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I've only driven one LSx engine, whatever is in the '08 C6 Z06 but one thing doesn't compute. In cross shopping cars I see that the '06 CTS-V weighs 3,850lbs and gets 16/26 mpg with 400hp. The '02 M5 weighs 4,080lbs and gets 12/19 mpg with 400hp.
Are the ITBs just that thirsty?
Is the 7000rpm V8 just so awesome the EPA couldn't resist some redline action during the test?
And damn new cars are heavy with all their safety equipment!
There are probably many factors in what can make that happen, but I'm going to say engine management and gearing have a lot to do with it.
'95 Jeep Cherokee / '80 Mazda Rx-7 / '68 Corvair Monza Coupe
What he meant to say was, "Yes, it is simply that awesome."
Don't know, but my 05 CTS-V averaged over 21 mpg over the course of a year, including autocrosses and drag races. Once I managed to get 27 mpg on a one-day road trip.
The LSX comes paired with a tranny that has 2 overdrives. Look at the rpm it cruises at on the hwy. There's the gas mileage.
"mobilito ergo sum" I drive therefore I am!
Then why is the city mileage 33% better than the M5? It's got to be more than just gearing.
Torque. The LSx has it (LS2 in this case with the 06 CTS-V), and the M3 doesn't. That means the Caddy can loaf along at 1500RPM's, take off in 2nd gear, and has a 1-4 skip shift. The Beemer has to rev to get going anywhere because it has no torque, and all of those RPM's makes for poor mileage.
Michael Pinto - 73 AMC Javelin 360 / GoKart / 86 944 Sport / 01 Grand Prix GT / 06 Mazda5 M5
^^ This.
And lower RPMs aren't the panacea of MPG. Proper RPMs are the best for MPG. Cruise too low and you are going to be lugging and wasting fuel.
I'm bringing sexy back
I pretty consistently got 28 mpg with my 5.3 LS with a carburetor, so its not necessarily engine management. Of course, that was in a 2000-lb S10 
I think it has more to do with head and cam design... not that they're anything magical, just well-designed.
I'm bringing sexy back
When I tell non-car people that V8s can actually get good fuel mileage, they look at me like I just fell out of the sky and are asking them to come back to my home planet.
I know a guy with a stock C6 Corvette that consistently gets 30 mpg on the highway. He says if he has to travel, he takes the Vette. 
'95 Jeep Cherokee / '80 Mazda Rx-7 / '68 Corvair Monza Coupe
Well, yes... it is that awesome. So is the BMW. The torque monster LS allows giggity power slides and gearing that saves fuel - the rev happy germans are all power up top and make a fantastic soundtrack. Both are silly fun to wail on.
The LSx wins for me because we can get them at a reasonable price here, aftermarket parts are plentiful, cheap and it fits in everything. Summit racing should list it under "Universal" in the parts menu.
Lord of drivel and harbinger of Floundering
Javelin wrote: Torque. The LSx has it (LS2 in this case with the 06 CTS-V), and the M3 doesn't. That means the Caddy can loaf along at 1500RPM's, take off in 2nd gear, and has a 1-4 skip shift. The Beemer has to rev to get going anywhere because it has no torque, and all of those RPM's makes for poor mileage.
while i agree with most points about gearing etc., if you've driven an e39 M5 i cant imagine describing its 5 liter V8 as a low torque engine.
Dave
In reply to WilberM3:
Compared to the LS2 it is. 
Michael Pinto - 73 AMC Javelin 360 / GoKart / 86 944 Sport / 01 Grand Prix GT / 06 Mazda5 M5
i own an LS2, though it's in front of an auto in a 4800# truck, and yea its got a lot of torque, but its never struck me as a stump puller at low rpm, just big enough to make good torque down there anyway. what always surprises me is how much top end the LS2 has. compared to the old vortec 350, THAT engine's a torquey stump puller, but cant breathe up high. maybe it's the auto and weight of my truck that's coloring my view?
anyway the LSx engines are just that awesome to the OP.
Dave
There is a difference in the age of the engines and management - the new LS engines are using displacement on demand, for example. And that E39 engine is good on torque, but it's not the stump-puller the Chevy is. Then again, the LS doesn't sound anywhere near as good as the BMW mill :)
In my experience, LS engines are thirsty around town even in light cars, and the BMW beats the mileage estimates in town. So maybe the difference isn't as big as you think.
Square left in 50 caution ocean!
the highest performance versions of the LS engines that are backed by manual transmissions don't use displacement on demand. the automatic versions do, tho, because i think they are trying to fool everyone into thinking that automatics are better and manual transmissions are for people that hate the planet or something. this is why the automatic V8 Camaros have a better mpg rating than the manual transmission versions.
what kind of gearing does the BMW's use? i don't think GM puts anything deeper than a 3.50 or so gear behind an LS engine in passenger cars, and they cople that with steep overdrive final gears in the transmissions. low cruising rpm+lotsa torque= good mileage when you want it and fun when you need it.
but GM V8's getting good mileage in performance cars is nothing new and didn't start with the LS engines. LT1 powered Corvettes, Camaros, and Firebirds from the mid 90's are known for getting close to 30mpg on a regular basis and the big LT1 powered Caprice wagons that weigh in north of 4300 pounds can also get mileage in the high 20's while being surprisingly quick and agile for something that size.
one other thing i noticed when poking around teh interwebs looking for random info on my 86 Camaro is that the carbureted 305 powered cars had the same EPA gas mileage ratings as the "economy" models with the fuel injected V6, despite having close to twice the horsepower and torque.. granted, it was the 80's and "high performance" is a relative term, but it shows that building efficient and torquey V8 engines is nothing new for GM.
Thanks for the info guys. The BMW does sound pretty awesome and of course has the BMW feel over the Caddy. Just not sure that's worth the price of entry or the price of maintaining/fueling it.
I can't say I'm a huge fan of my brother's Challenger R/T so maybe I won't like the CTS-V.
There's one other factor to keep in mind, the BMW will maintain it's value much longer than the caddy. And when it comes time to sell you have a much bigger market than the caddy market.
"mobilito ergo sum" I drive therefore I am!
My friend has an 05 GTO that he reports getting 27mpg at about 80 on the highway and mid-high teens around town. He drives generally drives more spirited than most. When he first got it an we where hooning it around we managed a sub 10mpg tank in one night.
MPG will probably depends more on how you drive it than the ratings.
As for CTS-V vs M5
I like both the CTS-V and M5 and have driven both a couple times. The CTS-V felt a bit quicker overall and pulled better down low.
The M5 has a nicer interior but I could live with either. If the M5 interior holds up better than the 3 series cars it might be worth it. If it needs the headliner, window regulators, dash pixels etc that my brothers E46 needed then no thanks.
The only real common issues I know of with the CTS-V are the rear end and radio button labels scraping off. I didn't research the M5 enough to know common trouble spots aside from the cooling system and MAF.
Both have depreciated down to the same levels ( $10-$20k depending on year and mileage) and I dont see either dropping down a whole lot further for well maintained examples so its probably a wash at this point.
I can't see going wrong with either at this point.
Fairly certain the current CTS-V and ZR-1 do not have cylinder deactivation.
Retained value is an issue and the BMW will hold value well.
Of course you could get a clean 996 and drive it without ever having it lose value as they are at their low point if not a bit past.
Some LS engines are much torquier than others. My V has the LS6, and that engine is all top end. Under 4k isn't that exciting, but get past 4500 and it's "cry havoc and let slip the dogs of war" time. A mildly-built LS1 will also make more torque for less money than an LS6, and make more power down low, but will run out of poop earlier.
As for gearing, my V does 55 mph at 1500 rpm. My 99 Z28 is a lot better--68 mph at 1500 rpm. It's just insane how tall sixth gear is in that car.
I don't believe the M5 has retained its value better thus far. Each seem to be about the same.
The 98-03 M5's stickered in the $70's to $80's.
The 04-07 CTS-V stickered in the $40's to $50's
True the BMW is a bit older but you can find either in the $10-$20k depending on mileage and condition. I haven't seen the prices of either falling a whole lot in the last year or two and dont forsee them falling a whole lot farther in the near future.
How does the Ford 302 fit into this discussion? The LS1 gets awesome gas mileage. (Dad claimed to have gotten over 30 on his road trip from Texas to Maine.) But the 302 hardly seems to be able to make these claims. Old notchbacks getting 17 mpg highway? My numbers are probably off, but the question remains the same...
I think the 6-speed trans provides a big advantage over the 5-speed that came with the 302. It makes it a little easier to get away with something like a .50 overdrive gear without an unreasonable amount of space between each gear.
Also, just in general...the LSx is probably the most advanced OHV engine in production, and the 5.0 is based on 1962 technology.
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