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Scott Costanzo's 1968 MGB with GM LS4 V8

Scott Costanzo · 1968 MGB

MG MGB

BritishV8: the site for enthusiasts of modified British sports carsOriginal How It Was Done article published in BritishV8 Magazine, Volume XVII Issue 1, July 2009; page updated with current build details

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 1968 MGB rebuilt around a GM LS4 5.3L V8 from a front-wheel-drive Impala

Scott Costanzo converted his MGB from its original four-cylinder, then a V6, into a V8 using a front-wheel-drive GM LS4 engine pulled from a 2006 Impala SS. The build kept the steering rack in its stock location and left the bonnet unmodified, solving the tricky problem of mounting a starter on an engine that never had one on the block. A decade on, the car has covered roughly 27,000 miles and the owner continues to sort and refine the conversion.

Specs

As stated in the original write-up.

Engine
GM 5.3L LS4 (FWD) V8 from a 2006 Chevrolet Impala SS, with LS6 intake manifold, stock 87mm DBC throttle body, GEN 4 timing cover, block-mounted starter, GM OBD2 0411 factory fuel injection
Fuel system
2004 Pontiac GTO in-tank fuel module
Cooling
Aluminum early Mustang style radiator, 180 degree thermostat, 16 inch Volvo puller fan controlled by engine ECM
Exhaust
Custom 1 5/8 inch headers into 2 inch pipe merged into a single 2.25 inch pipe, cherry bomb muffler and resonator
Transmission
Borg Warner T5 from a 1987 Ford Mustang, Spec Stage 3 clutch/pressure plate from a 1995 S-10 2.2L, external 1 inch slave cylinder, stock clutch master cylinder, Fastshafts drive shaft
Rear axle
GM 7.625 10-bolt, 3.23:1 gear, limited slip differential
Front suspension
Stock layout upgraded with polyurethane bushings, MGB GT springs, 3/4 inch sway bar
Rear suspension
Stock layout upgraded with polyurethane bushings, tube shocks, custom panhard bar
Wheels/Tyres
2010 Nissan Sentra alloy wheels, 205/45/16 Dunlop Direzza DZ102 tyres
Brakes front
Vented rotors from a 2006 Nissan Frontier, calipers from a 1997 Nissan Sentra
Brakes rear
Rotors from a 1994 Honda Accord, calipers from a 2006 Honda Civic, stock MGB 3/4 inch brake master cylinder
Steering
Electric power steering from a 2008 Toyota Yaris
Electrical
Stock MGB gauges, tachometer rebuilt with a Theo Smit circuit board for V8 use
Interior
77 to 80 MGB interior, custom gauge cluster, Fiero NA seats
Other
Moss Special Tuning spoiler
Weight
2483 lbs, measured with a full 16 gallon tank and full trunk

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 5

Fuel & Ignition 2

Cooling 3

Gearbox & Drivetrain 5

Suspension & Steering 6

Brakes 5

Wheels & Tyres 2

Body & Trim 1

Interior 3

Electrical 1

Other 2

Photos

29 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.

Scott Costanzo's 1968 MGB with GM 5.3 V8Photo: 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
The GM LS4 V8 installed in the engine bayPhoto: BritishV8: the site for enthusiasts of modified British sports cars
GM 3100 SFI V6Photo: BritishV8: the site for enthusiasts of modified British sports cars
GM 3.1 V6 Multi Port Injection.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Completed starter modification.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Steering shaft mock-up.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Motor mounts.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Firewall modifications completed!Photo: BritishV8: the site for enthusiasts of modified British sports cars
Left side motor mount.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Steering rack to harmonic balancer clearance.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Steering shaft to exhaust port clearance.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Left side header tacked together.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Left side header construction.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Right side header construction.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Electric power steering.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Vented front disc brakes.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Vented front disc brakes rear view.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Panhard bar mount under constuction.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Panhard bar mount test fitting to car.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Panhard bar mounting to unit body under construction.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Vented disc brakesPanhard bar installed in the car.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Panhard bar intallation details.Photo: BritishV8: the site for enthusiasts of modified British sports cars
Car rear viewPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Car front corner viewPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Car rear corner viewPhoto: BritishV8: the site for enthusiasts of modified British sports cars
Car interior view.Photo: BritishV8: the site for enthusiasts of modified British sports cars
2010 Nissan Sentra alloy wheels, 205/45/16 Dunlop Direzza DZ102 tires.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

From four cylinders to a V8

Scott had already converted his MGB to a V6 but wanted more power than that platform could give without forced induction. After weighing the common V8 swap engines, he chose the GM LS family, picking the front-wheel-drive LS4 variant because it is the shortest LS engine lengthwise, which suited his packaging goals.

Setting the ground rules

Before cutting metal, Scott set himself three constraints: the steering rack had to stay in its stock position, the bonnet could not be modified, and changes to the car's structure should be minimized. These goals shaped decisions on header routing, motor mounts and firewall work throughout the build.

Solving the starter problem

Because the LS4 came from a front-wheel-drive car, it had no starter mounting point on the block itself; the starter was originally carried on the transmission bellhousing. Scott fabricated a steel plate to mount a common Small Block Chevy mini starter directly to the block, a solution that has held up for about 27,000 miles.

Fitting the engine and steering

Mock-ups and photos show the steering shaft being lowered at the front of the column for header clearance, motor mounts welded in and later gusseted, and the firewall reconstructed to clear the new engine. Custom headers were built and tacked together on each side to route around the steering rack and column.

Brakes, steering and rear axle updates

Scott fitted electric power steering from a 2008 Toyota Yaris, vented front brakes using Nissan Frontier rotors and Nissan Sentra calipers, and rear brakes combining Honda Accord rotors with Honda Civic calipers. A GM 10-bolt rear axle with a limited-slip differential and 3.23 gears was installed to handle the V8's power.

Suspension and final details

A custom panhard bar was designed, mocked up, and mounted to the unit body to locate the rear axle, keeping the otherwise largely stock suspension working well with the new power. The interior was finished with a late-70s MGB dash, a custom gauge cluster, and Fiero seats, while 2010 Nissan Sentra alloy wheels wearing Dunlop tyres were fitted.

Ten years on

The car has been on the road since May 2015 and covered about 27,000 miles. Over the most recent year the owner has been sorting out remaining details of the conversion, with air conditioning and a new camshaft still on the to-do list.

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

  • Choosing the shortest LS variant (the FWD LS4) made it easier to keep the steering rack in its stock location.
  • A front-wheel-drive LS engine has no starter mount on the block, so plan to fabricate a bracket for a mini starter.
  • Clearing the steering column and shaft around the headers took careful mock-up before final fabrication.
  • A custom panhard bar was needed to properly locate the rear axle once the suspension was upgraded.
  • Keeping the suspension largely stock preserved the car's original handling character even with much more power.
  • Sorting out all the details of a major conversion can take years after the car is first on the road.

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