My only knowledge for that is from a 1986 Mustang GT 5.0 efi 5 speed manual I once owned. At 55 mph the tachometer would show 1400 rpm and at 60 mph it was turning about 1650 rpm, economy was around 25 mpg . As a comparison my 2002 s60 runs around 1800 and 2200 respectively and economy is around 27 mpg.

 

It's still eight cylinders guzzling gas verses five regardless of RPM at a given speed. More low-end torque means fewer gear changes are required though, even if both vehicles have the same peak horsepower.

 

J.A., I was speaking about the V8 in the XC90, but

Crito, true there are more cylinders in use, but with some members stating they are getting 23mpg on the highway - that's 10l/100km - a number I've seen on very rare occasions and only when going 60mph; I'm trying to figure out how!

 

60MPH with the V8 is around 1800 RPM. 70 is 2000+, 75 is 2200. Those are not exact, just trying to remember from a recent 600 mile trip. ...and I normally get 24+ highway MPG at 75. Sometimes a mile less if there is a lot of on/off throttle - like driving through L.A. Admittedly that is by the optimistic vehicle computer. On two lane roads driving 65 or so I'll get 26. The last time I did this was in November over 300 miles - 26+. I have gotten 29+ (only one tank in 38K miles) with my V8 on a two-lane...with a tail wind. BTW, I always use the cheapest gas I can find - 87 octane. During the summer at the cabin in WY (it's at 7,500') I use 85 octane (partial pressure of O2...rule of thumb is one octane point for every one thousand feet in altitude).

Today's vehicles are extensively wind tunnel tested and tweaked. As a result, when you pick up speed or have a head wind, the MPG drops more than "in the old days."

I often think what sort of over all MPG I'd get if Volvo had three things on the V8: Start/stop tech, direct injection, and cylinder deactivation. I'm thinking 28-29 would be the norm and around town would increase from the 18+ I now get to around 20. Not bad for a 4.4L V8. But the V8 is going away and we are all going to have to get used to turbo'ed 4cyl and sixes - they'll be fine. It's just the way it is in order to meet new CAFE requirements.

 

and I normally get 24+ highway MPG at 75. Sometimes a mile less if there is a lot of on/off throttle - like driving through L.A.
and around town the 18+ I now get

Wow!!! Are there no stop signs or lights where you live? Are all your town roads 55mph? Or are you using metric ? Or that is some real good fuel!

What year is your XC90? Maybe there were some improvements?

In any event, IMO comparing MPGs by the computer is pointless without real benchmarks. It only takes one slow down, hill, or stop sign to throw off the numbers. And short runs with the computer are not accurate either.

If I reset my computer while at speed and maintain that speed via cruise for as long as possible (and I live in flat fl so no major hills), I'm seeing

55mph - 25-26
65mph - 22-24
75mph - 20-21

It's not enough to reset the computer at speed and just drive a few miles at that speed. Do it long enough at that fixed speed on cruise, and the numbers do drop.

If you then factor in toll booths, rest stop, slowdowns, not using cruise control, on my typical long highway drive, the computer is usually down to 19-21 for my avg 75+ mph run to miami.

One thing I like about the V8 is that when I try my best to get the most mpg out it, one can drive around town and never need to go above 1500 rpms. If anything, they should add an "eco" mode to just limit rpms. But even then, I'm lucky if I hit 16-17mpg in town.

 

V8

At 60 mph I am turning over between 1750 and 1800. Gas mileage at this speed on a flat surface without a wind is 24.5 mpg. I have gotten that recently on a trip to Ottawa where my average was 22.7 for the whole 448 mile trip. Cruise was on 65 the whole way and there was absolutely no traffic (left at 10 pm and got in at 5:15 AM.

 

With modern engines at moderate speed even the v8's can get better milage than the smaller engines. They really gear up the larger engines. The 2.5 revs much
higher at speed than the v8 to get power. If you just drove freeway the v8 would get better overall milage, but factoring it all in and frequent stops
at the soccer fields drops the milage...

 

Well based on the engines speeds notes above, the 2.5T runs 500rpm higher at 60 and 70 mph (we're also missing a gear). Based on actual numbers (distance/fuel purchased), I see 16mpg in the city and 20mpg at a constant 70 mph (30 minutes or more). Should have bought the V8!

 

In the city (Westchester to Wall Street) stop and go I can drop to 13 mpg. But if I travel any distance that I can use cruise (set to 60) and if it is flat I can get 24 all day. As I pointed out based on the recent trip to Ottawa this is real world (albeit very late at night with absolutely no traffic for 100's of miles). Finally, does any one think that oil may have an effect. My Volvo is running the 3rd change of German Castrol 5W-30 and there was a noticeable improvement (2 to 3 mpg on the highway) when first changed from what ever was in the crankcase but this was at 2500 miles and the engine was new? Also I drove the new turbo X3 today. Did not like it as much as the Volvo. Louder and much busier body motion. Pretty quick. Also the GPS was really bad.