Edmunds.com | Inside Line | Auto Observer Your Account | Help | Directory
You are here:
![[F]](http://a332.g.akamai.net/f/332/936/12h/www.edmunds.com/media/townhall/webxicons/site.gif){kind=small}
Forums
Automotive News & Views GM News, New Models and Market Share
8456 messages, Last post on Nov 26, 2009 at 4:07 PM
You are in the Automotive News & Views Forum. Your Hosts are steve_ & claires
|
|
|---|---|
|
The XFE project began about 18 months ago, focusing on the overlooked ways in which fuel economy can be improved in everyday cars. "Every tenth [of a mile per gallon] counts," explains Al Manzor, Program Engineering Manager for Cobalt and G5, who led the quest for extra mpg. The GM team worked with tire manufacturers to develop low-rolling-resistance rubber specific to the Cobalt. XFEs are equipped either with Goodyear Integrity tires (running at 35 psi), or Continental Touring Contact AS rubber (which specify 33 psi). By adding intake and exhaust variable valve timing to the 2009 model's 2.2-liter Ecotec inline Four, peak power is boosted from 148 to 155 hp, with enough of an increase in low-end torque to encourage engineers to drop the rear axle ratio from 3.74 to 3.63, for improved fuel economy. The taller ratio enables this Cobalt to reach 60 mph in second gear instead of third, and its 0-to-60 mph time remains unchanged at 8 seconds flat. In spite of the tougher EPA certification guidelines in 2008, the highway fuel economy number jumped from 33 to 36, and again to 37 mpg for 2009. A few calibration changes also assist the fuel economy gain, including a fuel cutoff feature during deceleration, which GM engineers emphasize is transparent to the driver.
|
|
|
|
|
Replying to: 62vetteefp (Sep 25, 2008 3:44 am) I note that in a different thread I saw a number of posters talking about how "every car built today" has a feature that cuts off the fuel completely when the car is decelerating. At the time I suspected that was a lot less widespread than they thought it was. And now I see here that it appears no Cobalt had it until they put that feature in the '09 XFE. It would be nice to see them find a way to offer a slightly smaller engine in this car, thereby bringing up that city number, but it is right up there at the top of its class as it is. And I know that next year the Cruze will come along anyway, with its completely different engine and promises of 40 mpg, so that's great.
|
|
|
Replying to: nippononly (Sep 25, 2008 7:07 am) I'm still on the side that a fuel injection system cuts the fuel off while coasting in gear and I'd like to hear the Cobalt engineers expound on this. Someone please ring them up. 
|
|
|
Replying to: steve_ (Sep 25, 2008 7:24 am) One other thing to consider though, even if the fuel shuts off completely when you coast in gear, the car will still coast further in neutral than in drive. So in some situations, putting in neutral might still be best.
|
|
|
Replying to: andre1969 (Sep 25, 2008 7:28 am) When you pop it into neutral, you have to burn fuel to keep the motor running. Plus you have the safety issues of coasting in neutral (and it's illegal most places) and the engine won't run the water pump as fast coasting in neutral so your engine won't run as cool. If you have a carb instead of fuel injection, then the story is different. Or so I've read around here.
|
|
|
|
|
Replying to: steve_ (Sep 25, 2008 7:33 am) I know that if I shut off the engine while decelerating in gear, I won't get the smooth decel I get now leaving the engine running. It will lurch and jump as it rapidly comes to a stop. Or at least, I THINK I know that! 
|
|
|
Replying to: nippononly (Sep 25, 2008 8:24 am) ) they shut off the ICE at stop lights. Don't they shut down the ICE in town if you slow down to 30 mph or whatever and let the electric take over? I guess your method would work if you can juggle the ignition switch and the gearshift - and if you never need to accelerate away from a hazard quickly.
|
|
|
|
|
Replying to: steve_ (Sep 25, 2008 8:51 am) I think I'd like 5 minutes of chat time with those Cobalt engineers too...
|
|
|
Replying to: nippononly (Sep 25, 2008 10:08 am) Maybe they'll show up at the Chat tonight (9 ET, 6PT). 
|
|
|
I think that my 2002 Seville would shut down fuel flow when going downhill with my foot off the gas. Proof that the fuel flow was at least near zero is that I had climbed up to an observation point near Mt. St. Helens, and then started back down after a period of time. The engine coolant temperature gauge showed the engine at near operating temperature before starting a long downhill grade. I put the car into second gear and coasted for some distance. The engine cooled off to the point that the temperature gauge showed the engine was getting cold. So one has to assume that there was no fire keeping it warm. I think that the primary fuel savings is from a different axle ratio for th Cobalt. |
|
You are here:
Forums
Automotive News & Views GM News, New Models and Market Share
