2 hours ago, kats said:

Hi Roo,

Me neither, and also engineers were shocked when they saw the results of Cd and Cl at that time. I will upload the remaining pages. Before that I will try to explain

that Mr. Miyazaki told me about how bad the opening front end of S30 was. Just like you proposed, it was the issue of S30 which engineers had to deal with.

I will draw a picture by hand, Mr. Miyazaki said S30 front end is so wide that it leads too much air coming through the radiator. Then the air can't go through under the engine because the air was blocked by the air stream which is flowing underneath of the car. At the end, the pressure of inside of the engine bay becomes positive, it pushes the front end. The higher front end gets more Cd worse. This story I think it relates the story of 15mm lower front end of Europe model (except Portugal model). 

And Mr. Miyazaki even told me there was a test  car which had a factory air conditioning coupled with Z432!! (Z432 was not able to make a choice of air conditioning from the factory). During the test of aerodynamics, one day he was wondering why one car had a better value than other cars. The better one had an air conditioner condenser in front of the radiator. Less air gave less lift. That was a Z432.

Kats   

  

@katsexactly right about the engine bay pressurizing and increasing the drag. We spent a lot of time shrinking the size of the openings and also modifying their shape to cut front end lift and drag on my Aston race car. To de pressure the engine bay we vented the bonnet and ran some Gurney flap lips to help evacuate the stale air. I may try it on on old 240Z bonnet I have and see what happens. There is an old article from one of the car magazines over here in the USA that compared various aero mods.

 

 

Edited August 10, 20231 yr by SpeedRoo

Thanks Alan,

According to the comments of Mr. Uemura and other engineers and styling designers, the 1/4 scale model was tested in the facility of the University of Tokyo. According to the book "Prince/Nissan" Kazuo Higaki (Nigensha), as Alan said Prince used to have a wind tunnel at Ogikubo but it had been abandoned since the end of the world war two, impossible to operate. Just like Nissan, Prince engineers brought their 1/5 scale model to the same place, the University of Tokyo. By the way, 1/5 scale is a tradition of the Prince which used to be as an airplane manufacturer. Nissan's used 1/4 scale...

A full scale prototype car was tested in the wind tunnel freshly built at Nissan Oppama Chuo- kenkyujyo (Nissan Central Research Institute) at Dec 1968, started operating from April 1969.

Kats

Attached picture is testing a Prince R380. 

  

 

Edited August 10, 20231 yr by kats

51 minutes ago, SpeedRoo said:

@katsexactly right about the engine bay pressurizing and increasing the drag. We spent a lot of time shrinking the size of the openings and also modifying their shape to cut front end lift and drag on my Aston race car. To de pressure the engine bay we vented the bonnet and ran some Gurney flap lips to help evacuate the stale air. I may try it on on old 240Z bonnet I have and see what happens. There is an old article from one of the car magazines over here in the USA that compared various aero mods.

 

 

Thanks Roo, 

I have seen the magazine but haven't read through whole pages, thanks!

You don't need my drawings but hey, I put it just for fun.

I have one interesting story to tell which Mr. Miyazaki told me about "front chin spoiler" later on here.

Kats 

All I can say is my stock 240Z started to feel like the front end was flooting at around 90MPH. I put headlight cover on and an air dam and the car feels solid on the road at over 100MPH. As far as drag goes I believe that these changes to the front of the car added about 3MPG. No numbers here, just my own impressions.

If you want to talk drag, take a look at the front of my wifes truck in my sig. But the slightly modified small block made it not to noticeable.

Edited August 10, 20231 yr by w3wilkes

This is my new FAVOURITE all-time thread.

Thanks Kats and Alan for sharing such brilliant info.

What I don’t understand is - and bear with me pls, I know little about aerodynamics - given that the engine bay pressurises does the blunt nose improve cooling also? And does the standard under tray improve the pressurisation situation? (Apologies if it’s covered in the magazine articles that I haven’t had a chance to read yet).

A very experienced member of the UK club (the late Mr. F) used to tell me that the under tray also affect the cooling efficiency, so I’m wondering if this was the reason?

We have discussed that magazine article.  It's probably the best independent analysis available.  "Interpart" is / was Pete Brock - BRE.

This thread made me think of the Maru Z Keikaku Suishin Iinkai films and that NISSAN did aero testing of the chassis.

1 hour ago, AK260 said:

used to tell me that the under tray also affect the cooling efficiency, so I’m wondering if this was the reason?

Its my understanding too. I don't think Nissan would have added such a large undertray to the z432r otherwise.

 

If my grey cells recall, Ben240z (on UK forum) I think there are cut outs in the inner wing, on his race car, sort of where the battery goes, so the air entering the engine bay has a place to escape too...

The purpose of the undertray is to speed up the airflow under the car to reduce overall lift. It does cause cooling problems but careful attention to ducting and venting the air from the engine bay keeps those in check. At ordinary legal driving speeds none of this really has much effect but as you get nearer to 100mph the aero has a much bigger influence. The reason the Z432R has the undertray is to homologate the part for racing use, without the front airdam and cooling mods it wouldn't actually have much effect on the cars performance in normal use.

 

2 hours ago, AK260 said:

And does the standard under tray improve the pressurisation situation? (Apologies if it’s covered in the magazine articles that I haven’t had a chance to read yet).

A very experienced member of the UK club (the late Mr. F) used to tell me that the under tray also affect the cooling efficiency, so I’m wondering if this was the reason?

Hi Ali,

There's some potential for confusion here between the full-length engine bay undertray of the 432-R (as homologated for race use, made from FRP) and the much shorter splash pan (steel, as fitted to other models) which were designed to perform different functions.

The 432-R undertray has a reputation for causing overheating in normal street use during hot weather (it was designed to be used on circuit, at higher speeds of course) and I guess Mr. F would know what he was talking about with regard to the steel splash pan, although I imagine the effect would be less pronounced.

Here's what the 432-R undertray looked like:

     

The test data from HybridZ... the numbers for a stock Z (test #2)  Cd /CL etc  are pretty close to what Kats Posted.

@Carl Beck very interesting reading. I remember seeing that report somewhere, can you link to it still? Blocking off sections of the radiator opening seems to have the biggest effect, as we mentioned earlier in the tread.

Found it @Carl Beck https://forums.hybridz.org/topic/55944-windtunnel-test-data/