401 Tune Up

[Geoff Dowdle]

Ralph M ,
Thanks for your interesting post .

I dyno tuned my 400 on a rolling road about 15 years ago with similar results .
It's engine at the time was 85A block/crank/rods , 8.5 pistons , 403 cam , 100 head , 34ICH Weber carburettors and Mallory twin point (adjustable) distributor .
It achieved 71bhp at 4600rpm (at the rear wheels) . The operator thought it would be around 95 -100bhp at the flywheel. He was amazed by how much ignition advance was needed to achieve maximum bhp at various revs through the range . From memory the advance curve was
Idle/Static 12BTDC
3000rpm 36
5000rpm 45 or 47

Could you please advise the advance curve that your engine is now set on .

Distributors on a Bristol engine need to be properly earthed.
If one has the advance/retard mechanism operational it is best that the distributor body has an earth lead to the engine, as a smear of oil can give a bad earth . I have found that once the distributor advance is set, the distributor should be locked into position giving a positive earth as it is then not necessary to be adjusted.

Do you know what advance curve was used in the 123 distributor.

Thanks
Geoff