All Aston Martin DB4 GT and DB4 GT Zagatos were equipped with an advanced 3.7-litre in-line six-cylinder engine designed by the legendary Tadek Marek. Compared with a standard DB4, these engines benefitted from enhanced intake breathing, a higher 9.7:1 compression ratio, modified camshafts and a twin-plug cylinder-head design. Performance rose from an already very healthy 302bhp to a claimed 314bhp.
The design targeted high performance with the longevity to endure racing for 24 hours at Le Mans. It is to this motorsport-developed specification that Aston Workshop DB4 GT Zagato engines are engineered and also improved.
If desired, Aston Workshop can comprehensively rebuild the donor DB4 engine. However, we recommend starting with a new Aston Workshop engine block to provide the strongest and most reliable foundations to safely accommodate a higher level of tuning and increased capacity.
The bottom-end benefits from forged Cosworth pistons, forged con-rods and a specially balanced seven-bearing forged steel crankshaft engineered to Aston Workshop’s bespoke specification. Extend this engine beyond 6000rpm and you’ll notice the pronounced gain in refinement compared with original engines courtesy of the new crankshaft, which also helps liberate more horsepower and adds generous extra torque throughout the rev range for enhanced driveability. The rear end of the crankshaft is redesigned to incorporate a ‘lip’ seal to engineer out the oil leaks inherent in the original design.
A new aluminium cylinder head is fully gas-flowed and balanced to again ensure perfectly smooth running and a generous powerband. It is equipped with dual overhead Aston Workshop fast-road camshafts, with fuel supplied via triple twin-choke side-draught Weber DCOE 45 carburettors.
Aston Workshop offers a choice of engine capacities from the original 3.7 through to 4.7 litres for ultimate performance. In our experience the 4.2-litre conversion provides an ideal balance of power and driveability perfectly suited to our DB4 GT Zagato recreation’s grand-touring character – and faithfully mirrors the specification chosen by Aston Martin for the six ‘Sanction’ cars produced in the 1990s.
The original 3.7-litre stroke of 92mm is retained, while cylinder bores are increased to 95mm, combining the engine’s inherent willingness to rev with extra horsepower and torque. Upgrades to the cylinder head include larger diameter inlet and exhaust valves, oversize camshaft buckets, new valve guides and Vantage-specification valve springs. All oil and waterways are upgraded to suit. The finishing touch is a stainless steel exhaust to enhance the purposefully throaty engine note.
An uprated water pump, electronic ignition and an aluminium core radiator ensure modern-day reliability and suitability for all traffic conditions.
Once fully assembled, the new engine is run-in and tuned on Aston Workshop’s own dynamometer test cell to ensure everything is functioning as intended and all performance specifications have been achieved. The completed engine will typically produce 300bhp @ 5500rpm and 320lb ft torque @ 4000rpm – healthy increases over the already potent original, and all with enhanced driveability.
For additional peace of mind, we offer an industry-leading ten-year guarantee on our engine rebuilds and conversions *
An Aston Martin four-speed manual transmission is fitted as standard equipment, although different gear-ratio sets are available to customer requirements. Further options include a range or modern automatic and manual gearboxes ideally suited to long-distance touring.
* specification restrictions apply
