Hybrid Turbochargers

The definition of  "hybrid" within the turbocharger world is the modification of an original, standard unit by changing one or more parts to produce a unit which gives different results from the original. So what is a hybrid turbo and how does it differ from a standard turbo?

Typically, like car tuning, there are different stages to increasing performance (levels of ECU stages are different however to turbo stages), and traditionally this is broken down into 4 stages.

Standard - Self explanatory, a 100% standard unit.

Stage 1 - A Stage 1 Hybrid Turbo is conventionally upgraded bearings, seals (where available) and more precise balancing. The idea behind Stage 1 is to improve the structural strength and reliability of the standard turbocharger to allow the vehicle to be remapped, and boost increased, without the turbocharger becoming weak and unable to handle the increased boost pressure. With the recent growth in lightweight billet performance compressor wheels, often these can be included in the Stage 1 upgrade in the same size as the original, in this instance we recognise this as a Stage 1+ Hybrid upgrade.

 

Stage 2 - A Stage 2 Hybrid Turbo consists of all of the upgrades as found in the Stage 1 Hybrid Turbochargers, but instead of the standard size performance billet compressor wheel, a larger wheel is installed and the compressor inlet housing is machined precisely to ensure the correct clearance is maintained. How large a wheel you can use is impossible to confirm without extensive research and development (R&D), as every application can differ. But, as a rule of thumb, best practice is to not exceed the turbine wheel size as this can cause surge and potential engine and/or turbo damage. Think of it as simple as if the exhaust wheel cannot get the air out, the compressor cannot get it in, so huge compressors on standard turbine wheels, is pretty pointless in many cases, although as always there is an exception to the rule!

 

Stage 3 - A Stage 3 Hybrid Turbo combines the upgrades found in a Stage 1 and Stage 2 Hybrid Turbocharger, but also has flow increased in the turbine/exhaust side of the turbo. This can be with a larger A/R turbine housing or larger turbine wheel. If neither are possible, then there are the options of differing blade configurations, clearancing or cutback turbine wheels (or a mixture).

 Increasing the turbine-exhaust flow results in more air being taken away from the engine, allowing a larger compressor wheel than the Stage 2 Hybrid Turbo to be installed. At Stage 3, a Hybrid Turbocharger, in most cases, requires upgrades to the wastegate control in order to handle the increased boost pressures and turbine presures.

There are also many other modifications, including ball bearing conversions, VNT conversions, compound charging etc. which can be included in the stages above or completed seperately. It must be mentioned that with the wide range of shapes and sizes of turbochargers, some units cannot be machined to increase wheel size, as either there is not enough material thickness of the housing to maintain a good structural strength, or the machining complexity results in costs outweighing the gains. In these instances, custom made housings can be a solution, but come at a price, as normally a production run of 100+ quantity is required.

Stage 1 Hybrid Turbocharger - Upgrade Bearings & Seals

An example of an upgraded bearing. This particular bearing upgrade spreads the thrust loading over a larger surface area. The original bearing spreads the load over 270 degrees, whereas on the upgraded bearing the load is spread over 360 degrees. A larger thrust face will further increase the load spread, however in many cases will require machining to allow installation.

Stage 2 Hybrid Turbocharger - Larger Compressor Wheel

The Stage 2 Hybrid includes a larger compressor wheel. To enable installation, the compressor housing is precision machined to remove material, allowing the larger wheel to fit. Extra work can include porting of housings, burr removal and tapering transitions in the housing to ensure air velocity is free of restriction.

Stage 3 Hybrid Turbocharger - Larger Turbine

An example of a Stage 3 upgrade. The turbine wheel here is larger than the original, this will require the turbine housing to be machined to allow installation.  The larger turbine wheel will increase turbine flow, evacuating exhaust gases from the engine faster. This will allow a larger compressor to be installed to pump more air into the engine. More air in... More power out!