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
SUVs Chevrolet Suburban & Tahoe Chevrolet Suburban Active Fuel Management
26 messages, Last post on Jul 11, 2008 at 11:56 PM
You are in the Chevrolet Suburban & Tahoe Forum. Your Hosts are steve_ & tidester
|
Replying to: arrie (Jul 09, 2008 3:32 pm) I never said the engine would have two torque curves....I said it would have two different power (as in horsepower) curves. When running in 4 cylinder mode, you'll have 4 power strokes per 2 engine revolutions. When running in 8 cylinder mode, you'll have 8 power strokes per 2 engine revolutions. You're burning twice as much fuel in 8 cylinder mode. It just basically means that you will be spraying twice as much fuel/cylinder in those 4 cylinders to keep the vehicle going at set speed compared to using all 8 cylinders. The engine does not spray twice as much fuel/cylinder. The piston moving up and down is a given volume displacement. You do not vary the mixture in the cylinder to double the hp. If you doubled the amount of gas in the same volume of air, you would run extremely rich, the mixture would not burn completely, and it would clog up the cat converter. If you leaned out the mixture by not providing enough gasoline in that volume of air, you'd burn out the valves.
|
|
|
Replying to: kiawah (Jul 09, 2008 7:19 pm) You seem to have so good handle of this on your own level I'll let it be. but as an absolute last comment from me on this... It just is that the car takes certain amount of force (energy per mile) to push against wind resistance (and rolling resistance) at given speed. As long as that force (and energy) comes from the gasoline in the car's tank the same amount of that gasoline is needed to push that car with that given speed REGARDLESS OF HOW MANY CYLINDERS OF THE ENGINE IS DOING THE WORK! Arrie
|
|
|
Replying to: arrie (Jul 10, 2008 1:02 pm) It will take the some force and energy to move that vehicle forward cruising at 60mph (let's call it X, or better yet just assume /define it to be 65HP). I think we both can agree to that. Now lets talk about what energy the engine 'actually' produces. At 60mph, in high gear, let's for the sake of discussion say the gearing puts the engine RPM at 3000rpm. Using the prior 2GR Toyota chart, at 3000 rpm the engine is producing 140 HP. (Yes I know the Tahoe doesn't turn at 3K at 60mph, but we're using the Toyota charts since I already posted them, and the gearing for both are higher). Even though the vehicle only needs 65HP to move thru the air and down the highway, the engine is producing MORE horsepower than is needed. That extra energy (heat) is wasted and expelled (through the radiator and exhaust). Now what APM can do, is shut down 4 of the cylinders, and not fill them with fuel mixture. The engine's power curve now, since it's burning half as much fuel for any given RPM, would be approximately half. So now the engine at 3000 RPM is producing 70HP. 70HP is still more than the 65HP needed to move the vehicle thru the air at 60mph, so the speed is maintained. It doesn't slow down, or downshift. There is now a closer balance between the HP needed to move the vehicle, and the HP actually produced, so there is less wasted energy. Why then build engines that produce 140HP? Because when you are starting a vehicle from a stop sign, or carrying a heavy load, or driving up an incline......you need much more than the 65HP that the vehicle might need cruising on the flat interstate.
|
|
|
Replying to: kiawah (Jul 10, 2008 1:33 pm) First I need to correct my statement that the 4-cyl mode does not provide a new torque curve. Of course it does as the torque roughly is half of the 8-cyl mode at given rpm but what I mean is it does not provide a useful additional torque curve and I stay behind that. The only way 4-cyl mode could be helpful is that if it would take the 4-cyl mode every time the power requirement from the engine allows to do so. From what I have learned about it this is not how it works. Now about the torque curve. The engine does not produce torque (and power) by the curve when you normally drive the car. It only produces it when you pull the maximum torque from the engine, i.e. THE TORQUE CURVE ILLUSTRATES MAXIMUM TORQUE OUTPUT THAT THE ENGINE CAN PRODUCE WITH CORRESPONDING ENGINE REVOLUTION IN THE CHART! When you normally drive say that 60 mph speed the engine provides exactly that amount of torque (and power) to keep the car going that speed. If it would provide more than is required the car's speed would increase unless you step on brake pedal or other vice cause more "friction" for the engine to work against. The engine does not provide the torque (power) what the torque chart shows for that engine rpm unless the engine's performance is on the max limit for that engine rpm. Seems like you were a perfect customer to buy one of these AFM hoax vehicles. ...lol... This was my last post on this topic with you. Arrie
|
|
|
Replying to: arrie (Jul 11, 2008 2:12 pm) I found this reference for you if you'd like to read up on the theory of how Automobile Engines work. It's a little long and detailed for easy casual reading, but it covers the physics at work in an automobile internal combustion engine. Physics in an Automobile Engine
|
|
|
Replying to: kiawah (Jul 11, 2008 4:14 pm) This one's an easy read. It's written by Barry Parker, a physics teacher at one of our local colleges. tidester, host SUVs and Smart Shopper |
|
You are here:
Forums
SUVs Chevrolet Suburban & Tahoe Chevrolet Suburban Active Fuel Management
New? Join Now!
Forum Tools
Search Forums
Browse by Vehicle
2010 Chevrolet Suburban
Browse by Board
Browse by Topic
Today's Chats
