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Glenn Merrell's 1973 Triumph Stag with Rover SD1 Engine

Glenn Merrell · 1973 Triumph Stag

Triumph Stag

britishv8.orgas published in British V8 Newsletter, Volume XV Issue 3, December 2007

Read the full write-up at britishv8.org ↗

Photo: britishv8.org

A 1973 Triumph Stag converted to a Rover SD1 3.5-litre V8

Glenn Merrell replaced his Stag's original engine with a rebuilt Rover SD1 V8, paired to a five-speed manual gearbox and fitted with reprogrammed factory fuel injection. The write-up is a specification sheet with photos rather than a step-by-step story, but it lays out the custom mounting, cooling, exhaust and electrical work such a swap demands. Completed in 2003 and driven over 40,000 miles since, it shows a durable, road-proven take on the V8 Stag conversion.

Specs

As the owner states it.

Engine
Rover SD1 3.5L V8, rebuilt with Chevy HC pistons and connecting rods, Erson T020H cam with high-rev lifters, Edelbrock timing chain and gears
Induction
Rover 14CUX electronic fuel injection (circa 1993), reprogrammed, with Rover 3.9L intake manifold, plenum, throttle body and mass airflow sensor
Exhaust
Block hugger headers, Jet-Hot ceramic coated and wrapped, stainless steel exhaust system
Cooling
Stock radiator, 16 inch Permacool electric fan, 15 inch Permaflex engine fan and shroud, undersized water pump pulley
Transmission
5-speed manual (Rover LT77?), 9.5 inch clutch
Rear Axle
Triumph Stag 3.43:1 ratio with Phantom Grip limited slip differential
Front Suspension
Crossmember lowering blocks, lightened springs, polyurethane bushings
Rear Suspension
Stock
Brakes
Stock discs and drums, silicone DOT 5 fluid
Wheels/Tires
Stock 5-spoke alloy wheels, Yokohama Avid H4 195/70R14 tires
Instruments
Stock
Body
Stock, except for a TR6-style front air dam
Interior
Blaupunkt 4x50W stereo
Electrical
AC Delco 90 amp alternator
Performance
Top speed of about 140mph
Completed
2003, over 40,000 miles driven as of September 2007

Parts used

What the owner names in the write-up, grouped the way the Parts page groups them. Where one of the shops we index lists the same thing for this car, it is shown underneath with a link to the shop.

Engine 4

Fuel & Ignition 3

Cooling 3

Gearbox & Drivetrain 3

Suspension & Steering 3

Brakes 1

Wheels & Tyres 1

Body & Trim 1

  • TR6-style front air dam

    Added to the otherwise stock body

Interior 1

  • Blaupunkt 4x50W stereoBlaupunkt

    Fitted as the car's audio system

Electrical 1

Other 1

  • Stainless steel exhaust system

    Full custom exhaust routed around the differential

Photos

All 21 pictures in the write-up, in the order they were posted, shown from britishv8.org. A picture opens larger here, with the way through to the page it is on.

Glenn Merrell's 73 Triumph Stag with Rover SD1 EnginePhoto: britishv8.org
Rover SDI 3.5L V8 enginePhoto: britishv8.org
Rover 14CUX electronic ignition systemPhoto: britishv8.org
master cylinders and brake booster servoPhoto: britishv8.org
steering linkagePhoto: britishv8.org
k&n air filter and Lucas/Hitachi mass air flow sensorPhoto: britishv8.org
15 inch mechanical flex cooling fanPhoto: britishv8.org
a box of lead and acid? let's put it as far forward as possible!Photo: britishv8.org
AC Delco 90 amp alternatorPhoto: britishv8.org
relax, it's just 16 hosesPhoto: britishv8.org
wiper motorPhoto: britishv8.org
remote oil filter, steering rack and anti-roll barPhoto: britishv8.org
MacPherson strut independent suspensionPhoto: britishv8.org
MacPherson strut front suspensionPhoto: britishv8.org
Triumph Stag rear suspensionPhoto: britishv8.org
the exhaust wraps around the differentialPhoto: britishv8.org
Triumph Stag dashboard... what is it about Triumphs and veneer?Photo: britishv8.org
Triumph Stag instrumentsPhoto: britishv8.org
Triumph Stag seats and door panelsPhoto: britishv8.org
Yokohama Avid H4 195/70R14 tires.Photo: britishv8.org
Donate Now!Photo: britishv8.org

How it was done

The swap

Glenn Merrell took his 1973 Triumph Stag and fitted a rebuilt Rover SD1 3.5-litre V8 in place of the original engine, using Chevy high-compression pistons and rods with an Erson cam and Edelbrock timing components. The engine was matched to a five-speed manual gearbox and the Stag's own rear axle, fitted with a limited slip differential.

Fuel and ignition

The car retains a Rover 14CUX electronic fuel injection system from around 1993, reprogrammed for this application. The 3.9L-spec intake manifold, plenum, throttle body and mass airflow sensor were carried over from the donor Rover parts to feed the V8.

Cooling and exhaust

Keeping the V8 cool in the Stag's engine bay meant combining the stock radiator with both an electric fan and a mechanical flex fan under a shroud, plus an undersized water pump pulley. Exhaust gases exit through ceramic-coated, wrapped block hugger headers into a full stainless steel system.

Chassis and running gear

Front suspension was lowered with crossmember blocks and lightened springs, and polyurethane bushings were fitted throughout the front end. Brakes and rear suspension remain stock, running on silicone DOT 5 fluid, with the original 5-spoke alloy wheels shod in Yokohama Avid H4 tires.

Result

Completed in 2003, the car has covered more than 40,000 miles since and is reported capable of about 140mph. Merrell notes that a conversion like this requires custom work throughout, from mounts to wiring to driveline alignment, and says he took it on simply to prove he could, and now looks forward to building a Triumph-based V8 for the car instead.

A summary in our own words. The full account, with all its detail, is the owner's: read it at britishv8.org ↗

Worth knowing

  • A V8 swap requires custom fabrication throughout, including mounts, cooling, exhaust, electrical and driveline alignment.
  • These custom items add up in cost well beyond the parts list itself.
  • Managing cooling in a tight engine bay may need both electric and mechanical fans working together.
  • Reusing donor injection electronics can work well if reprogrammed for the new application.
  • The owner would consider building a Triumph-based V8 next time rather than the Rover unit.

britishv8.org

Read in full on 5 September 2026. The work, the words and the pictures are Glenn Merrell’s; this page is a catalogue of them in our own words, and a signpost.

Read the full write-up at britishv8.org ↗

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