Monday, 24 September 2012

Blending Fuels – the 1950’s way

I thought this blog post would give an insight to the method used for blending racing fuels in the 1940/50’s. The guidelines for fuel blending come from Jimmie Simpson’s notebook  (Jimmie Simpson Blog post)used when he was competitions manager of Shell-Mex and B.P. Ltd.

The blending process:

1)      Inspect the 50-gln. Barrels to see that they are thoroughly clean and unlined – for this inspection a special inspection lamp is being sent to the depot.

2)      Clean all equipment that is to be used (measures, funnels etc) by washing with spirit or benzol (dependent on the type of fuel being blended).

3)      Calculate the quantity of components required and stack the cans in separate piles near the blending barrels.

4)      Take a sample of each ingredient from the bottom of the packages by using the valinche and test the specific gravity (see table for specific gravities)  

5)      Calculate the specific gravity of the resultant mixture arithmetically (see example)

6)      Calculate the best means of having complete blends in each of the barrels at your disposal (i.e. halve the components and place half in barrel 1 and half in barrel 2, when blending operations commence).

7)      Start blending by filling into the barrels the ingredients having the lowest specific gravity. Then add alcohol and benzol alternatively. These latter components, having a greater gravity will fall to the bottom of the barrels, whilst the lighter spirit will tend to rise, and in so will mix to a certain extent with the other ingredients. As cans are emptied, stack on one side and leave until the blend is completed, mixed and sampled. Any error in the resultant specific gravity can then be checked against the actual components used. When figures are agreed, remove the empty packages and commence canning of the blend.

8)      Use either a 2-gln. or a 5-gln. measure each time to ensure that the correct quantity has been used. (Do not pour straight from the cans, as it is impossible to say whether they contain the exact tow gallons.)

9)      In adding the dye, care should be taken that it is added a little bit at a time, during the actual blending, to ensure complete mixing.

10)   If it is necessary to add Castor Oil to the mixture, then the oil should be mixed thoroughly with part of the Methanol and/or Ethanol, and added to the blend; vigorous stirring should accompany this process. A milky, frothy mixture will result when the Castor Oil is added to the mixture, but this will disappear when the mixture is assed to the bulk blend. The resultant fuel, however, will not have the same crystal clear appearance as a fuel with no oil addition.

11)   If, on the other hand, it is necessary to add a mineral oil to the mixture, e.g. Triple Shell (Heavy), the same process should be carried out, but the oil should be mixed with the benzol or petrol (preferably the benzol) and not to the alcohol.

12)   When the blend is finished, replace the bung and roll the barrels for a short while to ensure that the components are thoroughly mixed – alternatively stir the mixture with a clean, un-painted wooden or metal dip-stick during blending, which will reduce the rolling period required to a minimum.

13)   Replace the barrel on the stollard and by using the valinche take a sample from the bottom of the barrel and check for appearance and take the specific gravity. This latter should be the same as was calculated in (5) by calculation, but if there is a discrepancy check through all the process and make sure that the correct quantities have been added: also check your calculations.

14)   When the gravity is agreed, canning operations may be started (each can should be carefully examined beforehand to see that it is perfectly clean).

15)   When all filling is finished, carefully clean and dry the hydrometers and keep an exact record of the blend made in a special book, together with dates, quantities of ingredients, etc.

16)   If at any time it is necessary to blend a special mixture for anybody, full details are to be kept, together with the person’s name and performance of the fuel in the engine concerned.

Specific Gravities @ 60°F

Methanol                            .796

Ethanol/Benzol                 .820/.825

Ethanol/224                        .783

Ethanol/Shell                     .783

DTD 224                                .736

Shell                                      .736

Benzol                                  .860/.870

T.T. Benzol                          .873

Swan                                     .685

Acetone                               .796

Water                                   1.000

Shell Castor Oil G              .950


Specific Gravity Correction factors per every 1°F are:-

Petroleum Spirit of Specific gravity           .675/.714                             0.0005

do. do.                                                                  .715/.750                             0.00045

do. do.                                                                  .751/.800                             0.0004

Alcohol                                                                 .780/.820                             .0005

Benzol                                                                  .860/.880                             .0006


Spirit of specific gravity .730 @60°F – to calculate its specific gravity @ 50°F :-

Temperature difference = 60-50 = 10°F

Correction factor - .00045 per 1°F

0.000045 x 10 for 10°F = 0.0045

As temperature is lower than 60°F, add factor to specific gravity @ 60°F: .730 + .0045

= .7345 – Specific Gravity at 50°F


Spirit of specific gravity .730 @60°F – to calculate its specific gravity @ 70°F :-

Temperature difference = 70-60 = 10°F

Correction factor - .00045 per 1°F

0.000045 x 10 for 10°F = 0.0045

As temperature is lower than 60°F, subtract factor to specific gravity @ 60°F: .730 - .0045

= .7255 – Specific Gravity at 70°F


Method of calculating specific gravities:-

Note:    For the purposes of these examples gravities are quoted at 60°F. It should be remembered that should the temperature be below 60°F the component will have a higher specific grvity and if above 60°F, the component will have a lower specific gravity.


Specification:                     %                            S.G.

Methanol                            80x                         .796                        63680

Benzol                                  10x                         .862                        8620

Acetone                               10x                         .796                        7360


Specific gravity of resultant mixture is .7966 by calculation


Specification:                     %                            S.G.

Ethanol                                 70x                         .820                        57400

Benzol                                  20x                         .860                        17200

Shell                                      10x                         .736                        7360


Specific gravity of resultant mixture is .8196 by calculation

 BP Racing Ethyl

Specification:                     %                            S.G.

Methanol                            97x                         .796                        77212

Acetone                               3x                           .796                        2388


Specific gravity of resultant mixture is .796 by calculation


Dye addition = ½ pint Master Dye Solution per 100 gallons

=284 ccs. Master Dye Solution per 100 gallons.

=10 fluid ozs. Master Dye solution per 100 gallons.

Dye addition per gallon = 2.84 ccs. Master Dye Solution per 1 gallon – say 3ccs Master Dye Solution per 1 gallon.


  1. This is great stuff! Thanks for sharing the info with us. Did you get Simpon's black book at an auction?

    1. Yes that is correct. I have a few other posts planned around it - fuel blends for specific famous cars, sponsored drivers/riders etc.