Jump to content
HybridZ

Aerodynamics tip (front air dam mod)


jeromio

Recommended Posts

I don't know about the rest of you, but before I put a front spoiler on my car, it would float at speeds over 80mph - terrifying. With the air dam, I can cruise comfortably at 80 and go as high as 110 before noticing any significant float.

 

This weekend, I tried an experiment. There is a gap between the body work (the bottom of the radiator support) and the back lip of the dam (the back edge). Obviously air can flow back underneath the car via this large gap. So I took some plain thin sheet metal, trimmed it and screwed it down along this gap to cover it up. Now there is a sort of shelf. Pictures would help I'm sure, but if you're having a hard time visualizing: pre-mod, hood open, if I dropped something a few inches in front of the radiator, it would go straight to the ground. Post mod, there is metal from the front top edge of the airdam all the way to the radiator, so dropping something in front of the radiator will result in a clanging noise as it bounces off this sheet metal.

 

Mine looks rather ugly currently - need to actually go back and actually make something permanent.

 

However, the difference is noticeable. The car feels much more stable at 80MPH. I had it up to 100 this AM and it still felt very stable. It makes sense intuitively, and though I have no actual measurable proof, it does feel much better.

Link to comment
Share on other sites

  • Replies 76
  • Created
  • Last Reply

Top Posters In This Topic

I did the same thing but for different reasons.

 

I very rarely drive my Z faster than 80. Truth is, I hang around the speed limit.

 

But with my airdam blended into the fenders I was concerned about the pressure on the fiberglass airdam at highway speeds cracking the joint open where it's bonded to the fender. I used thickish aluminum, maybe 18 gauge, and made the same type of "shelf" as a support.

 

If you have a urathane airdam maybe what you are feeling in improved stability above 100mph is that the airdam is now holding shape and not bending over from the pressure and letting the air spill under the car.

 

Just a guess, I know very little about the aerodynamics of the Z car. But it seems I remember a thread several years back about how much airdams can distort at high speeds/air pressures.

 

The way to tell for sure is to barrow Hanns' fender mount video camera and do some high speed before and after runs.

Link to comment
Share on other sites

Assuming my understanding of aerodynamics is correct, this will also increase the amount of airflow throught the radiator/IC (if installed). Air that would previously have spilled under the car is now forced through the heat exchangers mounted in the rad support opening.

Link to comment
Share on other sites

I think you're correct, Tri-Star. Air would build up in that region. Perhaps some clever ducting would better direct the air away from the large flat areas of the rad support (areas running perpendicular to the air stream) and into the radiator. I wish I was an aerodynamicist... then I would know best how to tackle this issue!

Link to comment
Share on other sites

I think you're correct, Tri-Star. Air would build up in that region. Perhaps some clever ducting would better direct the air away from the large flat areas of the rad support (areas running perpendicular to the air stream) and into the radiator. I wish I was an aerodynamicist... then I would know best how to tackle this issue!

 

the solution to this would be to cut the radiator cross member out, tilt the top of the radiator towards the front of the car at about a 45* angle, and have some ductwork going from the back of the radiator to a hole in the hood.

 

check out blueovalz's albums

 

this is done quite abit on race cars. Turns trapped air into downforce :)

Link to comment
Share on other sites

I think you might have accomplished two things, Jeromio: the first is keeping the airdam deflection down, and the second is improving the airflow. I think the first is the most probable. Nice idea. Post some pics if you're proud of your work :mrgreen:

 

BTW, we're getting close to bellypans with this topic :see thread "Bellypans for aerodynamics" from a few years ago.

 

Davy

Link to comment
Share on other sites

Well, I'm an aerodynamicist, or at least I play one at work....

 

Automotive aerodynamics is very much a black art; or rather, it's much more of an art than a science. Airplane aerodynamics is in many regards much simpler. Over the years there have been several pages on the web describing why the S30 Z’s have such a high drag coefficient and so much front-end lift. While the gist of these explanations is generally correct, the technical arguments are at times fallacious.

 

The complexity comes from the role of ground effect, rotating tires, radiator flow, sharp protuberances and flow separation from aft-sloped surfaces. These effects don’t scale well between tunnel models and real life, and are hard to reproduce in the lab. Computations are difficult and unreliable, too. I’ve done some testing in my water tunnel regarding the “smelly exhaust†problem, using a ~1:24 wooden model with a plexiglass ground plate. Dye injection gives sort-of the right picture, but that’s a very crude experiment. The problem gets much more complex in figuring what happens with air dams, radiator flows and underbody flows – so much so, that I’d trust the fingers-and-toes expertise of track testing much more than I would laboratory or computational predictions.

 

That said, it is intuitively true that sealing off the area behind the air dam and underneath the engine compartment will improve downforce and reduce drag (slightly). If these areas are sealed completely, and the air dam extends close enough to the ground, then essentially what happens is that the low-pressure flow behind the car (it must be low pressure, because of overall vehicle drag!) bleeds forward underneath the car, and “piles up†(silly term, but gets the point across) behind the air dam. Hence, downforce. The reduced-drag effect is much smaller, but that’s not our primary concern, anyway.

 

All of this will improve if you do something about rounding-out the sharp front lip of the S30 hood.

.

Link to comment
Share on other sites

good idea jeromio. i know what you mean about float. years ago i had my 260 up to 132 mph on the highway and the front wheels would touch down every 100 feet or so. not the kind of thing you want to be doing for long.

Link to comment
Share on other sites

see now that to mee looks like it would almost cause lift... forcing air that that has to go under the spoiler to go down more. Hard to explain, but in my head that looks like a reverse wedges shape, which would cause lift, like an airplane wing.

 

-Ed

 

YOu beat me with more pics, the second batch sounds more of like what i'm designing, fromt the lower front lip, back to the cross support, then from there back to the tranny tunnel.

Link to comment
Share on other sites

Ed.... I dont think you are grasping the purpose of the lower splitter....

 

It forces the air that piles up in front of the air dam to GO AROUND left or right... instead of under.... that is why the lower splitter sticks out several inches in front of the lower lip of the air dam...It provides the same effect as dropping the airdam lower to the ground... but you can still pull your car on the trailer without removing the front facia...

 

And... if you close off the entire engine compartment all the way back to the tranny tunnel... your engine will overheat... unless you provide a large exit through the hood or out the sides through the fenders.

 

And.. for our resident aero heads.... your wind tunnel results are just as good as your models.... the last thing you should trust is your "feelings"... the Force Is Not With You... but facts and good modeling are...

Link to comment
Share on other sites

 

this is a lower angle to show ducts...

airdamsplitter2.jpg

 

 

I had considered doing something like this once I installed James Thagards intercooler that I have. With the intercooler in place, as best as I can tell, running this same aluminum shelf back to the leading lower edge of the intercooler would direct the air into the intercooler and give some slight downforce because the bottom of the intercooler is about 1" higher then the top edge of the front spoiler. Whether this would be to much of an angle or whether that 1" is correct, I'm not sure. I'll have to check it out once I get the Z back together and eventual convert to E.F.I. and turbo. Looking at the few pics I have of the intercooler mocked up in other Z's it appears that the bottom of the intercooler is around the same location as the top of the bottom radiator support.

In the pic above, putting a break in the aluminum shelf to angle it up to the top of the bottom radiator support would be about the same effect, but less extreme as what I will have to do.

Anyone with this intercooler installed that can verify the position?

Link to comment
Share on other sites

There is a double bend in the shelf near the back... it rises up about a half an inch... this allows it to bolt to the lower radiator support...

 

also notice that there are dual air ducts per side... the larger openings in the actual air dam feed air to the back of the rotors.... the smaller duct inside the radiator openings are there from the factory... I ran a 2" hose from them to the point where the calipers are bolted to the strut ears... this blows air into the calipers themselves...

Link to comment
Share on other sites

For a street driven car, it is enough to obtain relatively neutral lift at sane speeds. On the street you aren't looking for added downforce traction for handling curves at high speeds. The speeds would need to be ridiculously high and the wings ridiculously large to get that kind of traction assistance. I think that a properly mounted front airdam (as most of you have done here) of the common variety neutralizes the front end enough for normal highway use. If you were to go to excessive speeds competitively, a g-nose and rear lip spoiler are probably your best bets for stability. As far as reducing drag AND increasing downforce: That is a huge challenge since downforce creates drag but drag does not necessarily create downforce.

 

I also found that 80mph was the magic number for a totally stock S30. After 80mph the steering got light. With the air-dam, 1" suspension drop, good springs and shocks, it goes stable to 120 as far as I can tell. I don't know where the next step change happens. I'm guessing at about 135-140.

Link to comment
Share on other sites

Yes, it is a Poly dam - and it certainly flexes at speed. I hadn't thought of this mod helping to stiffen the dam. In my case, it's just a temporary deal - very thin sheet and it's only attached to the dam, not the car. I suppose it could be helping to stabilize the dam - but certainly not by much. I think the permanent mod would look like what bjhines has done with a piece of Al.

 

BTW, my car is lowered and the flexibility of the poly dam has saved it (and me) several times when I inevitably and inadvertently get too close to a parking lot curb. And actually, when jacking the car I have to deform the dam to get the jack under the car (even though I paid extra for a low profile jack). So, a nice splitter is just not in my future.

Link to comment
Share on other sites

Actually the splitter could be made of a flexible plastic as well. It doesn't have to be a full belly plate either. It just need to be a strip along the bottom of the air-dam. My air-dam scrapes the road at the bottom of my steep driveway unless I pull out diagonally, ughh.

 

I drive my car up onto pieces of lumber so I can fit the jack under it.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...