260DET Posted February 18, 2009 Share Posted February 18, 2009 Being trying to find out if the stock vents actually do vent engine bay air or are just there to look pretty. Also if they do vent air, are they in the optimum position? This http://autospeed.com/cms/A_2162/article.html is the only useful article I've found but given that the 280ZX bonnet slopes down at the front its different to the car in the article. May try to rig up some manometer tubes with outlets just under the vents and go for a drive. Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 18, 2009 Share Posted February 18, 2009 Please!! I found that article, and i've done a lot of reading and everything i've read says that the optimum spot is about 1/3 of the way down the bonnet from the front. This would be JUST behind the radiator on a zed though, so i'm not too sure. If you look at cars like the new evo and similar, a LOT of them have vents about 1/3 of the way from the front... I think i'm going to go for a drive tomorrow with some string sticky tapped to the car and see what's what. I've got a 260, but they are faily similar to the s130. I also have another thread in the body and paint section of the forum Quote Link to comment Share on other sites More sharing options...
PhilbertZ Posted February 18, 2009 Share Posted February 18, 2009 I thought I read somewhere that they were for venting the motor (exhaust versus intake), to avoid heatsoak....similar to the S130 blower fan that cools down the injectors. I could be totally wrong but I remember reading that...here somewhere. All mine do is let rain in!! Quote Link to comment Share on other sites More sharing options...
280zx 2by2 Posted February 18, 2009 Share Posted February 18, 2009 I thought I read somewhere that they were for venting the motor (exhaust versus intake), to avoid heatsoak....similar to the S130 blower fan that cools down the injectors. I could be totally wrong but I remember reading that...here somewhere. All mine do is let rain in!! yeah thats why if you notice the right side vent is almost actually blocked off... but they couldnt just have one vent!!!! that would look... race inspired... race inspired cosmetic enhancement... RICE... oh no Quote Link to comment Share on other sites More sharing options...
260DET Posted February 18, 2009 Author Share Posted February 18, 2009 Please!! I found that article, and i've done a lot of reading and everything i've read says that the optimum spot is about 1/3 of the way down the bonnet from the front. This would be JUST behind the radiator on a zed though, so i'm not too sure. If you look at cars like the new evo and similar, a LOT of them have vents about 1/3 of the way from the front... I think i'm going to go for a drive tomorrow with some string sticky tapped to the car and see what's what. I've got a 260, but they are faily similar to the s130. I also have another thread in the body and paint section of the forum Can't drive my car right now but wool tufts around the vents seem to be a practical way of seeing whats happening there at speed. But the 280ZX bonnet slopes to the front more than the S30, and most other cars, which is why it could well be different. What prompted me to check this out was what happended at the sprints the other day at speed. My bonnet is latched at both rear corners. One of the latches was not done up properly, the unlatched corner actually lifted up an inch or so due to the force of engine bay air exiting. To do that it had to twist the fibreglass bonnet a bit as well as lift the weight. Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 19, 2009 Share Posted February 19, 2009 260DET, From what i have read around these forums about the Z bonnets is that the low pressure on the middle of the bonnet and the high pressure air under the bonnet is what causes it. Sort of like an aero plane wing with the pressure on both sides interacting to lift the wing without transport of medium between the bottom and top of the wing. Also from what I've read is that the high pressure at the windscreen acts to STOP air flowing out of the rear of the bonnet. The heater inlet ducts are placed at the base of the windscreen so air is pushed into them, reducing the power required by the pump to suck air in. I'm going to go for a drive today so I'll also put some tape just rearward of the bonnet and try leaving it popped (on the secondary stop) and see if there is any wind flow out of or into the engine bay by doing that. Quote Link to comment Share on other sites More sharing options...
Ferrariferg Posted February 19, 2009 Share Posted February 19, 2009 I would imagine that the air flowing over them creates low pressure that draws the hot air out of the engine compartment. The turbo hood scoop draws in air to cool the turbo and a small portion to cool the brake and clutch master cylinder area. I'm sure they are not in the optimal position but these cars were a balance of style and performance. Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 19, 2009 Share Posted February 19, 2009 I taped some wool to the bonnet and did a few runs with a camera man. The videos can be seen here: http://www.youtube.com/view_play_list?p=027CE8EBC30ABA73 Doesn't show a whole lot except that the air cowling inlet to the cabin is a high pressure, at about the same pressure as the engine bay (the wool flicks in and out, indicating no real flow). The fan was OFF, btw, but the vents were open, so this is actual air pressure, not induced pressure from the fan pulling air in. Also shows that the inspection lids flow air around the window, so they might also be a good spot to put venting to promote air flow past the air filters I think the next step for me is to get a crappy rusted bonnet for almost nothing, cut some holes where i think they should go (couple inches behind the radiator, vents either side of the power bulge) and see what sort of air flow you get through the vents. Otherwise if anyone has a manometer then doing some testing with that would be far more beneficial than anything i can do any time soon. Quote Link to comment Share on other sites More sharing options...
capt_furious Posted February 20, 2009 Share Posted February 20, 2009 There is actually a precedent for this sort of vent placement, as evidenced by these photos which Alan posted in the 'Early '70s Japanese race car aero' thread. I'm really tempted to put some vents like this in my hood, but that means cutting and bending sheet metal for which I don't have the resources to do properly, nor are there schematics readily available for the placement of the vents. Also to consider is that it's a big gaping hole straight into the engine bay with no protection from elements or vandals. I'm quite enamored of this particular car, but there's not much information available on it. Quote Link to comment Share on other sites More sharing options...
260DET Posted February 21, 2009 Author Share Posted February 21, 2009 Going through my collection of racing S130's I could find only one (Bob Sharp Racing) which obviously had relocated bonnet vents. Surprise surprise, a bit forward of the stock location. See also the raised lip at the leading edge which I suggest is there to deflect air over the vents and so improve air extraction. May do leading edge lips on mine. Click to enlarge Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 21, 2009 Share Posted February 21, 2009 capt_furious, that is EXACTLY where i was thinking of putting them!! Although I was going to push the metal down in to the bonnet (space permitting) so nothing sticks up. Should cause the same effect. Essentially i was thinking 4 or 5 indented vents on either side. Here is a drawing of sort of what I was thinking. The top vents look the best. Placement will be pretty much exactly where they are on the red car. I am going to get a crappy rusty bonnet tomorrow and start cutting away and see what sort of results i get. Please excuse the bad drawing Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 21, 2009 Share Posted February 21, 2009 Here is an interesting pic. Look at the wool tabs on the far vent. They clearly show air flow up and out of the vent. These tests were done at 120mph allegedly. Pic stolen from the wind tunnel test data thread in this forum Quote Link to comment Share on other sites More sharing options...
260DET Posted February 21, 2009 Author Share Posted February 21, 2009 Re vents 'sticking up' or having a lip at the leading edge, consider the possible implications. The surface of the bonnet being curved promotes lift. Submerged vents will interfere with airflow over the bonnet by introducing emerging air thereby reducing lift. Vents or lips that project into the airflow will reduce lift even more by being even more intrusive. All at some slight increase in drag. Quote Link to comment Share on other sites More sharing options...
MJLamberson Posted February 21, 2009 Share Posted February 21, 2009 Came across this pic and just had to share. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted February 22, 2009 Share Posted February 22, 2009 The vents in stock location are for low speed/ idle venting of heat from the engine compartment. The "turbo" vent pulls air in to cool the turbo location when the car is moving. For venting under hood pressures, I'd use the fender vent idea as to avoid the high pressure from the windshield. But the high pressure under the hood is mainly from the firewall. I would assume vents closer to it would work better. Quote Link to comment Share on other sites More sharing options...
Whittie Posted February 27, 2009 Share Posted February 27, 2009 Well I picked up a crappy bonnet today and some interesting findings.... The bonnet I got has 280z vents added in the stock location. First port of call then was to get the bonnet on and go for a drive with some wool on the bonnet.... At 80kph the wool tabs were sticking up just like on the pic I posted from the wind tunnel. This occurred the whole way along the vent. This concludes that the stock vents DO vent air at speed. The bonnet was also substantially cooler along the front-rear axis around the vent, whilst the centre of the bonnet, where the engine is closest but where there is not a vent, was SIGNIFICANTLY hotter. Hopefully on Sunday I’ll be able to cut a few more holes in the bonnet and see the airflow from them. I still am convinced that you need to have the vents closer to the radiator. I'm thinking some diamond shaped cutouts with a mesh grill. Then have some sort of facility for covering them from underneath. Only need them whilst racing and don't want water dropping on the distributor! Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted February 27, 2009 Share Posted February 27, 2009 Whittie, Sounds great. If you get a chance it'd be great to see the difference a gurney would make at the leading edge of the vent. Maybe this could be evaluated by the length of the piece of wool that a constant speed will make stand totally upright? Dave Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 27, 2009 Share Posted February 27, 2009 Look at the wool tabs on the far vent. They clearly show air flow up and out of the vent. These tests were done at 120mph allegedly. Pic stolen from the wind tunnel test data thread in this forum Tests were done at 80 mph and the info was mathematically extrapolated to 120 mph figures. You probably noticed, but that is not stock vent placement. If you look they're about in line with the front wheels. Quote Link to comment Share on other sites More sharing options...
260DET Posted February 28, 2009 Author Share Posted February 28, 2009 Ended up putting lips in front of both the stock vents, which incidentially have been modified to flow a lot more air. Going out to the track tomorrow to do some laps, may stick some wool tufts along the drivers side vent to see what happens on the drive out there. Quote Link to comment Share on other sites More sharing options...
tonycharger72 Posted February 28, 2009 Share Posted February 28, 2009 Instead of hacking up your bonnet why not just use a Magnehelic gauge? They aren't exactly expensive............. http://shop.ebay.com/?_from=R40&_trksid=m38.l1313&_nkw=Magnehelic+gauge+&_sacat=See-All-Categories Some good reading !!! http://www.autospeed.com/cms/A_2160/article.html & then bonnet vents!!! http://www.autospeed.com/cms/A_2162/article.html Little snippet from the article, "This is exactly what we did on the Maxima, using the same 80 km/h road speed for all testing. The results were astounding – not because they reflected the textbook example shown in the graphic above, but because the pressure variations were so great! As can be seen here, the front half of the bonnet surface was clearly a negative pressure zone, while the rear half was all in positive pressure. And the further forwards the measurements were taken, the lower the pressure; and the further backwards, the higher the pressures!" Quote Link to comment Share on other sites More sharing options...
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