Quote:
Originally Posted by Leighos
Yes both my vehicles are manual, I've actually never owned an auto!
With the Subaru, when I'm driving economically, I drive totally off boost and change up around 3000. If figure keeping the manifold pressure low but still using adequate RPM to best use the engines torque, is a good way to keep the fuel burn low.
Although my concern with turbocharged petrol engines when driving off boost, is effectively they are acting as a normally aspirated engine, but having a very inefficient compression ratio (My Subaru is 8.0:1) and a restriction in the intake (the turbo and intercooler). I guess its all about compromise though with auto engines.
With the Isuzu, apart from idling, the engine is mostly always running in boost pressure, this is where turbo diesels are very efficient. I maintain around 5psi of boost and get to 2500 RPM before I change up, this seems to be a good balance of useful torque and economy. Incidentally, I also cruise at 2500 RPM in 5th gear, it give approx 85km/hr road speed which better suits the vehicle's aerodynamics also.
What sort of tyres do you run?
The Isuzu used to have 15" 'all terrain' tyres, not that great for rolling efficiency. I managed to get a set of 18" alloys with proper road tyres, I reckon that made quite a difference to economy (and road handling).
|
If your Subaru's gearing allows it, I'd recommend changing up around 2300rpm, as engines are typically more efficient at lower RPMs.
On the highway I try to stay at around 90km/h, which is around 2500RPM in the Camry and around 1900RPM in the Sonata (if only manuals had gearing like that). 90 is good because it's the legal limit for trucks, so people get less pissed off than if I was driving 85. Sometimes I'm impatient and drive at 100 though
