My first engines with Demo.

I decided to share some of my first engine with you guys. And because I use Demo, I can't use Turbos and such.
1. Low-Class "Metal" Engine:

2. Fake-Sports/Ricer Class "Irony" Engine

3. Performance-Class "Sports" Engine

4. Super-Performance-Class "Sports S"

5. Limited-Class "Sports SL"

Please give me a idea how to improve these engines.
1. Low-Class "Metal" Engine:

2. Fake-Sports/Ricer Class "Irony" Engine

3. Performance-Class "Sports" Engine

4. Super-Performance-Class "Sports S"

5. Limited-Class "Sports SL"

Please give me a idea how to improve these engines.