Bristol Dx6a and DXH6a differences

[flyinghorse1]

Does anyone know the key differences between these two distributors.
I know the DX6a is for a 400, but Bristol used the DXH6a on the later 100 series engines.
It’s the advance curve similarities I’m actually interested in as I’m working on a 100 d series engine that for some reason has the DX6A fitted.
Regards,
Graham

[Geoff Dowdle]

Graham,
The only difference is that the DXH6a has horizontal outlets in the cap for the spark plug leads , compared to vertical in the DX6a .
Both are very basic distributors . My experience over 50 plus years that even a new Lucas distributor is only good to about 3500- 4000 rpm , much over that they become erratic , probably due to points bounce .
I would not consider the original ignition advance curve ,as today's fuels, higher compressions of most Bristol engines today, often different valve timing etc etc , the large total advance of the 50's is not needed today.
I do not and will not run a Lucas distributor in either of my Bristols , especially if it was a D2 engine

What D2 engine are you working on ??
I have new horizontal outlet distributor caps if you need one .

Geoff
Sydney/Australia

[JoeF]

The key difference is the cap. The "H" denotes horizontal ( side entry ) exit holes for the HT leads. DXH6A was used for Bristol-engined AC Ace and Acecas. The cap part number is 407279. The DXH6A distributor part number for the AC cars is 40551 , which will be on the distributor body, as should be "WG-16". The part numbers determine the advance - in this case it is ECM curve 641 using spring set 424216. This is different from the other 2 litre distributors, but I don't know the actual curve, sorry. The Distributor Doctor should be able to supply the springs if you need new ones.