1999 s-70 black deposit ( carbon?

1999 s-70 turbo. black deposit on exost pipe.102000 miles on car.,
10W30 sintetic castrol .Engine uses 1/4 qt of oil on 1300 mile trip.
No any problem in 85-95 mph driving :

 

Hello, Your car's oil consumption isn't too high at all. Are you talking about 1 car or 2? Better gas can make a car run "cleaner". The knock sensor won't prompt the ECU to enrich the mixture as often if mid grade or premium gas is used. Check your plugs to see if they're blackened too. Carefully measure your mileage now then measure it when using better gas. Make your mind up then. There's probably nothing wrong with your car. Kira