jimgrms
NAXJA Forum User
- Location
- Oceanside Ca the beach
the big problem with the electric motor driven a/c is the extension cord
Last edited:
-
Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.
a possible way to improve mpg
- Thread starter fspell220
- Start date
goodburbon
NAXJA Forum User
- Location
- Westcliffe Colorado.
The reason dirty filters hurt mileage on older vehicles was because of carbeurators by the way. Dirty filter = less air + same ammount of fuel as with a clean filter. Therefore the same ammount of throttle given will yield less RPM and a rich condition.
Fuel injection negates that. Now less air+ Computer controlled less fuel = same fuel/air consumption ratio, less HP, Less RPM.
Also Our Jeeps do not have Mass Airflow sensors. They operate with a MAP sensor. (http://en.wikipedia.org/wiki/MAP_sensor)
Fuel injection negates that. Now less air+ Computer controlled less fuel = same fuel/air consumption ratio, less HP, Less RPM.
Also Our Jeeps do not have Mass Airflow sensors. They operate with a MAP sensor. (http://en.wikipedia.org/wiki/MAP_sensor)
fspell220 said:
lol, I use caps when I'm making a point. not trying to make it like I'm yelling...but it's just easier to caps than to click italics.
now, if there were a darn highlighter within reach, I'd just mark up the screen and send it to ya
course, it would never get through...cstilesiscool said:
DINGDINGDINGDING WINNER!
XJs just don't get good milage period, a stock xj with no lift and 27s thats in tip top mechanical shape will get mid-high teens city and low-mid 20s highway IF you drive like a granny, use cruise control, and don't speed...yes, believe it or not kids, the most effective way to get better mpg is a light right foot
my 97 isnt lifted yet but its running 29s and I most certainly don't drive like a granny, so my everyday city/hywy combo mpg is usually anywhere from 13-15 and the last time I drove to AZ I got 19mpg doing 80-85 the whole way (base model so no cruise) not too bad IMO for a big 6 and a vehicle with the airodynamics of a brick. I know thats all going to go to shit when I lift it, but like cstilesiscool I dont care :spin1:
Harlee&Tahoe
NAXJA Forum User
- Location
- South Lake Tahoe, CA
Remove a couple of injector connections and make it a 4 banger!! lol
- Location
- MilkyWay Galaxy
FoMoCo said:
I average 34 mpg in my 85 Cherokee pioneer. Not bad for a brick!
- Location
- MilkyWay Galaxy
You need to think in terms of power delivered per stroke. A severly restricted intake, like that caused by a suficiently dirty air filter reduces the intake manifold absolute pressure. So on a single stroke, which takes work to overcome friction in the engine, which consumes gas to do the work, if you have less air MASS because you have less air density, because the air filter is sufficiently dirty, you will get less power at a fixed A/F ratio out of each stroke. Some of the energy produced is used to move the vehicle, but some of the energy is also used to over come the friction losses in the engine, and to overcome inertia when you try to accelerate, plus gravity, wind resistance..... etc.
If the engine must do more rpms to deliver the same steady state power to the wheels while running at a steady state vehicle speed because the air density in the intake manifold dropped, because the air filter is real dirty, then it is doing more work per mile driven at a steady state vehicle speed because the engine must operate at higher rpms to maintain the steady state speed. This problem of waisted energy caused by a dirty air filter would be most noticable at WOT, and would be insignifcant at ilde. Since most of us do not drive 90% of our driving time on the road with the throttle plate open more than say 25% open, the throttle plate becomes the limiting factor as to intake manifold absolute pressure (air density that the engine cylinder fills with) and not the dirty air filter. During acceleration at about 60 to 100% of WOT the air filter when real dirty becomes the limiting factor of intake manifold pressure.
Inlet air temperature also affects intake manifold air density!
The biggest coast to coast waste of gas here in the USA is 5 mph bumper to bumper traffic at rush hours. The 4.0 uses just as much gas per hour cruising at 5 mph as it does at 60 mph. In other words fixed engine speed of 2000 rpm, cruising is the same gas consumption rate whether you are cruising at 5 mph or 60 mph, given equal engine rpms.
If the engine must do more rpms to deliver the same steady state power to the wheels while running at a steady state vehicle speed because the air density in the intake manifold dropped, because the air filter is real dirty, then it is doing more work per mile driven at a steady state vehicle speed because the engine must operate at higher rpms to maintain the steady state speed. This problem of waisted energy caused by a dirty air filter would be most noticable at WOT, and would be insignifcant at ilde. Since most of us do not drive 90% of our driving time on the road with the throttle plate open more than say 25% open, the throttle plate becomes the limiting factor as to intake manifold absolute pressure (air density that the engine cylinder fills with) and not the dirty air filter. During acceleration at about 60 to 100% of WOT the air filter when real dirty becomes the limiting factor of intake manifold pressure.
Inlet air temperature also affects intake manifold air density!
The biggest coast to coast waste of gas here in the USA is 5 mph bumper to bumper traffic at rush hours. The 4.0 uses just as much gas per hour cruising at 5 mph as it does at 60 mph. In other words fixed engine speed of 2000 rpm, cruising is the same gas consumption rate whether you are cruising at 5 mph or 60 mph, given equal engine rpms.
Ecomike said:
lol, no fair, you cheated and swapped in a diesel
I shoulda said XJs w/stock drivetrain get sh1t mpg (although there were a few oilburners from the factory weren't there?) even the 2.5 only gets a couple mpg better than the 4.0 cause it has to work so damn hard
j99xj
NAXJA Forum User
- Location
- Colorado Springs, CO, USA
Force=mass x acceleration.
The engine provides a force to accelerate our Jeeps and to keep them in motion. The best way to increase gas mileage is to reduce mass. What this effectively does is provide the same acceleration, but at less force (gas burned), or a faster acceleration with the same force.
This is why true economy cars and motorcycles get great gas mileage. This is also why the XJ was designed the way it was (unibody). We would get far worse gas mileage if we had an extra 500-1000 pounds to lug around all the time with a body on frame set up.
Next is drag. Drag is a force that increases dramatically with speed and subtracts from the force from the engine. Drag is literally trying to stop you all the time. Unfortunately, it is impossible to eliminate drag but it is possible to reduce it with better technology.
An example: If you were to shut your engine off while driving (thus eliminate the force it is providing) the net drag force takes over and you eventually roll to a stop no matter what.
Remove everything that you don't need from your Jeep to save weight. You might even want to consider taking out your spare wheel/tire and just carry a can of fix a flat.
Next, make sure your tires are inflated right, and your brakes are properly adjusted. Low psi and dragging brakes will lower mileage. Also when it comes time to buy new tires, get regular passenger/highway type tires. All terrains and certainly mudders increase drag.
And most of all: Accelerate smoothly and drive the speed limit or slightly slower; coast whenever possible. Don't drive when upset about something, not only is it dangerous its costing you more money. Using the a/c is also known to reduce mileage, so use your windows for ventilation.
Modding your intake to reduce the amount of air is a good idea to increase gas mileage, but like others have said, you can accomplish the same effect by keeping your throttle settings low. (foot out of it)
The engine provides a force to accelerate our Jeeps and to keep them in motion. The best way to increase gas mileage is to reduce mass. What this effectively does is provide the same acceleration, but at less force (gas burned), or a faster acceleration with the same force.
This is why true economy cars and motorcycles get great gas mileage. This is also why the XJ was designed the way it was (unibody). We would get far worse gas mileage if we had an extra 500-1000 pounds to lug around all the time with a body on frame set up.
Next is drag. Drag is a force that increases dramatically with speed and subtracts from the force from the engine. Drag is literally trying to stop you all the time. Unfortunately, it is impossible to eliminate drag but it is possible to reduce it with better technology.
An example: If you were to shut your engine off while driving (thus eliminate the force it is providing) the net drag force takes over and you eventually roll to a stop no matter what.
Remove everything that you don't need from your Jeep to save weight. You might even want to consider taking out your spare wheel/tire and just carry a can of fix a flat.
Next, make sure your tires are inflated right, and your brakes are properly adjusted. Low psi and dragging brakes will lower mileage. Also when it comes time to buy new tires, get regular passenger/highway type tires. All terrains and certainly mudders increase drag.
And most of all: Accelerate smoothly and drive the speed limit or slightly slower; coast whenever possible. Don't drive when upset about something, not only is it dangerous its costing you more money. Using the a/c is also known to reduce mileage, so use your windows for ventilation.
Modding your intake to reduce the amount of air is a good idea to increase gas mileage, but like others have said, you can accomplish the same effect by keeping your throttle settings low. (foot out of it)
caiquemacedo
NAXJA Forum User
- Location
- Curitiba - Brazil
Draag is responsible for about 70% of all fuel needeed to move a car like XJ, it doesnt matter if its heavy or not. In an average ride you´ll never use more than 1/3 of power or torque, so there´s no way to improve mpg unless changing the shape of the car, even addind more lentgh in the intake manifold or using cone air filter.
Cheers from Brazil.
Cheers from Brazil.
j99xj
NAXJA Forum User
- Location
- Colorado Springs, CO, USA
The only time when weight doesn't matter in fuel economy is when speed is constant on flat roads. Once you start accelerating or encounter hills/mountains, a lighter vehicle will get better gas mileage, I promise.
Weight is very much part of the equation when changing velocity (accelerating or braking).
Weight is very much part of the equation when changing velocity (accelerating or braking).
Your vehicle needs to produce a certain amount of horsepower to maintain a given speed........ This amount of horsepower will require a certain amount of air/fuel mixture...... You cannot cheat on this...... If your air filter is plugged or you air intake is restricted, you will have to use more throttle opening to get the required amount of air...... this will cause the air velocity in your intake manifold to drop which kills engine efficiency...... it can also skew your map readings, also not a good thing...... It simply will not work...... Making an engine breath better and easier is what you need to do...... If you make more air available, the engine will still only use what it needs...... high air speed velocity in the intake manifold and in the exhaust system are both key to producing an efficient engine....... this is why too large of an exhaust system kills low end power..... it kills the velocity of the exhaust air and hurts cylinder scavenging......
- Location
- MilkyWay Galaxy
I see some heavy weight comments I must reply to, LOL.
" lol, no fair, you cheated and swapped in a diesel"
Yes, I cheated, but physics teaches us how to cheat so can we elliminate multiple extraneous variables and arrive at ellegant equations that define things in terms of just a few simple variables. By cheating I proved that the XJ body design, shape and weight is capable of at least 34 MPG fuel mileage. So the question then becomes one of what can we do to get better mileage out of the stock engine and transmission. I am still trying to get past 16 mpg highway, 12 mpg city with a 4X4, 87, 4.0. I have been told by dozens of other XJ owners that they have gotten as much as 25 mpg out the entirely stock 4.0 XJ's ( 2WD and 4x4s ) in a thread I started about 10 days ago here.
"Remove everything that you don't need from your Jeep to save weight. You might even want to consider taking out your spare wheel/tire and just carry a can of fix a flat."
I will never use fix a flat again. Makes it impossible to spin balance the tire, and tire shops will not repair or put inner tubes in a tire that has had fix a flat put in it.
"Using the a/c is also known to reduce mileage, so use your windows for ventilation."
I disagree, I think, on the freeway at least, that the added drag of open windows, may exceed the savings of not running the AC compressor. Just a guess, opinion on my part, but based on some experience with the top end speed of my Diesel XJ, I get about 3-5 mph higher top vehicle speed with my AC on and windows closed, than I can I reach with my AC off and windows open. I only tested this once, so I am not possitive, it could just be a wash, and could vary with wind speed and direction!!!!!! But I would not say that open windows saves gas over AC on, windows closed, at least not at highway speeds.
"Modding your intake to reduce the amount of air is a good idea to increase gas mileage, but like others have said, you can accomplish the same effect by keeping your throttle settings low. (foot out of it)"
I simply disagree with this premise. The XJ idle speed and A/F ratio is computer (O2, MAP, CTS, and IAT sensor, ECU & IAC) controlled. Any small changes in intake air pressure will be insignificant in their effect because the IAC and throttle body plate restriction control the intake manifold absolute air pressure that the engine actually sees except at WOT where the air filter and throttle body throat, and injection port diameters become the limiting factors in intake absolute air pressure.
"Drag is responsible for about 70% of all fuel needeed to move a car like XJ, it doesnt matter if its heavy or not"
Don't think I agree with this. Depends on how you define drag. Air drag varies with vehicle speed, minimal at 35 mph, more significant at 80 mph with windows open, a good head wind, and luggage on top. Internal vehicle power train friction (another form of drag) varries with engine RPM and vehicle speed, transmission gear, and torque converter lock up, or non-lock up, brakes, differentials, oils.....).
A lot of fuel is used just idling, a lot of fuel is used to overcome inertia to get the XJ moving and up to speed. MPG is '0' at stop lights, stop signs, dead non-moving traffic & during warms ups in the driveway. MPG is lousy while braking and while accelerating.
"The only time when weight doesn't matter in fuel economy is when speed is constant on flat roads."
I agree with the point you are trying to make, but lets say its less, or not significant on flat roads. The heavier vehicle at constant velocity is going to contribute more to internal friction (energy - work) losses (bearings) since it must continually over come gravity of the heavier vehicle to keep it moving at constant velocity. But I agree an extra 100 lbs on a flat road at constant velocity should not be that significant. 10,000 extra lbs would be significant.
"If your air filter is plugged or you air intake is restricted, you will have to use more throttle opening to get the required amount of air"
I agree
"...... this will cause the air velocity in your intake manifold to drop"
I agree.
"which kills engine efficiency"
Not sure I agree with this, might have an effect on efficiency, not sure its significant, except maybe at WOT.
"...... it can also skew your map readings, also not a good thing......"
Interesting thought, I will have to dwell (LOL, think) on this a bit. Possible effect I can see, but possitive or negative, don't know, would need a lot more data on the program itself, map atbles, built in ECU PCM program equations, and maybe dyno test data to convince me of the actual overall effect.
"high air speed velocity in the intake manifold and in the exhaust system are both key to producing an efficient engine"
Yes, I agree, up to a point, but I suspect there is a peak air velocity at which efficiency suffers if the velocity is forced any higher. So how do we optimise that? I take it the idea is that a certain peak air velocity is critical to mixing the A & F to get a more uniform burn, combustion. But at what point does the effect become significant for fuel efficiency, mpgs?
"....... this is why too large of an exhaust system kills low end power..... it kills the velocity of the exhaust air and hurts cylinder scavenging......"
Can you elaborate on cylinder scavenging?
Is low end power significant to fuel economy? If so how?
Everything else I agreed with (so I did not cut and past it here).
" lol, no fair, you cheated and swapped in a diesel
"Yes, I cheated, but physics teaches us how to cheat so can we elliminate multiple extraneous variables and arrive at ellegant equations that define things in terms of just a few simple variables. By cheating I proved that the XJ body design, shape and weight is capable of at least 34 MPG fuel mileage. So the question then becomes one of what can we do to get better mileage out of the stock engine and transmission. I am still trying to get past 16 mpg highway, 12 mpg city with a 4X4, 87, 4.0. I have been told by dozens of other XJ owners that they have gotten as much as 25 mpg out the entirely stock 4.0 XJ's ( 2WD and 4x4s ) in a thread I started about 10 days ago here.
"Remove everything that you don't need from your Jeep to save weight. You might even want to consider taking out your spare wheel/tire and just carry a can of fix a flat."
I will never use fix a flat again. Makes it impossible to spin balance the tire, and tire shops will not repair or put inner tubes in a tire that has had fix a flat put in it.
"Using the a/c is also known to reduce mileage, so use your windows for ventilation."
I disagree, I think, on the freeway at least, that the added drag of open windows, may exceed the savings of not running the AC compressor. Just a guess, opinion on my part, but based on some experience with the top end speed of my Diesel XJ, I get about 3-5 mph higher top vehicle speed with my AC on and windows closed, than I can I reach with my AC off and windows open. I only tested this once, so I am not possitive, it could just be a wash, and could vary with wind speed and direction!!!!!! But I would not say that open windows saves gas over AC on, windows closed, at least not at highway speeds.
"Modding your intake to reduce the amount of air is a good idea to increase gas mileage, but like others have said, you can accomplish the same effect by keeping your throttle settings low. (foot out of it)"
I simply disagree with this premise. The XJ idle speed and A/F ratio is computer (O2, MAP, CTS, and IAT sensor, ECU & IAC) controlled. Any small changes in intake air pressure will be insignificant in their effect because the IAC and throttle body plate restriction control the intake manifold absolute air pressure that the engine actually sees except at WOT where the air filter and throttle body throat, and injection port diameters become the limiting factors in intake absolute air pressure.
"Drag is responsible for about 70% of all fuel needeed to move a car like XJ, it doesnt matter if its heavy or not"
Don't think I agree with this. Depends on how you define drag. Air drag varies with vehicle speed, minimal at 35 mph, more significant at 80 mph with windows open, a good head wind, and luggage on top. Internal vehicle power train friction (another form of drag) varries with engine RPM and vehicle speed, transmission gear, and torque converter lock up, or non-lock up, brakes, differentials, oils.....).
A lot of fuel is used just idling, a lot of fuel is used to overcome inertia to get the XJ moving and up to speed. MPG is '0' at stop lights, stop signs, dead non-moving traffic & during warms ups in the driveway. MPG is lousy while braking and while accelerating.
"The only time when weight doesn't matter in fuel economy is when speed is constant on flat roads."
I agree with the point you are trying to make, but lets say its less, or not significant on flat roads. The heavier vehicle at constant velocity is going to contribute more to internal friction (energy - work) losses (bearings) since it must continually over come gravity of the heavier vehicle to keep it moving at constant velocity. But I agree an extra 100 lbs on a flat road at constant velocity should not be that significant. 10,000 extra lbs would be significant.
"If your air filter is plugged or you air intake is restricted, you will have to use more throttle opening to get the required amount of air"
I agree
"...... this will cause the air velocity in your intake manifold to drop"
I agree.
"which kills engine efficiency"
Not sure I agree with this, might have an effect on efficiency, not sure its significant, except maybe at WOT.
"...... it can also skew your map readings, also not a good thing......"
Interesting thought, I will have to dwell (LOL, think) on this a bit. Possible effect I can see, but possitive or negative, don't know, would need a lot more data on the program itself, map atbles, built in ECU PCM program equations, and maybe dyno test data to convince me of the actual overall effect.
"high air speed velocity in the intake manifold and in the exhaust system are both key to producing an efficient engine"
Yes, I agree, up to a point, but I suspect there is a peak air velocity at which efficiency suffers if the velocity is forced any higher. So how do we optimise that? I take it the idea is that a certain peak air velocity is critical to mixing the A & F to get a more uniform burn, combustion. But at what point does the effect become significant for fuel efficiency, mpgs?
"....... this is why too large of an exhaust system kills low end power..... it kills the velocity of the exhaust air and hurts cylinder scavenging......"
Can you elaborate on cylinder scavenging?
Is low end power significant to fuel economy? If so how?
Everything else I agreed with (so I did not cut and past it here).
Last edited:
Ecomike said:I see some heavy weight comments I must reply to, LOL.
" lol, no fair, you cheated and swapped in a diesel
Yes, I cheated, but physics teaches us how to cheat so can we elliminate multiple extraneous variables and arrive at ellegant equations that define things in terms of just a few simple variables. By cheating I proved that the XJ body design, shape and weight is capable of at least 34 MPG fuel mileage. So the question then becomes one of what can we do to get better mileage out of the stock engine and transmission. I am still trying to get past 16 mpg highway, 12 mpg city with a 4X4, 87, 4.0. I have been told by dozens of other XJ owners that they have gotten as much as 25 mpg out the entirely stock 4.0 XJ's ( 2WD and 4x4s ) in a thread I started about 10 days ago here.
"Remove everything that you don't need from your Jeep to save weight. You might even want to consider taking out your spare wheel/tire and just carry a can of fix a flat."
I will never use fix a flat again. Makes it impossible to spin balance the tire, and tire shops will not repair or put inner tubes in a tire that has had fix a flat put in it.
"Using the a/c is also known to reduce mileage, so use your windows for ventilation."
I disagree, I think, on the freeway at least, that the added drag of open windows, may exceed the savings of not running the AC compressor. Just a guess, opinion on my part, but based on some experience with the top end speed of my Diesel XJ, I get about 3-5 mph higher top vehicle speed with my AC on and windows closed, than I can I reach with my AC off and windows open. I only tested this once, so I am not possitive, it could just be a wash, and could vary with wind speed and direction!!!!!! But I would not say that open windows saves gas over AC on, windows closed, at least not at highway speeds.
"Modding your intake to reduce the amount of air is a good idea to increase gas mileage, but like others have said, you can accomplish the same effect by keeping your throttle settings low. (foot out of it)"
I simply disagree with this premise. The XJ idle speed and A/F ratio is computer (O2, MAP, CTS, and IAT sensor, ECU & IAC) controlled. Any small changes in intake air pressure will be insignificant in their effect because the IAC and throttle body plate restriction control the intake manifold absolute air pressure that the engine actually sees except at WOT where the air filter and throttle body throat, and injection port diameters become the limiting factors in intake absolute air pressure.
"Drag is responsible for about 70% of all fuel needeed to move a car like XJ, it doesnt matter if its heavy or not"
Don't think I agree with this. Depends on how you define drag. Air drag varies with vehicle speed, minimal at 35 mph, more significant at 80 mph with windows open, a good head wind, and luggage on top. Internal vehicle power train friction (another form of drag) varries with engine RPM and vehicle speed, transmission gear, and torque converter lock up, or non-lock up, brakes, differentials, oils.....).
A lot of fuel is used just idling, a lot of fuel is used to overcome inertia to get the XJ moving and up to speed. MPG is '0' at stop lights, stop signs, dead non-moving traffic & during warms ups in the driveway. MPG is lousy while braking and while accelerating.
"The only time when weight doesn't matter in fuel economy is when speed is constant on flat roads."
I agree with the point you are trying to make, but lets say its less, or not significant on flat roads. The heavier vehicle at constant velocity is going to contribute more to internal friction (energy - work) losses (bearings) since it must continually over come gravity of the heavier vehicle to keep it moving at constant velocity. But I agree an extra 100 lbs on a flat road at constant velocity should not be that significant. 10,000 extra lbs would be significant.
"If your air filter is plugged or you air intake is restricted, you will have to use more throttle opening to get the required amount of air"
I agree
"...... this will cause the air velocity in your intake manifold to drop"
I agree.
"which kills engine efficiency"
Not sure I agree with this, might have an effect on efficiency, not sure its significant, except maybe at WOT.
"...... it can also skew your map readings, also not a good thing......"
Interesting thought, I will have to dwell (LOL, think) on this a bit. Possible effect I can see, but possitive or negative, don't know, would need a lot more data on the program itself, map atbles, built in ECU PCM program equations, and maybe dyno test data to convince me of the actual overall effect.
"high air speed velocity in the intake manifold and in the exhaust system are both key to producing an efficient engine"
Yes, I agree, up to a point, but I suspect there is a peak air velocity at which efficiency suffers if the velocity is forced any higher. So how do we optimise that? I take it the idea is that a certain peak air velocity is critical to mixing the A & F to get a more uniform burn, combustion. But at what point does the effect become significant for fuel efficiency, mpgs?
"....... this is why too large of an exhaust system kills low end power..... it kills the velocity of the exhaust air and hurts cylinder scavenging......"
Can you elaborate on cylinder scavenging?
Is low end power significant to fuel economy? If so how?
Everything else I agreed with (so I did not cut and past it here).
Cylinder scavenging is the act of the exhaust flow from cylinders helping to clean out each other...... Lets say for instance the #1 cylinder fires..... as its exhaust gas flows down the header pipe it flows past the other header pipes where all the cylinder header pipes adjoin..... as the gasses flow past the junctions, they pull or stretch the air in the pipes from the cylinders that are not in the exhaust stroke...... It basically is a venturi effect and creates basically a vacuum in the unused pipes...... what basically happens is the exhaust velocity working together helps to draw exhaust away from the engine..... this act coupled with the valve overlap will actually try to pull fresh air from the intake side through the cylinder at the end of the exhaust stroke..... It leaves a clean combustion chamber so the incoming air fuel charge isnt diluted by left over garbage from the combustion process that just occured.... This is a big factor why headers dont just pump into the collectors in any random order...... they are tuned to allow the pulses to help in scavenging....... It is also why primary tube length is different on header designs..... changing the primary tube length changes the rpm range that the header will scavenge most efficiently...... scavenging and exhaust pulses are why many v-8 street rods run balance tubes in between the two sides of the exhaust...... The entire intake/exhaust combination is very important to engine efficiency...... It must flow the correct amount of air........ for simplicity lets talk about a carbureted engine...... put on too big of carb and it will run like crap...... you can jet the carb down so it is not rich, but accelleration will be poor due to too much pressure drop in the manifold creating a lack of vacuum and intake air velocity...... to large of cylinder head runners, to large of an intake manifold, too large of valves and too large of an exhaust all have the same effect...... take a stock engine and put on any one or combination of the following, tunnel ram intake, big valve and runner heads, big primary tube headers etc etc on it and it will kill its low and mid range efficiency and the stock motor will never reach the rpms necessary to realize any gains from the bigger partor parts...... you will reduce the HP and torque the engine can produce......
As far as low end power affecting fuel economy, if you are trying to conserve fuel, does the motor not need to be most efficient at low cruising rpms and under light to moderate acceleration????
As far as you not being sure if the air velocity in your manifold dropping and you not sure you agree...... If the velocity drops, you have low manifold vacuum...... the map sensor sees this as high load such as towing, going up an incline, accelerating, etc..... It thinks the engine has more load.....lt compensates by adding fuel and retarding timing.........both of these are detrimental to economy......this is fact......
I have ceased to read the last 3 posts. they're just too darned long. I'm a windbag, and they've out-windbagged me. I'm surprised, and defeated. not from lack of intelligence, but lack of stamina to read their posts while simultaneously absorbing information.
- Location
- MilkyWay Galaxy
Jeepcomj,
Sorry but you never had a chance in this Old Windbag contest with me in the game.. Just take a short break, catch your WIND, and jump back in there, we promise take it easier on ya, LOL.:laugh2:
boogo35,
I was vaguely aware of most of the that about scavanging, but was not aware of any valve overlap that contributed to it. I was, am under the impression the tuning effect is mostly critical only up the about the inlet of the Cat converter, in otherwords a short distance after the merge point of the pipe in the header. I actully use the venturi effect in air injectors in waste water treatment in industry (I'm a chemical/environmental engineer, involved in industrial waste water) so I quite aware of and familiar with the power and utility of the ventury effect. I also read about headers and tunning 30 years ago, but did not recall hearing it called scavaging. Actually it's the perfect word for it. Anyway, thanks for the nice detailed description on scavaging, I am sure it will help clarify that topic for many readers here for along time to come.
So how significant is this valve overlap, and does it exist on stock 4.0s?
You asked, "As far as low end power affecting fuel economy, if you are trying to conserve fuel, does the motor not need to be most efficient at low cruising rpms and under light to moderate acceleration????"
I would say YES to that question!!!!
" As far as you not being sure if the air velocity in your manifold dropping and you not sure you agree...... If the velocity drops, you have low manifold vacuum...... the map sensor sees this as high load such as towing, going up an incline, accelerating, etc..... It thinks the engine has more load.....lt compensates by adding fuel and retarding timing.........both of these are detrimental to economy......this is fact......"
So one would need to retune /adjust the ECU/PCM tables and sensor equations , or even install an adjustable MAP if one added a turbocharger that increased the intake manifold absolute pressure over the operating range in order to avoid a huge drop in engine efficiency and MPGs?
Sounds like playing with the MAP sensor ( at least on my Renix jeeps) can be more rewarding than I previously thought, since I can not flash, or dable with the Renix ECU code itself.
Sorry but you never had a chance in this Old Windbag contest with me in the game.
. Just take a short break, catch your WIND, and jump back in there, we promise take it easier on ya, LOL.:laugh2:boogo35,
I was vaguely aware of most of the that about scavanging, but was not aware of any valve overlap that contributed to it. I was, am under the impression the tuning effect is mostly critical only up the about the inlet of the Cat converter, in otherwords a short distance after the merge point of the pipe in the header. I actully use the venturi effect in air injectors in waste water treatment in industry (I'm a chemical/environmental engineer, involved in industrial waste water) so I quite aware of and familiar with the power and utility of the ventury effect. I also read about headers and tunning 30 years ago, but did not recall hearing it called scavaging. Actually it's the perfect word for it. Anyway, thanks for the nice detailed description on scavaging, I am sure it will help clarify that topic for many readers here for along time to come.
So how significant is this valve overlap, and does it exist on stock 4.0s?
You asked, "As far as low end power affecting fuel economy, if you are trying to conserve fuel, does the motor not need to be most efficient at low cruising rpms and under light to moderate acceleration????"
I would say YES to that question!!!!
" As far as you not being sure if the air velocity in your manifold dropping and you not sure you agree...... If the velocity drops, you have low manifold vacuum...... the map sensor sees this as high load such as towing, going up an incline, accelerating, etc..... It thinks the engine has more load.....lt compensates by adding fuel and retarding timing.........both of these are detrimental to economy......this is fact......"
So one would need to retune /adjust the ECU/PCM tables and sensor equations , or even install an adjustable MAP if one added a turbocharger that increased the intake manifold absolute pressure over the operating range in order to avoid a huge drop in engine efficiency and MPGs?
Sounds like playing with the MAP sensor ( at least on my Renix jeeps) can be more rewarding than I previously thought, since I can not flash, or dable with the Renix ECU code itself.
Valve overlap exists on all 4 stoke engines....... It is the amount of time that both the intake and exhaust valves are open....... It is a big part of why high rpm motors have lousy idle characteristics...... As the cam duration is increased and sometimes the valve centerlines are changes, valve overlap is increased...... It helps the engine to scavenge well at very high RPM's, It kills manifold vacuum at idle...... this is why real high rpm motors "thump" at idle and generally have to run a much higher idle speed......
The turbo cars from GM such as the Grand National and the Sunbird Turbo used a map sensor that was unique....... Map sensors work with near 5v being the lack of vacuum and near 0v being the presense of very high vacuum..... There are sensors that have the voltages reversed, but are generally called a vacuum sensor and they have to be run in conjunction with a separate BARO sensor....... The turbo engine actually produces a postive pressure in the intake manifold....... What they did is made the sensor so between 5.0v and 2.5v was a negative pressure or a vacuum and from 2.5v down to 0v was a positive pressure or boost......
It is just too dogone hard to cram this much info that I have shared with all of you into a few short sentences...... I will try to be less of a windbag.........
RaccoonJoe
NAXJA Forum User
- Location
- Fort Wayne, IN
Interesting.....very interesting.
Ecomike, I'm curious to know what effects you get from playing with the MAP sensor. Unfortunately, $$ and time have conspired against me, and I'm not allowed to experiment too much on my Renix (daily driver and all....) However, I'm one of those who pulls an average of 21-22 MPG out of a stock Renix 4x4. How I wish I had the resources to do that diesel swap!!
Ecomike, I'm curious to know what effects you get from playing with the MAP sensor. Unfortunately, $$ and time have conspired against me, and I'm not allowed to experiment too much on my Renix (daily driver and all....) However, I'm one of those who pulls an average of 21-22 MPG out of a stock Renix 4x4. How I wish I had the resources to do that diesel swap!!
