Z aerodynamics

[ZwolleY]

I drive in the Columbia River Gorge where the east wind is really raging now. If it is not the east wind, it is a strong west wind. The car really gets pushed around by the wind. I read somewhere that the Z does not handle well with a cross wind and I can confirm that. Is it design or just the light weight of the car? '72 Z

[D-Webster]

I have driven through the gorge many times (my mother lived in Portland) in a variety of cars. Around The Dalls (sp) I haven't found anything that works very well ... but then I've never driven a M1 Abrams througth there either. I don't think the Z is at fault. I drove both models of the old 914 through there, both the four and the six, 68 Corvette, and even a Cobra and none of them relished the drive through there.

[260DET]

The usual stability enhancing mods should help, front spoiler, lowered with a bit of rake, rear spoiler, tight steering and suspension, right tyres, maybe more caster - mine is 5 degrees plus.

That run sounds like a good test.

[26th-Z]

The S30 was designed in the late sixties when air flow around a car was not given thorough consideration. Contemporary styling at the time did not take into account air flow modeling the way it affects design today. Air tunnel testing was performed on the S30 chassis, but remember that air tunnel technology was not what it is today. Coupled with the light weight of the car, it is no surprise that top speed is limited by air flow stability.

I remember driving through the Ocala National Forest one morning on my way down to Daytona. It was cool and calm. I noticed a great deal of front end drift at an indicated 120 mph - enough to awaken my better judgement and convince me to back off a bit.

We also complain about exhaust gasses coming back into the car because of the pressure differentials off the tail of the car. Another air flow fault.

The S30 sure is beautiful with classic flowing lines, but for all it's grace and beauty, it flies like a turkey and smells like turkey farts!

Later versions of the S30 included modifications to suppress some of the early faults. A small spoiler was added to the front valance and then the valance was lowered. Interior venting changed almost immediately. Later version weigh more as well.

[260DET]

While the first gen cars are old tech as far as aerodynamics go, in my experience they respond very well to the mods mentioned previously eg the nose lift problem is quite easily fixed.

Having driven my '77 at over 200 kph I can report that it is rock solid at high speed, has excellent directional stability, yet still turns nicely as required. But the proper work has to be done to get them that way.

[TomoHawk]

Originally posted by 260DET
... the proper work has to be done to get them that way.

I hate it when hes puts that little kicker in there..

OK, so what is the first thing you could do? Air dam? How far down would it have to be?

FYI: Enzo GTOs had 2 air dams- one under the nose and one in front of the rear axle.

[RB30-ZED]

I Also drive through an area which has bad gusty cross winds, and very early on I found that once I modified the inner lower control arm points to reduce "Bump steer", the problem of swerving in my lane durring cross winds went away.
If you think about it, ever with a small amount of bump steer this problem is worse in a cross wind situation as you have one side of the suspension compressing and the other side dropping.
I know this is slight but you have both wheel toeing in two different directions which will cause it to steer. If it steers in to the wind , its not to bad, but if it steers with the wind it will be all over the lane as mine did.
I raised my pick up points 30mm and I have very little trouble with cross winds now.
What do you guys think?
Steven

[TomoHawk]

wow, 30mm (~1 3/16 inches)?

That's more than the usual 3/4 to 7/8 inch (19-22 mm)


But if it's what you need, then that's exactly the right amount.

[RB30-ZED]

Yes its quite a bit.
I removed the springs set it at ride height on a jack and graphed the toe change up 50 mm and down 50mm till i found the least change. I used a slotted crossmember and once i had found the best spot, i redrilled a second cross member and rechecked.
Steven

[260DET]

Interesting point Steven, you may have something there. I've got rid of the bump steer on mine too, essential for nice handling.

TomoHawk, you start with the suspension and steering in first class condition. In view of Steven's point this includes no bump steer. Then lower the car all round but with a bit of rake. Fit a modern scraper type front spoiler, not a spook or similar, I've seen a US one that I would love to have. Rear spoiler as well.

That will make a hell of a difference. Other things to do include a fully adjustable front suspension particularly for more caster, bonnet air exit vents and a front undertray.

[TomoHawk]

Undertray....

I think I could build in a narrow air dam into that. Like an upside-down lip spoiler.

Those are about 2 feet wide ( about same width as radiator)?

You could use it to scoop air for the brakes too.

[zorro]

Its interesting to hear u say that i wondered why myself a car so low would blow around with a side wind the only thing i noticed was lowering it and putting a front air dam on helped mine to be more stable as has already been mentioned.....

[Mr Camouflage]

Originally posted by 26th-Z

I remember driving through the Ocala National Forest one morning on my way down to Daytona. It was cool and calm. I noticed a great deal of front end drift at an indicated 120 mph - enough to awaken my better judgement and convince me to back off a bit.

The problem with the front of the S30 is that you have all this air coming under the front of the car, and once the air that comes in through the radiator it has no where to go except out under the car.

A lower spoiler/air dam will stop airflow under the car preventing the lift. Bonnet vents will to, some extent, give the air somewhere to exit to, out over the top of the car, which is better aerodynamics than having it exit under the car.

We also complain about exhaust gasses coming back into the car because of the pressure differentials off the tail of the car. Another air flow fault.

All cars will have a low pressure zone at the back of the car (unless you drive a big tear drop shaped car). Even F1 racing cars. Nissan were silly to put air vents on the back of the car. Also the cabin of the S30 is closer to the rear of the car than most other cars.

And with 30 year old cars, seals perish or compress over time. If tyou cars ever been in a accident, iven a midle rear ender, then chances are the seams have opend a little.

Later versions of the S30 included modifications to suppress some of the early faults. A small spoiler was added to the front valance and then the valance was lowered. Interior venting changed almost immediately. Later version weigh more as well.

English 240z had a front spoiler, but probably just a styling exercise rather than a handling fix, otherwise all markets would have recieved them, right?

With Later S30's , I believe the spoiler was added to hide the lowerd crossmember, because the 260z and 280z had a bigger (taller) radiators (presumably because of cooling problems), the front cross member was also lowerd to accomodate.

As for weight, Have you seen the size of a 1970's Air cond Compressor!?

[TomoHawk]

Originally posted by Mr Camouflage
As for weight, Have you seen the size of a 1970's Air cond Compressor!?

I have. In my 280Z. I took out all the a/c stuff except the evaporator, and the compressor alone must have weighted 50+ pounds. I think my front came up an inch after I took it out!

[Marty Rogan]

260DET wrote:

"TomoHawk, you start with the suspension and steering in first class condition. In view of Steven's point this includes no bump steer. Then lower the car all round but with a bit of rake. Fit a modern scraper type front spoiler, not a spook or similar, I've seen a US one that I would love to have. Rear spoiler as well. "

I am wondering why you do not recommend a Spook spoiler? I have one on my 70 and seems work very well.

Marty

[260DET]

No great problem with the spook type spoiler, Marty, it is just that the scraper type seem to work a bit better and are more suitable for attaching an undertray/splitter.

[26th-Z]

Typical styling of the period. I thought you guys would enjoy this Cobra Daytona drawing. I'm sure it is copyrighted.

Notice the ducting through the hood and the rear duck-tail meant to increase the negative pressure behind the car.

[2ManyZs]

One thing you guys have overlooked is the simple things... like toe in, caster, camber and the tires(width, and the tread design as well)... they will all contribute a lot to the ability of the car to track straight, windy or not...
Ya gotta remember, these cars aren't all that heavy either, so crosswinds will be more pronounced than in heavier car...
A front spoiler will only do so much to contribute to the aero at highway speeds....

[TomoHawk]

Could you please explain the difference between a spook spoiler and a chin spoiler?
thx.

[26th-Z]

Tomohawk,

I searched for a thread discussing where the word "spook" actually came from and can't find it, but you may run across it. I think it is a word combining spoiler and scoop. Spooks started showing up on cars in the late 60's when designers started thinking about how air flows around cars and how much horse power is devoted to pushing a car through the air. They may been trying to scoop air into the radiator as well. Your question is really asking about differences in terminology and I don't think the word spoiler should be used for aerodynamic devices on the front of the car. Spoiler describes a device that spoils the air flowing off the back of the car. Spooks and air dams are used to control the air flowing underneath the car, although commonly refered to as front spoilers. An air dam is usually considered flat vertical where a spook protrudes forward scooping air and directing it upward. A chin spoiler is simply a shorter version with no real scoop or dam definition and generally acts to direct the air off to the sides.

The amount of horsepower used to push a car through the air is determined by frontal area - that which is perpendicular to the air flow. It is important to decrease frontal area as much as possible. Angled surfaces do have frontal area value, but contribute by directed air flow. Air dams may at first seem costly with a lot of frontal area, but they consolidate all the little frontal areas protruding underneath the car as well as directing air flow from underneath, thus creating negative pressure sucking the car to the road. Air dams usually hang pretty low. Spooks are angled, have less frontal area, direct air upwardly, but still allow air underneath.

In my opinion, adding a front spoiler to a Zed increases the frontal area and in theory slows the car. Without making modifications to decrease frontal area, you are kind of pissing into the wind, shall we say.

[TomoHawk]

It sounds like an air dam and a chin spoiler are the same thing?

[26th-Z]

Guys, Help me out with pictures, please.

Chin spoiler

[26th-Z]

Oops - try again

Chin spoiler

[26th-Z]

Chin spoiler on a fairlady

[26th-Z]

Spook

[26th-Z]

Here is a link to MSA front air dams as well as spooks. Take a look at the BRE spook they sell.

http://www.zcarparts.com/store/merch...gory_Code=7AD1

[TomoHawk]

From all this information, I gather that the 'chin' spoiler and 'air dam' are of the same design, although they might vary in the height. The 'spook' style has little to moderate height and the 'scoop' has moderate to great height, depending on it's use; i.e., one used to scoop air into the radiator would be taller than one ment for simple downforce/air displacement.

Overall, the definition seems to be based on what the advertisement Exec wants to sell it as., or to whom he wants to sell the stuff.

[Bambikiller240]

Originally posted by TomoHawk

Overall, the definition seems to be based on what the advertisement Exec wants to sell it as., or to whom he wants to sell the stuff.

Sounds about normal for everything sold in the world .

Marketing before substance.

[RB30-ZED]

Have you guy's read this article.
http://zccw.org/Tech/Body/09-97EarlyZAerodynamics.html
It is very interesting, especially the first part on air flow around the radiator area.
And one more worth a look.http://autozine.kyul.net/technical_s...g%20and%20Lift
Steven

[TomoHawk]

Has anybody seen these " turbulator strips in the roof near the forward edge of the hatch"? I'd like to try it and see if there's a difference. Probably not much if you drive below 80 mph. Maybe it will help a little any way.

thx.

[RB30-ZED]

No, I haven't seen them, but they sound easy to make.
Im now considering refitting my old rear window louver to break up the air flow over the rear of the hatch to stop the air flow attaching and coursing lift.
Any one noticed a difference with a rear window louver on or off?
Steven

[D-Webster]

I had a 71 without the louver and it was more stable than my current 73 with the louver. My current 83 doesn't have a louver either but the last 83 I had did but I doubt I've ever had either car where I would notice anyway.

[TomoHawk]

What do you think those turbulator strips look like? You could easily rivet or screw on a shallow rectangular or wedge-shaped strip on. Maybe even double-sided tape.

Something ELSE ricers don't have!

Yay!
Here's one on the keelfin of an r/c sailboat:
http://www.onemetre.net/Technicl/TripTurb/Turb2.jpg

[TomoHawk]

I was just watching "Victory By Design" On Speed Channel, and they had Porches . There was a comment about how why they put on the ducktail spoilers because it was "unstable at 150 MPH".

So there is your answer about what speed you need to get instability.

[260DET]

Originally posted by RB30-ZED
No, I haven't seen them, but they sound easy to make.
Im now considering refitting my old rear window louver to break up the air flow over the rear of the hatch to stop the air flow attaching and coursing lift.
Any one noticed a difference with a rear window louver on or off?
Steven

I'ts going to likely mess up your airflow around the rear something awful though. Lots of drag and any spoiler probably won't work well. Much better to leave it clean and use a spoiler IMHO.

[SteveK]

Sorry to go off topic for a moment but what on earth are "ricers"

I have seen the term used several times and cannot for the life of me think what it refers too.

[RB30-ZED]

Originally posted by 260DET
I'ts going to likely mess up your airflow around the rear something awful though. Lots of drag and any spoiler probably won't work well. Much better to leave it clean and use a spoiler IMHO.

Thats very true but from what ive read its a chioce between smooth air flow, which unfortunatly will cause lift as it races down the rear section of the 240's body or breaking up the air flow coursing drag but stopping lift.
Lift scares me more than drag.
Steven

[Alfadog]

Originally posted by SteveK
Sorry to go off topic for a moment but what on earth are "ricers"

I have seen the term used several times and cannot for the life of me think what it refers too.

Ricers are those who put really tacky things on their cars to make them look fast. Generally they own economy cars. A picture tells a thousand words.

[240znz]

Thanks Steven,

Those links made good reading. My 71 has a front dam fitted and factory rear spoiler. I was thinking of removing the rear spoiler but on reading those pages, I might as well keep it on there.

I have seen another Zed with the same front dam as is on mine. Mine was imported to NZ from Australia and I'm wondering if these dams were fitted in Japan or in Australia.

Here's a early pic

[260DET]

Originally posted by RB30-ZED
Thats very true but from what ive read its a chioce between smooth air flow, which unfortunatly will cause lift as it races down the rear section of the 240's body or breaking up the air flow coursing drag but stopping lift.
Lift scares me more than drag.
Steven

Well mine has a whale tail on it with a small air flap (Gurney lip) and it is rock solid at 200+ kph.

And are you sure that the hatch surface induces lift anyway? It is not the same as the bonnet surface, there air is being forced to speed up and so lose pressure which induces lift.

[RB30-ZED]

Originally posted by 260DET
And are you sure that the hatch surface induces lift anyway? It is not the same as the bonnet surface, there air is being forced to speed up and so lose pressure which induces lift.

No Richard im not 100% sure, but I believe it does. As you say air pressure drops with the increasing speed of the air, and true as it rises over the front of the car its speed goes up and its pressure goes down , but as it is dragged back down the slopping rear of the Zed it is also accelerating in speed back to were it started, so yes, I think it does.
Here is a quote from the ZCCW Newsletter
Source: James Lux
"The smooth top of the Z, gently falling to the tail, encourages high velocity air to remain attached to the roof surface and that attachment produces lift on the aft section of the body. The figure that comes to mind is 120 pounds of lift on the rear of the car, but I don't recall now at what speed that figure is reached, though I believe it was either 60 or 100 mph. Lift on the aft body relieves load on the springs and the aft body lifts slightly. The MacPherson strut rear suspension acts like the front suspension when the body is raised: camber becomes slightly more positive and toe-in changes slightly compared to the body's static setting. The mismatch of lift between front and rear at speed on the 240 is a major reason why the Z is known as an understeering car at low speeds and an oversteering car at high speeds. Oversteer and understeer characteristics are formed by more than suspension type and settings. An optional rear spoiler was available for the 240 almost from the beginning, though relatively few 240's possessed one. Changing the aft body lift characteristics of the 240 involves either creating downforce, as with the original rear spoiler, or "spoiling" the lift before it begins."

A very interesting topic.
Steven

[260DET]

Yes Steven it is interesting and I have some reservations about the ZCCW information. I'm not convinced that air moving down the back of the hatch would be significantly low pressure. After all it has already been accelerated when passing along the bonnet so it surely is still not accelerating by the time it reaches the hatch.

The air rushing in to fill the space behind the car is somewhat different, it is turbulent too. But anyway, as I said, there is no problem with my car there so..... IMHO it is at the front where gains are there to be made, just consider air flow through the radiator and its exit for one.

[beandip]

According to SCG on page 15 of the Gold Portfolio the forces on the 240 Z at 100mph is 270 lbs of drag including the tires . the LIFT to the body at 100 mph is - 85 lbs on the front and -95 on the rear. Which means positive down force . This is with out any air dam or spoiler. For what it is worth , I have noticed that the front of my '73 feels less light at speed after I added the sheet metal pan that was a factory mounted pannel or farring under the rad and front or the engine. I have read tests since, that have agreed with this , as was reported , helped to eliminate the air from building pressure in this area and helping to draw more of the flow from the engine bay. By helping to eliminate turbulance of the air traveling under the front vallance and crossmember. I have also added rear luvers on the hatch window , but I cannot feel any difference in the handeling in this reguard. to correct a miss statement the rear suspension is not Mc pherson , but is Chapmen strut type. Mc pherson is on the other end. No flame just information.

[RB30-ZED]

Originally posted by 260DET
I'm not convinced that air moving down the back of the hatch would be significantly low pressure. After all it has already been accelerated when passing along the bonnet so it surely is still not accelerating by the time it reaches the hatch.

But if the air accelerated up over the front to the roof, then it has to move back down just as fast, you see its not going any faster, but its still going just as fast as it did on the way up, and more importantly, its moving faster than the air under the car.
Its the imbalance of air speed under and over that courses lift, ether up or down.
Did that make any sense.
But I do agree that your best to stop it getting under in the first place. When I get time im going to hook a spring loaded resister to the rear suspension and take readings at different speeds with the louver on and off, to work out the suspension hight due to lift.
Steven

[PrOxLaMuS©]

Thanks to this conversation....

I have decided to.. buy BRE Spook front spoiler

Can't decide though.... With brake cooling holes or without?

[beandip]

According to the tests that were done there was a down force of 95 lbs on the hatch at 100mph and 85 lbs on the front end , not lift. The drag to the rear of the car was calculated to be 240lbs at the rear of the car . by adding a spoiler, the small one that was on the early Zs with the addition of the spook , that it moved the vacume bubble back away from the rear of the car about 4 or 5 ft. if I remember right . I had all this data down loaded but I was recently infected and lost the Hard drive and all the information so I cannot back up this info . With the exception of the figures of the down force on the rear hatch and hood. I will keep researching my books for the info. This was brought up also as a way of helping the smell of fumes entering the rear of the car as a side effect. by the way the front suspension is mcpherison and the rear is chapman.

[RB30-ZED]

Originally posted by beandip
According to SCG on page 15 of the Gold Portfolio :

Sounds interesting infomation, but what is SCG ?

Can't decide though.... With brake cooling holes or without?

Id go with the brake ducts, as they look better, but if you dont need them block them of from behind to stop air getting under the car.
Steven

[beandip]

S.C.G. Stands for Sports Car Graphic It was a magazine that did testing like Motor Trend and Road & Track. They published compairisons of the new offerings when they came out and tested everything such as cornering, brakeing , stopping , brake fade milage as well as the aerodynamics. they show 15.5 lbs per HP on a '70 240 Z The book DATSUN Gold Portfolio is a 172 pages of tests and articles about the 240 and 260 Z and a little on the 280.

[RB30-ZED]

Thanks beandip, now that you've mentioned it I think ive seen a scan of that page on the net somewhere. Did it have a drawing of the Zed over a grid ?
Steven

[Bambikiller240]

Originally posted by RB30-ZED
Id go with the brake ducts, as they look better, but if you dont need them block them of from behind to stop air getting under the car.
Steven

My 240Z that I owned in the late 70's through mid 80's had a Airdam without brake ducts (see my Gallery), and my current 240Z has one with brake ducts. I believe that I'll be going back to one without brake ducts before she gets to a paint shop. I thought my tastes had changed, but they really haven't. I like it without ducts.

[beandip]

bkiller I dident ask about the air dam but thanks for the info. rb-30-ZED , no it is different I dont have a scanner or I would send a page . This is a report on three different cars and as a compairson the '70 240Z , OPEL GT , MGB GT one and a third pages of results of testing of the three cars. as far as down force vs lift. the Opel GT front 130 lbs of LIFT and rear 155 lbs of LIFT and 230 lbs of drag. The MGB GT , front 70 lbs. LIFT and rear, 130 lbs LIFT and 285 lbs of drag. I don't know if any of this is of interest but I just thought I would pass it on I found it interesting because these were the cars of the era that were in compitition. All were priced at or near $3500.00 .

[260DET]

Steven, your proposed test sounds interesting, let us know the results if you can. On air flow over the hatch, the difference may be that over the bonnet the air is physically forced to speed up and hence lose pressure, while over the hatch air merely moves in to fill a lower pressure area. The bonnet being the forcing physical object therefore is subject to lift, the hatch is passive in that regard. But there is a fair dose of conjecture in this.

Beandip, good stuff but are you sure that the Z had pressure on the bonnet? The usually accepted situation is that there is lift there, eg see Steven's and my posts.

[TomoHawk]

Originally posted by 260DET
On air flow over the hatch, the difference may be that over the bonnet the air is physically forced to speed up and hence lose pressure,

I would disagree with that. If you lose pressure over the hood, than ram-air systems wouldn't work. Same with the cowl-induction hood scoop, which uses the high-pressure air from the front of the windsheild.

[RB30-ZED]

Originally posted by 260DET
while over the hatch air merely moves in to fill a lower pressure area.

Move in to fill a low pressure area ( how did it get there?) or was it that it was accelerating down the hatch to fill a increasing area that the low pressure formed in the first place ?
Steven

[beandip]

down force is what the tests show no kidding. I will look further and see how many other tests include this sort of data. The test I am quoteing also shows the G-forces and degree of lean on turn at speed , compaired to other cars. The Z showed 1.03 hp per cu Inch. but I think that was at the flywheel. I dont think the early Z had 150 HP at the rear wheels.

[TomoHawk]

Oh yeah?

TheL28 engine has175? cubes and 175 Hp, according ther the plate on the fenderwall.

And I still can't spin the tires unless the road is wet.

[Alfadog]

What, is it auto?

[Bambikiller240]

Originally posted by TomoHawk
Oh yeah?

TheL28 engine has175? cubes and 175 Hp, according ther the plate on the fenderwall.

And I still can't spin the tires unless the road is wet.

If it's not an auto, you need a tune-up, or new clutch, I would think.

[TomoHawk]

Yup. 3 speed auto,rebuilt, with the low first gear and 3.54 diff. Definitely need tuning (runs rich). Pickup off the line is not bad tho.

[beandip]

Tomahawk what we are talking of here is the 240 shape Z and the tests that were done were on the first of the Zcar . The facts that I have been refering to are for this car . Namely the '70 240 which were less than 2800ccs. Dont believe what you read on the plate. There is no way the engine ever made that HP at the wheels. Yes at the crankshaft on an engine stand with out a alternater or water pump or any other add ons. Figure about 135 HP on a good day at the wheels.

[Caen Fred]

Hi, I was reading this post and I wonder if any of us use the Pantera deck? According to your theory, this should handle better? No rear lift?

[TomoHawk]

beandip-

I know what you mean. The thing is, when I go to a cruise-in, people always talk about how powerful the engine is, with the straight-6 and f.i., but it doesn't feel like the things people infer. Peppy, yes, but rubber-rippin? dunno...
thx.

[wolf66]

Back to the aero drag/lift...

So i have read in a few post where the Z is suppose to have
"X pounds of lift at 100mph" (usually around 60-120ls lbs)

So i was thinking i had to get the air dam/rear lip spoiler for high speed stability but beandip's source's seem to say otherwise, anyway to scan the info beandip?

[Zrush]

Originally posted by TomoHawk
Yup. 3 speed auto,rebuilt, with the low first gear and 3.54 diff. Definitely need tuning (runs rich). Pickup off the line is not bad tho.

Do they make a shift kit for the automatic Z car? This would add a little pep.

Vicky