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  • All you need to know about "Big turbo conversions"

    Big turbo conversions Guide

    A turbo charger has a finite capacity to force air into the engine. The basic principle that more air equals more power holds true (as long as there is a sufficient supply of fuel to match this).

    Hybrid turbos are one way to increase the capacity of your turbo, with different impellers the characteristics can be changed. But for larger power gains you really need to add a larger turbo.

    Hybrid turbos

    A larger turbo is obviously physically bigger than an OEM one, and it will therefore require a custom exhaust header and different oil feed lines.

    The benefits of a big turbo conversion is a massive increase in power. The increase typically focuses on the top end of the rev range where you get a massive power increase. 

    There is a a downside, a large turbo takes a while to get up to speed and it can seem quite hesitant (a condition known as turbo lag) where the engine struggles for power below 3000 rpm. Big capacity engines (2.5 litres upwards) are best suited to large turbos as they can sustain the exhaust flow rates that the turbo needs to spool up.

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    Some tuners use a twin turbo setup fitting a smaller initial turbo (or even a supercharger) and then bringing the big turbo online when the exhaust flow rates can support it.

    A ball bearing turbo will spool up more quickly than a thrust bearing one and the ball bearing turbos are more tolerant of larger power figures. (Thrust bearings tend to prove unreliable when pushed beyond 350bhp).

    So can you just bolt on a big turbo and everything will work? Unfortunately things are not this easy and the car will need to be remapped. A standard ECU will usually have a failsafe that cuts in where boost exceeds a certain limit so this will need to be removed. 

    Also when increasing the power of an engine you will need to strengthen the bottom end of the engine and ensure the head is capable of flowing the supply of air and fuel correctly. This also means increasing the injector capacity and supplying fuel at a greater rate will usually need a higher capacity fuel pump.

    You will also need to uprate the intercooler as a standard intercooler can become restrictive when you have a larger turbo.

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    2 Responses to “Big turbo conversions”

    1. Daene says:

      I own a st170 and am just wondering if there is a turbo conversion and if so how much

    2. shaun warren says:

      do you know anyone who can do a turbo/supercharger conversion on a 1.4 corsa d