My completly stock 1998 Blazer just got 19.82mpg on my trip from Eureka Springs, Ar to Adrian, Mo. It was around 220 miles, and it was mainly highway. When I bought it, a mission of mine was to get over 20mpg and I'm thinking a simple drop-in K&N filter will allow that to happen.

 

I just added a drop in K&N filter and noticed about 1-1.5mpg boost in my normal driving habit. Plus the added power was really nice. Made me a believer in those filters.

 

Obviously more air makes for more power but I'm wondering how that freer air flow works for economy. I always thought the PCM controlled the mixture at cruise power level and speeds. I know in Carb cars a certain level of restriction made the engine run richer.. but it doesnt work the same in EFI.

Maybe one of you guys can explain how that works.. or point me to a link at K&N

 

More power means the engine doesn't have to work as hard to get up to and maintain speed. Not having to work as hard = more MPG.

This is subjective to not driving like it's a NASCAR because you feel the extra power LOL

 

"work as hard" to do what? That 'work harder to draw air through old filter' argument is bogus. In fact pulling air takes more power.. check it by putting hand over your shop vac hose.
And the gas used is determined by actual air flowing through the MAF
Your results are from subconscious behavior modification.

I'm not disputing more power from more air at WOT but I think you had better think about where the throttle plate is positioned at cruise.

That freer flowing filter affects available power.. not fuel economy unless we're talking really dirty air filter on a carburetor... but FI doesnt work like that.

 

Let me try to explain.

Let's say you're broken down on the side of the road. It's a slight uphill grade lets say. You have to push your vehicle by yourself to a safe spot. you'll expend x amount of energy to move the vehicle from where it is to where you need it to be. correct?

Now let's say someone stops and helps you push. Now you're using half of the energy that you would (if each person is pushing half the load which for this argument we will say is the case) if you were pushing yourself. so you have 2x the power but because of having 2xpower you only expend 1/2 x the energy of pushing it yourself.

The same principle applies. More available power = less energy consumed for an equal task.


I proved this point with my old diesel truck. got 14mpg at stock level, adjusting the injection pump to provide more fuel and thus more power i got 16 mpg.

 

Ummm... No.
Explain it all you want you cant make up s$$4t to repeal the laws of thermodynamics..
1 = 1 .... 2 x .5 = 1
'X' amount of work requires same amount of TOTAL power, no matter if ten guys are pushing.
You seem advocate that getting to cruise faster makes for better economy. Suggest you check out the fuel/air curve for open loop vs throttle angle.

That's beside the point... I'll say again.. at CRUISE, where you get your economy, a better filter means diddly, the restriction is your throttle plate.
- What do folks do to get hi mileage? They keep high manifold vacuum

AND the net work done by the engine pulling vacuum is nulled out on the compression cycle.

Got an air compressor? fill the tank.. listen to motor. Put hand over air intake. listen to motor again

 

yep you're right. I haven't experimented with things like this before. Making more power using the same amount of fuel moving the same weight the same distance at the same speed won't increase fuel economy. There's a million more factors in it than the way i explained it but i was simplifying.

I'll agree that simply an air filter may not make a noticable improvement because you aren't increasing the amount of air leaving the engine. However if the flow rate of the air filter is the most restrictive point of the flow path then yes it might. It depends on application.

For maximum power and economy you have to increase volumetric efficiency. Improve intake and exhaust and you'll achieve greater volumetric efficiency thereby improving overall efficiency. Granted it may only be a .5% increase without improving flow rates of the heads, reducing parasitic driveline loss, rolling resistance, and a myriad of other factors. It can still make an improvement.

Yes that is true. It REQUIRES the same amount of total power. However if you've got a 100 HP vehicle and it requires 50HP to do said task it's at a 50% load. If you've got a 200hp vehicle and need to do the same task it's at a 25% load. Provided both vehicles get the same fuel economy unloaded the one at a 25% load will use less fuel to do the task because it is more efficient. Remember that efficiency is not strictly measured by fuel economy. Power to weight ratio, parasitic loss, volumetric efficiency are all factors here.

 

Okay I'm done... I dont do circuitous arguments.

The application -issue- is fuel economy.
The most restrictive path is the throttle plate.
The PCM adjusts the fuel/air ratio based on Throttle angle, air temp and mass it sees going across the MAF, plus some other factors that have nothing to do with filter restrictions.
Let me ask you this... does the blazer PCM use a MAP sensor or a BAP sensor?
Pretty sure it's a MAP, right? So the PCM has NO real idea whether or not the airflow is restricted in front of the MAF. So all it can do is set the A/F by the flow through the MAF adjusted by air temperature. Even if it did.. {Fords use BAP} it wouldnt make any difference on the Cruise profile.
End of.
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Wanna score a point for you from my side? Folks go buy an air filter for a 1988 TBird turbo
Install it in your shop vac. Use duct tape or whatever to make sure all the air goes thru it.

It's like a solid wall.
But that has nothing to do with engine aspiration at cruise.. only WOT.