Does the Overdrive SUCK in these trucks? or is it me?
#31
10-12-2012, 04:32 PM
Grand Champion
Depends on the length of time the injector is open for each cycle. Higher load (heavier throttle at lower RPM) will result in a longer injector pulse.
3ms pulse x 1500 revolutions (x.5) x 8 injectors = 18000 ms
1ms pulse x 2000 revolutions (x.5) x 8 injectors = 8000 ms
Even though the engine is spinning faster, and the injectors are squirting more often, the duration of the squirt is lower, resulting in less fuel burned.
Clearly these are numbers pulled from my butt, but basically that's what we're talking about here. Lugging the motor requires more fuel than not lugging.
I think you're using the wrong fuel though. Even with a 14k pound trailer in tow I didn't have too many hills that slowed me down.
3ms pulse x 1500 revolutions (x.5) x 8 injectors = 18000 ms
1ms pulse x 2000 revolutions (x.5) x 8 injectors = 8000 ms
Even though the engine is spinning faster, and the injectors are squirting more often, the duration of the squirt is lower, resulting in less fuel burned.
Clearly these are numbers pulled from my butt, but basically that's what we're talking about here. Lugging the motor requires more fuel than not lugging.
I think you're using the wrong fuel though. Even with a 14k pound trailer in tow I didn't have too many hills that slowed me down.
Pretty much. When you hit that sweet spot where the throttle plates are open enough that the pumping losses are relatively low but the RPM's are still low enough that friction losses don't yet dominate the equation, everything just cruises along with the least necessary effort.
When RPMs are low and the throttle plates are mostly closed, a considerable bit of effort is required to move all of that air past the throttle plates. Open 'em up some, and the effort required drops at an inverse square rate... so if you had, say, one square inch of opening, then bumped it up to two square inches, the effort required to draw the same volume of air is four times less. That's how pumping losses work.
Imagine you've got a shot of whiskey, and your friend has a shot of whiskey, and you've got a bet about who can finish off his shot first -- you've got a regular drinking straw and he's got a swizzle straw. Same shot, relatively equal suck power available for both of you, but you're going to win the bet every time. Heck, you could finish off a five ounce glass of wine before he could get that shot down. And when it's done, he's likely to be gasping from the exertion.
Same gig when you're running in too high a gear for your road speed. The engine RPM is down and the throttle plates are less open so you've got big pumping losses, AND you're in the shallow part of the torque curve pushing against a shorter lever (lower final drive ratio). Drop a gear, get the throttle plates opened further to reduce pumping losses, and then as long as your RPM's are still low enough that you're not encountering big friction losses, you're in the steeper part of the torque curve AND pushing on a longer lever so you're demanding significantly less energy from each revolution of the engine.
There's more to it, of course, but that's the gist of the matter.
When RPMs are low and the throttle plates are mostly closed, a considerable bit of effort is required to move all of that air past the throttle plates. Open 'em up some, and the effort required drops at an inverse square rate... so if you had, say, one square inch of opening, then bumped it up to two square inches, the effort required to draw the same volume of air is four times less. That's how pumping losses work.
Imagine you've got a shot of whiskey, and your friend has a shot of whiskey, and you've got a bet about who can finish off his shot first -- you've got a regular drinking straw and he's got a swizzle straw. Same shot, relatively equal suck power available for both of you, but you're going to win the bet every time. Heck, you could finish off a five ounce glass of wine before he could get that shot down. And when it's done, he's likely to be gasping from the exertion.
Same gig when you're running in too high a gear for your road speed. The engine RPM is down and the throttle plates are less open so you've got big pumping losses, AND you're in the shallow part of the torque curve pushing against a shorter lever (lower final drive ratio). Drop a gear, get the throttle plates opened further to reduce pumping losses, and then as long as your RPM's are still low enough that you're not encountering big friction losses, you're in the steeper part of the torque curve AND pushing on a longer lever so you're demanding significantly less energy from each revolution of the engine.
There's more to it, of course, but that's the gist of the matter.
#33
10-12-2012, 09:45 PM
Yup, http://www.hemifevertuning.com/, I think $265 gets you the tuner and 3 "canned" tunes. Custom tunes can be made, but you really need those for heavy engine mods...
#34
10-12-2012, 09:46 PM
Grand Champion