To install the mod : 

1. Copy the SOUND folder to your game installation
2. Use the .nfsms file inside OGVI/VLTED with the import modscript button
3. This mod doesn't apply the new sounds to any car, it only adds the necessary stuff for them to function so you'll have to do it yourself.
To do this find the node for the car you wish to modify inside "pvehicle" (for example the old camaro is in pvehicle>default>cars>racers>muscle>camaro)
Once you found the node you want open it and go to TurboSND, you'll find multiple fields for it, each number corresponds to an upgrade inside the game so 0 = stock and the rest goes as you would expect, from there expand the number and the referenced row and you'll be able to change the collection key to the turbo you wish to apply.
Here are names of each new turbos to put in the collection key :
Forza Turbos :
- turbo_fh1_l1_1
- turbo_fh1_l1_2
- turbo_fh1_l1_3
- turbo_fh1_l2_1
- turbo_fh1_l2_2
- turbo_fh1_l2_3
- turbo_fh1_l3_1
- turbo_fh1_l3_2
- turbo_fh1_l3_3
- turbo_fh1_l3_4
- turbo_fh1_l3_5
- sc_fh1_vortech2
- sc_fh1_slr
- sc_fh1_gt500

Grid 2 Turbos :
- turbo_grid2_37r
- turbo_grid2_Civ
- turbo_grid2_s15
- turbo_dual_grid2_12c
- turbo_dual_grid2_r33
- turbo_dual_grid2_sl65
- sc_grid2_ccx
- sc_grid2_gen

NFS Edge Turbos : 
- turbo_dual_edge_agerar
- turbo_dual_edge_rx7

NFS The Run Turbos :
- turbo_tr_350z
- turbo_tr_kbfiesta
- turbo_tr_mmrx8
- turbo_tr_supra
- sc_tr_cobra

Once you've done your changes save everything, launch the game and equip the correct turbo

