[Max Tone]

Does anybody have info on Bristol's experiments using 3990 cc AS Star Sapphire engine in prototype 407s? BOC website estimates four such engines supplied to Bristol, one of which was tried in the "240 project mule", but found to be too heavy.

I'm also looking for info on said 240 project; might this have been the 'Bullet' that spawned Blenheim Speedster?

These were not the only 'special' uses of the AS lump; Frazer-Nash ordered two out of eight high-performance engines built by AS using earlier 3435 cc Sapphire 346 engine for their 550F Le Mans prototype, entered 1953/4, but not apparently run.

One is said to have had a special alloy head & triple Webers, producing c. 230 bhp, but ran its mains in testing, the other (still in 550F), has iron head & triple single-choke sidedraughts, said to produce 180-190 bhp. Standard 3.4 got 125 bhp with single carb, 150 with twins.

Another alloy headed example was fitted in the "Sphinx Allard", successfully campaigned by Tommy Sopwith.

These were advanced efficient hemi-headed short stroke lumps (97 x 90 for Star, 90 x 90 for 346), but block strenghthening for Star made it very heavy.

AS did, however, develop a lighter short-block version of the engine at 82.55 x 82.55 for 2651cc and 87.3 x 82.55 for 2965 cc, fitted in Series Humber Super-Snipes & Imperials.

Unlike Sapphire & Bristol lumps which are like hens teeth, this smaller AS Hemi is fairly readily available worldwide, long-lived, easily tuneable & CHEAP. I saw an engine (with plugs out!) & box sell on fleabay for £2.50, & rebuilt twin-carb 3-litre lump sell for £250, complete with the car!

With about six known examples of 'official' use of AS engine in place of usual Bristol lump, there is surely an opportunity to experiment further in the hope of finding a historically acceptable replacement for engine-less basket case 400-406 cars or even bare rolling chassis, that might otherwise be broken up or scrapped, not to mention saving such advanced engines from being weighed in with rotten Snipes.

Comments & any info on Bristol's experiments, state of tune of Star engine, comparative weights of the lumps they tried, inc. W.O Bentley Lagonda twin-cam, two of which I gather were fitted in Bristols, will be most welcome.

Happy New Year,

Rob