Lotus Elan

Diff Oil Cooler FIA

PostPost by: Vali » Fri Jun 25, 2021 12:23 pm

Do you know if a differential oil cooler is allowed for a Elan GTS?
Do not see any info about such oil cooler for the Elan in the No. 127 FIA papers but Lotus did delivered a few 26Rs with diff coolers and a Bendix pump like I found in the search here.
In the FIA rules Period F any oil coolers in the transmission (gearbox and differential) are not allowed as far as I know.
I´m planning to use the car for longer or endurance races.
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PostPost by: 661 » Fri Jun 25, 2021 2:52 pm

I don't know specifically but have trawled the regs for my car and never saw anything to suggest they were allowable.I didn't consider fitting one.
It might be worth seeking Vaughan's thoughts as I think his car has one (26R S2), and it may have had it in period.
My understanding is that scoops on the underside of the body may be frowned upon. I have seen endurance cars with a side scoop on either side and two ducts to the diff.
I only use one side scoop, My races are up to an hour, with a 4.4 diff. I don't have any temp data. I use the TTR recommended oil .
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PostPost by: vstibbard » Fri Jun 25, 2021 9:28 pm

Hi,

My S2 26R #40 was purchased to do 12 hour events here in Australia, it was delivered from factory with differential cooler and pump, the cooler is located under the spare wheel area with pump along side the fuel tank. The parts and manual for S2 26R references this option including the wiring.

These pictures are as the car was found, it had an accident in 1970 and was put way in damaged state untouched until 1990's. In top right photo you can see the oil pump along side the fuel tank with oil lines out of it and bottom left of same picture. Bottom right picture shows location of the oil cooler looking towards from of the car.

26-S2-40 as found after Ann Thompson accident #7.jpg and
Ref top right and bottom left pictures


Cheers

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PostPost by: Frogelan » Sat Jun 26, 2021 5:59 pm

Thank you Vaughan

You mention a "S2 26R manual". I have seen the S1 version, is this consultable somewhere ?

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PostPost by: vstibbard » Sun Jun 27, 2021 8:14 am

HI Andrew, the S2 version can be found on Golden Gate Lotus club site when last i looked.

Cheers

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PostPost by: Andy8421 » Sun Jun 27, 2021 11:27 am

Vaughan,

The lower right picture appears to show half a roller spline - used to avoid spline lockup under load. I was aware that Chapman used roller splines on his racing cars, this is the first time I have seen one on an Elan.

Do you know if this was fitted at the factory?
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PostPost by: Vali » Sun Jun 27, 2021 11:43 am

Thanks guys for your responses.


@Vaughan:
At GGLotus I did not find a manual. Only handling and maintenance notes.

But now I have found in the wiki here the parts list for the 26R "Section K" Diff Cooling:
https://lotuselan.net/w/images/5/57/26r_parts12.pdf
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PostPost by: 661 » Sun Jun 27, 2021 10:26 pm

There seems to be compelling evidence that a diff cooler is a period item, now you just have to deal with the HTP assessors.......good luck.
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PostPost by: vstibbard » Mon Jun 28, 2021 10:04 am

The roller spine rear drive shafts were fitted to S2 26R's as standard, from memory they may even have been introduced during the S1 26R run, they were certainly being used on S1 26Rs in period.

The oil cooler and pump were options from factory which also included an alloy long range fuel tank and optional standard fuel tank, both of which were on my car from the factory. The FIA papers I have copies of list all but the oil cooler and pump.

I have seen an S2 26R Factory Parts List, this is by exception and addresses the differences to a standard Elan. It clearly included a section on oil cooler and Bendix pump and pipe lengths, union sizes and how to wire it up!

Others referenced include a wide range of diff's including a 3.44 (FIA papers)!! Must've been homologated for a 24 hr speed record or maybe a Le Mans fuel efficiency objective!. I've driven mine with a 3.9 and 550x13 CR65's, certainly would have been difficult to pull max rev's and would have reduced number gear changes per lap, turtle and the hare comes to mind, with the elan a turtle!

Cheers

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PostPost by: Frogelan » Mon Jun 28, 2021 10:27 am

Gentlemen,

Thank you Vaughan for your post!

For my fellow "anoraks", could you supply any close up photos of the Bendix 476090 pump please? Is it the same as this one:
http://www.2040-parts.com/-vintage-bend ... n-i540432/

I was surprised to see 1/2" unions where I might have expected 3/8".

I have some practical suggestions to make to this hot subject...

Firstly, the weather for summer endurance events can be warm. The 2018 LM Classic was held when air temperatures were at about 36°C in the shade (probably 50-60° at the track surface). In 2019 the Spa 3H (not reputed for "outback" weather) in 2019 was just 2° cooler.

It would have been very interesting to know the temperatures reached by diffs in these conditions and to compare these to the recommendations of the oil and manufacturers of CW &P. My guess is that temperatures were off the chart and increased mechanical wear occurred.

Secondly, most of the fellows in E-types now have air-conditioned sous-vêtements and helmets. Is this really within the spirit of historic racing? [ I would suggest that driver comfort = health & safety and in certain conditions A/C should be authorised or the perhaps organisers should run the races at dawn]

Lastly, there are the physical appearance issues.

(a) I have seen no trace of "TTR" side scoops being "homologated", but there is photographic evidence of use in period. The elegant OEM S2/S3 underside scoops and opening in the boot N° plate panel also fall into the same category.
(b) Lotus listed the diff cooling and dry sumps in period (in 1964) but this were apparently not homologated pre-31/12/1965.
(c) I have sketchy notions of the classes of the period but perhaps some Lotus elements on the parts list were "GTS" and others were in a "GTP" class ?

For example...The GT40 and 250LM were not "homologated" until Feb 1966...Perhaps if a scrutineer refuses a diff oil cooler on an Elan he will also be refusing these motor cars at the same time?

Many thanks to all!

Andrew
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PostPost by: 661 » Mon Jun 28, 2021 11:40 am

I may be wrong, ,but , I seem to recall Dave Hughes saying the plan for an underbody scoop on his new shell was scraped, and I can't recall if this was related to HTP issues???? Perhaps Dave could let us know.
I see no reason to use a vintage Bendix pump when proper modern oil pumps are available ( we use modern fuel pumps after all). I used a bronze cogged affair for the Exige gearbox cooler
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PostPost by: Frogelan » Mon Jun 28, 2021 11:48 am

The S2 / S3 scoop was originally a post body moulding attachment (rivets?). They are almost designed to come off on contact to avoid more extensive damage!

These are available from various suppliers.

Without fins on the diff Cf Autodelta etc) I'm not convinced by the scoops.

The point about the Bendix pump is that I believe that it is indisguishable from the Facet but I'm hoping that Jerry or Vaughan can confirm this.

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PostPost by: rgh0 » Mon Jun 28, 2021 11:52 am

I suspect with modern polyolester gear oils, e.g. Redline 75W-90, that a diff cooler is probably not required even in historic endurance racing. Perhaps with the magnesium housings it may give you a problem through thermal expansion and bearings loosening at the temperatures these oils will tolerate and you need the diff cooler to keep the casing not the oil cool !!

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PostPost by: vstibbard » Mon Jun 28, 2021 2:12 pm

Thanks, for finding the parts list, I knew I'd seen it written, thought it was in the manual see section titled "Rear Axle" which is in the attached PDF.

26Rspecs_1965-66.pdf
(101.74 KiB) Downloaded 32 times


Between this and the parts list excerpt you have the details, essentially its a Facet / Bendix with 1/2Inch unions.

Cheers

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PostPost by: Vali » Mon Jun 28, 2021 2:24 pm

@Rohan:
What maximum temperatures would you want to have your gear oil?

In my experience the transmission/differential really really gets hot.
From my 10 years experience with tracking a Lotus Elise (gearbox and differential in one housing) I can tell that on track the gear oil rises up very very fast to 130 degrees Celsius after 15-20min driving and I always backed off to cool down again as I was told not to get it above 140 degrees Celsius because the gears and rings would become very weak and could break/loose their teeths. The Toyota gearbox is very fragile on 3./4. gear ... Shortly after the first experiences with measuring the oil temperatures I had an transmission oil cooler fitted with switch point on 95 degrees and never got above 120 degrees after. I think Graeme had the same transmission cooler like me on his Exige.
On road driving oil temperatures were only between 80-90 degrees so no cooler needed.

Of course I don´t know how it is/will be in the Elan but I would think it´s not much cooler?
And if the won´t get that hot the housing won´t too.


@Vaughan:
When did your car had been built and had the first race been pre ´66?
I will ask my assessor. He might say yes but I suspect the FIA would still reject the registration with diff cooler like with dry sumped engines.
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