260DET Posted October 9, 2001 Share Posted October 9, 2001 Can't see a recent discussion on this so here goes. My 77 is a road/track car with 220 RWHP and a standard radiator. It has a full front air dam and a rear whale tail spoiler, to which I fit a 1" Gurney lip for track work. The base of the front air dam is slightly higher than the front X member. Using around 1mm aluminium sheet, I have run a flat plate from the air dam thru to the X member and boxed in around the sway bar etc. On my reading, there should be some downforce generated at high speeds under the flat plate, which is reinforced so it won't deflect easily. Certainly the car handles well at high speed, no nose lift. And engine cooling is never a problem. What do you think? Has the above added much? At what speeds would any advantage come in? Quote Link to comment Share on other sites More sharing options...
DavyZ Posted October 9, 2001 Share Posted October 9, 2001 http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=13&t=000129 We had a whopper of a discussion on belly pans for increased aerodynamics, which it almost sounds like you are trying to do. The aerodynamics of the Z are very interesting and here is what we know: 1) the car is not very designed in terms of being vvery aerodynamic--even a VW Rabbit is better. 2) air flows under the car better than over the car (bad) 3) a belly pan or similar device may actually make the car lighter or flighty at speed (bad) Let us know how fast you have gone with your current mods--apparently, there are guys at the strip that are going almost 150 mph in the quarter with very little mods, which really scares me if the car gets squirrely. Davy Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 9, 2001 Share Posted October 9, 2001 I'm gonna be delving into this area as next spring approaches since I'm building an Open Road Racer. I've done some research as well and what Davy states is pretty much true. I've had several Zs up to the 150-165MPH mark and they get very scetchy at high speed, even with whale tails, spoilers and lowered and stiff suspension. There is software out that can aid in calculating the aerodynamic issues but your absolute best bet will be using a wind tunnel and some talented engineers. Be carefull what you add, as these cars CAN take flight. Just read in the latest Chevy HiPo about the quickest Corvette on the open Road Race circuit taking flight at the April running of the Silver state Challenge. Seems it crossed a small bridge and gained enough lift to cause the car to leave the pavement, spin, and roll into an embankment. All this happened in excess of 185mph (Althought the article claimed it happened at 200MPH). Driver and Navegator walked away safely. Mike Quote Link to comment Share on other sites More sharing options...
Tim240z Posted October 9, 2001 Share Posted October 9, 2001 From what I know, the only way to stablize the car at high speed is obviously to minimize the undercar turbulance. The belly of the Z is already pretty flat, so the only other things to do would be: 1. Make the spoiler/splitter on the front very low (unreasonable on a road car) to keep as much of the air flowing over the car instead of under it. 2. Duct the air flowing through the radiator up through the hood (ala GT40 style). Work well enough that my Dad uses this on his racing Camaro. 3. Rear diffuser. This creates a vacuum at the rear of the car, thus 'sucking' out the under car air cusion. This would also be unreasonable on a road car as you would have to run the fuel cell at floor level in the 'trunk' of the car to make room for the diffuser. Tim Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted October 9, 2001 Share Posted October 9, 2001 Some articles worth reading - not Z specific - are onthis page -> http://www.autospeed.com/S_technical/show_free/section.html Several things about aero in there including pics in tunnels etc. Might give some help to ya' all. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 9, 2001 Share Posted October 9, 2001 260DET, A couple questions: 1. Is your front belly pan solid from the air dam to the crossmember? If so, where is the air exiting the radiator going? On a stock Z Nissan designed the radiator air to exit down right behind the radiator. If you've blocked that off then you are pressurizing the engine compartment and creating a lot of drag. One option is to cut some openings in the front wheel wells (a low pressure area) and build some aluminum panels to duct the radiator air there. 2. You said the front lip of the air dam is higher than the lower front edge of the crossmember. By running a flat plate from the air dam to the crossmsmber haven't you created an undertray that's angled up at the front? That would create front lift. Any front undertray must be perfectly flat at racing speed. Hopefully 1 and 2 are not the case. [ October 09, 2001: Message edited by: johnc ] Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 9, 2001 Share Posted October 9, 2001 Last 4th, I took some of the smoke bombs and placed them at several locations around and under the car, and using a jet of fast air (open air hose from an 80 gallon 125 psi air tank) I was able to observe the effects of the vents over the front wheels. I'm sure this not a very accurate model of air flow over the whole body at one instant, but the air drawn out from under the car was quite obvious from the smoke trail. Quote Link to comment Share on other sites More sharing options...
260DET Posted October 10, 2001 Author Share Posted October 10, 2001 Didn't mention that the bonnet is vented near the rear for air exit purposes, plus cut some holes in the rear sides of the engine bay for the same reason. The guards (fenders) are also vented behind the wheel arches. Given that the engine stays cool without an engine driven fan I figure that the cooling aspect is OK. Belly Pan. Yes, John, the pan is slightly higher at the front. The reason for this is to increase air speed under there which will lower air pressure, on my understanding a venturi effect. The car is slightly raked ie the front is lower than the rear. About 190 kph (120 mph ?) so far on what track is available and she feels rock solid. Film shows that the nose stays down at that speed. Have looked at making a rear diffuser but, yes, the fuel tank restricts that option a bit. Thanks for the references, will look them up. Quote Link to comment Share on other sites More sharing options...
260DET Posted October 10, 2001 Author Share Posted October 10, 2001 OK, have looked at the previous discussion on aerodynamics. Someone made the point about disrupting airflow to spoil any lift effect. It now occurs to me that an alternative airflow for radiator exit air could be made near the front of the bonnet, or hood if you prefer. As you know, some cars do this, large rear facing scoops. Air exiting from the front of the bonnet may also disrupt airflow further back along the bonnet, so reducing lift generated over the stock curved surface? 200 mph in a Z !?! Best of luck, mate, I'll stick to going round and round on a circuit Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 10, 2001 Share Posted October 10, 2001 http://www.datsuns.com/Tech/tech_dept.htm This one talks more about cooling than downforce, but you hay find it helpful. The guy seems have the experience to know what he is talking about. Quote Link to comment Share on other sites More sharing options...
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