Originally Posted by: RedZedX3 
It really depends on what you want the car to do and on which track. I tend to build based on a car's weaknesses. If it's heavy, lighten it. If it's underpowered, beef up the engine. If it's riding on garbage tires, mount some stickier rubber. In reality, the best thing to do for a circuit car is reduce weight and take advantage of upgrades that will get the most out of the engine like a race transmission with adjustable gearing. The game seems to work a bit differently sometimes.
If you're looking to post leaderboard times, download the top couple of people's tunes and see what they did for a build. You'll at least have a starting point and can then tune to your driving style.
My favorite S700 tune I have right now is a Porsche GT2 with race weight reduction, stock-width slicks, and 475 horsepower. It is very quick, but doesn't do well on high-speed tracks like Nurburgring due to the aero.
Hope this helps and certainly let us know what you come up with.
How can I see other ppl's build once I DL the tune. it will not let me open it? what to look forin the Tele windows