Turbocharged engine tuning

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When deciding on a power train which should you go for?We looked at NASP engines in our previous article and here we shall examine the tuning options for turbocharged engines.

Personally the thing about turbos is the power hike you get as the turbo spools up and kicks in. The big plus is turbo engines are light and produce the same power as bigger NASP engines.


The downside of a turbo is the lag low down. This is caused when a turbo is starved of exhaust flow, typically at low RPM and there is not enough there for it to spool up. Many turbo cars suffer from lag but this can be a plus, you get economy when in lag mode and lots of power as it comes on boost. Modern turbo engines are designed to minimise lag and on many you will hardly notice this.

Due to the extra pressures involved a turbocharged engine is over engineered and much stronger than a standard block. There is about 40% of a safe power hike on turbo petrol engines and 30% gains on a diesel before you need to start uprating the internals.

A remap is quite simply a resetting  of the cars computer parameters which controls the fuelling, wastegate and thereby the amount of boost. The typical cost of a remap is around the same as a decent sports catalyst around £300 or $500, but shop around as prices and power gains vary. A remap will yield an increase in the order of 30%.

In addition to a remap you can still do a lot to improve a turbo engine. Strip down the engine and get the head gas flowed and ported, with a 3 angle valve job, strengthen the rods,pistons and crank and get it balanced you can look at nearly doubling the power output of the engine. (This depends a lot on the base car you are working with, some can handle this others will still have reliability issues.

A turbo upgrade will also yield substantial power gains, so look out for an OEM (standard case with uprated internals) or after market (bigger housing requiring minor modifications to the cars exhaust, wastegate and air intake housing diameters.) We note that ball bearing turbo tend to spool up quicker and cope with much higher power figures than a thrust bearing one.

Smaller turbos tend to reduce the problem with lag. A twin turbo setup with a boost controller will control the sheer power and manage the delivery to a more progressive level again minimising lag we have seen a twin turbo setup with a small and large turbo that come on in stages. This seems to reduce the lag and gives a very steady power hike throughout the rev range. Big turbo conversions where a larger turbo is bolted on makes bigger power figures at the high end of the rev range. However a big turbo tends to suffer more from lag at the lower end of the rev range.

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