Toyota Celica GT4 ST165 turbo modifications

Turbo

Mod	Benefit	Drawback	Is it a problem?	Notes

Increase boost pressure What is and How to fit an RV	More power More fun	Increased air intake temps Detonation much more likely Likelihood of engine failure increased Stock turbo limited in pressure/flow	ish, depends on prior modifications	An SBC is far superior than the RV method, but an RV is much cheaper!
Dump Valve How to fit a DV What is a DV	Get a 'tish' sound like a boy racer on gear changes Improve driveability Helps to keep turbo spinning between gear changes Helps to prolong turbo life	£ Noise	No	Atmospheric type will foul up fuelling when changing gears as metered is vented to atmos. Recirculating type will help to correctly meter fuel Try not get a diaphragm DV - these fail more often and wear quicker than the piston type Select the correct spring or idling may be a problem - 5psi
Fuel Cut Defencer What is an FCD? Make & fit an FCD	To generate more boost than the stock ECU will allow	£ if bought, cheap to make Require ECU wiring diagram and a soldering iron - ECU pin out article here	ish - depends if you are any good at soldering!	Allows more boost pressure by overcoming the fuel cut level set by the ECU ~12psi (exact level varies from car to car)
Uprate/hybridise stock turbo Pictures	More power, more fun More efficient at a higher boost pressure As it is more efficient, the likelihood of detonation at higher boost pressures reduced Will flow better Will help cure the wastegate crack you probably have May cure the smoking at idle!	£ dependant upon choice of size Upgrading stock turbo good for oil & water pipes and support brackets etc but not nearly as good as a GT30 or GT25 etc for power and efficiency Watch the size of the compressor as the stock wastegate may not be able to flow out enough exhaust gases	No	Popular sizes for CT26 inducer: 42mm - 12psi (ST165) 44mm - 15psi (ST185) 48mm - 18psi (ST185 CS/RC) 48mm - 18psi (ST205) 52mm - 18psi 54mm - 24psi 56mm - 24psi (based on Garret T04 wheel) Note - this is only a very sketchy rough guide You might also want to ask about: Gas flowing the wastegate Inconel wastegate seat, for 165 Polishing the compressor housing Gas flowing the exhaust housing 360 degree thrust bearing
Fit larger aftermarket turbo	Much more power, more fun You'll probably want go for a Ball Bearing turbo... Less lag More efficient Able to produce more pressure and more importantly increased flow	££ May require a custom exhaust manifold or adaptor May need a custom down pipe May require custom oil feed and drain, water cooling to/from the turbo Dependant upon turbo type may require an external wastegate...£ Some way of controlling this lot - an aftermarket ECU Shortening the life of the stock engine, maybe not your daily driver car?	Yes	By now you are into some serious power - you'll definitely need an aftermarket ECU or addon/piggyback, go for a complete ECU... Reliability shortened. Fuelling needs to be addressed, maybe larger injectors fitted, replacement/addon ECU, forged pistons may also be required etc
External wastegate	Better exhaust gas flow Improved turbo control Improved power output	£ Specialist external dump valve required Need to fabricate a custom downpipe to accommodate the output from the external wastegate and the turbo You'll obviously need an external wastegate turbo. NOT the stock CT26!	Yes	Expensive!
Disable TVSV How to article	Better control of boost pressure Run same pressure in all gears	Will run the same LOWER pressure in all gears	No	This is normally carried out when fitting some sort of boost controller. Doing this mod without fitting a boost controller is pointless and will make the car slower!