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Q: - I run an Aston Martin automatic V8, and with fuel costs and the current lazy performance that comes with the present 3 speed box, it would be a considerable advantage to be able to replace it with a more modern 4 or 5 speed auto, and in doing so, reduce the fuel consumption and improve range and performance. What are the realistic options?
Ans: - As the question implies, gearbox design has come on leaps and bounds since the mid 60's and 70's. In those days the only auto's available used 3 speed autos, all adapted from those used by many mainstream US made cars. They have given good service; there are many of them around, but they are heavy, power sapping and inherently lazy in response. In contrast, modern gearboxes, often with up to 6 speeds have lock-up clutches, are much more efficient and permit a much improved optimisation of gearing to aid performance with marked improvement in fuel consumption. A ZF 4-speed gearbox, as used by BMW in their 7 series cars of the mid 80's, have been adapted for use with the DB4, 5 and 6 and with the DBS 6 cylinder models. They provide a significant improvement over the old Borg Warner 35. They do offer a significant advantage in the cruise and around town, though present autos now around do better.
The question asks, what are the realistic options for the V8 owner and in principle, there are several that could be suggested. All have their good and bad points and to an extent, it therefore depends on what the owner really wants to achieve and how much to spend. In summary the key options available are in order of cost and complexity:
• Change the final drive gearing to give more speed for a given engine speed as a means of improving fuel economy - has the advantages of simplicity and minimal cost but at the considerable disadvantage of performance and flexibility. Unless you just want improved economy in the cruise, maybe be a viable option, but performance will suffer significantly and around town and in traffic, economy will actually suffer as the car spends more time in an intermediate gear.
• Fit a 4 speed with an overdrive 4th gear - now a realistic option for the V8 owner. This upgrade gives improved responsiveness and flexibility and is a practical way forward. Still not as good an option for town use or in hilly country as a more modern 5 speed option, but a good compromise and is all round a marked advantage over the current 3 speed. Can be offered at a price comparable to a full gearbox overhaul. Available now and can be recommended.
• Fit a 5 speed gearbox - brings increased complexity and there will be a cost in adaptation of a suitable auto for the V8, but it removes a number of compromises that come with the 4 speed auto. Invariably, the 5 speed autos are computer governed and are designed to integrate with an engine management system. However, Aston V8s, at least until the Virage was introduced, have been carburettor fuelled or used a hydraulically governed fuel injection system. Even the Virage uses an analogue type of fuel management system, and this offers little possibility of integration. Having now solved the integration problem, we expect to be able to offer a 5 speed ZF auto gearbox for use in V8s and the DB4,5 and 6 range before the end of this year. This offers no compromises in flexibility, will give much improved responsiveness and marked improvement in economy. It will be a little more expensive than the 4 speed auto, and depending on type of use, may be even better optimised with a minor change to the final drive ratio. Probably the best long term option for the V8 owner. It will be available soon.
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