Can I add modifications to my vehicle as deductions? The modifications are all for Youtube reviews on my channel. I do not sell the mods, I keep them.

It sounds like you have a hobby.  You can deduct expenses up to the amount of your income.

1. On the menu bar on the left that shows.
   1. My Info
   2. Federal
   3. State
   4. Review
   5. File
2. Select Tax Tools
3. On the drop-down select Tools
4. There will be 4 green boxes
5. Select Tax Topics
6. Type Hobby 
7. Do you have hobby income or expenses for 2021? > Yes
8. Post your information

It was a hobby before YouTube. My revenue from YouTube was around $8000. It is my side business which is growing into a full time business. 
 You’re saying I can add up to only $8000 of expenses?

Another factor to consider is if you are a business the car is an asset and any modifications that increase its value should be added to the basis of the car and not expensed.

I wouldn’t say it added value. It’s modifications rather than a restoration.  Value of the vehicles themselves are pretty low. 

It's still an asset.  Generally, modifications do add value in the car world, its definitely a niche market. A jacked up truck with 6" body lift, 6" suspension lift and 43" tires has more value than a standard truck.  Installing a turbo on an older car or modifying a 53 Ford so it can handle AC and a stereo would all be value added modifications. 

Modifications are not typical maintenance. They do add somewhat to the value of your vehicle. 

Also, don't forget if you have a loss 3 out of 5 years and you are trying to claim it as a business, the IRS can change it back to a Hobby.