Tuning tips for the Subaru Impreza WRX and STi

"That does Impreza me much!"

With their phenomenal success in rally, Subaru have really carved out a niche and created a truly easy to own practical high performance car.

A few of our members have been completely converted to Impreza ownership after driving one. The power and handling is really something special.

There are many aftermarket parts around for the Impreza from suspension and handling kits to turbo conversions, stroker kits and off the shelf performance flowed heads.

The WRX and STi both appeal to those with family obligations as they are such good all round cars. The engines are very solid and can tolerate a great deal of tuning.

There was a problem with the early fuel pickups which would cause fuel starvation on long fast sweeping bends. A new design pickup/pump will address this issue.

The flat four boxer engine is certainly one of the most distinctive sounding engines around, and the engine configuration means that the weight is carried low down in the engine bay which helps the handling characteristics.

Due to the engine shape the exhausts are a work of art and the various twists and bends allow equal lengths of pipe from each cylinder. Performance exhausts cost a fortune and we suggest you get a good quality exhaust as some cheap upgrades are inferior to the OEM setup. A decent exhaust really enhances the sound of the engine.

The early (1992) WRX came with an impressive flat four 2.0 H4 engine block. There were quite a few revisions over the years and we see power steadily increasing with various limited edition tuning packs from Prodrive.

From around the year 2000 JDM models received regular revisions and cosmetic enhancements, with a few handling mods thrown in like the 2003 Transmission upgrade and the 2005 WRX being fitted with the better viscous rear slip differential. Other markets followed the Jap Spec upgrades and had various limited edition models introduced.

Most limited edition cars were produced in very small numbers of around 400 and in most cases these were customisable by the buyer with various performance, handling and styling packs. It does pay to do your research before buying and decide which options and year model you really need rather than buying a car at random and spending your way to the spec you want.

TorqueCars would recommend the following tuning modifications for the Subaru Impreza WRX and STi. Firstly the turbo can fairly easily be upgraded with one which has re-machined internals. A remap will yield large power gains but this is best left until last so you can wring out the benefit of all of the other modifications you have. If you increase the power you will certainly benefit from an uprated intercooler, indeed many owners of standard Impreza WRX and STi report a power increase from adding a front mounted intercooler.

A sports cam profile will lift the power in the upper part of the rev band, however this will affect the smooth tickover of the engine so this is only really recommend for serious track day use.

If you fit a lighter flywheel your engine will be more free revving and will feel more powerful. You will also certainly want to uprate the clutch although the original clutch should be good for 350 bhp, unless it is particularly worn.

The engine capacity can be increased to around 2.5 litres. This should not overly affect the reliability of the engine but we would recommend a thorough testing of your block for fatigue. A sports catalyst and sports exhaust will help the breathing of the engine. Fitting the later 2.5 turbo engine is another option in your Impreza tuning project and provides a good solid base to work on.

If you are increasing the power by a significant margin you should also uprate the fuel pump and injectors to keep the air to fuel mixture within their optimum parameters.

Alloy wheels of over 18 inches seem to compromise the handling so stick with the 17's or 18's unless you are not too concerned about this and want the looks of a large wheel.

Read our tuning articles for more details on the many Impreza modifications available. It would certainly be worth you joining our friendly Impreza owners forum where we debate all types of modification and tuning for the full range of Subaru engines.