More Boost, More Power?

Now I knew what I wanted to do. I modeled up the Crank pulley and the alternator pulley on the CAD package we used at work. I bought the steel billets and machined the pulley on a conventional lathe and mill at work. The pulleys came out really well, now it was just fitment and some tuning. The next weekend I did the fitment, everything went together just like I planned. After everything was fitted, I just had to measure the belt lengths and go buy some belts.

Running more boost.

Later that day everything was fitted. I started the car and it was as previously, no issues. It revved without issues. I now just had to take the car back to the tuning guy. He had to make certain that the fueling and timing are good. He checked it out and all was fine. Now I was getting 0.7 bar boost vs the original 0.4 bar. This does not sound like a lot but it made a difference. The Polo pulled allot stronger than before. Speeding up the supercharger also made a change in sound. The supercharger had a much higher pitch sound.

Bigger exhaust needed.

Now that I had the more boost, I had a thought. The exhaust on the Polo is still a 50-millimeter Freeflow system. That exhaust must be way too small for the route I am going into. I took it to one of the local performance exhaust shops where we get all our exhaust work done. I had a chat with the owner and he said, that is way too small for what I have. They took the complete system out and rebuild a new system. Until the first box, they fitted a 57-millimeter pipe. After the first box, they went 63 millimeters all the way to the back.

It sounds great.

On startup, the car had a much deeper sound. Driving it made the small hares on the back of my neck stand up. The car wasn’t excessively loud it just sounded really well, and I could feel the car pulling even stronger. The next step was to get the car on the dyno. I took the car to the same place I had it the previous time. Had to get a back to back run. It is always good practice to do back to back runs on the same dyno. Dyno readings do differ from shop to shop.

How much power and Torque did it make?

The Polo got strapped down on the dyno and they did the run, the Polo made 133kW and 274Nm torque. I couldn’t understand that the power was only 1 kW more but the Torque was up by approx 31Nm. If you looked at the power graph you could see the power just drops away. I started doing some research on superchargers and here is where I learned a lot about superchargers. When you get to the point that you need to specify the speed you want to spin a supercharger. You must look at the compressor map of the supercharger if you can get one. It looks something like:

Above is a compressor map for a Lysholm 2300AX Supercharger. You will see the rings make like an island. The closer you are to the center island the more efficient the supercharger is. The Higher the boost the more temperature the air will have and the more cooling you need. The faster the supercharger turns the more power it consumes from the crank.

Why is the torque higher nut not the power?

The problem I had was that the supercharger that is used by Toyota on their engines isn’t a very efficient supercharger. To start off with a lower boost it works great. The higher you spin the supercharger the hotter the air gets. This is power out the door. It will also consume more power from the crank leaving less power to go to the wheels. Although the car ran really well it wasn’t the most efficient. The fuel that it used for the power it made wasn’t great.