Many people have inquired about the way we Shelbyophiles differentiate one turbo setup from another. To help clear up some of the confusion, I decided to write a page which describes the four types. They are referred to an Turbo I, Turbo II, Turbo III, and Turbo IV. Here they are, in order.
As introduced in 1984, the engine displaced 2.2 liters (135 cubes for you old musclecar types). A Garrett T03 turbo was used; it featured a mechanical wastegate which limited boost to 7psi.
For 1985 the wastegate was upgraded to computer-controlled action. Also, an 'overboost' feature was added: the peak boost was increased to 9psi; this higher amount of boost could be held for 10 seconds at WOT before being reduced to 7psi for the remainder of WOT. Once your 10 seconds were up, you had to back out of it and wait in order to return to overboost. For each second you weren't at WOT, a second was added to the overboost's clock (so to speak). When you went back to WOT then you could overboost for as much as time as was 'on the clock' before again being reduced to 7psi. Power ratings were 146 HP at 5200 rpm and 168 ft-lb at 3600 rpm.
The next significant change came in 1988: The induction system was changed. A new blow-through intake manifold was installed, as was a smaller Mitsubishi TE04H (13C) turbo. This redesign made the engine look quite different but performance-wise little actually changed. Displacement was still 2.2 liters.
1989 marked the most significant changes yet: the displacement was increased to 2.5 liters (153 cubic inches) and balance shafts were added for smoothness. The factory's goal was to increase low-end power rather than top-end punch. The factory created a new, stronger block this year; it was called the common block because it was used for both the Turbo I and the Turbo II. Peak boost 'spike' was raised to 11psi. The result was 150 HP at 4800rpm and 180 ft-lbs at 2000rpm.
1991 marked the next significant change but few people are aware of it. This was the year that the Turbo II was dropped so the Turbo I had to take up the slack. Thus the computer was reprogrammed; more aggressive fuel, ignition, and boost curves were added until the torque peak was at 210 pound-feet (horsepower was barely changed at 152). Note that this high-torque version was only available with a manual transmission; if you opted for an automatic then you got the lesser 180 lb-ft engine.
These Turbo I engines continued unchanged until their demise.
It should be noted here that there are two versions of the Turbo II--the converted Shelby engines and the 'true' Turbo II produced by the factory. The differences are all in the bottom end: the true Turbo II is notably stronger. Mother Mopar was backing these engines with a 5/50 warranty (Shelby did not) so durability was a top concern. Thus the factory improved the block with cross-drilled cooling vents, added a forged crankshaft, stronger rods, and so on--all items that the '87 Turbo I didn't have. At this time, the only large piece common to a Turbo I and a true Turbo II was the cylinder head. The Shelby engines all began life as mere Turbo I powerplants which had the top end converted at Shelby's plant. Functionally they were Turbo II cars but the bottom end wasn't as beefy. In either case, peak boost was set at 12 psi; the power rating was 175 HP at 5200 rpm and the torque peak measured 175 lb-ft from 2200-4800 rpm.
1988 marked one noticeable change: the intake manifold was switched to a new one-piece design. This meant the Turbo II and Turbo I now used the exact same intake manifold. It has tuned-length runners like the two-piece manifold it replaced but these were shorter than before. Power figures were unchanged.
1989 was the year of the common block; it was added to the Turbo II. Displacement for the Turbo II remained at 2.2 liters, however, and this engine did not have balance shafts. Power ratings were still unchanged. Nothing would change in 1990, which was the last year of the Turbo II.
For 1992 the engine wasn't changed. However, it was now available in the Daytona IROC R/T in addition to the Spirit R/T. In 1993 the Spirit R/T is discontinued, leaving only the IROC R/T to carry the Turbo III flag. 1993 would be the last year for the Turbo III (and the Daytona, too).
Like the Turbo II before it, Shelby's version was not like the one built by Dodge. Shelby's version was used exclusively in the 1989 Shelby CSX; these engines were actually converted from 1988 Turbo II engines. Therefore, these engines did not use the common block or any other new-for-89 hardware. Peak boost was still 12psi. A unique computer was installed to control the turbo's wizardry; three solenoids are required just to operate the VNT blades! Peak power was still 175 HP but maximum torque was up to 200 lb-ft at 3700 rpm.
1990 was the first and only year that this engine was factory offered. This version was based on the (stronger) common block. As such, it featured all the related hardware such as balance shafts and so on. Power output changed slightly; it was now rated 174 HP and 210 lb-ft. This engine could be had in the Shadow ES, the Daytona Shelby, and the LeBaron GTC (coupe and convertible); it was standard in the Shadow Competition package and the 1990 Daytona C/S Competition model. Few were built, though. There were 141 TurboIV Shadow ESes, 536 TurboIV Daytona Shelbys, only 25 TurboIV LeBarons (coupe and convertible combined), plus 27 Shadow Competition packages and 21 Daytona C/S Competition cars.
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Modified: 10-2-02.