I am not sure your technique is "wrong" per say. I agree with Purple Derple that overrev'ing and then waiting for the "right" RPM is staying out of gear, i.e. coasting, for longer than necessary. Not using engine braking is also a factor but to a lesser extent I think.
The way I try to do it is wait for the right moment to shift:
- As you approach a corner, brake hard. I try to do all my braking and shifting before the actual turn in, or at least before the apex.
- As the car decelerates, the RPM goes down
- Right before you feel that you are ready for let go of the brakes, blip the throttle slightly past the optimum RPM for the gear you are going into (sometimes 2 gears down) and shift. I think it's better to be a bit over than under in terms of RPM so it doesn't upset the balance of the car.
- Smoothly start applying throttle
It's hard to put in writing the sequence of events as it all happens so fast but I think that's what I do. With that said, I don't think you're doing it wrong. You just may be leaving a little time on the table :-)
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