What product do you recommend to clean.....

From underneath the bonnet cover, use Simple Green (diluted, NOT full strength) then wipe with clear water after the soot has been removed. You will have stripped off any wax with the Simple Green, so you need to either...

1. Use a Microfine (1500) Polish to smooth up the surface paint.
2. Alternatively, use a Paint Cleaning "pre wax" (too many brands to name).
3. Then top coat with your favorite wax.

You will find while you're using the Simple Green that your rag will get very dirty and black - even in the places that do NOT appear sooty. Thus, be prepared to do the whole underside. Many times, the top of the bonnet will also be discolored, both from heat and light soot (or exhaust 'blooms' as they're sometimes called) and the above can work as well, SKIPPING the Simple Green step for the outer surface unless it is BADLY sooted on the exterior. Be ready to rinse completely.

This is the best way I've found to effectively clean and preserve the paint without using too much unnecessary abrasive.

Have fun. Your results should be dramatic.