Upgrades & Conversions
Triumph Stag Upgrades & Conversions
Almost everything held against the Stag when it was new has a modern answer. Sort the cooling first, then the ignition, then decide what kind of car you want it to be, the drivetrain and chassis changes below are choices, not cures.
This is the index to every upgrade and conversion covered on the archive, in the order a sensible owner tackles them. One principle runs through all of it: reversible improvements that preserve the original Triumph V8 are welcomed by the market, while changes that remove originality have to earn their keep in how the car drives. Whatever you fit, declare it: see the insurance guide.
Do these first
Reliability work, not modification. These are the changes that turn a Stag from a car you worry about into one you use.
Start here
Cooling upgrades
The one upgrade every Stag deserves. Radiator, header tank, fans, coolant and the temperature-sender blind spot, the difference between the car's reputation and its reality.
Reliability
Electronic ignition
Replacing the contact-breaker points with an electronic trigger: what it fixes, what it does not, the reversible and non-reversible routes, and how it interacts with the coil and ballast.
Service item
Timing chains & tensioners
Not an upgrade so much as the maintenance that makes every other upgrade worth doing. Uprated tensioners and guides are fitted as a matter of course during the job.
Engine & drivetrain conversions
The bigger decisions, where character and value are both at stake.
Most-read
The ZF automatic conversion
Swapping the three-speed Borg-Warner for the four-speed ZF automatic, why owners do it, what is involved, and how it changes the way the car drives.
The big decision
Rover V8 and other engine conversions
The most divisive change you can make to a Stag. What a well-engineered conversion gains, what it costs in originality, and what it does to the car's value.
Manual cars
Clutch & overdrive
Keeping the Laycock overdrive working, and what to do when it does not, the manual car's most valuable single feature.
Before you convert
Manual vs automatic
The comparison to read before spending money on any transmission change, including the Borg-Warner 35's real character and buying checks.
Chassis, brakes & electrics
Quieter improvements that change how the car feels far more than their cost suggests.
Chassis
Brakes
Discs, drums and the servo, what the standard system can do, what wears, and where sensible improvement is possible.
Chassis
Suspension & steering
Bushes, dampers, geometry and the power-assisted steering, the changes that most improve how a Stag feels on the road.
Chassis
Wheels & tyres
Original sizes and fitments, modern tyre choices, and the age question that matters more than tread depth on a low-mileage classic.
Underpinning
Electrics, earths & fans
Earths and the loom underpin nearly every upgrade on this page, most 'Lucas' faults are connection faults.
Tuning, rather than upgrading
A great many Stags described as needing an upgrade simply need setting up correctly. Before buying parts, work through the tuning guide , ignition timing, the distributor's advance curves and the twin Zenith-Strombergs, and the servicing section. A correctly timed, correctly fuelled V8 in good health is a surprisingly quick and very smooth engine.
Frequently asked questions
What is the best upgrade for a Triumph Stag?
The cooling system, without argument. The Triumph V8's period reputation came from overheating and the damage that followed, so a properly sorted radiator, fans, header tank and correct inhibited coolant do more for reliability, and for the car's resale, than anything else you can spend money on.
Do upgrades reduce a Triumph Stag's value?
It depends entirely on reversibility and on the engine. Cooling improvements, electronic ignition and suspension refreshment are welcomed by buyers and generally add value. Replacing the original Triumph V8 with another engine is the one change that consistently reduces value against an equivalent-condition original car.
Should I convert my Stag to the ZF automatic?
It suits owners who cover distance and want a fourth ratio and more relaxed cruising than the three-speed Borg-Warner 35 offers. It is a well-regarded conversion that buyers usually view positively, but it is not a fix for a car whose cooling system or chains have been neglected, sort those first.
Do I have to tell my insurer about modifications?
Yes. Declare every modification, including engine, transmission, cooling, ignition, brake and wheel changes. Undeclared modifications can invalidate a claim, and on an agreed-value classic policy the modifications are part of what the value is agreed on.