Guest Mike Posted November 27, 2006 Share Posted November 27, 2006 Dtsnlvrs... I'll bet money that the vented inspection lids help remove that heat reasonably well at speed. Very good write up. With the heat issue though....It is not that the air builds up and spills back into the front, the air actually flows under the car. The heat becomes a factor when the temperature of the hood gets way over ambient. It affects the boundry layer on the top of the hood, and thereby affects the drag on the car. As far as getting rid of the heat....just remove the cowl to hood seal....instant 15-20 deg temp drop on a hot Alabama day. Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 27, 2006 Share Posted November 27, 2006 Dtsnlvrs... I'll bet money that the vented inspection lids help remove that heat reasonably well at speed. Yes that helps as well....just that every time I open my hood at a show I get the "where is your cowl seal" question.....It aint there for a reason.. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 27, 2006 Share Posted November 27, 2006 Are you losing heat because hot air is flowing out, or is that in the high pressure zone at the base of the window and getting air forced in, cowl induction style, do you think? I guess you'd have to do the yarn test to tell... Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 27, 2006 Share Posted November 27, 2006 Are you losing heat because hot air is flowing out, or is that in the high pressure zone at the base of the window and getting air forced in, cowl induction style, do you think? I guess you'd have to do the yarn test to tell... Ya'll did not take High School Physics did ya' The base of the widshield / cowl area is actually a low pressure zone, remember Bernoilli's principle. The faster air moves, the lower the pressure. That being said, the "hot" air in the engine bay is at a higher pressure than the air flowing over the cowl, so it gets sucked out...kinda like smoke from a cigarette gets "sucked" out of a cracked car window at speed. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 27, 2006 Share Posted November 27, 2006 Actually, no, that's not the way it works (and i was in honors physics in high school, it was just a while ago). The base of the window is a high pressure zone, that's why cowl induction hoods work. The point of those hoods is to feed fresh air into the engine intake, not to vent heat out. http://www.camaro-untoldsecrets.com/articles/rpo_zl2.htm Here is a lengthy thread about S30 aerodynamics that I found interesting... http://forums.hybridz.org/showthread.php?t=108665&highlight=aerodynamics Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 27, 2006 Share Posted November 27, 2006 Actually, no, that's not the way it works (and i was in honors physics in high school, it was just a while ago). The base of the window is a high pressure zone, that's why cowl induction hoods work. The point of those hoods is to feed fresh air into the engine intake, not to vent heat out. http://www.camaro-untoldsecrets.com/articles/rpo_zl2.htm Here is a lengthy thread about S30 aerodynamics that I found interesting... http://forums.hybridz.org/showthread.php?t=108665&highlight=aerodynamics Actually the cowl induction works becuse it is just that...induction. The Low pressure air at the cowl is actually higher in pressure than the opening of the carburettor, and they were not trying to "force feed" the carburettor, but provide it with cold air. But I stand by my last statement..one that is backed up by the same theory and principle that allows airplanes to fly. And the HS phsyics reference was a friggin joke. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 27, 2006 Share Posted November 27, 2006 Think about it a little harder: If you hold your hand out of the window at speed, you can feel the air pressure build up and push back on your hand. Imagine your hand is as big as the windshield of your car, and set at about the same angle. High pressure there, or low pressure? Your basic theory seems sound, that's why nissan chose to put the hood vents on the 280z where they chose to put them, but the interaction of the air with the windshield changes what's happening there a little bit. Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 27, 2006 Share Posted November 27, 2006 Think about it a little harder: If you hold your hand out of the window at speed, you can feel the air pressure build up and push back on your hand. Imagine your hand is as big as the windshield of your car, and set at about the same angle. High pressure there, or low pressure? Your basic theory seems sound, that's why nissan chose to put the hood vents on the 280z where they chose to put them, but the interaction of the air with the windshield changes what's happening there a little bit. I see where you are coming from, but you are thinking "too small".. Think about the entire upper surface of the car..it is kinda cambered like the upper surface of a wing right. This is why we "float" at high speed, the Car is itself a wing...low pressure on top, high pressure on bottom. As far as the cowl area goes...alot of people think it is a high pressure area, but it is relative. The pressure at the cowl is higher than the pressure at say the hatch vent..which is why flow thru venting works, but it is lower than the pressure in the engine bay....remember, the faster the air is moving, the lower the pressure. Now having said that, there is turb at the cowl, but right at the windshield base. Now in keeping with the aero theme, why does an airdam keep us from floating at high speed? It depends on the type of dam...the BRE type worked mostly on the drag principle. It created drag at the lower cowl that helped to "hold" the nose down. The larger "dam" types work on two principles. Drag and Vacuum. There is a little drag created by having the dam, and if the car is set-up low enough...a little bit of vacuum right under the nose...dont ask me exactly how it works, A F1 or Indy car engineer could explain it better. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 27, 2006 Share Posted November 27, 2006 I suppose we'll just have to wait unitl Bjhine's forthcoming wind tunnel testing is finished to see what's really going on with some actual hard data... Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted November 27, 2006 Share Posted November 27, 2006 Someone should just yarn their Z and take it on the highway. Along with a chase vehicle and a camera. I'd do it to my Z but it can't drive. I think with a standard xenon airdam that is sealed to the radiator crossmember and the car low enough then stability can be dramatically raised. Here are the plans for me aerodynamic work. Standard xenon poly air dam sealed to radiator belly pan to engine crossmember with splitter bottom of wheelwells completely sealed serious venting of engine bay through fenders transmission tunnel sealed around transmission rear diffuser (W/ fuel cell) front opening closed by half Nascar style adjustable rear spoiler rubber side skirts I think the most important thing to focus on (IMO) is what is causing lift at speed. It's not easy to add downforce to the front end of a Z by adding things onto the body. An airdam is about all you can do other than lowering the snot out of the car. Sealing the underside and redirecting the flow of engine bay air from going underneath the car to the side or top would have more of an effect at reducing lift than adding an airdam alone. Just my .02 Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 27, 2006 Share Posted November 27, 2006 I suppose we'll just have to wait unitl Bjhine's forthcoming wind tunnel testing is finished to see what's really going on with some actual hard data... Whatever, Nissan already did this...back in 69 I should not be so harsh, I think I was about your age when the bernoilli principle, and how it relates to cars finally hit me and I truly began to understand it. I do not remember what the trigger was, oh yes I do, I had just finished a class on Rotor Smoothing, thats when I began to fully understand. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 27, 2006 Share Posted November 27, 2006 Russell, the yarn test has been done. The air goes INTO the engine compartment. The base of the windshield is a high pressure area. The base of a spoiler that you put on the hatch is a similarly high pressure area. There are a bunch of other aerodynamic threads on this site where these topics have been covered pretty thoroughly. OTM's yarn test with the chase vehicle has been tried as well. Let's not let this one get too argumentative or redundant. What is interesting about this thread is the drag information. If you want to talk about downforce or upforce or vented hoods or spoilers or any of that, try one of the other threads. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted November 27, 2006 Share Posted November 27, 2006 Whatever, Nissan already did this...back in 69 I should not be so harsh, I think I was about your age when the bernoilli principle, and how it relates to cars finally hit me and I truly began to understand it. I do not remember what the trigger was, oh yes I do, I had just finished a class on Rotor Smoothing, thats when I began to fully understand. Jon and veritech-z are correct. The base of the hood is a high pressure area which forces air into the engine compartment. In terms of airflow there is dead area at the base of the windshield due to the bend between the hood and the windshield. The airstream is deflected above this area. Think of those car commercials where they do a smoke test of a car in a wind tunnel. Those illustrate the principle pretty well. Put a vent in the middle of the hood where the airflow is uninterrupted and it will draw air out of the engine bay. This is exactly what Nissan did with the later 70 Z cars. Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted November 27, 2006 Share Posted November 27, 2006 Here's a nice read on the subject. This article mentions the G-nose and its affect on drag. The G-nose is longer and slopes farther downward. This will have the benefit of downward push thereby minimizing or eliminating unwanted lift at speed... at least this seems logical to me. http://www.zccw.org/Tech/Body/early_aero.asp EDIT: After reading this article, I've come to the conclusion that the four biggest improvements for a 1st generation Z are the G-nose, hood/side venting, Pantera hatch, and rear wing. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted November 27, 2006 Share Posted November 27, 2006 The heat becomes a factor when the temperature of the hood gets way over ambient. It affects the boundry layer on the top of the hood, and thereby affects the drag on the car. Care to elaborate on that some more? I don't really see how the temperature of the bonnet would affect the boundary layer. Dave Quote Link to comment Share on other sites More sharing options...
Mikelly Posted November 27, 2006 Share Posted November 27, 2006 Russell, the yarn test has been done. The air goes INTO the engine compartment. The base of the windshield is a high pressure area. The base of a spoiler that you put on the hatch is a similarly high pressure area. There are a bunch of other aerodynamic threads on this site where these topics have been covered pretty thoroughly. OTM's yarn test with the chase vehicle has been tried as well. Let's not let this one get too argumentative or redundant. What is interesting about this thread is the drag information. If you want to talk about downforce or upforce or vented hoods or spoilers or any of that, try one of the other threads. Ding Ding Ding Ding... You sir would be correct... On that note, We the admin staff are endorsing the Test being conducted by bjhines... More to follow, but we need YOUR support to confirm or deny which aero devices work on the Datsun Zcar... Wouldn't you like to know if that new spoiler you've been eyeing will DO what you intend??? More to follow... Mike Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 27, 2006 Share Posted November 27, 2006 Whatever, Nissan already did this...back in 69 I should not be so harsh, I think I was about your age when the bernoilli principle, and how it relates to cars finally hit me and I truly began to understand it. I do not remember what the trigger was, oh yes I do, I had just finished a class on Rotor Smoothing, thats when I began to fully understand. While I'm sure that Nissan DID in fact perform extensive wind tunnel testing, I don't have access to those results, nor does anyone I know of (with the possible exception of Alan T. HS30-H, which wouldn't surprise me one bit to find out). So I assume that once Bjhines and the guys do their testing, those results and possibly some video of the proceedings will be openly available, declassified for the masses, however you want to put it. At least I hope that to be the case, anyway. As for being harsh, you are free to present your perspective in whatever fashion you choose, though since you and I have neither met in person, nor interacted online prior to this thread that I can recall, I personally prefer to try to make a neutral to positive first impression with my posting if at all possible, and provide links to illuminate where my ideas are coming from... Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted November 28, 2006 Share Posted November 28, 2006 ScottiGNZ has already proven that the base of the windshield is higher pressure - he had to close the baqck side of his hood scoop off in order to get his car to cool properly of course, this was an RX7. Datsun also had that (IMO ugly) hood for the Z with the opening ON THE SIDE of the scoop. Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted November 28, 2006 Share Posted November 28, 2006 Man did this thread go south. Rudypoochris came up with some really interesting numbers and a whole new perspective on our old cars and their legendary bad cd numbers. The discussion had attracted some of the big players in this community and was shaping up to be a really interesting thread. Then I got involved with some other threads of greater importance to my specific project and come back and it has degenerated into almost a flame war. (although the hybrid z guys really showed their class by staying civil) That the base of the windshield is a high pressure zone is FACT, common knowledge around here. This isn't a bunch of ricer kids. These guys aren't talking out of there hind quarters. A lot of them are degreed engineers. The discussions of aerodynamics that I've read on this forum are extremely technical and include posts written by guys far brighter and more well educated then me. I'd think twice before I stated my opinion in this crowd. sorry... it had to be said so... lets see if we can save this... does anybody know the actual frontal area of a z in sq. ft.? I swear I just read that somewhere. Quote Link to comment Share on other sites More sharing options...
bjhines Posted November 28, 2006 Share Posted November 28, 2006 Roodypooh, Thanks for those very well thought out estimates... I need some input on these details... for as many factors as you can come up with... Factor in the addition of a 2.5" dropped body and an airdam, with 10" wide, zero-offset wheels, 275/40/17??? on 17x10 Medium sized sport mirrors on both sides, Mild fender flares (ZG or round)... That would be a good baseline for our ~typical~ car... frontal area is really the most important for this test.. but we need some initial numbers to plug in... Quote Link to comment Share on other sites More sharing options...
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