Here's grooved Metro #2;

Here's the grooves in the head;

Another angle;

"Powre Lynz".... I threaded the intake ports about an inch using a 1 inch NPT pipe tap for turbulence for fuel vaporization.

Update; this modification appears to have the greatest effect on cold starts and low RPM operation. The car does not run "weak" when you start it up in very cold weather, like below freezing... it has plenty of torque from the get-go. Also, the car will run down to 20 miles per hour in 5th gear, with low RPM feeling more stable and smooth than usual.

Fuel economy is about 46 miles per gallon in the winter, mostly highway driving at 65-70 miles per hour.