Z aerodynamics

[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