Aston Martin DB4/5/6

For many a standard Aston DB is a dream come true, but with selected mods this AM can become magnificent. Here’s the advice from top specialists

Regular readers will know that our Road and Track articles look at various ways to tune and improve a certain model to suit all pockets – but there’s no such thing as a budget mods for Aston Martins!

There again, you need to put modification costs in relation to the car’s value. Perhaps more importantly you need to look at hurting the car’s originality and value, although done right using accepted Aston mods via an established Aston specialist, this should not pose a problem.

BEFORE YOU START

With a straight six engine, hammering out well in excess of a claimed 270bhp already, these old timers can still cut a rug so any improvements have to be put into perspective. It could well be that all your car needs is a thorough service and sorting by a good specialist, before you start considering upping the ante. The majority will be in good shape already but obviously structural rust is the main worry and repairs to its special Superlegga structure is never going to be cheap.

The straight six engine is pretty similar in design to the Jaguar XK engine and it’s not unknown to see some use the 4.2 Jaguar XK lump because it’s a far cheaper alternative to a proper rebuild. It works quite well with similar power outputs but will understandably adversely hurt the car’s value and with DB prices ever on the rise that’s a fact never to be overlooked.

That straight six Aston engine is a gem but horrendously expensive to repair. For instance, fixing up the Weber carbs on Vantage models can see a bill in excess of £1000 to do properly although stuttering or fuel starvation under load is normally due to the SU pump packing up.

The engine relies on replaceable iron piston liners and can become slugged up (Aston advised at the time regular doses of Barsleaks!) especially the rearmost cylinders which leads to overheating.

A total rebuild can run to a cool £25,000+ while even a simple pep up decoke with new valves and guides costs something like six grand! Oil pressure is meant to be high – 89-90lbft @3000 rpm as it contains something like 23 pints of good old 20W/50 which Aston recommended should be changed every 2500 miles – Valvoline 20W/50 seems a popular lube, against modern synthetics.

Perhaps just a super service and a set up on a rolling road (see Hotting Up) will satisfy you. However, a superior radiator coupled to an electric fan conversion are worthy mods as are a higher output starter motor and alternator. Aston specialists favour the 123 Distributor electronic ignition, incidentally.

HOTTING UP

On the one hand, Aston tuning is an extremely expensive business but on the other, if upgrades become part of a general overhaul then the extra costs are fairly moderate in relation to the car’s value.

For example, if the pistons and liners require replacing, leading Aston specialist Rikki Cann invariably fits the 4.2-litre upgrades as a matter of course because the costs are broadly similar at around £15,000 and it makes for a nicer lustier engine plus is undetectable. The Aston Workshop says the 4.2 (which was the capacity Aston used to race with) can actually work out cheaper than if an owner wanted to keep the same engine size!

Similarly during a decoke, Cann can fit larger, superior Vantage valves for a bit more pep and at minimal cost.

A 4.2 with the mild head mods will see some 300bhp. That may sound slightly unimpressive – given that a 4.0 hammered out 282bhp from the factory – but, unlike Aston’s optimistic power output claims, these are genuine horses. Further power can be gained from Aston’s still worthy Vantage spec C-Type cams; this state of tune is ideal for the road and track day stuff.

For racing, the engine can yield some 450bhp if further enlarged to 4.7 and as large as 5.3-litres but this is mega dear as the crank and rods need changing.

Apart from the C-Type cams, a variety of aftermarket alternatives are available. One aspect of fitting racier cams will be an increase in tappet noise, however. The Aston Workshop offers two states of tune, Fast Road and High Lift. The former is said to retain the flexibility and smoothness of the standard engine, but provide a general improvement in mid and top range torque. These suit best those who want a more lively car, but do not wish to reduce flexibility in traffic, says the specialist. High Lift – best suited to use with the DB5 and DB6 Vantage with triple Webers – provide “a very noticeable and consistent increase in engine torque of the region of 25 percent or so over the standard spec”. The downsides to consider is slightly lumpy idle and some loss of flexibility below 2000 rpm, it admits.

Of course, the most logical ‘budget’ step is to bring a standard engine up to triple carb Vantage tune, especially if you can get hold of old parts but Cann says don’t instantly junk the SUs (twin set up on 3.7, triple thereafter) as with some mods and re-jetting with a set up on a rolling road can see power outputs not far short of Vantage tune and of course are inherently easier to keep in tune.

The Aston Workshop agrees and says it runs a DB4 racer still on SU HD8s. Later, with the introduction of the 4-litre DB5, the triple SU HD8s became the default choice with the Vantage tune standardising with triple twin choke Weber DCO-Es.

Fuel injection can be used and for those who like the original look, The Aston Workshop is finalising what it calls ‘invisible fuel injection’ where the gubbins are neatly concealed with the stock looking SU carb bodies. Better performance, economy, emissions are claimed along with easier starting.

Tim Butcher of Surrey-based Trinity Engineering is more the traditionalist and prefers using existing designs rather than going all modern for the sake of it and advises a lightly modified 4.2 engine using DB6 Vantage cams.

HANDLING THE POWER

Your wallet’s in for an easier time when it comes to running gear upgrades and we can even use the term ‘budget’ in certain areas, albeit loosely!

The Aston’s chassis is a bit like a curate’s egg. On the one hand, it stuck with old fashioned lever arm damping although DBs also featured adjustable stiffness at the rear.

Most owners will have been pragmatic and probably by now ditched the quirky Armstrong Selecatride set up for modern Konis or similar although Harvey Bailey is said to make a modern alternative but it costs some £1500.

You can go a stage further and swap the lever arm units for a telescopic conversion (like the MGB) but that’s mostly for track work and competition. All DBs are heavy cars, so it’s likely that the original springs will have weakened by now. So if replacements are needed, then it’s a good time to switch to uprated alternatives although lowering the car further isn’t widely recommended for road use.

But watch it when considering replacing the cluster of insulating bushes with harder ‘poly’ alternatives, which are available in road touring firmness or even harder track types because they transmit more road noise and harshness. Rikki Cann only recommends ‘poly’ bushing the anti-roll bar and using standard or nylon types (which he makes in-house) elsewhere. Complete tailored handling kits are available from most AM specialists, such as Cann and Astonparts.com, costing over £1000 comprising of better springs and a stouter front anti-roll bar.

In their day the meaty all round disc brakes were rated as brilliant so are okay for normal classic driving if serviced right. That said, an upgrade to better discs and pads is a good idea – perhaps parts taken from the later DBS V8 if you’ve an eye on originality or you can opt for a superior kit made by AP specially for the car but with fitting it’s going to cost around a cool £3000.

It’s not really necessary says Cann and Butcher if the brakes are in good order although both advise fitting EBC Green Stuff pads which they rate highly. One ‘mod’ Cann always carries out during a service is to replace the standard brake fluid with Castrol SRF; it costs a whopping £45 a litre but it is the business.

For the DB4, Trinity Engineering of Surrey offers improved brake calipers with larger brake discs to replace the original Dunlop pistons. For the DB5 and DB6, the factory brake servo upgrade replacing the original units along with the new spec master cylinder is superb says Trinity and yet it’s not too dear either; the AP master cylinder kit about £600 with the new servo costing some £1200.

Still from Trinity are steering revamps. Power steering was fitted from the DB6 onwards and standard on the MkII.

Tim Butcher specialises in fitting the electric EPAC system to earlier cars which he describes as “the best on the planet”and even worth replacing the conventional PAS set up with because it’s that much better.

Apart from the DB4 which featured overdrive, five-speed transmissions (or automatic) were fitted. It depends what you’re after; the four-speed plus overdrive is quite okay but it can be converted to five-speed (either with an Aston ZF or modern alternative) easily enough.

If that’s not enough gears for you, specialists can now offer a six-speeder care of BMW, although owners are advised to also consider changing the final drive ratio at the same time. If you find the lorry-like clutch too heavy there’s a modern diaphragm clutch assembly which lightens the load appreciably.

Automatic Astons aren’t generally liked because it’s an antiquated three-speed design that saps performance and enjoyment. However, while converting to manual is popular and adds value, if you still want self shifting, fear not as upgrades are available for this too, such as The Aston Workshop’s four or even five-speed auto conversions.

Tyres?  Some still run on the original spec crossplies but that’s for die-hards. Tim Butcher recommends Avon CR28 for the DB5 and DB6, say 185 section size and 205 for the flared arched DB6 MKII.

HOTTING YOUR CAR UP

BUDGET

• Thorough service
• Electronic ignition
• Uprated radiator
• Rolling road tune up
• Re-jetted SU carbs

FULL THROTTLE

• Engine enlargement (4.2)
• Vantage head valves
• Uprated/Vantage cams
• Vantage Weber carbs
• Fuel injection/mapping

HANDLING THE POWER

BUDGET

• Polybushing where required
• Uprated dampers
• Sports suspension springs
• EBC Green Stuff brake pads

FULL THROTTLE

• Tailored suspension package
• Electric power steering