mom'sZ Posted November 28, 2006 Share Posted November 28, 2006 and have those numbers taken from two identical cars but one with and one w/o AC Well russel, if heat has anywhere near the effect you state, then that AC is a killer because here in the sunshine state (and I know vegas ain't exactly cool) my dual core dual pass nascar radiator with tiny 10" electric fan barely allows my 180* thermostat to stay open. But the minute I switch on that air...up she goes. Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted November 28, 2006 Share Posted November 28, 2006 Well russel, if heat has anywhere near the effect you state, then that AC is a killer because here in the sunshine state (and I know vegas ain't exactly cool) my dual core dual pass nascar radiator with tiny 10" electric fan barely allows my 180* thermostat to stay open. But the minute I switch on that air...up she goes. I think that may be one of the reasons why I have NEVER encountered vapor lock in my Z's. None of them have AC when I am done with them....now my Dad's Z that I learned to drive in, that was a different story. 2.8L w/Janspeed head and BSR Headers, oh and AC Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted November 28, 2006 Administrators Share Posted November 28, 2006 I'd be curious to know what the radiator does to the speed of the air passing through it, and in turn how that affects the pressure of the underhood air. I'm sure its more complicated than this... the radiator is a restriction... it should cause a 'pressure drop', and concurrently an increase in drag. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted November 28, 2006 Administrators Share Posted November 28, 2006 uhh shucks ron...... Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 28, 2006 Share Posted November 28, 2006 I'm sure its more complicated than this but... the radiator is a restriction... it should cause a 'pressure drop' (and concurrently an increase in drag) That's pretty much what I was thinking, although it seems that the mechanical fan moves some SERIOUS cfm's when you rev the engine with the hood open... Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted November 28, 2006 Share Posted November 28, 2006 Max, I think he is refering to his own car. I wish I could run 17s The 2.5" drop seems pretty typical Quote Link to comment Share on other sites More sharing options...
Challenger Posted November 28, 2006 Share Posted November 28, 2006 I've seen some pictures of a piece of sheet metat being put from the back of the air dam to the front of the core support right below the radiator. This would solve air leaking below from the front as long as the airdam is very low. But you still have the problem of air in the engine bay that need to escape. My idea is a cowl type hood that starts at the front of the hood and extends only about halfway up the hood. This would let air escape rather then suck air in. Like I said Im not old enough to get my license quite yet and my car isnt on the road anyways right now so all my thoughts are well.... thoughts. Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted November 28, 2006 Share Posted November 28, 2006 although it seems that the mechanical fan moves some SERIOUS cfm's when you rev the engine with the hood open... mechanical fan? what mechanical fan? I ditched that baby awhile ago Quote Link to comment Share on other sites More sharing options...
veritech-z Posted November 28, 2006 Share Posted November 28, 2006 Max, I think he is refering to his own car. I wish I could run 17s The 2.5" drop seems pretty typical I would bet the readily available 1" drop and a 15X8" wheel is more typical on a street car, but hey, he's doing the work, he gets to pick the settings! (same concept as if I'm driving, don't touch my radio!) I tried to ditch my mechanical fan, but the electric fan I chose was weak in the extreme, and ended up costing me a head gasket... Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted November 28, 2006 Author Share Posted November 28, 2006 BJ I am not qualified to tell you how much frontal area there is on a Z simply because I asked someone to take a FSM picture which may or may not be correctly scared and basically count squares (using the comp) with AutoCAD. The result is posted in post #17 of this thread thanks to JIM. The numbers seem high, 17.78 for no wheels just car. With airdam the guestimate is somewhere between 20-21. Multiply that by .43/.46 not even sure which it is, and your answer is recieved. Ah HA! It is not that simple though. Since when you add on an airdamn and such the coefficent of drag is infact changed. Not sure if the number goes up or down. Now that is all up to you. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted November 28, 2006 Share Posted November 28, 2006 Dave, I'll take a stab at this (thats all it will be). Generally, heat is transfered to air at the surface. For example, our weather comes from the sun heating the surface, the surface heating the air, the air becoming lighter and rising, etc, etc. The boundary layer is largely stagnant, yes? If you heated the surface enough, the boundary air would heat and rise, potentially upsetting the boundary layer. My guess, though, is that its 'no factor' in our automobile. Ron, That makes sense in theory. I would also guess that it would not be a significant factor in the S30. Oh and bonnet vents should all be like blueovalz's. Dave Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted November 28, 2006 Share Posted November 28, 2006 MOM... No need to crawl under a rock. Maybe you saw something that I didn't/don't. I probably overreacted to your post as you might have to others. FWIW, I have the market cornered on the ignoramous thing. All one must do is read a few of my posts;-) FOLKS... sorry for the side bar... won't do it again... please continue this very INTERESTING thread!!! Mike... NO NO no, I didn't mean you or anybody else who's post count is above one hundred. tenth grade drop out here. No intellectual... ignoramous is more like it. Sorry man, I just hated to see what looked like a good discussion get muddled by some blow hard know it all telling everybody they must have slept through high school physics. Even though he later came back and said he was joking, if he typed aerodynamics into the search and read for a few hours, he'd come to realize that there are some heavy hitters on this site. If I offended anyone, I appologize. I'll crawl back under my rock now. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted November 28, 2006 Share Posted November 28, 2006 Well, I know one thing I can add. The z has hood pins, no latch, no springs and if I drive the z at any speed over 20mph with the hood pins minus the ritch pins to hold it down. the hood comes up in the back to the point where you can't see the road. Now this hood isn't your ordinary hood either, 6 inch cowl in duction chevy type scoop riveted onto the a huge hole cut in the stock datsun hood. IMO there is substantial underhood air pressure based on my real world observations, even at low speeds. Whether the cowl induction hood contributes to this high underhood pressure or helps is anyone's guess at this point. I'm not going to guess, but rather wait for the "real deal", the results may be totally suprising!!! I'm soo looking forward to the wind tunnel testing and the results that could help us all in our endeavors to achieve more stable, higher speed z cars. Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted November 28, 2006 Share Posted November 28, 2006 DOC... Yeah, the hood on my Alpha 1 does the same thing... and it has fender vents. Excessive under hood air pressure is caused by too much air scooped into the engine bay (obviously). To aerodynamically block all unwanted incoming air before it enters is the best solution, IMO. The only air coming in should be the "minimal amount needed" to cool the car and that should be carefully focused through the radiator. EDIT: And that "minimal amount" of necessary air pressure should be strategically vented to aid in other aerodynamic issues... to kill the lift. BTW, that's some hood cowl you've got there!! It looks like it would help on both counts. Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted November 28, 2006 Share Posted November 28, 2006 i took the picture and scaled it in acad. not perfect because of the fuzzy lines but it should be close. if a coupls of people were to get a good photo of their car head on and give me a few hard dimensions, i can get a better scale from the photos and get more realistic #'s. several different cars would be good. no dam. bre dam. full air dam. flares. wheels if needed, ect. jimbo Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted November 28, 2006 Share Posted November 28, 2006 I suggest you tell them at what distance to shoot the photos... and at what precise angles. Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted November 28, 2006 Share Posted November 28, 2006 straight on front shot just like the wind sees it. as far as how far back, i could care less as long as i have a had dimension to a known point. i would think that the closes you are the finer the details and the more of a chance that i hit the mark. if i could get a dimension of ground to drip edge or outside edge of fender to outside edge of fender, that will work. the larger the dimesion the better. start sending pics. jimbo Quote Link to comment Share on other sites More sharing options...
bjhines Posted November 28, 2006 Share Posted November 28, 2006 Hmmm... pictures... You should set your Zoom to full tight(longest distance)... Back away from the car as far as you can to get the front to fill the entire width of the viewfinder... If you have a high resolution 5Mp or better... then you can back up even further until the car only fills half the width of the frame... Shots like this REQUIRE a tripod... set it up and shoot with the timer to avoid disturbing the mount when pushing the button... To make things easier you should use a contrasting backdrop.. this can be done with lighting, placement, or drapery... You will need a FLAT level parking lot and you need a vertical point of reference... like the lower edge in the middle of the windshield... level the car and use a laser level to set the tripod height... set your camera veiwfinder to display the grid... use the grid to level and center your shot on the lower windshield lip... alternately you can use the level bubble on the tripod by roughly setting tripod height and then using the level bubble and height jack until the bubble reads level with the camera lined up on the lower lip of the windshield... By using this method you reduce the angular distortion of the image... this nets good returns up to about 5 car WIDTHS away... any more than that and the distances get much further for similar gains... Getting even more scientific and detail oriented you could grid the front of the car with tape... divide it into 2, 4, 6 or even more individual shots and then spend a lot of time piecing them back together... Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted November 28, 2006 Share Posted November 28, 2006 um, ok. if you want to go that far i guess. i think a good close up shot will do it as well. if the car is on a slope, i can rotate the picture so that the car is now "level". the big thing is a loarge enough distance from one point to another. ie, from ground to windshield base could give a larger error than ground to drip edge. if i am off by 1/4" by scaling the windshield that the total error would be colser to 1/2". if i am off by 1/4" at the drip edge i will only be off by 1/4". jimbo Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted November 28, 2006 Share Posted November 28, 2006 You guys do realize that the smooth air flow over the hood causes a low pressure area above the hood. Just like an airplane wing. This causes lift, regardless of what the fan/radiator/front air dam is or isn't doing. It is not so much a high pressure inside the engine compartment that lifts the hood (although with the large radiator opening I am sure there is some of that) as it is the flow over the top of the smooth hood. The same thing happens to the back end. Making the rear of the Z so smooth and sloping was actually a mistake on Nissan's part. This causes the rear end to lift (be sucked up) at speed. If you look at the early Z car aerodynamics link that I think Mike posted (an absolutely excellent article by the way), the author recommends putting some turbulence strips along the top of the car just in front of the rear hatch. Says they should disrupt the air flow preventing lift just like the turbulence strips on the top of Indy car racing helmets. I know Smokey Yunick use to put a lip at the back of the roof line in all of his race cars. Quote Link to comment Share on other sites More sharing options...
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