pparaska Posted July 18, 2000 Share Posted July 18, 2000 Last week I mentioned that an old Z racer I know had seen aero data for the 240Z that showed a low pressure area above the hood in the first several feet from the leading edge. I'm looking for any detailed info on that phenomenon for the 240Z that anyone might have - especially what the pressure profile along the hood is, and how it might vary across the width of the hood. I plan on using that phenomenon to aid in underhood temp reduction and radiator scavenging. Supposedly, the GT40 used this idea, and Terry Oxandale used a similar method on his Ford V8 Z race car. Instead of a huge hole/duct in the hood, I'd like to employ NACA outlet duct shapes cut into the hood and epoxied ducts on the underside of the hood, a la 1969 GT500 Shelby. Our grandparents and/or parents tax dollars paid for that research many years ago to come up with those inlet and outlet duct designs, so I figure why not use it? I'll pull my Fluid Dynamics book out of the packed up boxes and see if I can figure a size and number of ducts needed to make this idea work. With a high pressure area in front of the radiator, some good ducting from the grill opening to the radiator, and the low pressure area above the hood in the area behind the radiator, I hope that more than two ducts will not be needed. BTW, this old racer kind of poo-poohed the idea of muffin fans in the wheel wells, as alot of racers have shown that the wheel well is a high pressure area and the fan would have to fight that at speed. Same thing for vents toward the trailing edge of the hood since that is getting into a high pressure area. No doubt it would help in traffic, as the heat would rise through the vents at ambient static pressure. BTW, I saw some pics from the latest National Z convention somewhere lately on the web, and I saw a Z with louvers in the front area of the hood. Another shot had two tubes connected to the firewall leading to the cowl area. This was on a red Chevy V8 car. One tube and hose lead to the air cleaner, but the other went toward the carb? Not sure what's up there. Anyway, I also plan on tapping into the cowl area for high pressure intake air, although the ram air box with hose(s) to the radiator support looks promising. Any ideas or prior work appreciated! ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@tidalwave.net">pparaska@tidalwave.net - Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted July 18, 2000 Share Posted July 18, 2000 You can actualy do some of this documentation yourself if you wanted to. Tape small strips of plastic or paper to the hood such that they can flap a little - like small streamers. Drive the car at various speeds and observe the streamers. You might be surprised to find that at certain speeds they reside in a clam area whereas at others they may flap madly. The trick will be to find out if this low pressure area is far enough back to be behind the radiator and to figure out just how much air you'd need to vent there. Louvers would work but I don't like the look. Motorsport sells a louvered hood if you're so inclined. I think the muffin fans would be pretty useless. A cowl hood would work though, I've seen that occur on my Mustang. At low speeds heat streams out of it, at higher speeds the air may actually reverse and go into the cowl - I'm not sure. The thread on the fiberglass hoods mentioned some of this. I'm getting pretty darned tempted to order one of those BTW. Anyone in Northern VA interested in doing a group thing to save on shipping? I've got a business address they can be sent to to save still more! Lemme' know. For carb intake I'll likely use Mike's idea of taking ram air from the radiator core. Cutting into the cowl is a little scary Some Mustang racers DO this tho' and it works well - especially for supercharged motors that have the intake facing the driver's compartment. You might also consider drawing air from the wheelwells as many Mustangs do. All in all I think the radiator support is easiest and requires less cutting up of the car short of going under the spoiler for air and risking water ingestion... Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 18, 2000 Share Posted July 18, 2000 A similar idea that I've seen in "How to make your car handle" by Fred Puhn. Instead of just tape, tape individual pieces of wool or string onto the areas you want to test. It would help to have a video camera setup to record the questioned area. Maybe in your case pete, you can borrow another Z for a day, or get the owner to help you out? I'm all for the idea. Aerodynamically the Z isn't too hot, and I'd love to see some more people improve on it. (I wonder what jim biondo's Cd is with the new front end?) Please post your findings as you look into this further. ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted July 18, 2000 Share Posted July 18, 2000 I'm guess you must have seen this, but is the "twin turbo hood" under this link http://www.arizonazcar.com./hoods.html close to what you're thinking about? If I understood your discussion I think it's in the ballpark, but the ducts are not the right way around (?) Wonder if these guys would make you one to your spec? Sorry if it's a bum steer. Quote Link to comment Share on other sites More sharing options...
pparaska Posted July 19, 2000 Author Share Posted July 19, 2000 Thanks for all the input guys! Yeah, I'd need to borrow a car to do some testing! And I looked at that AZ Zcar hood - those NACA ducts are pointed the wrong way, and the geometry looks suspect also. Since I'd need $1000 worth of parts to get anything shipped, I guess I'll stay away. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 19, 2000 Share Posted July 19, 2000 Something for you to ponder Pete. I've noticed on occasion the use of a NACA duct in the front passanger side fender. (ahead of the front wheel) Its probably specific to the particular cars aerodynamics, I'm just wondering if you think it'd benefit an early Z at all. Have you seen the louvered access panels over the battery & clutch master cylinder? (I believe Scotties GNZ has them) Do you feel they are beneficial from a cooling standpoint? ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
pparaska Posted July 19, 2000 Author Share Posted July 19, 2000 Drax, - NACA ducts in front of wheel. I have no idea if that would work. - Louvered inspection lids next to hood. Yeah, I bet they leave the hot air out at a stand still. I wonder if there is positive or negative pressure there at the side of the windshield when the car is on the freeway? Motorsport used to sell those, I wonder if they still do. You could get that done at a rod type body shop also. Hmm. But I kind of agree with Jim - I don't like the louver look on a Z. I think the NACA ones look more fitting to the visually (not actually) slippery lines of the Z - just my opinion. Thank for the input! Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted July 19, 2000 Share Posted July 19, 2000 Pete, I do not know exactly how effective the louvers are but I can tell you that when the engine is hot enough to kick the fan on, you can feel heat being forced out. I imagine air flowing over the louvers must have a positive effect. I am considering buying an MR2 for my son and as I was closely inspecting the car I noticed an electric fan about 6-8" in diameter that pulled hot air from the engine compartment. That triggered my memory on an article from the GA Z club on a member who placed 2 4" fans on the lower rear of the inner fenderwells and proved to be effective. After all, we know that the overheating problems most V-8 Z face are inadequate airflow and heat being trapped underhood. i am sure thye NACA ducts, appropiately placed, will look and be effective, but I just thought I would throw that alternative out. Scottie Quote Link to comment Share on other sites More sharing options...
pparaska Posted July 20, 2000 Author Share Posted July 20, 2000 Thanks Scottie, Yeah, in my original post on this thread, when I said "muffin fans in the wheel wells", I was referring top Henry Costanzo's 4" fans in the inner fenders. If you look on this site's (or my) links page you can see the article on the GA Z Clubs site documenting this modification. I remember seeing Henry's car at the 95 Convention in Atlanta, where he gave a V8 Z conversion tech session and used his car as a centerpiece for discussion. That's one nice show Z by the way. Anyway, he said it worked to cool the engine, but I was just relaying some info the Z racer had told me. He said that Lotus had tried that method and went away from it. I'll bet it helps in slow traffic though! I hate being snobbish about technology, but the NACA ducts "look" hi tech to me (even though they are 40-50 years old), and I like that they are efficient for their size as I don't want a lot of holes in the hood. I'd really like it to look understated - just my style. I believe the NACA ducts work best with laminar flow over them, so I'm not sure if they will work, as I don't know what the flow regime over the hood in that area is. Still hoping to get info. I still may go with fans that exit to the inner fenders. The more I think about it, the further up on my list the cold air induction gets. Thanks for the info! Any details of where the fan on the Mr. 2 exited to? Those are neat go karts! ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@tidalwave.net">pparaska@tidalwave.net - Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 20, 2000 Share Posted July 20, 2000 Pete, I'm with you. The more I think about it (cold air induction, and cooling engine bay) the more it moves up on my list. My turbo engine will be hotter than most NA engines I am sure. All the more reason to look into this... I'm not really sure I can help you much in aquiring the tech data though. Wish I could. (My Z is barely on the road) ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
Michael Posted August 6, 2000 Share Posted August 6, 2000 The technique of taping tufts or strings to the surface of a body to get a sense of the flow around it, is a tried and true method. It tells if the flow is smoothly following the surface, or if it’s “separatedâ€, which generally (but not always) means low pressure. It also can give clues about flow reversal, such as in a large separation eddy or local backflow. Unfortunately, tuft flow visualization says nothing about how much air is flowing, how fast it’s flowing, etc. What makes engineering an effective cooling flow scheme difficult is that to do it right, other aspects of the flowfield about the front end of the car have to be considered, and that means taking into account front end lift (or downforce), contribution to the vehicle’s total drag, supply of dense, cool air to the carburetor, etc. For example, how to integrate the radiator ducting with the front air dam. On some late model cars, the radiator actually draws from behind the air dam. This reduces cooling flow (tapping the air in a low pressure zone) and reduces effectiveness of the air dam. As Pete pointed out, Terry Oxandale’s setup is an excellent compromise of the above factors. But, besides requiring major sheet metal surgery, it may not be practical with even the JTR engine setup (engine needs to be VERY far back), plus it will have problems in the rain. As for the 70-78 Z’s aerodynamics, well, they are not very good, to say the least. Taking a survey of information reported in several coffee table books on the Z, I get an average Cd of 0.45. So, the Z is no better (and occasionally worse) that sedans of the same vintage. Why – especially because it looks so “swoopyâ€? Well, I tested a model of a Z in a water tunnel. I did not have a wind tunnel, just a water tunnel. I made a 6†long model out of wood, bolted it to a “ground plate†and put the assembly on a supporting arm, inside a 18â€x24â€x72†test section of a low speed, low turbulence water tunnel (max flow rate: about 1 ft/s). With such a small model and such a low flow speed, scaling effects will invalidate any attempt at gathering quantitative data. But, injecting a carefully controlled stream of dye (food coloring) at various point in the vicinity of the model, I found three curious things: 1) that sharp hood front lip is a killer. A large swirling eddy (when scaled to full size about 1 ft long) sit on top of the hood lip. The front stagnation point is just below that region, and the accelerating flow can not go around the lip without separating. 2) Flow over the roof separates at the vicinity of hatch (deck lid) front lip. The Datsun engineers made a very poor choice of hatch slope. It’s not low enough for the flow to remain attached, and not steep enough to keep the separation controlled. The VW Rabbit, for example, has a steep hatch angle, and that design actually has a lower drag! 3) Flow from underneath the car will swirl up towards the rear of the deck lid. This accounts for the infamous Z exhaust smell inside the cabin, and also has a role in why the drag is so high. Unfortunately I do not have information on longitudinal and especially the transverse pressure profile over the hood. Why is the Z so screwed up? Part of the blame rests with Albrecht Goertz. It’s his “reverse swept†grill shape that motivates the sharp hood forward lip. But Nissan conducted wind tunnel tests on the Z (including tuft grid visualization!!). One photo that I found on the subject shows the Z in a wind tunnel test section, sitting on foot-high blocks underneath the wheels. These blocks evidently housed force balances. Possibly they did not want to set the car on the tunnel bottom, to avoid tunnel boundary layer effects. But what they did is an awful way to test cars! Not only does it miss ground effects, but their testing condition severely alters the flow about the front grill. They could easily have concluded that the sharp hood is “streamlinedâ€. So, what to do about this? As a first cut, modify the hood front lip and grill. But, as for cooling, my reaction is to first run the car and then see if it actually overheats. Chances are, it will be fine as is. Shakedown tests of my big block ’78 Z show no overheating, and that’s with a 28â€x19†Griffin radiator (I cut out the stock radiator supporting structure to accommodate a larger radiator and leave room for later mods) and Flex-a-Lite “Black Magic†electric fan. About NACA ducts…. I’ve been following the discussion on Carl Beck’s Z-car mailing list. Generally, NACA ducts are designed to draw ambient air inside a cavity, but some designs do the reverse (expel air). However, this works best when large pressure gradients are involved – for example, expelling the exhaust of an aircraft piston engine. I doubt that the pressure difference between the flow over the Z’s hood and inside the engine compartment is sufficient to make the NACA duct worthwhile. But if you can fabricate a duct system that fits over the housing of your radiator fan, and completely routes that air outside of the engine compartment, that should work much better. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 6, 2000 Share Posted August 6, 2000 Michael, interesting stuff. Knew the Z was not the best but did not realize it was as bad as you state. The issue of the front lip is probably what inspired the design of the G-nose. Wonder if it really showed any improvements? Pity it looks so.... Thats just my opinion, so apologies to anyone using a G-nose. ------------------ Scottie 71 240GN-Z http://www.mindspring.com/~vscott911/gnz.html Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 6, 2000 Share Posted August 6, 2000 Now you've all got me wondering. The Stock driver's side louvers on the Z hood I'm going to use ( can't remember what year hood I bought 280?) are directly over my air filter for the procharger. Its been sucking air right over the exhaust, so I thought I'd do some heat taping and maybe build an air box to take advantage of the cooler air from the vent. Is this a high or low pressure area? Also, if anyone sucessfully pilots thier Z into the 170s and beyond. I'd like to know what other aero tricks can be done to help glue these over powered land rockets to earth. I feel many cars here will be airborne long before the hp runs out! JS [This message has been edited by John Scott (edited August 06, 2000).] Quote Link to comment Share on other sites More sharing options...
Drax240z Posted August 6, 2000 Share Posted August 6, 2000 Very interesting stuff! John, for high speed runs and stability, probably the best mods to make to the Z are belly pans, rear diffuser, and side skirts. I'd also think that the G-nose (and headlight covers?) would help quite a bit. After reading all this, I go back to wondering about Jim Biondo's front end on his car... It certainly looks to be a much more aerodynamic shape, but as we've seen with the Z, looks can be decieving. But Jim's setup eliminated the sharp hood lip, as well as the reverse swept grill. ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
John Scott Posted August 6, 2000 Share Posted August 6, 2000 Head light covers. I love the look of them. My wife bought me a set a few years back...the ones with the no-drill nounting kit. AHHH!!! never could get them to fit the contour or the body and couldn't force myself to drill into one of my favorite areas of the Z's body. Ended up badly scratched and in the trash! Found the comment in Automobile magazine on the BMW Z8's aeros entertaining. "We didn't go into the wind tunnel. With 400 horsepower, we didn't think we needed to."... I guess with a weenie 155mph speed limiter. I've heard it more than once, when you get much above 150, aerodynamics can get pretty interesting. Anyone have ideas about the neg/pos airflow around the Z's hood louvers? JS [This message has been edited by John Scott (edited August 06, 2000).] Quote Link to comment Share on other sites More sharing options...
Drax240z Posted August 6, 2000 Share Posted August 6, 2000 You know, the more I heard about the Z8 the less I like about it. I'm a bit of a BMW fan, I love the e30 3 series especially, and the M coupe... but the Z8 seems all wrong. A 3500lbs, all aluminum car? Did they add in ballast? No wind tunnel data? Yeesh... Making a high end sports car without running it through a wind tunnel seems like suicide to me, but I guess their 155mph rev limiter covers up any mistakes that might be made. Can you picture ferrari/lambo/porsche not caring about their cars aerodynamic characteristics about 150mph? I can't. Still no idea about the Z hood. Sorry. But I'd say the headlight covers would be a pretty small improvement just themselves. (as far as aerodynamics goes, they look great) ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted August 6, 2000 Share Posted August 6, 2000 Intuition would seem to say that the headlights "sugar scoop" look would make for some pretty bad airflow. these days I can't imagine a manufacturer building a car that might block air like that! However it's pretty obvious that when it comes to aerodynamics intuition doesn't count for much. I can tell you my Miata gets a bit scary at say 95mph - top up or down. I'll have to check it out with the hardtop on come Fall I guess. John (smack! I meant Micahel - sorry about that!) I found the water tunnel data fascinating! Do you still have access to it? I'd be interested in hearing about any further testing. Would say a scale model form the hobby shop be worth testing? Would love to hear what a G-nose does for the airflow. I actually don't find them ugly but finding one at all nowadays would be pretty tricky I wonder if any of the kit and spoiler manufacturers bother to tunnel test. I thought Kamei did but some of their stuff was pretty butt ugly too [This message has been edited by BLKMGK (edited August 06, 2000).] Quote Link to comment Share on other sites More sharing options...
Michael Posted August 6, 2000 Share Posted August 6, 2000 My guess is that the BMW Z8 guy’s comments about no aero testing were just bravado. At the very least, they must have done some kind of wind-induced NVH testing, to make sure that the playboy in the driver’s seat isn’t subjected to too much wind buffeting, and that his escort’s hair doesn’t get messed up. As for the headlight covers – all of the ones that I’ve seen follow the contour of the hood’s sharp front lip. Cosmetically, that makes sense, but I’m not impressed by the design. Jim Biondo’s fiberglass “front clip†looks like a very sensible route (does he have any data on his design?), albeit the Ford Taurus-looking front “face†is not very appealing, at least to me. Forward of the radiator supports, there isn’t much structural metal in the Z – even in the 280’s. My impression is that the stock hood can be cut with a sawz-all just forward of where it bolts to the hinge mounts, and the resulting “hole†can be filled with fiberglass. For a template, a piece of pvc drainage pipe (say, 6†or 8†diameter) might work! By that I mean, wrap fiberglass cloth around the pipe, held laterally across where the hood lip used to be. The resulting “hump†will probably have to be reinforced somehow, but it’s a start. Then, the headlight sugarscoops would be cut to match, the remainder of the scoops filled in, and the headlights moved down and inboard. My guess (unscientific, of course!) is that this will get the total Cd down below 0.4. By the way, apparently Nissan claimed a Cd of 0.385 for the 280 ZX! That's a huge drop from the Z, considering that the two cars are of similar shape. I have pictures of the water tunnel tests, but until I figure out how to scan in slides, I won’t have anything to post. Ditto for the rest of my project. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted August 6, 2000 Share Posted August 6, 2000 I'll bet that nearly the entire improvement in Cd from the Z to the ZX is from the front end. The ZX did away with the sharp front hood lip and more or less intregated the bumper too... a lot more similar to the early G-Noses than the regular 70-78 Z's. I suppose for the ultimate ride, a G-nose conversion is really something that should be taken seriously... I just wish it looked better. ------------------ Drax240z 1973 240z - L28TURBO transplant on the way! http://members.xoom.com/r_lewis/datsun.html Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 6, 2000 Share Posted August 6, 2000 Excellent info, people.... Over on zdriver.com, under "Photoalbum", there's the "June car of the month". It's a Z with a "color-coded" G nose (incredible attention to detail elsewhere too!). For mine, this looks good (I also don't like the look of the "standard" G nose). Looks like I might also have to add this to the shopping list. I hadn't realised the Zs were that bad. To look at, you don't intuitively see it.... [This message has been edited by zedskid (edited August 06, 2000).] Quote Link to comment Share on other sites More sharing options...
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