TVR from Britain has long built some of the most engaging sports cars that skip driver aids and extra safety gear. Started in 1947 by Trevor Wilkinson, the firm used engines from Rover and Ford for many years. After Peter Wheeler acquired the company in 1981 he pushed it to design and build its own powerplants, something few small makers tried.

The Speed Six is a 24-valve twin-cam inline-six offered in 4.0-liter and later 3.6-liter sizes that share the same bore with different strokes. Each cylinder has its own throttle body and injector along with equal-length tubular headers. An aluminum block and dry-sump oil system let the engine sit lower in the chassis for better balance and handling.

The 3.6-liter version made 350 horsepower and 290 pound-feet of torque. The 4.0-liter S model in the Tuscan Speed Six S reached 390 horsepower at 7000 rpm and 310 lb-ft at 5250 rpm. Later Mark I Tuscans hit 400 horsepower and 315 lb-ft. At that output the engine delivered 100 horsepower per liter in naturally aspirated form without direct injection in a roughly 2425-pound car that had no ABS or traction control.

So what happens when you double it

Under Wheeler TVR stayed active through the 1990s and 2000s. He wanted a car for the Le Mans GT1 class so the firm created the Speed Twelve, a 7.7-liter V12 built from two Speed Six cylinder banks.

The Speed Twelve made so much power it broke the input shaft on the factory dyno rated for 1000 horsepower. No official figure was recorded. Rules forced a limit of 660 horsepower. The car never reached Le Mans because of later regulation shifts. TVR still planned a road version but only one lightly tuned example reached a buyer after the rest were used for parts.

Stories say Wheeler drove a prototype and returned so unsettled that he canceled plans for sale. The main issue on the road was not missing electronics but tires that could not put the power down. The high-revving Speed Six stayed in production until TVR closed in 2006 and stands as the firm's finest engine.