JMortensen Posted April 21, 2006 Share Posted April 21, 2006 I've never had a problem at 100+ either, but I do have an air dam and the car is lowered. A friend of mine took me probably past 120 in her Z which has no air dam and is higher than mine. I think Clifton's onto something. Certainly the air dam helps, and helps more when that big hole in the front is sealed up, but I don't think a Z is going to attempt lift off at over 100 mph. Worn out suspension at 100+ is definitely going to be a scary ride. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted April 21, 2006 Share Posted April 21, 2006 Actually everyone feels it a different way. I am very sensitive to instability in all my cars. Wether it's 80,90,100, or 150; lowering the car, tightening the suspension, and adding the front dam (open bottom), made a BIG difference in stability. BTW, I added the air-dam before all the suspension work and that alone made a noticeable difference in straight line stability at speed. Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 21, 2006 Share Posted April 21, 2006 It definitely makes a difference... but I don't want anyone to get the impression that it is necessary for any Z car to go fast and maintain control... I notice the biggest difference at highway speeds in strong gusts or crosswinds... the car does not get pushed around as easily... which for me is counterintuitive... I would think the the larger frontal area would get blown around more.... but I am not an aerodynamicist... There are some cool videos of really fast ... hatchback cars(like RX7s and Zs) lifting off and flying backwards at speeds over 170MPH.... They had air damns... but they did not look at the body as a whole... and they paid the price AS far as suspension and stability... I noticed a HUGE HUGE!!! improvement in stability when I finally went with solid bushings and TC ball/socket joints.... But it did not contribute as much to high speed stability... It made the biggest improvement in hard braking stability and turn in response... I did not find the urethane bushings to be much of an improvement over new stock rubber bushings... Quote Link to comment Share on other sites More sharing options...
j260z Posted April 22, 2006 Share Posted April 22, 2006 Were you drinking? I've been over 140 many times, 150 a few times with no spoiler. and no wandering or wheeling at all. I think alot of this wandering/floating is on Z's with bad alignments, shocks, and soft stock springs. have you ever driven a z with the stock steering damper? Quote Link to comment Share on other sites More sharing options...
Clifton Posted April 22, 2006 Share Posted April 22, 2006 Well Clifton - I guess you must have a 1:1,000,000 Z.Aerodynamic instability of the S30 at speeds over 100 is a well documented behavior. Mine has new ball joints, new tie-rod ends, urethane bushings, 4-wheel alignment, european spec springs, and gas struts. It runs at stock ride height - not lowered. I've encountered the problem in both of the S30's that I've owned and the thing that seems to have made the most improvement it was the aero kit. Well.... I'm not saying there aren't areo issues but the front end coming of the ground was just too much. I'm just stating the lack of issues I've had. Euro springs aren't that stiff and gas struts could be $19 Autozone specials that are Cadi soft. Sounds almost stock. I know I wouldn't take my Z31 over 100 as it floats around a little too much for me. Also how did you get a 4 wheel alignment. There is no toe adjustment on the rear, I see poly bushings but not eccentric or adj rear lca's. How much toe and caster are you running? Not trying to down your setup, just don't know. have you ever driven a z with the stock steering damper? Steering damper, huh? Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 22, 2006 Share Posted April 22, 2006 Great thread guys, I am also wondering what a steering damper is? I am also wondering bjhines, why do the side vertical things on the blue car's lip have a gap between the rest of the dam? Wouldn't this be letting air through and onto the wheel? I also don't really understand the function of this lip at all? Dave Quote Link to comment Share on other sites More sharing options...
spotfitz Posted April 22, 2006 Share Posted April 22, 2006 Great thread guys' date=' I am also wondering what a steering damper is?Dave[/quote'] I do believe the damper refered to is the coupler between the steering wheel assembly and the rack and pinion shaft. Some people have used hockey pucks to replace it. I noticed a tighter steering wheel once I switched the stock rubber coupler with poly, but also noticed alot more vibration from road irregularities. If I'm wrong in my assumption of the damper, just ignore this post... Quote Link to comment Share on other sites More sharing options...
olie05 Posted April 22, 2006 Share Posted April 22, 2006 steering damper... like the kind you see on motorcycles and on the front of the steering rack on jacked up trucks... didn't come stock on z's... j/k Quote Link to comment Share on other sites More sharing options...
j260z Posted April 24, 2006 Share Posted April 24, 2006 spotfitz got it right. it is called the steering coupler. when the origional coupler starts to wear out it can introduce alot more play into the steering wheel without actually turning the wheels. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted April 25, 2006 Share Posted April 25, 2006 The whole purpose of the front facia is not to force air to the sides of the car. If you think that air does not go under you car while driving your just not being realistic. It is necessary for air to go UNDER the car in order to get downforce ontop of the car. the whole idea is to get the air that goes under the car to move faster than the air going over the car, thus creating a low pressure zone or if you look at indy cars, even a suction. By lowering the car you are forcing the air that goes under the car to accelerate in a smaller space to get back out. Think of it like water, yes the air does go around the car, but air going around the car doesn't help to provide ground force or lift. Otherwise there would be wings and spoilers on the sides of cars. Most front facia/splitters are trying to "scoop" up more air to push it over the car. Now the silver "shround" you installed that goes from the middle of your spoiler down to the top of the radiator brace is simply directing the air, air above the middle of that splitter is going into the radiator/engine compartment. Air below is hitting the underside of that silver shroud, the radiator core support, the radiator, and whatever ever else gets in it's way, but unless the whole bottom of you car is covered, they are going to meet back up in the engine compartment. As for your comment about the engine overheating if i put paneling under the car that is nonsense. Look at ALL new cars. They have plastic paneling blocking off as much of the underside of the car as possible. Look at the fastest cars in the world, they all have under body paneling for multiple reasons. Even the pics you posted of the rear diffuser. By paneling the bottom of the car it forces the air coming into the front facia to go through the radiato and not down out the bottom (which would be the path of least resistance). Also.. Nissan put vents in the hood for a reason, but i dont think it was for airodynamic reasons. I believe it was more to alleviate the heat produced on the driver side of the engine. At anyrate, if the front airdamns sole purpose was to force air to the sides why wouldn't it just it be shaped like a big wedge? two planes going to the left and right. -Ed EDIT: Sorry for the long post but i wanted to get my point across. Quote Link to comment Share on other sites More sharing options...
Phantom Posted April 25, 2006 Share Posted April 25, 2006 The shape of a car is generally the shape of an airfoil - that is designed to give lift. THe distance from the front bumper to the rear bumper is further across the top of the car than under it. Air, therefore, must travel faster over the top of the car to meet up with its brother that went under the car. The higher velocity over the top creates a lower pressure area thus producing lift. Lowering the car does not affect this principle - the distances, and therefore the required velocities, remain the same. You lower a car foremost to improve handling. A secondary benefit is less air under the car and therefore less parasitic drag off all that crap hanging under the car - same reason for under car shrouds - smooth out the underside and reduce drag. The reasons for an air dam are to first and foremost create downforce based on its shape and, secondarily, reduce the amount of air going under the car - like lowering it - and thus reduce drag. The reason for ground effects that include side panels is to keep the air that the air dam has pushed around the car from re-entering under the car from the sides - again reducing parasitic drag but also contributing to a Bernoulli effect (vacuum) that actually reduces pressure under the car and helps offset the lower pressure above the car. Quote Link to comment Share on other sites More sharing options...
spotfitz Posted April 25, 2006 Share Posted April 25, 2006 The shape of a car is generally the shape of an airfoil - that is designed to give lift. THe distance from the front bumper to the rear bumper is further across the top of the car than under it. Air, therefore, must travel faster over the top of the car to meet up with its brother that went under the car. The higher velocity over the top creates a lower pressure area thus producing lift. Lowering the car does not affect this principle - the distances, and therefore the required velocities, remain the same. You lower a car foremost to improve handling. A secondary benefit is less air under the car and therefore less parasitic drive off all that crap hanging under the car - same reason for under car shrouds - smooth out the underside and reduce drag. The reasons for an air dam are to first and foremost create downforce based on its shape and, secondarily, reduce the amount of air going under the car - like lowering it - and thus reduce drag. The reason for ground effects that include side panels is to keep the air that the air dam has pushed around the car from re-entering under the car from the sides - again reducing parasitic drag but also contributing to a Bernoulli effect (vacuum) that actually reduces pressure under the car and helps offset the lower pressure above the car. And here I thought you were just another pretty face. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 25, 2006 Share Posted April 25, 2006 My understanding of it was that the side skirts were mainly to keep air from going under the sides of the car while turning, but I'm sure there is some benefit to keeping the air that comes off the air dam from re-entering the underside of the car, and when turning that's probably a lot of the same air... Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 25, 2006 Share Posted April 25, 2006 lol..... Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted April 25, 2006 Share Posted April 25, 2006 yeah i realize lowering the car does not change the principles of the air speed going over and under, but to keep some of the air from going under. I was simply trying to prove my point that the front airdamn was not designed mainly to split the air to the sides of the car, but like you said for down force. As you mentioned the shape of the car, and how the air moves around it I compare it to an airplane wing. The wing is one of the most airdynamic pieces made. So you look at that and understand how that works. And try to do the opposite or Reverse I guess to a car, that's my thinking. The car moves faster over the top than the bottom as you mentioned thus creating a low pressure creating lift. Cars would want the opposite of that if you wanted to go to the extreme, although i'm pretty sure it's next to impossible for street as the shape of the car itself fights the principle. Thus my thinking to make the air under the car move faster than the air over the car. Well i'm going to go install my underpaneling that is going to "over heat" my engine now... -Ed Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 25, 2006 Share Posted April 25, 2006 the low mounted splitter that sticks out a few inches in front of the airdam is there to further reduce air going under the car(without sacrificing anymore ground clearance).. the primary purpose of an airdam is to reduce air going under the car... If your next question is "how does that thin sheet metal (edge on) into the wind help reduce air under the car..?????"""".... Then I suggest you read one of the many books available on automotive aerodynamics... You guys are missing soo many points in this that it is getting herd to respond in short posts... The wings on the sides are there to reduce vortex induced drag... again.. if you have to ask.. it is beyond the scope of this forum... The rear diffuser has 2 critical components... it expands exponentially in the vertical plane... and it expands linearly in the horizontal plane... the vertical strakes must reach low to the ground from front to rear to trap air in their expanding troughs... Side skirts block air rushing under the car from the sides..... It does not have anything to do with turning the car.. or air entering while turning... The low pressure under the car that was caused by the airdam will draw air rapidly under the car from the sides. The more effective your front airdam is.. the more effective/necessary side skirts will become... If you block airflow from the radiator and engine compartment with a sealed underbelly pan.. your car will overheat...granted.. it is unlikely that you could block all airflow from the engine compartment... but I was making a suggestion.... All of these answers are a $20 book.. or a trip to a university library away... You guys will notice a few more neat tricks once you understand what is actually going on under your car... Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted April 25, 2006 Share Posted April 25, 2006 yeah but your looking at this very narrow mindedly. Your assuming your going straight with no other air. In real world driving you turn, wind blows, you have tail wind, head wind, etc. All of these factor in. My point is taking this to an extreme, some of the things your trying to accomplish with eliminating vortexes around the wheel well are kinda pointless in my opinion... what happens when you turn? that big *** tire sticks out into oncoming air... see what i'm getting at? I'm not bashing you or flaming you, i'm saying you should just add underbelly panels to help reduce drag since your going through all this effort. I still don't see how blocking off the bottom of the car will overheat my engine, the radiator is mounted infront and uses oncoming air to make it effective, i'm not using the air from under the car to cool my engine coolant. All i was originally staing in my first post was that the silver piece you mounted from the middle of the airdamn to the top of the radiator core support is not helping in down force, all it is doing is directing air to the radiator. I know what a splitter does and have no problem with it. -Ed Quote Link to comment Share on other sites More sharing options...
deMideon Posted April 25, 2006 Share Posted April 25, 2006 I think I am very sensitive to the lift as well... I have the MSA fiberglass air dam on mine it had about 6 inches between it and the ground... I have a plate between the radiator and the air dam as well and I still was getting noticable lift over 100. So I just added an additional 3 inches to the air dam and what a difference that made! BTW I had a urethane dam on my old 240... I ended up having to put a piece of steel behind it and then build braces for it... you can see at least the bolt sfor it under the link in my sig and under the old Z car folder! Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted April 25, 2006 Share Posted April 25, 2006 I just wanted to say I hope nismo280zed and bjhines can continue this discussion without spoiling it by getting personal/offended. I for one am learning a lot. Keep it up. BTW, when a tyre sticks out, the inside tyre is likely to create more drag due to the more flat surface correct? And if you create a drag force on this side more so than the other it will produce a moment on the car and assist turning yes? I guess, this stuff is already complicated enough without trying to expand into non-straight line stuff for me. Dave Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 25, 2006 Share Posted April 25, 2006 Side skirts block air rushing under the car from the sides..... It does not have anything to do with turning the car.. or air entering while turning... The low pressure under the car that was caused by the airdam will draw air rapidly under the car from the sides.The more effective your front airdam is.. the more effective/necessary side skirts will become... I think you've been reading too much about the Chapparal sucker car. You're not creating a whole bunch of low pressure under a Z, nor are you likely to create a whole bunch of downforce unless you're going really crazy with the aero mods. The idea is mostly to prevent lift. If you can get a bit of downforce more power to you, but we're not dealing with 1500 lb springs because we're making 1000 lbs of downforce like a real aero car. What you're trying to do with the air dam and side skirts is block the air from going under the car. Yes, this will produce a little bit of a low pressure area, but without venting the radiator air to the hood exclusively I think the low pressure is pretty much gone by the time you get to the firewall because most of the air going through the radiator ends up under the car. What does happen is as you drive the car around a corner at 120 mph the air hits the car at an angle and can get under the rear of the car. You might also have a good side wind. Skirts keep this air out and help cancel that lift. That's my understanding after reading some books, thanks for that suggestion though. Quote Link to comment Share on other sites More sharing options...
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