I'm trying to make the V6 Turbo sound for rF2 from real samples. However in Sony Vegas it is very hard to do it without any abnormalty. How do the professional modders usually use the real samples and generate them into the game sounds?
Edit the samples start/stop so the waveform is crossing zero in the proper direction.
If you can't get steady-state samples (usually recorded on electric dynos that attach directly to the wheel hub to avoid the whine of rolling road dynos), then you have to resort to sound bending for samples that are rising/falling.
Once you have good samples, then you have to mix them and test the mix. AIW editor has the tools for fiddling with mix settings on the fly.