Garrett T03 Compressor Maps
The Garrett T03 family has long been the mainstay of turbocharged Saabs. Originally designed by Garrett for Saab when the first successful attempt at turbocharging a 'family car', the Saab 99 Turbo, was on the drawing board, it was a radical change from conventional turbocharger applications on petrol engines. Where the installations on Porsche 911's and race cars were meant to give an already powerful engine a bit of extra top end power, Saab laid their turbo and wastegate design out so that the blower would have it's maximum effect in the lower and mid rpm's (i.e. where most road driving takes place) and taper down towards the engine's red line. During the Eighties, the T03 design was used by many other major car manufacturers, for instance Ford on their Sierra/Sapphire Cosworth, and later the Escort Cosworth. All Saab 900 Turbo's up to MY '90, and 9000 Turbo's up to MY '88 are equipped with Garrett T03 turbo's. 9000T's from '87, and 900T's from '88 have a watercooled bearing housing.
All T03's are not the same. All they share is the basic 'frame', i.e. the center housing with bearings (which was made in a watercooled and non-watercooled version), which in turn roughly determines the size and application range of the turbocharger. A turbo is matched to the characteristics of the engine it's destined to work with by fitting various turbine and compressor housings with their corresponding wheels. When 'uprating' a turbo to allow for more airflow on an existing engine, the turbine side is mostly left alone as this largely determines spool up time. On the compressor (inlet) side of things, however, various 'trim' levels are available to match the engine's airflow capabilities. What you want is a turbo that will work at close to maximum efficiency at most of the operating range of the engine. Too big and spool up will be affected (though not by as much as with a turbine housing/wheel combo that is too large for the application, too small and compressor efficiency will drop at high rpm/boost pressures, which means it will produce more heat than a correctly sized turbo when trying to flow enough air through it for a given hp level - up to a point where the efficiency losses from the superheated charge air (remember cooler air contains more oxygen for a given volume, which in turn makes more power) will more than offset the gains from running higher boost pressure! Obviously, too much heat will affect life and reliability of the turbo, but also the engine itself.
On the other hand, sizing a turbo application so that it runs at maximum compressor efficiency (indicated by a percentage - 74%/72%, 70%, 65%- in the compressor map graphs) at the projected maximum engine hp (corresponding with a certain airflow level at the turbo inlet, indicated at the bottom of the graphs in lbs/min) will prove less than satisfactory for all but oval racing. On the road, you mostly find yourself at lower revs and part throttle, so you want to have the best possible turbo response. Conversely, you are mostly accelerating towards peak power rpm rather than staying there for a long time (unless you own your own stretch of Autobahn!). Correct turbo sizing for a given road car application means finding a good balance between compressor efficiency at the top end of the engine's power band and fast spool up for maximum torque in the lower/mid rpm ranges.
Of the compressor maps shown, the '40' and '45' trim compressors are OEM applications for Saab. 8 Valve 900 Turbo's have what's generally is referred to as a '40 trim' of which the compressor wheel and inlet have a 34 mm diameter. The 16 valve turbo engine on 900 and 9000 Turbo's uses a T03 with '45 trim' compressor: diameter of compressor wheel and inlet opening is 40 mm (see picture here). Typically, the compressor map of the latter translates to a realistic maximum of ~240 hp before efficiency drops too much. The '60' and 'Super 60' maps represent popular upgrades for 2.0 litre Saab applications. All these are available as 'off the shelf' components by certified Garrett rebuilders. When miximg and matching components that were not originally destined for the T03 (like a T04 compressor on a T03 center housing and turbine, or a turbine listed for the T25, together with a compressor wheel and housing out of the T03 part of the catalogue on a T2 center housing), or machining out housings to improve flow and/or accept bigger wheels) for a 'one off', we generally talk of 'hybrid' or 'modified' turbo's. For improved reliability at sustained high boost levels and/or faster spool up, turbo builders use tricks like 360 degree thrust bearings (standard is 270 degrees), or even ceramic ball bearings. Uprating the bearings of a standard turbo for motorsport applications etc., can however easily double the cost of a turbo (rebuild).
"40" Trim
"45" Trim
"60" Trim
"Super 60" Trim
