Turbo sizes
#3
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If you count all the non-OE fitments and hybrids, there is a huge variety of distinct turbocharger types available for the Impreza.
Your car is fitted with a Mitsubishi TD04L, which is the smallest unit that Subaru have fitted to a production car, and has been standard fitment on most of the non-STi's since the 1997 model year.
Its small size means low rotating mass, which fosters very good throttle response and spool-up. However, its ultimate flow potential is obviously limited by the smaller turbine, and the practical ceiling with these units is around 265-280bhp.
Larger turbos are capable of higher flow rates without heating the air, but the downsides are increased levels of lag. Thus, while the bigger units can theoretically unleash higher levels of power, there's a delicate balance between outright bhp and driveability.
There's loads been written on the merits of various turbos, and people like David, Harvey, Pat and Bob (and a host of others) have written more good stuff about this subject than would ever fit in one post. Thus, perfect time to hit the search button (or read the "Talk to me about TURBOS" thread further down for starters.
Your car is fitted with a Mitsubishi TD04L, which is the smallest unit that Subaru have fitted to a production car, and has been standard fitment on most of the non-STi's since the 1997 model year.
Its small size means low rotating mass, which fosters very good throttle response and spool-up. However, its ultimate flow potential is obviously limited by the smaller turbine, and the practical ceiling with these units is around 265-280bhp.
Larger turbos are capable of higher flow rates without heating the air, but the downsides are increased levels of lag. Thus, while the bigger units can theoretically unleash higher levels of power, there's a delicate balance between outright bhp and driveability.
There's loads been written on the merits of various turbos, and people like David, Harvey, Pat and Bob (and a host of others) have written more good stuff about this subject than would ever fit in one post. Thus, perfect time to hit the search button (or read the "Talk to me about TURBOS" thread further down for starters.
#4
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Standard one does up to 300 BHP max (bigger on MY01 than before that) and spools up nicely by 3000 RPM in any gear.
Rough rule of thumb is that you can have 100 BHP extra for each 1000 RPM worsening in spool up, up until about 500 BHP on ordinary pump fuel, but beyond 350 BHP your standard engine internals are at risk of orbiting to oblivion.
Rough rule of thumb is that you can have 100 BHP extra for each 1000 RPM worsening in spool up, up until about 500 BHP on ordinary pump fuel, but beyond 350 BHP your standard engine internals are at risk of orbiting to oblivion.
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