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Well...some speculation...
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Posted by Bryce [Email] (more from Bryce) on Thu, 9 Aug 2001 11:39:09 Share Post by Email
In Reply to: Good day to check your turbos!, JTMav, Thu, 9 Aug 2001 11:09:57
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As I understand it, the T7 system will let boost rise until a specified level of power (230/240 hp, 258/273 ft-lbs) is achieved. At that point, it dumps additional boost. At sea level, in normal conditions (not sure what temp), this is about 14psi (~1 bar?). When the air is less dense, it will increase boost to ~21psi (1.4 bar I believe).

So, as the air gets hotter it expands and thus density falls (just like increasing altitude). Therefore, the T7 system will increase boost to achieve the desired power curve. More boost = more time.

I'd love to see some actual math behind this. For example, is 60F air 10% more dense than 100F air? Is it linear? How long is our normal lag on the turbo, at various RPM's?

Subjectively, I notice a small decrease in performance of my 00 Aero. It reaches the same very fast speeds but the lag is just a little longer, which is quite consistent with the theory.

I've also noticed that when launching onto an open on-ramp to the freeway on a nice 20F morning in November, the car will definitely seem to react faster, probably due to the lower turbo lag.

Anyway, I've never driven older turbos that are said to be much more prone to lag. Only once has the lag EVER been an issue for me in the 9-5, as I pulled across traffic, making a left from a stop. I didn't apply enough throttle, it spooled up slowly, I got worried and mashed it and all of a sudden I was spinning and TC was kicking in. I've adjusted my driving accordingly and now mash it and back off a bit. :)

Bryce

00 9-5 Aero
85 900S
83 Alfa Spider

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