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Z aerodynamics

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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

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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.

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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.

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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.

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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.:)

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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.

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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

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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.

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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

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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.

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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. :D

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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.....

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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!?

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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!

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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

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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.

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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.

post-4148-14150793432167_thumb.jpg

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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...:ermm:

A front spoiler will only do so much to contribute to the aero at highway speeds....

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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.

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