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Bill Davidson's 1974 MGB GT V6 Conversion

Bill Davidson · 1974 MGB

MG MGB

BritishV8: the site for enthusiasts of modified British sports carsas published in BritishV8 Magazine, Volume XX Issue 1, July 2012

Read the full write-up at BritishV8: the site for enthusiasts of modified British sports cars ↗

Photo: BritishV8: the site for enthusiasts of modified British sports cars

A 1974 MGB GT converted to a GM 3.4L V6 by its owner

Bill Davidson rebuilt his 1974 MGB GT around a GM 3.4L V6, pairing it with a T5 five-speed gearbox and a reworked exterior inspired by the MG RV8. The write-up details the engine, cooling, suspension, brake, electrical and body work, including custom touches like a relocated fuel filler and hand-painted pinstripes. It's worth reading for the level of detail on sourcing parts from specialist suppliers and small fabrication solutions.

Specs

As stated in the original write-up.

Engine
GM 3.4L V6, bored 0.030" over, mild aftermarket camshaft, 1.6:1 roller rockers
Induction
Edelbrock lower intake manifold with Classic Conversions Engineering upper manifold (CC-105), Holley 390 carburetor, Edelbrock air cleaner
Ignition
GM style distributor with electronic module, Lucas ignition coil, Accel Super Stock spiral core 8mm plug wires
Motor mounts
Classic Conversions Engineering motor mounts
Cooling
Stock size aluminum radiator, dual 8" electric cooling fans, Flex-a-lite fan shroud, oil cooler
Exhaust
Classic Conversions Engineering headers, 2" Y-pipe, single Magnaflow muffler
Gearbox
Borg-Warner T5 5-speed (Chevy V8 ratios)
Rear Axle
Stock MGB Salisbury axle, open differential, 3.909:1 ring and pinion
Front Suspension
Stock MGB with polyurethane control arm and anti-sway bar bushes
Rear Suspension
Stock MGB except for Victoria British "rally" rear springs
Brakes (master)
Stock later model MGB (Lockheed) cylinder and power booster
Brakes (front)
Slotted and drilled front rotors with stock MGB calipers
Brakes (rear)
Stock MGB drums
Wheels
VTO Classic 8 15" aluminum wheels
Tyres
General Altimax HP (185/65R15)
Electrical
EZ Wiring harness kit (12 fuses), Dolphin gauges, Sony stereo (52Wx4), Delco-Remy alternator
Interior
1964 dashboard, power door locks, power windows, ergonomic steering wheel, Flaming River tilt steering column, cruise control, pull-out cup holder, Nostalgic Air air conditioning
Body
Custom grille, MG RV8 fiberglass hood, bumpers removed, Sebring-style front and rear valances, It's a Snap Wire and Cable headlamps with LED turn signals, shaved side marker lights, side trim removed, early MGB taillights, shaved back-up lights, relocated fuel filler
Paint
Hot Rod (satin) black with hand-painted red pinstripes

Parts used

Parts named as used in the original 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 6

Fuel & Ignition 6

Cooling 4

  • Aluminum radiator

    Stock size radiator used for cooling the V6

    In the shops
    Aluminum Radiator ↗Moss Motors – Triumph TR6/TR250· $355.00 USD
    Aluminum Radiator ↗Moss Motors – Triumph TR6/TR250· $358.50 USD
    Aluminum Radiator ↗Moss Motors – Triumph TR6/TR250· $364.00 USD
  • Dual 8" electric cooling fans

    Provide airflow across the radiator

    In the shops
    Cooling Fan ↗Moss Motors – Triumph TR6/TR250· $17.99 USD
    Cooling Fan Motor ↗Moss Motors – Triumph TR6/TR250· $158.50 USD
    Cooling Fan Spacer ↗Moss Motors – Triumph TR6/TR250· $1.35 USD
  • Flex-a-lite fan shroudFlex-a-lite

    Shrouds the electric fans for efficiency

    In the shops
    Fan Shroud ↗Moss Motors – Triumph TR6/TR250· $79.99 USD
    Fan Shroud, radiator, air flow improver ↗Moss Europe (UK)· £85.00 GBP
    Fan Shroud ↗Moss Europe (UK)· £42.25 GBP
  • Oil cooler

    Helps manage oil temperature in the conversion

Gearbox & Drivetrain 2

Suspension & Steering 2

Brakes 2

Wheels & Tyres 2

Body & Trim 6

Interior 7

Electrical 6

  • EZ Wiring 12-fuse wiring harnessEZ Wiring

    Installed by Bill Young to rewire the car

    In the shops
    Black Wiring Harness Tape ↗Moss Motors – Triumph TR6/TR250· $12.75 USD
    Main Wiring Harness (Vinyl) ↗Moss Motors – Triumph TR6/TR250· $663.25 USD
    Main Wiring Harness (Vinyl) ↗Moss Motors – Triumph TR6/TR250· $736.50 USD
  • Dolphin gaugesEZ Wiring

    Tachometer, speedometer and quad gauge instrumentation

  • Sony stereo (52Wx4)Sony

    Installed as the car's audio system

  • Delco-Remy alternatorDelco-Remy

    Charges the system under the V6 conversion

  • It's a Snap Wire and Cable headlampsIt's a Snap Wire and Cable

    H4 halogen headlamps with built-in LED turn signals

    In the shops
    Headlamp Chrome Rim Outer (Snap On) ↗James Paddock Ltd· £14.95 GBP
    Headlamp Chrome Rim (Outer, Snap-On, Mk1/2) ↗James Paddock Ltd· £14.95 GBP
  • TaillightKing.com Flush Mount LED Rod Light assembliesTaillightKing.com

    Five-lamp LED units wired parallel to the turn signals

Other 2

Photos

40 pictures collected from the write-up, in the order they were posted, shown from BritishV8: the site for enthusiasts of modified British sports cars. A picture opens larger here, with the way through to the page it is on.

Bill Davidson's 1974 MGB GT with GM 3.4l V6 EnginePhoto: BritishV8: the site for enthusiasts of modified British sports cars
Bill Guzman at Classic Conversions Engineering specializes in MGB V6 kitsPhoto: BritishV8: the site for enthusiasts of modified British sports cars
GM 3.4L V6, bored 0.030 over. Mild aftermarket cam with 1.6:1 roller rockers.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Edelbrock lower intake manifold with Classic Conversions Engineering upper manifold (CC-105).Photo: BritishV8: the site for enthusiasts of modified British sports cars
Stock later model MGB (Lockheed) brake master cylinder and power booster.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Holley 390 four barrel carburetor.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Classic Conversions Engineering motor mounts and exhaust header.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Flex-a-lite fan shroud.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Aluminum radiator.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Oil cooler.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Edelbrock air cleaner.Photo: BritishV8: the site for enthusiasts of modified British sports cars
GM style distributor with electronic module, Lucas coil, and Accel Super Stock spark plug wires.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Air conditioning compressor.Photo: BritishV8: the site for enthusiasts of modified British sports cars
The electric choke mechanism on Holley's 390 carburetor.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Pretty much stock front suspension.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Red polyurethane bushes on the lower control arms and the anti-sway bar.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Drilled and slotted front brake rotors.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Basically stock rear suspension except for uprated leaf springs.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Single Magnaflow muffler.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Flaming River tilting steering column.Photo: BritishV8: the site for enthusiasts of modified British sports cars
The pushbutton at the end of the turn signal stalk is the high beam switch.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Dolphin tachometer (0-10,000rpm) and speedometer (0-140mph).Photo: BritishV8: the site for enthusiasts of modified British sports cars
Dolphin Quad instrumentPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Uncommonly subtle air conditioning controls. Note also the pop-out cupholder.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Gear shifter falls right where MG put theirs. Note power window switches.Photo: BritishV8: the site for enthusiasts of modified British sports cars
The drivetrain installation doesn't encroach at all on the pedal box.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Bill Young installed the EZ Wiring 12-fuse wiring harness.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Various used MGB parts for the restoration came from Joe Blackwood at Joe's British Parts.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Hot Rod satin black paint.Photo: BritishV8: the site for enthusiasts of modified British sports cars
MG RV8 fiberglass hood, purchased from Dave Craddock at Preform Resources.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Ford V6 badge.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Scott Blaine of Kansas City, Kansas hand-painted some classic pin stripes and flourishes.Photo: BritishV8: the site for enthusiasts of modified British sports cars
It's a Snap Wire and Cable headlamps take H4 halogen bulbs.Photo: BritishV8: the site for enthusiasts of modified British sports cars
LED front turn signals.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Putting a leaf screen across the cowl vent is a big improvement from stock.Photo: BritishV8: the site for enthusiasts of modified British sports cars
MG offered this style of mirror in chrome or flat black.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Radio antenna.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Fuel filler hidden under license plate.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Early-model MGB taillights give a more streamlined appearance.Photo: BritishV8: the site for enthusiasts of modified British sports cars
VTO Classic 8 15 inch aluminum wheels.Photo: BritishV8: the site for enthusiasts of modified British sports cars

How it was done

Starting point

Bill Davidson bought the MGB GT in 2005 with the intention of converting it to V6 power himself, documenting the progress through photos including an in-process shot from February 2010.

Engine and drivetrain

He installed a GM 3.4L V6, bored 0.030 inch over, fitted with a mild aftermarket cam and 1.6:1 roller rockers. Induction came from an Edelbrock lower intake paired with a Classic Conversions Engineering upper manifold and Holley 390 carburetor. Classic Conversions Engineering also supplied the motor mounts and headers, with power routed through a Borg-Warner T5 five-speed using Chevy V8 ratios to the stock MGB Salisbury rear axle.

Cooling and exhaust

To keep the V6 cool he used a stock-size aluminum radiator with dual 8 inch electric fans and a Flex-a-lite shroud, plus an oil cooler. Exhaust gases exit through Classic Conversions Engineering headers, a 2 inch Y-pipe and a single Magnaflow muffler.

Suspension and brakes

The front suspension remained largely stock MGB, refreshed with polyurethane control arm and anti-sway bar bushes, and uprated with slotted and drilled front rotors. The rear stayed stock apart from Victoria British rally springs. Braking retained a stock later-model MGB Lockheed master cylinder and booster, stock calipers up front and stock drums at the rear.

Electrical and interior

Bill Young installed an EZ Wiring 12-fuse harness along with EZ Wiring's Dolphin gauges. The cabin was updated with a 1964 dashboard, power windows and locks, an ergonomic wheel, a Flaming River tilt steering column, cruise control, a pull-out cup holder, and air conditioning from Nostalgic Air, plus a Sony stereo.

Body and finishing touches

Exterior changes included an MG RV8-style fiberglass hood from Dave Craddock at Preform Resources, removed bumpers, fabricated Sebring-style valances, It's a Snap Wire and Cable headlamps with built-in LED turn signals, shaved marker and back-up lights, and early MGB taillights. The fuel filler was relocated behind a hinged, magnetically latched license plate mount. Don Bonar helped with bodywork and Scott Blaine hand-painted pinstripes over Hot Rod satin black paint.

A summary in our own words. The full account, with all its detail, is in the original write-up: read it at BritishV8: the site for enthusiasts of modified British sports cars ↗

Worth knowing

  • Sourcing a dedicated V6 conversion kit from a specialist simplifies motor mounts, headers and intake matching.
  • Using a stock later MGB brake master cylinder and booster keeps braking upgrades straightforward.
  • Relocating the fuel filler behind the license plate preserves a clean rear end without custom tank work.
  • Finding used MGB parts through a known parts specialist helps keep the restoration period-correct.
  • Planning for air conditioning early lets it integrate neatly with the dash and controls.

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