My LT's don't have ports for it.
MPG Question (point me in the right direction)
- Thread starter TylerZ281500
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My LT's don't have ports for it.
TylerZ281500
Yukon Ridin High
i thought you could buy some that had it. i havent done headers yet its on my to do list. i feel really stupid about this gas tank thing
Yes, if you get ride of the EGR, you must have it programed out in order to obtain the benefits of not having it. Other wise your wasting your time and money. A common problem with our trucks is a little part called the CTS/ Coolant Temp Sensor. Once the engine is up to operating temp (around 195-210 degrees) the engine enters "closed loop operation", until then the engine is in "open loop operation". When in open loop the ECM uses a single value for the fuel map- very rich (it works on the same principles that carburetors using a choke. Once it transitions into closed loop the O2 sensor and CTS take over with the fuel maps. For the most part the O2 does most of the work, but if the ECM never knows when to enter closed loop, it will remain in open loop and cause very poor fuel economy. This is caused by the CTS not sending the correct resistance readings the ECM is looking for. It will not "throw a code" when it goes bad, because the ECM is still seeing a value for it. It is a $20 part, so its not really that big of a deal if it doesnt solve fuel economy problems.
Word!, I have seen that several times. I even bought a truck that supposedly had OD burned out, and the day I bought I put my live data scanner on it and the ecm was showing -20 on the engine temp when the engine was at operating temp so I changed out the ecm temp sender and then the truck would go in to OD and it worked perfect!
Your gage runs off of a resistance measurement from the sending unit. So before you go swapping in a new sending unit, clean all of your electrical connections really well and see if that helps any. If not, then yes I would agree, your sender is bad.
I've made several posts about this, I can probably give you a brief rundown before I leave. If it's only mildly understandable, oh well.
Fuel economy and engine RPM are not necessarily related to one another. More important in the equation (sans aerodynamic drag) is volumetric efficiency. TBI engines are fairly unique (and just plain weird) in some of the things they like, and don't like.
For example: Cylinder heads. They're a swirl port/fast burn design so they require very little ignition advance at cruise. This is the first mistake tuners and most backyard Joes make in tuning for economy. The stock timing tables are decent in this respect. The EGR system is another quirk these engines have as well. They can be tuned to run just as well in part throttle applications without EGR, however at light cruise you're going to see significantly better economy with a functioning EGR for two reasons. One is charge cooling. You probably know the intake already benefits from the principle called latent heat of vaporization in which the intake charge is cooled significantly when the liquid fuel vaporizes in the intact tract due as a result of the flash change from ambient atmosphere to negative atmosphere. (vacuum) EGR compliments this action by introducing an inert into the intake as well, which although much warmer than the incoming intake charge has the chemical effect of "cooling" the combustion chamber and preventing detonation. Cooling is a bit of a misnomer, but it has the same general effect. In practice it effectively decreases cylinder volume thereby reducing the chance of preignition with a lean mixture. Another benefit is reducing throttling loss. An engine operating at peak efficiency is an engine operating at wide open throttle. (WOT) Since obviously you can't run around all day wide open, you're not operating the engine anywhere near its peak efficiency. That's where the EGR system comes in. On TBI engines the valve is pulse modulated. Basically what that means is it doesn't open and stay open, it's constantly pulsed. By introducing a known volume of inert exhaust into the intake, you reduce the pumping action needed to pull air and fuel through the throttle body because it's effectively no longer a 5.7L engine. That's making a very complicated subject simple, but you'll get the general idea.
Here's why all that matters in relation to RPM and mileage. Say you're driving along at 55mph and the engine is turning 1400rpm or so. On paper you'd think it would use less fuel than if it were turning say 2500rpm, but is that true? Not necessarily. Depending on factors like aerodynamic drag and vehicle weight, the engine could achieve much better efficiency and thus fuel economy operating in a higher RPM range. Of course YMMV, but in practice it's proven to be very effective for me since I travel all around the USA east of the Mississippi and I have nothing better to do. I don't have an expensive enough calculator handy to show you exactly what I'm talking about though. Now there are limits obviously. Aerodynamic drag increases by the square of velocity so even though your engine may be operating at peak efficiency in overdrive at 75mph, the drag created by that speed more than negates it. In practice I've judged 63mph to be the best speed for all combinations of axle ratio paired with a 4L60. The more you get into this stuff the more interesting it gets. A strong (read:not a 300K mile hunk) engine, good tires and a tune matched for modern E10/E15 fuel with lean cruise enabled and you'll get as good or better fuel economy than any new fullsize truck on the road. Case in point, I can easily see 485-530 miles per tank (i usually suck down 2 or 3 tanks a week without taking side trips) which equates to the neighborhood of 23-23.5mpg, while my ladyfriend is lucky to ever see 20 on the highway running the same speed in her 2011 5.0L F150. Food for thought.
Fuel economy and engine RPM are not necessarily related to one another. More important in the equation (sans aerodynamic drag) is volumetric efficiency. TBI engines are fairly unique (and just plain weird) in some of the things they like, and don't like.
For example: Cylinder heads. They're a swirl port/fast burn design so they require very little ignition advance at cruise. This is the first mistake tuners and most backyard Joes make in tuning for economy. The stock timing tables are decent in this respect. The EGR system is another quirk these engines have as well. They can be tuned to run just as well in part throttle applications without EGR, however at light cruise you're going to see significantly better economy with a functioning EGR for two reasons. One is charge cooling. You probably know the intake already benefits from the principle called latent heat of vaporization in which the intake charge is cooled significantly when the liquid fuel vaporizes in the intact tract due as a result of the flash change from ambient atmosphere to negative atmosphere. (vacuum) EGR compliments this action by introducing an inert into the intake as well, which although much warmer than the incoming intake charge has the chemical effect of "cooling" the combustion chamber and preventing detonation. Cooling is a bit of a misnomer, but it has the same general effect. In practice it effectively decreases cylinder volume thereby reducing the chance of preignition with a lean mixture. Another benefit is reducing throttling loss. An engine operating at peak efficiency is an engine operating at wide open throttle. (WOT) Since obviously you can't run around all day wide open, you're not operating the engine anywhere near its peak efficiency. That's where the EGR system comes in. On TBI engines the valve is pulse modulated. Basically what that means is it doesn't open and stay open, it's constantly pulsed. By introducing a known volume of inert exhaust into the intake, you reduce the pumping action needed to pull air and fuel through the throttle body because it's effectively no longer a 5.7L engine. That's making a very complicated subject simple, but you'll get the general idea.
Here's why all that matters in relation to RPM and mileage. Say you're driving along at 55mph and the engine is turning 1400rpm or so. On paper you'd think it would use less fuel than if it were turning say 2500rpm, but is that true? Not necessarily. Depending on factors like aerodynamic drag and vehicle weight, the engine could achieve much better efficiency and thus fuel economy operating in a higher RPM range. Of course YMMV, but in practice it's proven to be very effective for me since I travel all around the USA east of the Mississippi and I have nothing better to do. I don't have an expensive enough calculator handy to show you exactly what I'm talking about though. Now there are limits obviously. Aerodynamic drag increases by the square of velocity so even though your engine may be operating at peak efficiency in overdrive at 75mph, the drag created by that speed more than negates it. In practice I've judged 63mph to be the best speed for all combinations of axle ratio paired with a 4L60. The more you get into this stuff the more interesting it gets. A strong (read:not a 300K mile hunk) engine, good tires and a tune matched for modern E10/E15 fuel with lean cruise enabled and you'll get as good or better fuel economy than any new fullsize truck on the road. Case in point, I can easily see 485-530 miles per tank (i usually suck down 2 or 3 tanks a week without taking side trips) which equates to the neighborhood of 23-23.5mpg, while my ladyfriend is lucky to ever see 20 on the highway running the same speed in her 2011 5.0L F150. Food for thought.
TylerZ281500
Yukon Ridin High
i have a 700r4 but i understand what your saying. 23 on an obs is insane how the heck are you doing that exactly? i think what you said makes alot of sense. so as you were saying there are more variables to mileage and rpms's such as drag wieght etc, and its dependant on these thing, so i cant really make a validated statement saying ill burn more or less gas at this rpm as opposed to this one. is that correct or am i off track?
MPG is alot more complex than just simply keeping RPMs down....granted, lower RPMs can be important, however, lower RPMs don't always mean better MPG...it has to do with where the engine is at it's peak efficiency, cams, heads, injection type/setup, maintenance...even things like filters, tires, road and weather conditions, etc will all play a role in the efficiency of the engine. the key is to get your gearing correct in order to keep your engine in it's peak efficiency area of the torque curve, because the less work the engine has to do in order to get and keep the truck moving, the less fuel it uses.
now with that said, the peak of the torque curve is typically lower in RPM, but not necissarily as low as you can get. here's a couple examples from my vehicles...on my truck, when I first swapped to the T56 (which has vastly different gearing than the 60e I had before it), I had 3.73 gears in, now in 6th, I would cruize on the freeway at a really low RPM, around 1400-1600...and I'd get around 11-12mpg....however when I re-geared to 4.88's, I can cruise around 2000-2200 or so, and my mpg jumpped back up to 16-17mpg with no other changes.....another example is my little commuter honda car, I commute around 70-80 miles round trip every day to work, always along the same route, etc...well, I can cruize along the freeway at 75mph in 6th spinning roughly 2800 and getting 35-37 mpg....however, when I cruize at around 90mph in 6th spinning roughly 3200, I get 38-39mpg...so absolute lower RPM doesn't necissarily mean higher mpg, unless that is where you're engine is most efficient.
now with that said, there is one thing that will increase mpg regardless of engine design or efficiency...which is driving style, most all of your mpg are lost from things like getting the truck rolling from a stop, and idling, road rage, throttle feathering....y'know, the stuff that mainly constitutes city driving, so if you can help stabilize that sort of stuff by being aware of how you're driving, and keeping your driving stable and conservative....you'll be able to increase MPG, at least to some extent.
of course there are MANY other things that play a role in MPG like aerodynamic drag, weight, etc, etc, etc....but I mainly focused on RPMs since that's what you asked about...
now with that said, the peak of the torque curve is typically lower in RPM, but not necissarily as low as you can get. here's a couple examples from my vehicles...on my truck, when I first swapped to the T56 (which has vastly different gearing than the 60e I had before it), I had 3.73 gears in, now in 6th, I would cruize on the freeway at a really low RPM, around 1400-1600...and I'd get around 11-12mpg....however when I re-geared to 4.88's, I can cruise around 2000-2200 or so, and my mpg jumpped back up to 16-17mpg with no other changes.....another example is my little commuter honda car, I commute around 70-80 miles round trip every day to work, always along the same route, etc...well, I can cruize along the freeway at 75mph in 6th spinning roughly 2800 and getting 35-37 mpg....however, when I cruize at around 90mph in 6th spinning roughly 3200, I get 38-39mpg...so absolute lower RPM doesn't necissarily mean higher mpg, unless that is where you're engine is most efficient.
now with that said, there is one thing that will increase mpg regardless of engine design or efficiency...which is driving style, most all of your mpg are lost from things like getting the truck rolling from a stop, and idling, road rage, throttle feathering....y'know, the stuff that mainly constitutes city driving, so if you can help stabilize that sort of stuff by being aware of how you're driving, and keeping your driving stable and conservative....you'll be able to increase MPG, at least to some extent.
of course there are MANY other things that play a role in MPG like aerodynamic drag, weight, etc, etc, etc....but I mainly focused on RPMs since that's what you asked about...
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An engine at WOT, max RPM is not at its most efficient. Power curves fall off after the cam exceeds the RPMs that it was ground to perform in. Max efficiency of every motor, electric or combustion, is where it makes its max power. Where it gets sticky is how much the engine will over produce at any given RPM. Lets say it takes 60hp to maintain 70mph on a flat road in my truck. My engine makes 120hp at peak. Lets say peak is 4500 rpms, WOT. I have double the power I need. So what now needs to happen is the RPMs and fuel need to drop until I am making only 60hp. I am at 100% max efficiency then. I am using exactly the same amount of power I need to maintain speed. Now lets say I have a 300hp engine, but all dimensions of the truck are same. This engine is larger in displacement and peaks at 6k rpms. The 300hp engine should get less fuel economy. Well that isn't correct. One part fuel makes Y amount of energy. It doesn't matter if it is in a 10hp gocart or 1000hp turbo Vette. That one part fuel has the potential for Y amount of energy in any engine. Now the 300hp engine needs to reduce rpms and fuel to get to 60hp.
Y = energy output per part of fuel
X = parts of fuel
P = total power required
P/Y = X
The 120hp engine and 300hp engine use exactly the same amount of fuel to make 60hp.
Now, that is in a perfect world. In real world our engines always produce an excess of power or do not completely burn the fuel and spit it out the exhaust. But even so it takes approximately the same amount of fuel to move a 5k lb vehicle at 60mph whether you have a 3 cylinder or V10.
Y = energy output per part of fuel
X = parts of fuel
P = total power required
P/Y = X
The 120hp engine and 300hp engine use exactly the same amount of fuel to make 60hp.
Now, that is in a perfect world. In real world our engines always produce an excess of power or do not completely burn the fuel and spit it out the exhaust. But even so it takes approximately the same amount of fuel to move a 5k lb vehicle at 60mph whether you have a 3 cylinder or V10.
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