I agree with the above post. Having driven diesels, turbodiesels, petrol, and turbocharged petrol engined cars (and trucks) I can, without a doubt, tell you that the turbodiesel engine is better in 95% of the situations in which you may find yourself in any given day. The only situation in which a petrol engine is better is the "emergency acceleration" situation, where you might need to pour the proverbial coals on to escape a collision with a tractor-trailer that is merging your direction on a multi-lane interstate. In that situation, where diesel engines have a tendency for long turbocharger spool, the more instantaneous thrust of a downshifted petrol engine is probably better. That, and redline-hunting freeway merging on short onramps. So basically, petrol engines are better when screaming at WOT toward redline.

Diesels and turbodiesels require lower RPMs to achieve excellent daily driveability. Due to the fact that most diesel engines redline in the 4K-4.5K range, much of the broad, flat torque curve of a diesel engine is at considerably lower RPMs. As a point of reference, my 6.0 Powerstroke in my Ford Excursion hits maximum torque (560 ft/lb) at right around 2,000 RPM. Remember, also, that the most important factor of what determines excellent driveability and performance is the so-called "area under the curve" of a basic horsepower and torque chart. Peak HP and peak TQ don't mean a lot if it is a narrow band at the highest RPM, with sharp dropoffs on either side. Again to cite my Powerstroke, it makes 400 ft/lb at 1,000 RPM (idles at about 700 RPM), makes 500 ft/lb at 1,500 RPM, and doesn't drop below 500 ft/lb again (after peaking right around 2,000 RPM) until the engine hits about 3,500 RPM. Given that it redlines at 4,000 RPM, that's a pretty broad torque curve, as roughly 50% of the useable engine rev range is at or above 500 ft/lb.

As anecdotal evidence, on my Excursion, at 55 MPH, I can toe in more throttle and rather comfortably accelerate to 70 MPH quickly without downshifting to a lower (4th) gear. On a 5-speed transmission, that's a considerable accomplishment. I can only wonder at what my truck would drive like with a 7-speed or 8-speed transmission as one finds in most luxury automakers cars now.

More anecdotal evidence: I loaded up the wife's X5 (2007 X5 4.8i) with a full load of camping gear and drove it almost 400 miles to my camping destination. It was the two of us, so there was a LOT of stuff (wife can't camp light LOL), and the X5 did OKAY, but there was a considerable dropoff in performance, especially going up any grade at all. The car lugged a lot, and downshifted frequently. My Excursion did the same trip, this time with 2 adults, two children, and two infants, with an even larger amount of stuff (thanks to the presence of children), and the truck barely seemed to "notice" the additional weight. Granted, there is a marked difference in curb weight between a 4,000 lb X5 and an 8,000 lb Excursion, but the added few hundred pounds of gear and food didn't slow me down at all. In fact, I still averaged 23+ MPG on highway and rural roads during both legs of the trip in my Excursion.

The point to the discussion is, if you want a racecar, or something that drives more like a sports car, a factory tuned diesel isn't for you. Stick with petrol. But if you want something that can pull loads, trailers, full cabins, or just give you civilized street manners without requiring lots of throttle to get you around town, the diesel is the way to go. Now that I drive a diesel full-time, I can't imagine driving anything else.

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2007 BMW X5 4.8i - Sport Package, Wife's Car

2001 BMW 325i - My Car.

2005 Ford Excursion Limited 4x4, 6.0 Powerstroke Diesel. My first "grown up" car.