1994-2002 [Subscribe to Daily Digest] |
There is nothing wrong with an ECU mod, some folks are interested in something less expensive. Some will get an older Saab and spend its book value on mods. Whatever turns your crank. Many really get satisfaction in getting more from less, IE big improvements with little cost. And some are basically penny pinching. But at least with the T5's, one has this choice.
The stock IC that you have is very restrictive. And the pressure drop across the IC increases as the square (if not worse) of the air flow. So the stage III will really bring out the weakness of the IC. The T5 will maintain a pressure target, not a mass flow target as the T7 does. The net result is that the turbo compressor works harder to get the pressure that the MAP needs to see. This higher pressure to overcome the IC flow resistance makes the compressor work harder, which means that the compressed air is hotter than it would be with a better IC. The result is that the engine gets hotter less dense air*. Yes the engine does then produce less power. The ECU sees the high intake temps and backs off the ignition timing to be less agressive. There is less air mass flow and fuel. The issue though, with stage III setups, is that the engine is getting close to the edge in terms of thermal and octane issues. The temperatures in the combustion chambers and the exhaust valves can become unsafe. The big issue is that detonation can occur when things are severely hot. So lower restriction intakes and exhaust do make more power, but also are a engine safely issue at some point when increasing power.
* a secondary effect is that the wastegate is then more closed to make the exhaust turbine work harder to diliver more shaft HP to the compressor wheel. This increases the pressure in the exhaust manifold. For 18PSI of boost, the exhaust pressure might be 40PSI. That directly decreases engine torque/HP. So by eliminating intake pressure drops, (that includes the IC and TBTC etc) the air mass flow on a T5 increases and temperature drops, the exhaust back pressure is reduces, which also increases power, and when the exhaust back pressure is reduced, the combustion chamber temperatures are reduced.
And the DIC and ECU see detonation conditions via the spark plugs. The characteristics of the spark gap are vital. As the plugs get hotter, the conditions are seen as closer to detonation. And as the spark gap is decreased the same is seen. These effects really have no significant impact at OEM boost levels, but as you push things to higher power and temperature levels, the DIC and ECU can chicken out. So the 7ES plugs and larger gaps, .039 - .040 do reduce the 'false readings' that can occur with high power applications. And some careful trimming of the ground electrode to reduce its temperature rise can good. And the electrode trimming can also reduce the "spark ignition kernel shrouding". High boost applications do make the mixture hard to ignite, so combustion kernel shrouding can become an issue. The results are subtle, but real. Perhaps a perception of an increase willingness to get up and go.
The performance down pipe does have benefits that become significant with the gas flows of a stage III setup.
What do do with the MBC+A? You can keep it intact and sell it or pass it on. Otherwise, a SMBC with the stage III ECU would preserve the fast boost response that you are probably addicted too. This would let you have the high boost of the stage III and have the abiltiy of the ECU and BPC to reduce boost if anthing gets out of hand. I would not use the SMBC to increase peak boost, as you have then killed the abilily of the ECU to go to lower boost levels. You could try adjusting it to get the max torque that the tires can handle in 2nd gear runs, but then first gear then requires feathering the throttle... which you are familiar enough with now. You can experiment and see what happens. With a stage III, without a SMBC, full throttle might smoke the tires in any case. The high rate of boost increase with a MBC, MBC+A or SMBC does create a weight shift that does unload the fron tires and create traction limits that way. One of the horrible consequences of too much power! ;-)
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