AC or Bristol?

[rsk289]

Could someone enlighten me as to the various pros and cons of AC and Bristol engines?  As in earlier post, I'm thinking about an Aceca.  What are the reliability and driveability elements of the two - and parts availability, prices, etc.  Did the Aceca always have the Moss box, with either engine?  I'm getting the impression that the 100 D2 motor might have the capacity to make my XK's engine look cheap...
Thanks,
Roger

[James Eastwood]

Have a look for the 'Original AC Ace and Cobra' book by Rinsey Mills. ISBN 1-870979-14-1. The book includes a guide to the Ace powertrains. Cost wise, yes I think the Bristol is very expensive as are the parts, there are occasional Bristol engines on eBay, but in need of a complete rebuild and not of 100D2 spec.

I haven't ever drive one, but as I Ford employee, I'll put a mention in of the Ford 2.6L 'Zephyr Six' engine, these were bored in period to 2.8  and are mush less expensive. I did see a freshly built Zephyr engine on Race Cars Direct which with a 12 port Mays head, but without carbs or manifolds was about the same as a Bristol needing complete rebuild on eBay. So in my mind it's a very cost effective period engine, that could perhaps be a 2nd engine if you bought an Aceca with the AC engine.

Regards James

[rsk289]

Thanks James, very helpful.  I do have Rinsey Mills' book and have read it thoroughly several times over the years, but you can't beat actual owner feedback.  I like the Ford suggestion, that engine is much more 'my era'.  Would you happen to know anything about engine mounts?  Presumably anything Aceca will translate to Ace, but I assume engine mounting brackets for the AC and Ford engines are quite different animals.  Purely guesswork on my part, though.

[AC Ace Bristol]

.
I haven't been down this path.  Not a straight forward swap...........

Engine mounts would be different,
The exhaust system is on the opposite side, which would need addressing,
wiring of dynamo, starter etc could be different  so major workon the wirning loom,   
Change the Propshaft, 
Then getting towards the rear end The fuel tank would also need attention as the exhaust would be on the opposite side.

Just a few pointers,  Hopefully one or two who have been down this avenue can give guidance before you commit.

Keith

[B.P.Bird]

Roger,
The Weller designed A.C. Six is an elegant engineering solution which could be built from very ordinary materials. The BMW designed six is a quick fix to allow inclined valves to be fitted to a conventional pushrod engine. The very highest quality aero engine materials went in to its Bristol production which is why it works so well.
Both designs are long stroke and high RPM will shorten life. In this respect the A.C. has the longer stroke and the lower RPM limit. On the other hand the A.C. produces a wider range of torque.
Quoted power outputs need to be looked at with care: A.C. in particular had an archaic and possibly under reading engine test bed. The figures published do not seem to be born out by performance on road and track.
Finally Weller laid out his engine design ideas in the later stages of The Great War. The BMW quick fix was carried out two decades later on the threshold of The Second.
Modern technology has been applied to both designs and there are great increases of power available in each case.
As an aside the BMW six philosophy reminds me of the MGA Twin Cam. In both cases a conventional block and bottom end were furnished with new cylinder head arrangements to increase power. The BMW was successful in its aim of a limited competition advantage in the 328. The MG had to deal with exposure to the ordinary motorist in which challenge it was not successful, albeit the problems were subsequently remedied.
As to current choices: First matching numbers cars. Second correct engine for the chassis. Third and a distant third at that, incorrect engine for the chassis.
I won't be here to see it, but all those AE cars will one day be correctly returned to their A.C. straight six and various Bristol, Ford Zephyr and Ford V8 and other odd engines will be removed. Why ? Simply market forces, originality is already at a premium
Barrie

[rsk289]

Thanks Barrie, that's rather where I was going in the decision-making process.  I'm halfway through a full restoration of a '55 140DHC, and was very careful to buy a matching-numbers car with sound provenance - and won't be putting a 5-speed in it any time soon.  Actually, I won't be doing very much in it all for a while as I've just sectioned the body which is now at the blasters:  which brings me to the next question.  I do as much as I can myself, bar paintwork (and XK drophead hoods), and would plan to continue this with an Aceca as far as possible.  I'm familiar with transverse leaves etc., having built a super-accurate Cobra replica.  I don't imagine there's anything technically in an Aceca that's more of a challenge, but what about parts availability for the DIY-er?  I don't think Halfords will have a late-AC engine water pump on the shelf.

[Robin A Woolmer]

Parts for the AC Weller engine are available , engine performance has been improved considerably also, so supporting the cars into the future is not a major problem.

Robin

[rsk289]

Thanks Robin.  From what I've read, the CLBN WT engine gets close to the standard Bristol output in bare numbers.  I have a few minor concerns, such as not being able to remove a piston without the liner, but I guess if you're removing pistons the chances are that the bores will be needing attention too, possibly.  It's general parts availability, ball joints, dampers, bushes etc. that I was thinking about but I guess that would all apply to Aces anyway.  I'm not aware of any big difference in service items, but am willing to be corrected.

[Robin A Woolmer]

Brian Eacott can supply most maintenance wear parts including suspension bushings & special bolts etc, more major parts such as wishbones & uprights can be sourced from various specialists , the rear uprights have been a problem sourcing but there is a guy in USA that has tooling & can supply!
In terms of engine performance the AC Weller engine is limited in RPM terms but as has been indicated the Weller engine cars does have good basic torque so can be good on bends etc., New Weller engines can however achieve high RPM removing the straight line speed constraint!
There are some good intermediate parts available that can offer improvements though to the original AC engines, one fundamental is however to fit a viscous crankshaft damper where possible, there is a specialist who can offer a suitable solution!

Robin