Only a 4/5 because of the onboard and the pops which I think are a little over the top, but I know you wanted to fix the onboard, honestly it would probably be good if you increased the pitch, or made the revs higher, because the note and quality is about the same as this video, just way lower pitch, but the shifts in the current one make it much better than it would be without them.
https://youtu.be/CSpmaXwq-2o?t=213
this one is also quite good but with less servicable upshift sounds and a buzzing in the background off throttle.
https://www.youtube.com/watch?v=ALaF-5SKI8o