Air Flow Maps


Here you can look at air flow maps for both compressor and turbine wheels. There is a lot of misunderstanding about flow maps. A flow map is there to assist turbocharger designers in choosing the best compressor and turbine wheels for a given application. The flow map graphs themselves are produced in laboratory type, controlled conditions with little or no variances in altitude, temperatures, barometric pressures etc. Conditions in 'real life' or 'in car' can be radically different. As such, in our opinion a flow map can at best be used as a guide. We have heard of experts being able to map a car just from a flow map! Remarkable!

The corrected air flow is shown on the 'X' axis, normally in Lb/min but sometimes in CFM or Kg/sec. The Pressure Ratio is shown on the Y axis. Plotted on the graph are the 'efficiency islands', 'speed lines', the 'surge line or area' and the 'choke line or area'. The basic idea is to calculate various pressure ratio and air flow figures for different engine speeds and the plot these onto the graph, choosing one that offers the best efficiency. It must be noted however that the flow map graphs are produced with a compressor wheel running in a particular A/R compressor housing. If we have produced a Hybrid turbocharger using a different air ratio compressor housing than that used on the standard unit, this in itself radically changes the map. So looking at the flow map for a particular compressor wheel does not guarantee you are looking at the results of the complete turbocharger. Similarly, modifications to the turbine wheel, compressor housing inlet, compression face clearance and angle and ported shroud conversions all affect the flow characteristics.

 
 
 
 

This brings us back to the map just being a guide. There is no substitute for experience. We have designed Hybrid turbochargers in the past, where the map looks fantastic but on the vehicle in real life situations it has been a disaster. Likewise the other way around, where the map looks all wrong but perfect on the car.

In any case, the turbochargers performance is so radically affected by the engine and manifold designs; that unless the turbocharger designers and engine builders 'talk', normally a disaster is just around the corner. The most common mistake is over camshaft selection and cylinder head modifications. You can read more about this in 'Turbo Matching & Engine Requirements'.