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The T5 is a speed-density type system and uses only a manifold absolute temperature sensor for AF regulation. The T5 will accept a MBC that bypasses the BPC and will allow the boost to be increased to 15 PSI. A blowoff (BOV) valve can be used. Uses a red DI, will also work with the black DI. The red DI's don't last forever, they all fail in time. In the NG900s and 9-3s, the throttle body transition casting (TBTC)is very restrictive, as is the IC. The TBTC needs to be reworked. The turbo discharge silencer needs to be removed and the air box needs to be modified. A Viggen intercooler caan be retrofitted. These T5 applications were crippled by some very stupid design errors and features. These had a plug gap spec of .039 that is silly, the plugs should be gapped to .039". Loose a hose on a T5 BPV and you loose boost, the DI does not care.
The T7 uses a MAP and MAF. A MBC cannot be used to bypass the BPC, you will get a CEL. You cannot use a BOV, you will get rich AF, stumbling and CEL. You can improve spool up and responsiveness with an series MBC (SMBC) with a mild adjustment. (A T5 will also work with a SMBC) T7 uses only the black DI. Uses a motorized throttle body (MTB). Both the black DI and MTBs seem to have reliability problems. I get the impression that black DIs have more failure problems than red ones. A least I never saw a report of a red DI DIed at 18K miles. At some point one should have a spare DI in the back. This applies to the T5's as well. The T7's control the action of the BPV with an ECU controlled soleniod valve. The early or ?all? T5's had a simple BOV tubbed to the TB. Loose a hose on a BPV on a T7 and you will loose boost and get a cel. The T7 checks many things and will cel if things get out of a map of expected values.
2.3L T7 Viggens and 9-5's both get better mpg's than 2.0L T5's. The T7 would appear to be more fuel efficient. The 9-5 Aero 2.3L is rated for 250HP, so the T7 is doing something right!
Both the T5 and T7 have a variety of ECU mods available for more power.
Both the T5 and T7 use the spark plug to sense and avoid knocking condtions. Each also boosts against the MAP sensor as a reference. This means that these turbo applications can loose performance with the lower octane fuels that get pumped in California and in regions of higher elevation. These engines will perform better with some octane enhancement if the pump gas octane is lacking. But off the shelf octane boosters are not a good alternative.
posted by 208.24.17...
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