OTIS Accuracy

[Marlon_JB2]

So jeepjeepster is it not possible to get anything higher than 22MPG in a KJ then? I had MANY 24MPG runs with my '04 KJ. It all depends on the conditions.

 

[kjpilot]

Mine said I was getting 24mpg at 75mph on the way home this past weekend. It was a 100mile trip home and there is no way I was getting that at 75 mph. I do have the flowmaster and K&N but there is no way it helped that much. I wish I was getting that though..

Did you do it (the calculation) long hand? Maybe you were, or maybe there was a computer error. Everything I've said would be predicated on a properly functioning system. However, with the efficiency improvements you made, plus variables you may not have been aware of, like a tail wind, atmospheric pressure, temperature, a good batch of gasoline and the like, you may have had an improvement. weren't you one of those guys getting low 20's for MPG already?

 

[JeepJeepster]

I would believe it if I was going 45-50mph, but at 75mph I just cannot see it.. Maybe Im wrong though? I was going west to east so I tail wind is possible.

 

[kjpilot]

I would believe it if I was going 45-50mph, but at 75mph I just cannot see it.. Maybe Im wrong though? I was going west to east so I tail wind is possible.

The wind blows in all directions. The west to east thing is a simplification of general weather movements in the mid latitudes of the northern hemisphere. The jet stream always moves west to east, but it's way up where the troposphere meets the stratosphere. Down here at the surface, wind flows clockwise around high pressure systems & counter-clockwise around low pressure systems. So the direction of the wind varies with your relative location to the center of pressure systems.

Just ask a pilot, & he'll tell you more than you cared to know!

 

[Dave]

The wind blows in all directions.

I like that one.......haha...that's so true.

There's so many variables. The main constant thing going against us is the lack of good aerodynamics (compared to a car) and the weight. The only way to overcome that is to get a car. For instance, my 99 Cutlass that has about the same size motor and A/T but weighs 1500 pounds less and is much much more aerodynamic and lower to the ground will get an easy 28-29 on the highway. But I like pushing a brick through the wind better.

Dave

 

[MoladoGuy]

People who drive during the daytime with their headlights on may want to reconsider that decision! The calculations below show that the vehicle's gas mileage is significantly reduced by having the headlights on!

Driving with your headlights on

 

[KeswickDave]

Driving with your headlights on

Interesting... although I always thought (as a lay-person), that since the alternator was always spinning, it was generating that electricity whether you had the lights on or not. Sounds like this article's point is the alternator puts a larger load on the engine when it is required to produce more power? I'll be interested to hear what those more knowledgable in this area have to say about this guy's theory.

On a side-note, in Canada where daytime running lights are required by law on new vehicles, they run only the high beams, at a reduced power level. I am not sure what the reduction is, I recall hearing it was half power, in which case there would be a savings over running your full complement of running lights and low beams, for example.

Dave

 

[tjkj2002]

Interesting... although I always thought (as a lay-person), that since the alternator was always spinning, it was generating that electricity whether you had the lights on or not. Sounds like this article's point is the alternator puts a larger load on the engine when it is required to produce more power? I'll be interested to hear what those more knowledgable in this area have to say about this guy's theory.

On a side-note, in Canada where daytime running lights are required by law on new vehicles, they run only the high beams, at a reduced power level. I am not sure what the reduction is, I recall hearing it was half power, in which case there would be a savings over running your full complement of running lights and low beams, for example.

Dave

The more power you need(running DTRL,big stereo) will make the alternator cause more drag on the engine,it's a known fact.Why do you think alot of motorsports(drag racing and short circle track races) run no alternators but 2-4 batteries,more power from the engine.The alternator does put out power all the time but only for the current needs,increase the needs and the alternator increases the drag on the engine,same as a engine driven fan,power steering pump,and A/C compressor.

 

[Atrus]

Mine said I was getting 24mpg at 75mph on the way home this past weekend. It was a 100mile trip home and there is no way I was getting that at 75 mph. I do have the flowmaster and K&N but there is no way it helped that much. I wish I was getting that though..

Completely stock '07, I had about 2500 miles on it. I took a 250 mile trip (for the MI people, left Mackinac and took I-75 down to M-59). I did make one pit stop, and I drove to work the next day (50% freeway). On the trip home I was doing 80mph the majority of the way with light traffic (cruise on 90% of the way). I had the air on with 4 adults and the rear filled with luggage and two small dogs. I pulled 22.5 mpg (manually calculated). It can be done.

 

[JeepJeepster]

ohh, I also had my sub up fairly loud, so that adds to it. I didnt have the A/C on though. I almost never use that unless Im sitting in traffic or the Girl in in with me..

 

[kjpilot]

I'm sorry, but this alternator thing makes no sense to me.

Yes, the alternator needs to be spun by the engine to make electrical current, & that causes parasite drag that the engine needs to overcome. One of the advantages of an alternator over a generator is that once it is spinning at a certain speed or above, it is producing it's rated power. You can use it or not, but it is being produced.

When you turn on your A/C, & the engine has to overcome the parasite drag from the compressor, the engines RPM rises. So, if the alternator becomes physically more difficult to turn due to a high electrical load, & there by increases parasite drag on the engine, wouldn't the engine's RPM also increase to overcome this drag as with the A/C?

But when I start my KJ, with everything off it idles at ~610 RPM, When I crank the stereo with electronic dance music (lots of bass) from my XM reciever, GPS on, high beams on, flashers on, rolling the windows up & down while locking & unlocking the doors & holding my foot on the brake... well, it remained at ~610 RPM, with not even a twitch.

If anything, you guys that have off-road lights & winches may be able to get the RPMs to move, but downwards. Not because of physical drag on the engine from the alternator, but because the current draw of all the other equipment is exceeding the output of the alternator, which now cannot produce enough energy to make the engine run properly.

As far as race cars... I don't know, maybe they decided the added weight of extra batteries slows them down less than having the weight & drag of an alternator. That has to be it, because I've not seen too many serious race cars with headlights, 12" subs, or a winch.

I may be wrong, but I have a call in to an electrical engineer just to double check.

 

[tjkj2002]

I'm sorry, but this alternator thing makes no sense to me.

Yes, the alternator needs to be spun by the engine to make electrical current, & that causes parasite drag that the engine needs to overcome. One of the advantages of an alternator over a generator is that once it is spinning at a certain speed or above, it is producing it's rated power. You can use it or not, but it is being produced.

When you turn on your A/C, & the engine has to overcome the parasite drag from the compressor, the engines RPM rises. So, if the alternator becomes physically more difficult to turn due to a high electrical load, & there by increases parasite drag on the engine, wouldn't the engine's RPM also increase to overcome this drag as with the A/C?

But when I start my KJ, with everything off it idles at ~610 RPM, When I crank the stereo with electronic dance music (lots of bass) from my XM reciever, GPS on, high beams on, flashers on, rolling the windows up & down while locking & unlocking the doors & holding my foot on the brake... well, it remained at ~610 RPM, with not even a twitch.

If anything, you guys that have off-road lights & winches may be able to get the RPMs to move, but downwards. Not because of physical drag on the engine from the alternator, but because the current draw of all the other equipment is exceeding the output of the alternator, which now cannot produce enough energy to make the engine run properly.

As far as race cars... I don't know, maybe they decided the added weight of extra batteries slows them down less than having the weight & drag of an alternator. That has to be it, because I've not seen too many serious race cars with headlights, 12" subs, or a winch.

I may be wrong, but I have a call in to an electrical engineer just to double check.

The IAC(Idle Air Control) keeps the idle at a constant RPM.The more demand on the alternator does increase drag on the engine,when the alternator's limit is reached it starts drawing of the battery.You can drive around without a alternator as long as your battery is good,the ignition system doesn't draw that much energy.The reason for the higher output alternators in today's vehicles is all those electrical gismo's that you don't need(ie-power seats,heated seats,navagation,sunroofs,ESP,ABS,and such).

The alternator puts out power according to RPM and load(you where half right),that is what the regulator is for(also as not to overcharge the battery).The regulator in a KJ is part of the PCM,and is not replaceable.Funny thing is the newer alternators need power to make power.When I use my lights(or winch) it will initially drop the RPM's but the PCM and the IAC will keep the rpms constant at idle.Try this,at idle turn your steering wheel real quick,the rpms will drop then shoot up,the sudden drag on the engine drives the RPM's down and then the IAC compenstates for it.Same thing applies to the alternator.Heck on my '84 F-150 I had 9 KC Daylighter's mounted on it and if I turned them all on at once it would kill my engine unless it was turning at least 2500RPM's,that F-150 only had a 55amp alternator but a 2000CCA tractor battery,bjut the sudden load placed on the alternator created such a drag it would kill the engine.

And as for race cars,most drag cars will "short belt" the water pump(use a small electric motor to spin the water pump),or run a electric water pump.So they have high amp draws but don't want the added drag of a alternator to loss HP,hence having a electric motor run the water pump and using a electric cooling fan.They opted to use more batteries to make up for it,plus by moving the extra batteries(all of them) to the trunk it helps with the weight transfer helping them get off the line faster for a better ET.

 

[Atrus]

What TJKJ says is true. The other thing is a lot of alternators don't really make any power until you hit a good 1,000 RPM's. It's that way with the Delco 10SI anyways.

 

[JeepJeepster]

yea, you cant just get free power from the alternator. When you need power its going to put a load on the engine(or whatever is driving it).

It would be crazy if the alternator was putting out 100% amps when you were not using any of it.

 

[kjpilot]

You guys are misunderstanding what I'm stating. I stated:

"...once it is spinning at a certain speed or above, it is producing it's rated power."

clearly, I wasn't thinking you could get "free power" from the alternator! Give me a little bit of credit here!headscratch.gif

OK, so the critical RPM 1000 RPM; the alternator is capable of producing 140 amps at 14.4V at 1000 rpm. It won't produce more at 5000 rpm, still only 140amps @14.4v.

(And yes, we are talking about engine RPM not alternator RPMsmashfreakB.gif)

TJKJ, your F-150 was doing exactly what I thought it would do, it died unless you spun the alternator at the critical speed. Apparently 2500 RPM for your F-150.

As you stated when the power steering pump requires more power from the engine, the RPMs rise, when the A/C compressor clutch engages, RPMs rise. there is no rise in RPM when you turn on your stereo or lights, even when driving at a constant RPM.

There is a big difference between the alternator & the two other engine driven devices, the work they do varies. The PS pump moves more fluid when the tiller is actually turned, so the pump works harder to move the required fluid. The A/C compressor physically engages & disengages as needed, when it is off, even though the pulley spins, the compressor does not. The alternator is different all together.

The alternator is spinning magnets past a copper wire coil, they are not in physical contact with each other. What force is causing the alternator to be more difficult to spin? I don't think the magnets become more powerful, & if the engine rpm doesn't rise, then they aren't spinning faster to make the energy, so that's not it.

My EE has not returned my call yet, but guess what? I have to drive back to Cincinnati from Minneapolis over the next two days. 750 miles to check this notion. I can turn the lights off & on, but I can't go 20 miles with out the radio! Any suggestions for the parameters?

When I did the AWD/2wd comparo, I did 20 mile blocks at 73.5 MPH, alternating between awd & 2wd. This time, according to the hypothesis you guys have, will turning on the lights be enough to make a difference? My only requirements are the radio, GPS & A/C stays on, But I can keep the volume & fan speed constant.

 

[kjpilot]

Okeedoke,

I still haven't heard from the EE, but I had to run to the airport, so I stopped & talked to my mechanic.

He confirms that yes, it takes more energy from the engine to turn the altimeter with an electrical load than without. The resistance comes from the magnetic field ( I didn't think about it being an electro-magnet, as opposed to a standard magnet) But, he also stated that while this is technically true... who cares? The required extra effort to run the added load on the alternator is so small, no one will notice.

According to him, 1 HP will produce 746 watts of electricity, our head lights are 55 watts X2= 110 watts, that means the engine needs to produce 0.15 horsepower more to run the headlights. I don't have a dyno chart for the 3.7 available, but I cant believe that the engine needs to spin much faster, or use any appreciable amount of fuel to produce 0.15 HP.

In fact, even if you had the system totally maxed out at 140 amps @ 14.4 volts, that equals 2016 watts, which means the engine has to make a scant 2.7 more horsepower.

That is an explanation I can buy!

 

[Atrus]

I'd agree with that explanation. I drive with parking lights or fogs on all the time (carried over habit from my last car, I just thought it looked cool like that). I don't worry about the MPG effect.

For racing, keep in mind you have not only the electromagnic field increase, but the resistance and inertia of the free-spinning unit as well. Sure, it's small, but it adds up. Otherwise people wouldn't put in aluminum rocker arms and lightweight push rods

 

[kjpilot]

I'd agree with that explanation. I drive with parking lights or fogs on all the time (carried over habit from my last car, I just thought it looked cool like that). I don't worry about the MPG effect.

For racing, keep in mind you have not only the electromagnic field increase, but the resistance and inertia of the free-spinning unit as well. Sure, it's small, but it adds up. Otherwise people wouldn't put in aluminum rocker arms and lightweight push rods

If I'm racing in a KJ, I've got more problems than electromagnets!

That web site seems a bit of a silly straw man argument anyway. I've never met anyone who thinks driving with their headlights on will give better gas mileage, so why go through the effort to prove that "theory" wrong?