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Old 01-03-2007, 07:27 PM   #40
Join Date: May 2002
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Originally Posted by bimmerZ5 View Post
You're right about the twin turbo setup. I was thinking of BMW's twin turbo diesel engine that has a sequencial turbo setup.

However, gearing does influence the drivability of a turbo engine car. Just as an example, off line in 1st gear, the car with the higher multiplying gear ratio is going to reach a lower RPM than the same car with a lower multiplying gear ratio at the same speed. Hence, as an example, at say 40mph, one car will be at 3000 RPM vs the other car will be at 4500 RPM. If your boost doesn't kick in until 4000RPM, then having the gear ratio that gets you in that RPM range quicker will make getting into the "boosted zone" easier. Typically, the car that gets into the boost zone quicker will be faster. At higher speeds, this becomes less significant as you can choose to use a lower gear to keep your revs up, and hence in boost. At lower speeds, you only have a few choices in gears and you can't go lower than 1st.

In any case, if this engine uses smaller turbos that kick in at lower RPM ranges, then a lot of this matter less.

Oh indeed gearing changes drive ability but not actual power output of the engine. We reach agreement on that. As you said at the end BMW has elimated both of the cons of FI engines by going with this setup. Gearing can be kept the same as their NA engines because torque is available throughout the range and boost lag is non existant as well.
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