240Z Aerodynamics

[jmorrison146]

Recently purchased a silver 1972 Z that is bone stock - . I've owned Zs before and know that the front end gets a little light at higher speeds, so I want to add a BRE-style spook to the front. Both of my previous Zs also had a BRE-style rear spoiler.

The more I look at this car and others on this site without a rear spoiler, I like the clean lines of the rear of the car without the rear spoiler. So . . . what would be the net effect of a spook in front and a clear rear end? Are front and rear spoilers a package deal aerodynamically?

[JLPurcell]

Recently purchased a silver 1972 Z that is bone stock - . I've owned Zs before and know that the front end gets a little light at higher speeds, so I want to add a BRE-style spook to the front. Both of my previous Zs also had a BRE-style rear spoiler.

The more I look at this car and others on this site without a rear spoiler, I like the clean lines of the rear of the car without the rear spoiler. So . . . what would be the net effect of a spook in front and a clear rear end? Are front and rear spoilers a package deal aerodynamically?

My 1972, of which I am the original owner, has always had just the front BRE (Datsun Competition) style spook without the brake ducts, and it definitely helps at high speeds with the front end stability.

[Pop's Z]

You won't notice any effect from a rear spoiler unless you are driving over 100 mph. I have both spook and spoiler. You will notice a difference with the spook at highway speeds especially in a cross wind.

Cheers, mike

[jmorrison146]

Doing a little more research, I found this great thread (http://www.classiczcars.com/forums/misc-s30/17453-bre-not-bre.html) in which Carl Beck references 1970s Car and Driver magazine testing. I couldn’t find a link to the original Car and Driver “Crisis Fighter Z Car” article, but I’ll take Carl’s word for it.

Stock configuration at 70 mph = 140 lbs lift at the front, 35 lbs lift at the rear.

An unducted BRE-style front spook generates 115 lbs of downforce at the front but adds 20 lbs lift to the rear (55 lbs total). Adding a BRE-style rear spoiler creates 75 lbs downforce a the rear, balancing out the package nicely.

BUT adding the front spook (required, in my opinion, for stability at highway speeds) without the rear spoiler results in only 55 lbs lift at the rear. 55 lbs is one suitcase or the difference between a full tank of gas and an empty tank. BUT Carl (who should know) recommends both. Pete Brock (who should also know) used both.

Z Car Home has a great Z Aerodynamics article by Dr. Ben Millspaugh from Z Car Magazine, June 2005:

Part I Z Aerodynamics by Dr. Ben Millspaugh

Part II -Z Aerodynamics by Dr. Ben Millspaugh

Part III -Z Aerodynamics by Dr. Ben Millspaugh

[SteveJ]

I have a copy of the article in a book at home. I won't have time to look for it until probably next Monday.

[LeonV]

Doing a little more research, I found this great thread (http://www.classiczcars.com/forums/misc-s30/17453-bre-not-bre.html) in which Carl Beck references 1970s Car and Driver magazine testing. I couldn’t find a link to the original Car and Driver “Crisis Fighter Z Car” article, but I’ll take Carl’s word for it.

Stock configuration at 70 mph = 140 lbs lift at the front, 35 lbs lift at the rear.

An unducted BRE-style front spook generates 115 lbs of downforce at the front but adds 20 lbs lift to the rear (55 lbs total). Adding a BRE-style rear spoiler creates 75 lbs downforce a the rear, balancing out the package nicely.

BUT adding the front spook (required, in my opinion, for stability at highway speeds) without the rear spoiler results in only 55 lbs lift at the rear. 55 lbs is one suitcase or the difference between a full tank of gas and an empty tank. BUT Carl (who should know) recommends both. Pete Brock (who should also know) used both.

Z Car Home has a great Z Aerodynamics article by Dr. Ben Millspaugh from Z Car Magazine, June 2005:

Part I Z Aerodynamics by Dr. Ben Millspaugh

Part II -Z Aerodynamics by Dr. Ben Millspaugh

Part III -Z Aerodynamics by Dr. Ben Millspaugh

There's absolutely no way that adding a front air dam will take you from 140lb of lift to 115lb of downforce (negative lift), especially at 70mph.

EDIT: I'll add that you will always have lift at the front on a Z, unless you make some serious modifications to the car, i.e. it won't look stock-ish anymore...

Edited September 30, 2013 by LeonV

[psdenno]

I've had a BRE front spoiler on my '71 for most of the 40+ years I've driven it. It did wonders for keeping the front end planted, especially in strong cross winds. I never installed a rear spoiler as it seemed unnecessary.

For a couple years, I lived in Kansas and experienced extreme downforce when plowing through two foot winter snow drifts on the highway with the spoiler.

Dennis

[26th-Z]

We have had huge conversations about this topic; I guess you found the references in the archives. I don't recall the Car & Driver article but the Millspaugh articles are very good and will give you a good understanding of what is going on with the car at speed. The front spook, in my opinion, is extremely effective in cross-wind situations. It is also my opinion that the spook and spoiler apply most effectively as a pair. This is how Nissan set up the car. The BRE stuff is really not much more than a copy of the Nissan competition parts.

[SteveJ]

If the C&D article is the one I remember, they took a 73 and tried to improve gas mileage via aerodynamics. I found the article in a book that is a compilation of car magazine articles on Z cars (and sometimes roadsters, too).

[Jarvo2]

From my massive archive...

[jmorrison146]

Yep, you're right. The 115 lbs of downforce created by the spook negates some of the 140 lbs lift observed at the front of the Z.

[jmorrison146]

Jarvo - thanks for forwarding the Car and Driver article!