1970 240Z Works Rally - the road to restoration

[xs10shl]

1 hour ago, Patcon said:

I assume they are using the fuel to cool the diff. Liquid to liquid intercooler. Seems an interesting choice but I'm sure some engineer worked it out

Correct- it is a heat exchanger, which cools the differential fluid with gas.  I've yet to get it working, so I can't speak to how well it works, unfortunately. Worth noting, this diff cooler is not a new "discovery" by me, as it's been previously well documented many years ago, via a 1992 article in Race & Rally, which told the story of the early days of the 240Z Works rally program through the lens of the mechanics at Old Woking Station.

Edited December 23, 2022 by xs10shl

[Carl Beck]

From Mr. Uemura’s Story:

 

DEVELOPMENT PROCESS

- - Vehicle Durability Tests

- - - Heat Resistance and Cold Resistance Tests

 

The heat resistant performance was evaluated at an external temperature of 95ºF

(35°C) for the domestic models, and at 104ºF (40°C) for the North American models.

The tests were mainly conducted on the heat-resistant chassis dynamometer. However,

because the wind flow can be different from the vehicle tests, performance was also

evaluated on the test course. Eventually, field tests for this model were done in the

United States and Canada.

 

The heat resistance test done on the chassis dynamometer includes many items, such

as whether the temperature of the water or oil is normal during high speed operation,

whether the engine speed becomes unstable while the engine is idling after high speed

operation, and whether the engine can be restarted after the ignition is turned off. If it

fails any of these items, heat resistance performance is considered insufficient.

We aimed at keeping the engine oil temperature within a specified range even if the

car ran continuously for 118 miles (190 km) without an oil cooler. In fact, we had no

problems with the engine oil temperature. The differential was also designed to keep

the oil temperature in a specified range even after 118 miles (190 km) of continuous

driving. However, because it was at the far rear of the floor, the differential did not

get sufficient wind even if a baffle plate was used. In the end, it was not able to clear

the 118 miles (190 km) continuous driving at a 104ºF (40°C) external temperature. If

consumers complained, we were prepared to offer an optional oil cooler for the differential

oil, but this problem did not arise. Probably as no one drives a car continuously

at such high speeds in the United States, and because temperatures do not go up that

high in Europe.

 

 

DATSUN 240Z Engineering Development

https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=Datsun+240Z

[HS30-H]

2 hours ago, Carl Beck said:

From Mr. Uemura’s Story:

 

DEVELOPMENT PROCESS

- - Vehicle Durability Tests

- - - Heat Resistance and Cold Resistance Tests

 

The heat resistant performance was evaluated at an external temperature of 95ºF

(35°C) for the domestic models, and at 104ºF (40°C) for the North American models.

The tests were mainly conducted on the heat-resistant chassis dynamometer. However,

because the wind flow can be different from the vehicle tests, performance was also

evaluated on the test course. Eventually, field tests for this model were done in the

United States and Canada.

 

The heat resistance test done on the chassis dynamometer includes many items, such

as whether the temperature of the water or oil is normal during high speed operation,

whether the engine speed becomes unstable while the engine is idling after high speed

operation, and whether the engine can be restarted after the ignition is turned off. If it

fails any of these items, heat resistance performance is considered insufficient.

We aimed at keeping the engine oil temperature within a specified range even if the

car ran continuously for 118 miles (190 km) without an oil cooler. In fact, we had no

problems with the engine oil temperature. The differential was also designed to keep

the oil temperature in a specified range even after 118 miles (190 km) of continuous

driving. However, because it was at the far rear of the floor, the differential did not

get sufficient wind even if a baffle plate was used. In the end, it was not able to clear

the 118 miles (190 km) continuous driving at a 104ºF (40°C) external temperature. If

consumers complained, we were prepared to offer an optional oil cooler for the differential

oil, but this problem did not arise. Probably as no one drives a car continuously

at such high speeds in the United States, and because temperatures do not go up that

high in Europe.

 

 

DATSUN 240Z Engineering Development

https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=Datsun+240Z

Although Uemura san's stories are always very interesting, I somehow doubt he would pitch them into a conversation around the diffs on the Works 240Z rally cars.

Nissan's Works rally team already had the experience and data accumulated from the use of the R160, R180 and R190 Fuji Heavy Industries differentials that had been used in competition before the 'Kaku U' 240Z team had pitched up in North America, and there will have been very little transferable/comparable data between the (3.3:1 ratio) 2-pinion 'open' R180 used in the North American 240Z and the 4.375~5.1 ratio 4-pinion plate LSD-equipped R180s used in the Works rally cars.

   

[xs10shl]

5 hours ago, Carl Beck said:

From Mr. Uemura’s Story:

 Ifconsumers complained, we were prepared to offer an optional oil cooler for the differential

oil, but this problem did not arise. Probably as no one drives a car continuously

at such high speeds in the United States, and because temperatures do not go up that

high in Europe.

Interesting - I would love to know exactly what diff coolers they were prepared to install for customers, and where they would put it.  This is the point where we as enthusiasts wish the designers would be able to to start quoting part numbers, haha!  

For others who are following this thread:  anecdotally (and I don't have the exact figures in front of me ), differentials seemed to play a significant role in rally retirements during the early years. As a solution, the "Fuel-as-diff-coolant" strategy does appear a bit outlandish to me on its surface, and it's effectiveness is clearly very dependent on the amount of fuel left in the tank, among other things. I can't really speak to whether it actually provided a noticeable reliability improvement versus not having it at all. But it is certainly a creative, compact solution!

Edited December 23, 2022 by xs10shl

[Mark Maras]

I've never heard of a differential cooled with fuel. I doubt I would have even considered it as an option.

[HS30-H]

14 hours ago, xs10shl said:

For others who are following this thread:  anecdotally (and I don't have the exact figures in front of me ), differentials seemed to play a significant role in rally retirements during the early years. As a solution, the "Fuel-as-diff-coolant" strategy does appear a bit outlandish to me on its surface, and it's effectiveness is clearly very dependent on the amount of fuel left in the tank, among other things. I can't really speak to whether it actually provided a noticeable reliability improvement versus not having it at all. But it is certainly a creative, compact solution!

Nissan had used the little fuel/oil heat exchanger (its actually a 130-series Cedric/Gloria part) as a diff cooler on the 510-series Bluebird Works rally cars (winning the East African Safari Rally with them in 1970) and engineered a similar system for the first batch of 240Z Works rally cars (entered in the 1970 RAC Rally).

However, there was some debate over whether diff cooling would be an issue given that the RAC Rally was traditionally held in the depths of the British winter, and before the rally the team mechanics removed the heat exchangers and pumps from the cars in a quest to save weight and simplify. Cue trouble. Without the coolers the diffs got very hot indeed and that extreme heat weakened the thread locking compound on the crownwheels, causing bolts to loosen, back out and catch on the housing. Spare diffs were carried on the team service cars, but they used them all up. The replacements - of course - failed in the same way.

Aaltonen and Easter managed to nurse their car to a 7th place finish, but Fall/Phillips, Herrmann/Schuller and Bloxham/Salt all retired with differential failures. Seems the diff coolers would have been beneficial after all. 

[HS30-H]

I was told that the advantage of the oil/fuel heat exchanger diff cooler was that - on a rally car - it was not so vulnerable to damage and/or blockage in the way that a traditional air-cooled 'radiator' would be. It gets pretty messy underneath the car in rally conditions.

Nissan's Works team used traditional type coolers on their diffs for circuit racing duties. The parts were available to buy from the Sports/Race Options list and the Nissan Sports 'Yellow Books' gave advice on fitting:

 

[HS30-H]

By the way, compliments of the season to all Works rally Z fans!

 

[kats]

Hi, I looked at magazines in my room and I couldn’t find any clear pictures of the diff oil cooler installed on other Works cars. There is a picture of 1973 Safari Winner car’s fuel filters and pumps, and hand written diagram! 
By the way, I didn’t know the 1973 Safari Winner has extended seat brackets like a Fairlady Z series even that car is LHD. Is it unusual isn’t it? 

Note the steel protector underneath of the diff, the picture is 1971 Safari Winner. It has straight floors, unbelievable for the car won the toughest rally at that time.
 

Kats

 

[xs10shl]

@kats Thanks for the scans.  The steel plate on 8D-433 shades our view of the differential area. Without a clearer photo, it would be hard to tell what is in the cavity between the tank and the differential, where the diff cooler is situated on my car.

As to the extended seat brackets: that detail is also present on my car (pictured).  I don't know if these extensions were also present on LHD Euro delivery s30s, so I can't speak to how uncommon it is.  The rubber mats were carefully altered to accommodate them.

 

 

 

[xs10shl]

Something else caught my eye in @kats photos, namely this dangling 6-point plug (pictured), presumably taped to the steering column of the '73 car.  I'd imagine it's designed to plug into the ignition switch in place of the standard harness, and potentially make the car drivable in "hobble" mode, or at the very least, to bypass some of the wiring in order to debug something engine-related.  I also had one of these in my car, taped in the same location, with a bare-bones collection of stand-alone wires leading to the fuel pumps, and I believe the starter and alternator (and perhaps more - I'll have to reconstruct my notes).  I was fairly certain at the time I removed it that this was something wired up by a prior owner, and not original Works, based on what appeared to me as haphazard wiring.  Seeing this dangling plug in the same spot on the 73 car makes me question my original assessment.  I've often heard "dual wiring harness" being used in descriptions of Works cars, but I always assumed that people were referring to the 2 fuse boxes, and not the presence of a "redundant wiring harness".  More study will be required- any further thoughts?

 

 

Edited December 29, 2022 by xs10shl

[HS30-H]

On 12/25/2022 at 2:49 PM, kats said:

By the way, I didn’t know the 1973 Safari Winner has extended seat brackets like a Fairlady Z series even that car is LHD. Is it unusual isn’t it? 

5 hours ago, xs10shl said:

As to the extended seat brackets: that detail is also present on my car (pictured).  I don't know if these extensions were also present on LHD Euro delivery s30s, so I can't speak to how uncommon it is. 

I can't recall having seen a Works 240Z rally car *without* the Japanese market style extended seat mount brackets. As far as I am aware they all had them. Certainly all the cars that still exist have them.

They would not normally be seen on any Export market cars. This seems to be another built-for-purpose quirk of the Works rally cars.