Re: Water Injection and T7 - Saab Performance Bulletin Board - Saabnet.com
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Re: Water Injection and T7
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Posted by Ravi [Email] (more from Ravi) on Fri, 21 Nov 2003 11:49:26 Share Post by Email
In Reply to: Re: Water Injection and T7, Dean, Fri, 21 Nov 2003 10:19:33
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There are multiple phases for the ion current sensing that Saab uses.
Right around the time the spark is applied, the ion current is used to determine if the engine is knocking. T5 uses only this signal for boost and timing control purposes.
But later in the cycle, as the piston is being pushed down during the power stroke, the ion current can be used to measure the cylinder pressure. Cylinder pressure is a direct measure of torque. T7 uses this signal to keep the torque constant regardless of altitude or gas type, but with the caveat that one can't allow engine knock. This is why T7 cars can generate 20 psi in Denver and meet their torque and hp specs all the way there.

I believe that water injection distorts this later phase of the ion current, making T7 think that the cylinder pressure is too high and it dials back the boost accordingly. So that's why it bogs the car. With a modest amount of water spray, really well atomized, you may get away with it, but then you aren't doing much for knock suppression or cylinder charge cooling at that point, so why bother ?

Ravi
2003 9-3SS SPort Launch and Touring

posted by 198.20.40...

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