ST185 CS Modifications


This page contains details about the modifications I have done to my car. They have all been carried out by myself as a result of gathering information from around the internet and the various owners I have met or spoken to. Check out my links page for sites and information sources I have found useful and informative.

Check out my navigable engine bay page and my current 'work in progress' page.

You will find pictures and links to relevant articles for many of the modifications in the following table ...




Relief valve Boost Controller


What can I say - this is the most cost effective and impressive modification I can think of. Boost is variable, by underbonnet adjustment, and the boost curve is altered dramatically.

Check out my boost controller pages and links !

Click to see my relief valves  for sale

relief valve components

Fuel Cut Defender (FCD)


A mod which allows the boost to be increased without the annoying fuel cut which occurs at around 12 - 14 psi.

Check out my FCD pages and links !

Click to see my fuel cut defenders for sale

DIY FCD made up ready for sale

Take a look at my electronic circuits page for this and other DIY electronic mods.

21st Century Performance Book

Strictly speaking this isn't a modification but it is certainly allowing me to consider what further modifications I should be thinking of and how to go about them.

Click the following link to buy/review this book at Amazon

Click to buy from Amazon

Check out this brilliant book !

Air/Fuel Meter


A simple meter which allows the air/fuel mixture to be monitored, which is a good idea after fitting an FCD.

A simple DIY kit for one of these can be purchased from the shop at autospeed part number KC5195.

Autospeed kit made up and fitted

Take a look at my electronic circuits page for this and other DIY electronic mods.

Mongoose 2.5 inch S/S Exhaust System


This subtle 2.5 inch system fits well, sounds good and with it's twin tailpipe looks fairly standard. All in all great if you don't want to attract undue attention.

Mongoose exhaust fitted

mongoose logo

Cold Air Intake


I got up one morning and thought this would be a good idea. I don't like induction kits due to them allowing hot air from the engine compartment into the filter. I didn't feel comfortable building a custom air box as I want to keep the standard air box and location. I therefore decided to remove the resonator box from under the inner wing and use the exposed 50 mm inlet on the the intake snorkel to feed cold air from a brake duct on my CS bumper. The whole build and fit took about 3 hours and parts cost me 15 GBP.

the resonator box from under the inner wingold resonator box location showing 50 mm inlet to the intake snorkelbrake duct on my CS bumperparts for the new cold air intake
new intake assembled and ready to fitnew intake fittedbrake duct showing the intake feedintake viewed from under the car
view of the intake snorkel entering the airboxinner wing cover back onsome cosmetic finishingbrake duct grille re-fitted

De-Cat Pipe


A popular mod which had been long overdue. Fitting went fairly well although one stud snapped when removing the old cat. I had to fit a spare turbo stay as there wasn't one and, while I was at it, I removed the old cat stays as I had to take the turbine elbow off anyway to gain access - there is now a lot of room available under the turbo ;-) The exhaust is loader and throttle response is better, full boost seems to be available about 500 rpm lower down the rev range (14 psi at 2500 rpm).

de-cat pipe ready to fitde-cat pipe ready to fitde-cat pipe ready to fitde-cat pipe fitted
some parts I removedturbo with no cloths onold catold cat

Powder Coated Rocker Cover


I had a spare powder coated rocker cover which I decided to fit when I had to replace the spark plugs. This is purely a cosmetic modification which I think looks cool.

powder coated rocker cover - ready to fitsome parts removed to allow the old recoker cover to be removedrocker cover removed
powder coated rocker cover - fittedback together againback together again, again

Bailey DV26 Dump Valve


One of the most popular dump valves. For the GT4 make sure you purchase the valve with the Subaru spring which release at 5 psi - this will improve driveability no end.

 DV26 dump valve install picture

bailey logo

Chargecooler Heat Shield

This simple modification helps prevent heat soak from the engine to the chargecooler when the car is stationary i.e. no air flow. Check out the excellent instructions page at the GT4FAQ site.

chargecooler heat shield

Chargecooler Lagging

This simple modification also helps prevent heat soak from the engine to the chargecooler when the car is stationary i.e. no air flow. The chargecooler is definately much cooler now that this lagging has been fitted - even after being stuck in traffic for several minutes the chargecooler is cold !

chargecooler lagging - frontchargecooler lagging - side

Constant 13.5 Fuel Pump Voltage

A simple mod which ensures your fuel pump is delivering maximum flow just when the engine needs it. Check out these pages for details - page 1 , page 2 & page 3.

fuse box13.5v fuel modification

PIAA Super White Bulbs

I always tend to use uprated bulbs in my car so when the opportunity arose to get hold of some of these PIAA super white bulbs from a fellow GT4OC member, and at a discount price, I jumped at the chance. They are rated at 135/115w output but consume only 80w of power and are very bright. My car also has cockpit adjustable headlights which allows me to easily alter the beam height, and therefore length, from inside the car.

PIAA super white bulbs as receivedthe equivalent of 135/115wheadlight cover removednaked headlight mechanism
headlight showing the bulb holderheadlight from the frontheadlight ready to go back infull beam on a bright sunny day

KYB Struts

The Carlos Sainz edition has 20% uprated struts as standard so the KYB shocks are basically just restoring the 'as new' feeling - which is pretty good and better than you would think.

TIM Boost Gauge

An aftermarket boost gauge is a must if you plan to increase your boost - lets face it the stock gauge is pretty innacurate.

TIM gauge showing a healthy idle vacuumTIM gauge at restgauge mountinggauge mounting

Removed Underbonnet Insulation

Helps to improve the air flow through the engine bay reducing temperatures - a must for a cooking turbo-charged car. This required a bit of work to re-direct the cam-belt snorkel. I also decided to use reflective foil to help protect the paintwork.

insulation removedsnorkel plumbing

Underbonnet Water Deflector

A home-made mod to prevent too much water soaking the engine when it rains - it really works too.

water deflector - left sidewater deflector - from the topwater deflector - right side

Synthetic Oil


This is not really a modification but a good quality synthetic oil is probably one of the best investments you can make on you Celica GT4. Check out the enlightening oil recommendations article at

I originally used Castrol RS oil but decided to change to Mobil 1 when the Castrol grade changed from 10w-60 to 0w-40 which I consider to be far too thin.

Castrol site

The Mobil 1 grade I used was 15w-50 which is slightly thinner than the Castrol RS but still a very good, and well known, oil.

Mobil 1 site

More recently I have switched to Valvoline Synpower as it offers good value for money and choice of grades of 5w-40 and 20w-50.

Valcoline Synpower

AFM (air flow meter) Mixture Adjustment

This relatively simple mod will provide a better throttle response. Check out the AFM article and a similar one for EFI mixture adjustment - if you are feeling more adventurous.

Optimax Super Unleaded Petrol

The latest super unleaded everyone is talking about with a rating of over 98 RON.

Shell Optimax site

Octane Booster

Again, not really a modification but essential to increase the octane rating of the Super Unleaded fuel from 97 RON to 99 RON. When swapping to and from different fuel grades or after adding octane booster, it is a good idea to reset the ECU.

The pic shows the brand I buy from Demon Tweeks ...

octane booster

Go-Faster Windscreen Wiper Motor

A completely cosmetic modification pioneered by fellow Carlos Sainz owner Paul Bartolo. Click here for his version :-)

You've been Tango'd

Alloy Wheels


I bought 3 of these Stilauto 17 ESA rims in a breakers yard and, after a long search, managed to find and buy the fourth at MarkAlloys in Oldham. Mark is a great chap and often has single wheels available.

Stilauto logo on the rimouside view of the riminside view of the rim

Check out some pictures of the wheels on the car like this one ...

new wheels fitted

Starbo RS-601 Remote Engine Starter

This is my favourite modification. It is basically a remote engine starter and turbo timer combination. Frosty windscreens on a winters morning are a thing of the past and the added benefit of the turbo timer make for an excellent piece of kit. I bought the unit second hand with no instructions so it took some wiring up - but it's all working now and was well worth the effort.

in situfor those who can read japanese - the dip switch setting instructionsdip switches for triggering various features
messy wiringtidy wiringStarbo remote transmitter

Amazing Glaze Paint Treatment

I was introduced to this product by a friend at work. I was so taken by it that I bought some - I will post pictures and further details when I have applied it. This mod is absolutely insurance friendly ;-)

Check out the Amazing Glaze site for the ultimate paint treatment

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