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Brad Chapman's 1975 MGB GT V8 conversion

Brad Chapman · 1975 MGB GT

MG MGB

BritishV8: the site for enthusiasts of modified British sports carsas published in BritishV8 Magazine, Volume XVII Issue 1, July 2009

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 1975 MGB GT converted to Rover 3.5L V8 power

Brad Chapman converted his 1975 MGB GT to Rover V8 power, pairing it with a Toyota Supra W55 five-speed gearbox via a Dellow bellhousing. The write-up is useful for its detailed discussion of engine placement and gearbox choice, including the various Supra box lengths available in Australia and their suitability for this swap.

Specs

As stated in the original write-up.

Engine
Rover 3.5L V8 with Holley 600cfm carburetor (vacuum secondaries) on Offenhauser "360" single-plane intake manifold, Pertronix Ignitor electronic ignition, rebuilt SD1 starter motor, pre-facelift P6 alternator bracket
Cooling
Modified stock MGB four-cylinder radiator with relocated ports
Exhaust
Custom headers, purchased used from a racer
Transmission
Toyota Supra alloy-case W55 5-speed manual with Dellow bellhousing and Dellow clutch kit (mounts, slave cylinder, throw-out fork and bearing)
Front Suspension
Stock MGB
Rear Suspension
Stock MGB
Brakes
Stock, except MGB GT V8 front calipers
Wheels/Tires
Minator 15x6 8-spoke alloy wheels
Body
Sebring front and rear valances, rubber bumpers removed, 1974-spec grille fitted
Interior
Stock MGB
Weight
1020kg (2248 lbs)
Completed
February 2009

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 1

  • Rover 3.5L V8 engine

    Donor engine used for the conversion

Fuel & Ignition 3

Cooling 1

Gearbox & Drivetrain 3

  • Toyota Supra W55 5-speed manual gearbox

    Longest alloy-case version used, locating gearstick near stock MGB position, rated for about 500hp

    In the shops
    5-Speed Gearbox Conversion Kit by Vitesse ↗Moss Motors – Triumph TR6/TR250· $6,622.25 USD
    Front Gearbox Seal (Manual) ↗James Paddock Ltd· £5.25 GBP
    Bellhousing Gasket (4-Speed Gearbox) ↗James Paddock Ltd· £0.95 GBP
  • Dellow bellhousingDellow

    Mated the Supra gearbox to the Rover V8, cleared the tunnel without modification

  • Dellow clutch kitDellow

    Included transmission mounts, slave cylinder, throw-out fork and bearing

Suspension & Steering 1

  • Engine mountsMGOC

    Sourced for positioning the Rover V8 in the engine bay

Brakes 1

Wheels & Tyres 1

Body & Trim 3

Electrical 2

Other 1

  • Custom four-into-one block-hugger headers

    Bought used from a racer for the exhaust system

Photos

19 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.

Brad Chapman's 1975 MGB GT with Rover 3.5L V8Photo: BritishV8: the site for enthusiasts of modified British sports cars
completed engine installationPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Holley 600 (vacuum secondaries) on Offenhauser 360 single-plane intake manifold.Photo: BritishV8: the site for enthusiasts of modified British sports cars
dual exhaust pipe routingPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Dellow transmission crossmemberPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Custom four-into-one, block-hugger headers.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Toyota Supra W55 5-speed gearbox.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Dellow bellhousing.Photo: BritishV8: the site for enthusiasts of modified British sports cars
modified radiator shelfPhoto: BritishV8: the site for enthusiasts of modified British sports cars
modified slam panelPhoto: BritishV8: the site for enthusiasts of modified British sports cars
modified turn signal mountingPhoto: BritishV8: the site for enthusiasts of modified British sports cars
single circuit, servo-assisted brake systemPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Installation of a Sebring front valancePhoto: BritishV8: the site for enthusiasts of modified British sports cars
Installation of a 1974 MGB grillePhoto: BritishV8: the site for enthusiasts of modified British sports cars
very pretty new paint jobPhoto: BritishV8: the site for enthusiasts of modified British sports cars
stock MGB GT interiorPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Sebring front valance.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Sebring rear valance.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Donate Now!Photo: BritishV8: the site for enthusiasts of modified British sports cars

How it was done

Choosing the drivetrain

Brad's biggest concerns were engine placement and gearbox selection. He settled on a Rover 3.5L V8 and a Toyota Supra five-speed manual, available in Australia in four case lengths. He chose the longest (21 inch) W55 variant, which located the gearstick near the MGB's original position and offered gear ratios similar to the MG RV8.

Engine fitment

The Rover V8 was fitted with enough clearance to remove the sump pan without lifting the engine out. In hindsight, Brad felt the engine could have been mounted an inch or so further back. Engine mounts were sourced from the MGOC website.

Gearbox and bellhousing

The Dellow bellhousing proved straightforward to install, clearing the transmission tunnel by 10-12mm on each side without needing modification. A Dellow clutch kit supplied the transmission mounts, slave cylinder, throw-out fork and bearing.

Fuel, ignition and exhaust

Induction was handled by a Holley 600cfm carburetor with vacuum secondaries on an Offenhauser single-plane intake manifold. A Pertronix Ignitor module replaced the points inside the distributor. Custom four-into-one block-hugger headers were bought secondhand from a racer.

Cooling and brakes

The stock four-cylinder MGB radiator was modified with relocated ports to suit the V8 installation. Braking was left largely stock, apart from fitting MGB GT V8 front calipers.

Body and finishing touches

Sebring front and rear valances were fitted, the heavy rubber bumpers removed, and a 1974-spec grille installed, giving the car a cleaner look. The interior and suspension were left in stock MGB form.

Remaining work

At the time of writing the differential had not yet been upgraded, with Brad planning to fit a limited slip differential in the future.

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

  • Would have mounted the engine an inch or so further back for better balance.
  • The longest Toyota Supra gearbox casing (21 inch) best matches the MGB's original gearstick location.
  • A Dellow bellhousing can clear the stock transmission tunnel without cutting, saving fabrication work.
  • The W55 Supra gearbox is strong enough (rated to about 500hp) to handle the V8 with margin to spare.
  • Upgrading the differential to a limited slip unit is worth planning for once the swap is otherwise sorted.

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