next wind tunnel" event. I'm curious to know if there is a handy location to snatch air for rear brake ducts. Snatch (verb) as in to obtain... Edited July 18, 2013 by duragg Quote Link to comment Share on other sites More sharing options...
Sideways Posted July 19, 2013 Share Posted July 19, 2013 I think there is a thread about the "next wind tunnel" event. I'm curious to know if there is a handy location to snatch air for rear brake ducts. Snatch (verb) as in to obtain... Indeed there is- And im super anxious to see the results if theyre kind enough to share. Sadly however as time there is rather pricey, it will be limited. Theres a lot of things many of us would love to see tested but sadly wont be able to (& Understandably so! It is their money and I cant blame them for not wanting to waste time on things they dont think will be relevant to their cars or as fruitful to experiment with as other venues) see tested in the tunnel. Like a flat bottom Z. As for if theres a handy location to snatch air for the rear brakes? Surely there will be. Ironically enough though, I dont believe the wind tunnel testing will tell you "where" exactly though (Although the operators might be inclined to divulge where they think would be good places)- However my testing will haha Quote Link to comment Share on other sites More sharing options...
Xnke Posted July 23, 2013 Share Posted July 23, 2013 (edited) I purchased a Dwyer Magnahelic gauge to measure differential pressure over the hood, and found that the highest difference was right about the middle of the S30 hood. This is measuring both top and bottom of the hood at the same time, on a differential measuring tool. About a 10" long section, from the side of the hood bulge out toward the outer frame of the hood, starting at the front corners of the bulge and coming back. This is where I measured the highest differential pressure, of 4.8 inches WC at 80MPH...too chicken to go faster on a public road. Fun part...the gauge showed low pressure on this spot of the hood from about 15MPH up! Edited July 23, 2013 by Xnke Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 23, 2013 Share Posted July 23, 2013 It should be possible to calculate roughly how many inches are at what pressure and do a rough estimate of how much pressure differential there is, how much lift is being caused with no vents. After vents are added the same test could be done and you could get a similar estimate of reduced lift/downforce. Google "inches water psi" and you get this: 1 inch of water = 0.0361396333 pounds per square inch Quote Link to comment Share on other sites More sharing options...
heavy85 Posted July 24, 2013 Share Posted July 24, 2013 Someone say hood vents? These are working well for me. Also on the topic of fender vents. Just did this but haven't had a good test to understand effectiveness. Quote Link to comment Share on other sites More sharing options...
duragg Posted July 24, 2013 Share Posted July 24, 2013 Someone say hood vents? These are working well for me. Also on the topic of fender vents. Just did this but haven't had a good test to understand effectiveness. THank you for the pictures... some ideas of yours I like. Quote Link to comment Share on other sites More sharing options...
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