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What is a Celica GT4 How do I know which model is which What fuel should I use?
How much fuel will it use What Engine Oil should I use How often should I change the oil
What else should I change when changing the oil What Gearbox oil should I use What's the wheel stud pattern i need
What offset wheels do I need Do I need spacers with my new wheels Stock Boost Levels
When you start to modify a car beyond the manufacturer's specification you have to accept the risks that go with it. The GT4 Drivers Club take no responsibility for any damage arising from information provided here
Things to do before modding your car First Modifications Increasing Boost

GT-Four - What Is It
The GT-Four is a turbo-charged, four wheel drive, coupé style sports car produced by Toyota, and is a derivative of the Celica range. Confusingly, it is not known as the GT4 in all markets. In the US, it goes by the name of All-Trac. In Europe, it is badged 4WD Turbo. Other markets know it by the name GT-Four - We use GT4 as shorthand.

The GT4 hails from the days of rallying when manufacturers were required to produce road going versions of their Rally cars (In actuality the reverse is true. Manufacturers had to produce their rally cars from their road going variants. Either way the end result is the same :-)

Model runs were quite limited, which probably explains why you are reading this part of the FAQ although the GT4 has been in production in various guises since 1987 and has been successfully rallied by Toyota and privateers for many years.

I see lots of references to STxxx on this site, what does that mean?
STxxx is the Toyota model code for each generation of Celica.

The last digit in the model code indicates the exact model or engine type. Traditionally, 5 has been used to denote the turbo 4WD models, hence ST165, ST185 and ST205

The ST16x was manufactured between 1986 and 1989


The ST18x between 1989 and 1993 The ST185CS(Europe) and ST185RC(Japan) versions were homologation special versions of the 185

They featured a number of upgrades over the standard 185 cars and indeed share some parts with the later ST205 models. The most notable difference is in the charge cooling system. Standard ST185s have a top mounted air to air cooler whereas the CS/RC versions have a water to air charge cooler system as found in the 165 and 205 cars.
The pictures show the difference in front bumpers to accommodate the radiator for the charge cooler
There are a few other variations such as limited slip rear differentials


The ST20x between 1994 and 1999


What fuel should I use?
As high an octane as possible - 98 octane should be the minimum!

Japanese cars are designed and mapped to run on their 100 RON octane fuel. A lower octane rating can cause the engine to detonate/knock under load causing internal damage. In an ideal world the ECU will compensate for this using the knock sensor system but it is still far and away better to use the highest octane available. JDM models running standard ECUs will also make progressively more power with higher octane fuel up to 100RON

For heavy abuse days such as dragstrip events, trackdays etc. it is worth considering running octane booster. While this will not generally produce more power from the engine it will provide an additional safety margin from detonation


How much fuel will it use?
The GT-Four is a performance 4wd car so do not expect great economy.

Average on road figures for a standard car would probably work out around 22-27mpg. Those with a heavy right foot may struggle to even reach the lower end of this band. People with gentle right feet have been known to get 350+ miles out of a 13 gallon tank on long runs. So 30mpg is possible but not common! On track expect less than 10 mpg!


What engine oil should I use?
Brand choice is a very personal thing. Some owners use Castrol, some use Millers, some use Silkolene etc. etc.

The Toyota recommendation is for a 10W50 multigrade. The important thing is that any turbo car should be using 100% synthetic oil to handle the extra heat generated by turbo applications.

At the end of the day the choice is yours. Some people use cheap semi-synth and change it every couple of thousand miles with no apparent side effects

It is worth bearing in mind though that a couple of microns thickness of your engine oil is all that comes between the crankshaft spinning at 6000 rpm and the soft metal big end bearings!

Running in a new or rebuilt engine requires mineral or semi-synthetic oil for a limited mileage, usually between 500 and 1000 miles.


When should I change the oil?
It depends on the sort of use the car gets

Turbo cars in general burn large amounts of fuel (in case you have not noticed!). This can lead to rapid contamination of engine oil with hydrocarbons

The general recommendation for "average" cars would be 3000 to 6000 miles of "average" use, however, those subjected to spirited use should aim for the lower end of that range and if the car is tracked or run up the dragstrip on a regular basis it might be a good idea to change it in between trackdays.

At the end of the day there are no hard and fast rules but as with choice of oil it is worth remembering that oil is the engine's blood.


What else should I change when changing the oil?
It is important that you also change the oil filter when replacing oil...

If it has done it's job then the old filter will be full of particulate contaminates removed from the old oil. The last thing you want to do when putting fresh oil in is to run the risk of immediately contaminating it with this!

It is tempting to nip down to your local discount parts supplier and pick up the cheapest oil filter they have that will fit. This may be a false economy. The Toyota filter has an anti-drain valve to prevent all of the oil from draining out of the block when the engine is not running. In some cheaper filters this valve has been found wanting which could lead to short term oil starvation at startup. This should not be a problem with a genuine Toyota part. As with oil the choice is ultimately yours but bear in mind the oil system is the blood of your engine


What gearbox oil should I use?
Toyota specify a 75W90 GL5 gear oil. Again brand is a personal choice but as with engine oil you should be considering a fully synthetic oil only

Ensure that you get GL-5 specification

The differential should hold around 5 litres.

Some users have experimented with ATF in worn gearboxes. This is an attempt to try and prolong it's life once it has begun to get crunchy on changes etc. While results on the whole have been neutral to positive you must be aware that by doing this you are working outside of the Toyota specified conditions and your results may be negative!


What is the wheel bolt pattern for my GT-Four? What is the offset required when ordering aftermarket wheels? Should I use spacers with my wheels?
For a simple quick start guide to wheels see the wheel information article


What is the standard boost on my car?
ST165 approximately up to 7psi
ST185 approximately up to 12psi
ST185 (CS/RC) approximately up to 12psi
ST205 approximately up to 14.7psi


What should I do before I start modifying the car
The first things aren’t really mods, more maintenance but are still recommended:

In addition to the above, things that you could do that are free would be to;


What should be my first modifications?
Early modifications could include;


What Boost can I run with mild modifications?
With sensible "breathing and exhaling" mods you should be able to achieve:-

ST165 approximately up to 12psi *
ST185 approximately up to 12psi *
ST185 (CS/RC) approximately up to 14psi
ST205 approximately up to 17psi

* You will probably need a Fuel Cut defenser to achieve these figures