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A few questions about turbocharging...

Hi, I have a few related questions please about turbo petrol cars. I'm thinking of changing my car soon and might actually go for petrol over diesel this time, mainly due to cheaper purchase price and reliability concerns about diesel cars when warranty runs out.

Do modern turbo petrol cars typically have EGR valves and Dual Mass Flywheels, two parts that often cause problems in diesel cars? Also most turbo petrols of today don't have particle filters, do they?

Final question please: why, if petrol is meant to have more potent power than diesel in many ways and I know petrols can generally manage higher revs and top speeds than diesels, do turbo petrol cars usually have much less torque/pulling power figures than equivalent sized turbo diesel engines? I've found diesels to have much more pulling power and responsiveness at speeds that are actually legal and under the limit, than petrols, in cars I've driven. Why is this when both types have turbos?

K Holden, Waterford.

Kieran Holden (Waterford)

Jan 2017 Filed under: diesel

Expert answer

Hi Kieran,

Yes, turbocharged petrol engines do often have exhaust gas recirculation (EGR) systems and dual-mass flywheels, but they are far less likely to cause problems due to, respectively, the different exhaust gases and the torque characteristics of the engine. Added to which, petrol engines work at lower combustions pressures and with less vibration than diesel engines so there's a little less wear and tear to worry about.

No, turbocharged petrol engines don't have particulate filters as, for now, they're considered 'clean' enough not to need them. That will change in the coming years, however.

Finally, the low-down-power thing is simple physics. Most turbocharged petrol engines and their diesel counterparts are pretty close on top-end power numbers (generally grouping around the 110-120hp level), but the difference you're talking about is torque - turning force, that low-down lugging sensation. Some of that is down to turbo design and the fact that a heavier diesel engine can accept higher turbocharger pressures, but most is simply down to the fact that diesel burns from compression ignition, which generates more torque and makes the engine feel more muscular at lower rpm. 

Neil Briscoe - Complete Car Advisor

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