4 replies to this topic

[carvad]

For the moment I'm writing the detailed article about 1938 Alfa Romeo 8C 2900B MM Le Mans.

 

I've read the latest edition of the Simon Moore's Immortal 2.9 but some details are still unclear. Would love to clarify these points and I'll grateful for opinions from local experts. So, the questions.

 

 

Technical questions:

 

 

1. Weight of the 2900 LM

 

The information about the weight of the car is almost unclear. I asked Maurizio Monti (former chief mechanic of Museo Storico Alfa Romeo) to check the customs documents, because the car regularly participates in AR Museum historical activities. But he responded that they don’t put the weight of the car in documents. Moreover, they never weighted the car. Probably this information possible to find in the conclusion of the aerodynamic researches of the car, made by Alfa Romeo in Pininfarina wind tunnel.

 

 

2.  What was the final drive ratio for 1938 Le Mans coupe?

 

In the Moore's Immortal 2.9 book the final ratio showed as 12/50 for the 1938 Le Mans race. After brief calculations estimated maximum speed of the car with 12/50 ratio, 6.00-19 rear tires and 0.887 4th gear ratio at 5500 rpm is equal to 137 mph, and at 5700 rpm – 142 mph. To reach the speed 150 mph the final ratio had to be 13/50. Only under this condition maximum speed of the car could be 149 mph at 5500 rpm.

 

 

Questions about car history

 

 

1. What was the original 2900 MM Spider serial number, before it was rebuilt to 2900 LM?

 

2. Who was the owner of the car between June-October 1946?

 

By reading the book the owner for that period is still unclear. May be it’s just my misunderstanding?

 

3. Was Franco Venturi the owner of the car?

 

By the link, provided by RIAR you can find the pictures of Franco Venturi in front of the 2900 LM. I know it’s not evidence of the ownership, but probably it helps to find the truth. Additionally it’s still unclear in what race the car got the damages.

 

http://blogriar.blog...-8c-2900-b.html

 

4. The date of 1947 Vermicino - Rocca di Papa. In the book is written 16 November of 1947, but the date of the race was 7 November of 1947 not 16 November.

 

During research I looked for the information about the race, but Italian newspapers had not information about the race the held on 16 of November. I could find the reports in Corrierre dello Sport of 6, 8 and 10 November of 1947

 

http://dlib.coninet....der.php?&f=6950

 

http://dlib.coninet....der.php?&f=6952

 

http://dlib.coninet....der.php?&f=6953

 

 5.  When Lurani and Cuppelini bought the car?

 

In the book Simon Moor mentioned March of 1968. However the advertisement about the 2900 LM was published in Motor Sport Magazine in December of 1967 (please, see the link below). The car at the picture looks restored, it means Giovannino Lurani and Corrado Cuppelini already had spent several months for the restoration. I think it may be just misprint for the 1968 in the book .

 

http://media.motorsp...967/full/82.jpg

 

6. When the Lord Doune became the owner of the 412033?

 

It’s still unclear what year Lord Doune bought the car.

 

[D-Type]

I once read that when calculating speed from RPM, final drive ratio and tyre size, you have to allow for the tyres 'growing' from centrifugal force.  This may explain the discrepancy.

[Joe Bosworth]

D'

 

You are correct that tyres grow with cenrifugal force and you are also correct that you must take into account the tyre rolling radius/diameter when calculating RPM/speeds.

 

However from reading the above the discrepancy is 149 mph at 5500 rpm versus 137 mph at 5700 rpm.  For these numbers to occur that the tyres would have needed to grow 12.7%.  This would result in the 600 by 19 becoming the equivalent size to 800 by 19s.

 

Now none of us are experts on 1938 era tryes but that much growth is quite out of the question.  A 3% growth possible; 12.7%, quite out of the realm of possibilties.  There has to be better answer to the quoted discrpancy.

 

Regards

[D-Type]

How accurate were 1938 rev counters?

[Joe Bosworth]

It is clearly impossible to vouch for the accuracy of any tacho decades after the event.  However, I have 1950s experience with several 1930s tachos and can vouch for their accuracy includng one fitted on in 1934 Le mans Aston.  Besides, tacho error can hardly explain the discrepancy raised by Cavard in post one.  The tach would have to be 700 rpm in error to be the cause.  Hardly likely on an ex-Le Mans car which with that kind of error would likely have either resulted in a  blow up or being badly off the pace.  The techntians of the day were far  better than that.

 

I have checked Carvac's calculations with my own programme and his RPM/MPH/gear ratio calculations are spot on assuming a 1.0 tyre aspect ratio.  I do know the source of his data nor do I know of the Alfa's race history other than Le Mans.  But I can offer a more likely expnantion from my own experience.

 

I once owned the 1955 Lotus raced by Chapman at Le Mans in 1955.  The car was leading the Index of Performance class when the French found an excuse to disqualify it.  The car went on to race every major English race in 1955 before going to Doc Wylie and then myself shortly after.  I inherited the entire Le mans kit.  Included therein were four gear sets from 3.87 to 4.55 to 1.  I can well believe that the 3.87 gears were in the dif for the long race.

 

The Lotus went on to race widely in the US and Oz.  In the US it ran at Watkins Glen to Sebring to Road America and most places in between.  In Oz it ran primarily at Warwick Farm and Oran Park while setting an U2L lap record at the latter.  No where at any of these were the longer gear set used.  The 4.22 and 4.55 were the most prevalently used.  If I had taken it to Bathurst I would have used either the 4.11 or 4.22.  The longest ratio was most unsuitable for competition other than at Le mans.

 

So It is quite in the realm of my experience that the Alfa ran a 13/50 at Le Mans and ran a 12/50 most elsewhere and the ratio change was un-recorded.   It is also possible that the Alfa never reached 149 mph.  My far more streamlined Lotus would not exceed 132.

 

Regards