Modified GT 4 door

General info

1965 4 door GT
Geoff originally built this car for Julie over 20 years ago.  It’s had several makeovers and iterations in that time and return visitors to this site will be aware of the many changes it has undergone.


The Story
Our 4 door has been resprayed with the original colours, Silver Blue metallic with a White roof. Code AZZ. It retains the original chrome moldings as Australian GT’s had. The 13 inch wheels were replaced with 15 inch genuine satin Centerlines that have recently been swapped out for genuine Convo Pros – still very much with the drag racing theme of the car, but a bit ‘fresher’.

Car still retains original registration.  Inside, it has a factory push button radio and fan heater demister. We have replaced the original seats with a more comfortable and safer bucket seat trimmed in cloth dark blue and light blue.

The only non-original extras inside are the boost gauge, mechanical oil pressure gauge and roll cage. Only the front side intrusion bars are visible.  Otherwise, it’s all standard GT.


Originally, we fitted a non turbo CA18 engine to the car, but very soon wanted more power and replaced it with a mostly standard turbo engine.  With this engine we were able to run 8.2 second eighth mile times, which is about 12.9 second quarter mile time.  This was pleasing and held promise for when we decided to go for even more power – of which you can never have enough.

When aiming for more power we had to rethink all aspects of the engines operation. Looking at all components inside and out.

The engine was built by Geoff S. (Shirley Engines).  Most internals, with exception of a couple of Japanese sourced parts were all made here in Australia, partly to support local businesses and partly because when we first built it, aftermarket parts were not nearly as common as they are today.  The car is now mostly driven on the street, making regular interstate jaunts to various shows, but is practically retired from racing duties.

Forged pistons & Perfect Seal rings (SPS Melbourne)
‘I’ beam connecting rods (Argo Sydney)
Steel ML head gasket (Grex)
Fully balanced (Crank drilled and plugged)
Decked, CCd & blueprinted
Head ported and flowed. (Standard valves)
New valve springs.
Tomei hydraulic cams.
ARP head studs
Tomei vernier cam pulleys
Siemens 770cc fuel injectors and custom fuel rail
Gates ‘racing’ performance timing belt
Modified harmonic balancer
Standard flywheel
Custom built single plate and cover by ‘Race clutch’
GT series Garrett roller internal waste gate turbo (.7 comp cover)
Inch 5/8 HPC coated exhaust manifold (Low mount) with thermocouple ports.
Grex oil cooler and remote filter
BMC air filter
Engine still displaces 1.8 litre’s
Autronic SMC engine management & CDI
Gearbox is still a standard Nissan Silvia S13 5 speed

Thanx to Mark & Paul @ JPC for their tuning prowess.


Dyno pulls after the last rebuild saw 304kw’s (~407HP) @ rear wheels.

However, this was before being ‘turned down’ slightly because the turbo was straying outside its efficiency zone.

Best terminal speed we have achieved was 123mph recorded in 2005.

With 18psi (1.2bar the 200Kw level) the car went 12.5 @112.6 mph on street radials.

The best we have managed on a higher boost setting (260Kw level) was 11.5 @123 mph on street radials. We have now run on the 1/8th mile a best time of and MPH of 7.31 @ 97 MPH.

These times all recorded on street radials, 5 speed manual and full exhaust system.



Here are the brakes we have fitted to our 4 door Cortina. You can ONLY purchase the master cylinder and PBR power boosters (if you have a changeover unit) from us. The conversion was done with minimum modifications.

Front brakes
Consist of four piston calipers and ventilated rotors.

This bolt-on conversion required no cutting or welding and still utilizes original Cortina front hubs so our steering geometry remains unchanged.  The beauty of this conversion is that we can still run our original 13 inch wheels if we wish.  This conversion is virtually redundant these days with a bolt on ‘Hoppers Stoppers’ conversion being a simple answer to your braking issues.  Only issue is that you cannot run 13 inch wheels…

Rear brakes
Our rear brakes consist of a solid rotor with a single piston caliper on a slide arrangement. All pipes fit to original locations, handbrake is fully functional and we can still use original 13 inch wheels.




With this 7/8 dual circuit master cylinder fitted to our Cortina, we have appropriately matched the bore size to the calipers and increased the safety of our car.  Should we be in the unfortunate position to loose brake fluid e.g. to the front brakes, we will still be able to stop the car with the rear brakes because a tandem master cylinder still retains fluid in the remaining chamber.

Fitting a tandem master cylinder has complimented our 4 piston calliper conversion.  The increase in piston area can require the use of a bigger bore master cylinder in order to push the pistons onto the pads.  This master cylinder will bolt into original bolt locations of the existing master cylinder.  Pipe’s exit on the motor side NOT on the inner guard side.  You can purchase a new master cylinder from us.  Pricing is here.



Front end consists of 24mm adjustable castor sway bar mounted to adjustable control arms.  KYB inserts fill GT strut tubes which are fitted with adjustable spring platforms.  K-Mac adjustable strut tops secure the strut to the tower.  A custom strut brace connects the towers for extra rigidity.  The red ‘thing’ you can see on the bottom of the gearbox bell housing is a ballistic blanket that prevents the flywheel from severing our legs should it catastrophically explode; it’s fitted for safety and racing requirements.

Lower control arms
These units are fabricated to make the range of camber adjustment wider, and operation easier.  We do NOT make these arms and do NOT sell them either.  These particular items have been inspected and tested for fatigue stress using magnetic particle testing and are fully certified.

The Struts

These front struts are fitted to our 4 door. The adjustability certainly gives us plenty of options along with our adjustable front sway bar, lower control arms, top strut mounts.  We can certainly ‘play’ around with a lot of front end settings and are currently running 1 degree negative camber, 2 degrees positive caster and 1.5 toe-in.  The car feels very stable and is very easy to steer.  Very pleased with the results.




Rear suspension
Because of the extra power and torque generated with the turbo engine, we had substantial problems with the original leaf springs.  We found the leaf springs were just bending at the front causing bad handling, so we have now fitted 10mm solid leaf springs in addition to the original GT anti-tramp arms.  This made getting the car off the line much more predictable.  However, it never ends, so the issues reoccurred when we upped the ante in the horsepower stakes.  We have now fitted Caltrac bars to support the leaf springs and have permanently prevented axle tramp and introduced much more traction both on the street, and the strip.  They certainly make the car significantly better to drive in any situation or condition.


The extra horsepower the 4 door produces made it difficult for the standard GT diff and axles to keep up with the task. We had to assess stronger alternatives and determine what would suit us for the intended purpose of the car.


We eventually decided on a tried and true Ford 9 inch.  This diff is fitted with a Harrop alloy carrier, steel hat and pinion support and LSD.  Fitting this diff meant we didn’t have to worry about rear end failure so much.  Or so we thought.

The axles
We had fitted 28 spline axles to the diff. They were fine up until they failed on the start line at Calder park Friday night street drag back February 2006. After that failure we had no choice but to fit 31 spline custom billet axles. We choose an Australian maker to supply the axles, GDS in Geelong.

The housing and center was fabricated by local diff guru Dennis Smith. Much time and expertise was put into ensuring correct alignment and tolerances.  We thank him for his patience and help with our projects over the years.