HEADERS & CATBACK Increase or Decrease GAS MILEAGE...???

[nemss1]

I've noticed that a lot of mods like CAI or underdrive pullies actually decrease gas mileage because of the engine computer making adjustments.

Will the computer make any adjustments with headers & catback to decrease gas mileage?

 

[Luke]

That's how I understand it ... but I'm just an old newb. You'll get the straight dope soon I think.

Cheers,

 

[Atrus]

My experience says that I think overall you'd see an increase IF you can keep your foot out of it.

Here's the deal - $1,000 in exhaust upgrades isn't going to pay for itself in increased fuel economy.

Not to mention, there's a reason you want the extra power, so you'll use it, which will most likely decrease economy.

If you want more power, then so be it, but don't do what I used to and try to justify it with better economy. Because of the above mentioned factors, it doesn't make sense to do the mod for the sake of economy.

 

[jnaut]

Here's the deal - $1,000 in exhaust upgrades isn't going to pay for itself in increased fuel economy.

$1000 worth of anything will take forever to recover with increased fuel economy. You'd have to dramatically increase fuel economy to recover $1000 in any reasonable time. And by dramatically, I mean double.

I drive around 15k miles a year. At 17mpg (and let's face it, I'm being generous) I'm spending around $2200 a year in gas. If I double that mileage to 34mpg that's $1100 and some change at current gas prices. Meaning it would take me 1 year to recover my investment.

Knowing you're NEVER going to double your gas mileage with any mod on the vehicle, less sellling it and buying a small Honda Civic, you're probably wasting your time.

 

[ridenby]

Your foot is the deciding factor in gas mileage, especially in a jeep.

Well stated,Grasshopper

 

[Dave]

Your foot is the deciding factor in gas mileage, especially in a jeep.

You are absolutely correct in my opinion.

Dave

 

[HoosierJeeper]

The money is 100% worth if you want more performance, but otherwise it's not worth it.

Just my two bits.

 

[Redbone]

Will the computer make any adjustments with headers & catback to decrease gas mileage?

I don't think We have answered his question. I don't see a desire for MORE mpg. Just a concern for LESS mpg if mods are done. My generic* answer would be no change to mpg - maybe even a slight gain bit negated by..

Originally Posted by budke
Your foot is the deciding factor in gas mileage, especially in a jeep

. ... the budke factor.


*My answer is based on my experience with GM computers and my '99 Dakota. MPGs increased with headers, pulleys, etc. I wanted power. MPG gains were welcome.

 

[nemss1]

Haha thanks redbone for actually answereing my question regarding the computer playing a role, making adjustments to air/fuel ratio.

 

[Redbone]

The standard question is will I get more mpg. Folks aren't accustomed to a more reasonable question such as yours.

 

[lil black liberty]

Hmm I wonder even with the B&G PCM Flash would this still not help improve MPG? I mean because if the STOCK PCM is trying to compensate for something new to keep it limited to what it was programmed for then why wouldn't a B&G PCM help?

Just my two cents and curiosity..

 

[Redbone]

I installed the Mopar PCM in my Dakota & both performance and mpg went up slightly. Since I had already installed long tube headers I can't say how much of each was attributed to either. Increases were so small I prolly couldn't do so with much accuracy anyhow.

 

[Powerslave]

The underdrive pulley is not for gas mileage or other related learning curve items. It is to free up horse power you already have, by under driving the accessories, meaning, the serpentine belt travels at a slower speed across all the accessory pulleys. It does not ADD anything, it only takes the HP away from the accessories, allowing more HP to the wheels. They work, and pretty well. The downside is our A/C compressor may not pump out cold enough air at idle, and the Alternator may not like that either. I drove an Avenger with one, and saw a nice difference in launching the car. I was going to get one, never got around to it.

The fake stuff are the resistors people put in parallel with sensors to FOOL the ECM into thinking the air charge is cooler, thus using a little more gas. People forget the ECT sensor as well...

 

[nemss1]

The underdrive pulley is not for gas mileage or other related learning curve items. It is to free up horse power you already have, by under driving the accessories, meaning, the serpentine belt travels at a slower speed across all the accessory pulleys. It does not ADD anything, it only takes the HP away from the accessories, allowing more HP to the wheels. They work, and pretty well. The downside is our A/C compressor may not pump out cold enough air at idle, and the Alternator may not like that either. I drove an Avenger with one, and saw a nice difference in launching the car. I was going to get one, never got around to it.

The fake stuff are the resistors people put in parallel with sensors to FOOL the ECM into thinking the air charge is cooler, thus using a little more gas. People forget the ECT sensor as well...

Well said Powerslave. Makes perfect sense

 

[lil black liberty]

Uh.. Maybe I'm confused who were you referring to Powerslave? Because a B&G Flash is not a little resistor that is 5 cents..

 

[Redbone]

The underdrive pulley is not for gas mileage .....

By freeing up more h.p. it is taking some load off of engine at all speeds. This, in turn, will improve m.p.g. It has no effect on the PCM whatsoever.

Under drive pulleys on my Dakota resulted in no noticable loss of AC @ idle but altenator was not charging when headlights were on. Lights dimmed considerably.

 

[Powerslave]

Uh.. Maybe I'm confused who were you referring to Powerslave? Because a B&G Flash is not a little resistor that is 5 cents..

Was not referring to anyone, it was just data. Anyone who would even think a resistor is "programming," is very stupid, it only alters the voltage specs. I started out with "The fake stuff", because people buy them thinking they work. They might for a week or so, but then the ECM adjusts. You would need one for the ECT as well, people don't even consider that when using one for just the IAT.

UD Pulley: I only said it was not for gas mileage, because that's not the primary reason people buy them. They are not really advertised for increasing MPG, but they do focus on the performance side. If you can't find one for the 3.7 (though they are there), you can put one from a 4.7 too.

 

[Redbone]

UD Pulley: I only said it was not for gas mileage, because that's not the primary reason people buy them. They are not really advertised for increasing MPG, but they do focus on the performance side. If you can't find one for the 3.7 (though they are there), you can put one from a 4.7 too.

10-4. Understood. Due to the crowd they are intended for they prolly cause m.p.g. to drop.

 

[lil black liberty]

Well correct me if I'm wrong but isn't the UDP's usually seen in those Race Cars? I mean now I've had my ideas of a 500hp Jeep Liberty but... only ideas..

 

[Redbone]

Well correct me if I'm wrong but isn't the UDP's usually seen in those Race Cars? I mean now I've had my ideas of a 500hp Jeep Liberty but... only ideas..

Why only 500 noob!