The Kyosho FW04 Superten was the 2nd generation of Superten cars based on the FW03 Superten.

These cars are a bit larger than 1:10 scale and they were very realistic model cars.
The FW04 is legendary for fantastic handling while at the same time having exotic components.

While most FW04s had 2 stroke engines, Kyosho or OS Max, there was a limited version with a 4 stroke OS Max engine.
This engine was a car modified version of the FS OS Max engine and it was named FS-26S-C and FS-26S-CX (the 'X' is for the recoil version).
The key differences of the FS-26S-C and the airplane FS-26 are:

• Engine block and cylinderhead painted black
• Modified camshaft (more duration and lift) for higher rpm
• Modified valve springs
• Different intake and carburetor 

Here's a couple of pictures of the cylinderhead

Additionally, the 4-stroke Superten had a modified exhaust, heavier flywheel, significantly longer gearing and a belt driven fan to cool the engine.

You can watch a video of how it sounds here https://www.youtube.com/watch?v=Nq0zjKg6idM

And more pictures follow.