They won't do anything benificial for your car. The twinky was designed to be very efficient which is why it runs so hot and has such a low diff ratio. With a massivly upped wheel rpm ratio I've seen over 70 mpg from one of my old cars on a big motorway run, my best being a 138 mile trip using just 8.14 litres of fuel with another trip of 400 odd miles being done for around 35 litres, and it was all 70/75 mph speeds