interesting stats there pager.

the airdam/front spoiler/spook definitely made a difference to my 1200. Not only does it increase high speed stability and 'feel' slightly, but it also made the engine run cooler - even on the street. simple explanation for that is that more air is forced through the radiator rather than passing under the front of the car, and there is a resultant lower pressure behind the airdam (ie under the engine bay) for the hot air in the engine bay to escape to. So a big decrease in front end lift and underbonnent temps. definitely a worthwhile investment for anyone who does track days.

the rear spoiler felt like it made a noticeable difference to my car on the fast bumpy 4th gear sweeper under Dunlop Bridge at Lakeside. The rear was more stable and less affected by the bumps. Before the rear spoiler was fitted it was easy to get sideways there. But this was when I was first starting out - still running on road tyres and didn't really have the suspension sorted back then.

bonnet scoops? not an aerodynamic aid. will only increase turbulance. most will do very little for performance or cooling. scoops are just ricey unless you have a top mount intercooler, or you're very serious about drags or salt flats. for road cars there are much less obtrusive and cheaper ways of getting cold air induction to carbs.

bonnet vents on the other hand can do a useful job of lowering underbonnet temps when fitted properly - particularly on turbo cars. i.e. not like most ricers do fitting them backwards on the front half of the bonnet trying to use them to draw air in! a big ducted vent just behind the radiator can help allow hot air out, but would look out of place on an old car

air flow plates around the radiator are cooling aids. forces air to go through the radiator core rather than escaping via the paths of lower resistance over the rad support panel or through other openings in the panel. not really an aero aid.

lowering? well there's a minor reduction to amount of air passing under the vehicle, but there is also a reduction in the volume under the car for it to pass. I don't think it would be a significant reduction in lift on these old cars. With the shape of the front apron you're still going to get plenty of air being forced under them.

rake will be of no benefit aerodynamically than a level car at the same ride height. the lift effects of air getting forced under the front of the car at higher speeds are felt at the front 1/3rd of the car. its the air getting squashed under the front and being slowed down that creates the high pressure and lift. having the rear slightly higher will not change that at all.

with the 120Y coupe I'm building, I'll definitely be running a front spoiler. No rear spoiler though. with good semi slicks and suspension setup, I doubt a rear spoiler would be any real benefit - just extra weight and a bit of drag. vents and scoops are not allowed in IPRA, but I wouldn't use them even if they were!

correct, this is only relevant above 100 kph, but for me I'm pushing the envelope for what the car was intended just driving to work. I used to have a commute that went on a highway where regularly the flow of traffic was up to 160kph.

I've been pondering how it is that the little car can even go that fast.

i think that aerodynamics will start to come into play between 60 t0 100 km/h
Before this any effect is neglible i think

i guess thats why wrx and other realy good sports cars have one ram air intake and two vents so it blows looks of air in with out getting upforce

In most cases aftermarket stuff is just there for looks. Car & Driver found in their tests in 74.
On a datsun 240z
Stock:
140 lbs of Lift on front wheels @ 70mph
20 lbs of Lift on the rear wheels @70 mph

BRE Front Spook canceled 105 lbs of Lift and increased gas mileage by 0.4 mpg
BRE Street Spook (no brake ducts) canceled 115 lbs of Lift

BRE Rear Spoiler added 75 lbs. of down force @ 70 mph and 0.2mpg

C & D custom 7" rear spoiler (at 50 degrees from horizontal)
Added 160 lbs of down-force to the rear but off loaded an additional 20 lbs from the front. It also hurt gas mileage by 0.6 mpg.

Remeber 60 mph is roughly 100kmph so these tests where done not that much over the speed limit also 10 pounds ~ equal to 4.5 kg

I reccon these things really only affect race cars. Dont get me wrong, having a vent/scoop strategecially placed on the bonnet can aid in engine bay cooling and may give gome performance in forcing air in and around the air intake. But when you are talking spoilers, air dams, splitters, wings etc I think they have no real bearing on a road car other than looks and "BLING".

Let's have a discussion about aerodynamic theory as it applies to datsuns.

Some of the things to think about are:
Airdams
Lowering
Hood Scoops
Air splitters at the top of the radiator whatever you call it.

I guess I'm getting at more downforce, and less air resistance.

ideas?

It seems to me that unless the hood scoop goes to the engine, it needs to be no further forward than the strut tower, and facing backward, so it lets air out from under the hood, not facing forward, putting pressurized air under the car.

The Airdam significantly improves high speed stability. I don't have before data, but it's possible to get 30 mpg at 80 mph with an A15. I've been wondering about screwing some garden edging to the airdam and seeing how low i can get before it starts to rub often.

Lowering the vehicle...
If the vehicle is just lower that would cause more air to go over the top, if the front is raked down a little then that should have a double benefit of letting less air under and allowing it to slow down under the car and create a lower pressure area.
... I think ...