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KKR 01-03-18 12:44 AM

1954 Arnolt Bristol Gear Ratios
I am looking for the proper gear ratios for an Arnolt Bristol BWCR11 404 with overdrive. Any gurus out here who might be able to help?


412usa 02-03-18 06:01 PM


The BWCR 11 is not an Arnolt gearbox but a gearbox used in the 405. The Arnolt gearbox is a BWCR 9 and does not have overdrive. The ratio of the Arnolt Bristol final drive is 3.9 and the 405 4.22 and the ratios of the gear box are matched to those. Unless you have changed the ratio of the Arnolt back axle your overdrive ratio is going to be very high.

Geoff Dowdle 03-03-18 01:40 AM

Bob ,
as 412USA mentioned the BWCR11 was originally fitted to a 405 ,
it has a low first gear with freewheel incorporated , overdrive of 28% and remote shift lever.

Comparing the ratios to Arnolt BW CR9 is as follows

4th & OD .72 /
4th Gear 1.0 / 1.0
3rd 1.292 / 1.292
2nd 1.824 / 1.824
1st 3.611 (freewheel) / 2.918

To fit the CR11 box into an Arnolt with the overdrive attached you would have to cut the gearbox cross member out and fabricate and strengthen a gearbox mount further back in the chassis.

The 3.611 first gear is way too low for a relatively light Arnolt with a sports engine and there is a significant gap to 3rd.

Additionally with a 28% overdrive using the standard 3.9 to 1 diff the gearing in 4th overdrive would be too high for the characteristics of the engine .

If you dont have a CR9 gearbox available you could do one of the following .

1. To the CR11 ,fit a 2.918 first gear & layshaft , remove the overdrive & fit a non overdrive rear casting and shaft . This would give you the equivalent to a CR9 with remote shift . (Arnolt converted a number of CR9 to remote shift.)

2. to the CR11 fit a 2.918 gear set retain the overdrive , modify the chassis , transmission tunnel and propshaft to suit .The Speedo would also need re calibrating . All of this is not a simple procedure.
Then fit a 4.22 Crown Wheel and pinion from a wrecked 405 if you can find one

3. Try to locate a CR9 box and sell the CR11 to fund it or use it to swap .

Where are you located??
I have a few gearbox spare that I might be able to help you with


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