Analyze Your System – Adjust Accordingly

To analyze your turbocharger combo, you’re going to need 3 pressure sensors installed in certain places. In this case we’re going to use the PCS dashlogger (Dashlogger.com) as our data acquisition unit. PCS has some of the best sensors and logging units available, especially for high boost applications such as drag racing. Their sensors are accurate from 0-100psi. We’re going to need the intake plenum, the compressor cover and the exhaust manifold pressures. The trickiest is the exhaust manifold sensor because it’s so hot, you really need to put a length of copper or steel line to dissipate the heat. Using approximately 12”-14” should work. Then you can attach silicon hose to the end of that coil. We don’t want to burn the hose up.

We now have our three sensors installed and are ready to read and interpret the information. There are several different ways to get these readings and they can change during different tune ups or different weather. These readings are as important as your A/F ratios and should be monitored just as much. Changing the cam shafts, headers, intakes or intercoolers can make major differences in these pressures. The basic principle is to have the same pressure in all 3 places. On some setups, such as if the intercooler is the restriction; you’ll see more pressure at the compressor cover than the intake manifold. The rule of thumb is that if there is more than 1 psi of difference on the compressor side, you need to make an adjustment. In our drag application we’d like to keep a 1:1:1 ratio (1 psi of intake manifold pressure:1 psi compressor cover pressure: 1 psi exhaust manifold pressure ). So if we have 30 psi of boost at the compressor cover and the intake manifold, then we want to see 30 psi of exhaust backpressure. Those numbers would be great for a SFWD car, whereas on a PROFWD car we’d like to see a slightly better ratio of 30 psi at the Intake manifold and compressor cover and 28 psi at the exhaust manifold. The idea is to stop the exhaust gas from stacking up and going backwards into the motor thereby clogging the engine with hot gas and losing HP overall. 1:1:1 is an ideal setup for a heavier less radical car however in a more radical situation such as a PROFWD car the different ratio of 1 : 1 : .8 is closer to the ideal.

Let’s say we’ve checked our pressure readings and our exhaust manifold pressure is 1.5:1 (assuming the compressor cover and intake manifold pressure are the same), which means 30 psi of boost measured on the intake side and 45 psi of exhaust pressure. We’ve discovered that the numbers don’t match our 1:1:1 theory. The easier way to make the necessary adjustment is to go to a larger A/R which increases the overall flow on the turbine side which in turn slows the exhaust gas down thereby lowering the pressure. This is normally the most cost effective way to achieve our goal. With money being no object we’d change the exhaust wheel. If our intercooler is the problem, obviously the easiest way to solve this is to get a larger intercooler. Last but not least, if our turbine pressure is staying the same and the compressor pressures are dropping (boost starts to drop), then our compressor is too small. If this is the case our inlet air temperature will start to rise.

So we’ve covered the very basics of flow characteristics of our turbocharger system. Obviously there are going to be varying opinions on some of what you’ve read here, but from our personal experience this stuff just flat out works.