The thieves struck at around 8.15am on Saturday, June 20 from Newark Engines, Great North Road, while the owner and a mechanic were working in a rear yard.
Pc Tony Hayes of Notts Police said: "The engines were on pallets in the entrance area to the garage by reception.
"The door had been left closed but unlocked whilst the owner and a mechanic worked on a vehicle in the rear yard.
"The mechanic has said he heard a noise about 8.15am but thought nothing of it. When they returned the property had been stolen."
The engines are for Lotus racing cars and cannot be used for any other purpose.
Anyone who has information about these offences should contact Pc Hayes on (01636) 605 999 ext 7670 or to ring anonymously Crimestoppers (0800) 555 111.