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Do aftermarket headers and exhaust systems really improve fuel economy?

19K views 58 replies 31 participants last post by  CB3 
#1 ·
Do aftermarket headers and exhaust systems really improve fuel economy?

I've heard so from a few local guys. They say aftermarket header, exhaust system, and a new chip and the fuel economy goes up. Any truth to that?
 
#27 ·
I am with Jerry on this one. I have done from header, cat and cat-back. I have gained MAYBE 1mpg. I didn't notice anything really other than the sound and MAYBE the better throttle response. I wasn't impressed at all.

I have 4.56 w/ 33" on 5spd, 4L engine.

Michael K.
 
#28 ·
Anyone who thinks they have GAINED fuel economy after having installed heavy and drag inducing items like 35" tires, winch, 5+ inches of lift, skids, sliders, OBA by only installing an exhaust system, gears, and different air intake system either hasn't recalibrated his speedometer yet or he has crossed over the space-time continuum. :laugh: Seriously, I would bet you simply haven't recalibrated your speedometer yet. Bigger tires will make it appear you've picked up fuel economy but with all the weight and drag you've added to your TJ, nothing you've done would actually improve your fuel economy over stock. My 4.0L TJ has all those goodies and it's lucky to get 13 mpg but I have recalibrated its speedometer so it is dead-nuts on. :)
 
#57 ·
Anyone who thinks they have GAINED fuel economy after having installed heavy and drag inducing items like 35" tires, winch, 5+ inches of lift, skids, sliders, OBA by only installing an exhaust system, gears, and different air intake system either hasn't recalibrated his speedometer yet or he has crossed over the space-time continuum. :laugh: Seriously, I would bet you simply haven't recalibrated your speedometer yet. Bigger tires will make it appear you've picked up fuel economy but with all the weight and drag you've added to your TJ, nothing you've done would actually improve your fuel economy over stock. My 4.0L TJ has all those goodies and it's lucky to get 13 mpg but I have recalibrated its speedometer so it is dead-nuts on. :)
Wrong. Bigger tires will make it appear as if you have travelled less miles because of the larger circumference of the tire. Meaning you will be dividing the number of miles driven (which will be lower than how far you have really drove) by the same amount of gallons. Recallibrating the speedo will make the milage go up..not down.
 
#30 ·
will228 said:
y does this subject always come up... yyyyyyyyyyyy.
Because gas is $3 @ gallon, and we are looking for miracles! :D

I'm always suspicious of claimed mileage improvements; guy bolts on some thingy, goes and runs a tank of gas, does the average, and announces it as gospel. Too many opportunities for error in measurement.

Now if somebody had been keeping track of their mileage for, say, six months, makes some mod, does the numbers for ANOTHER six months, then maybe I'd believe it.

Courtesy of a long fillup followed by a short one, I once got 24 mpg. I don't try to claim that as my average. :rolleyes:
Moon
 
#49 ·
To be fair; on my 96 ZJ 5.2L after doing an intake/muffler/JET chip, I went from 11.9MPG to 12.4MPG (all city). I did log it for quite a while before and after, of course and did drive it a little harder with the intake and exhaust.

Of course, .5 MPG is hardly worth the $1000 I spent (Yeah, I was young and was making too much money haha) but Im sure if I had driven the same as before I 'modded' it, I probably wouldve gained a little more MPG

EDIT: Whoops, didnt see how old this topic was... used the search function.
 
#50 ·
Tell me about it I put 600-700 bucks into mine every month. Thats why I'm looking for a DD right now
 
#34 ·
halfmoonclip said:
Because gas is $3 @ gallon, and we are looking for miracles! :D
Moon
Right, its $3.00 a gallon now just went up this week, My D/D went down so been driving the jeep who hoooooooo 13 mpg SUCKS

BUT THAT IS WHY I BOUGHT SOMETHING ELSE TO DRIVE

Your driving a box on wheels if your going to try and figure out how to get 20mpg just buy a Chevy V8 350 and to a transplant, you might get about 18mpg but hey better then 13mpg right

:repost:
 
#35 ·
The biggest gains to be had for the money, drum roll............














































............Run smoother tires, less rolling resistance. Find yourself some 16x7 alum wheels spec'd for a Liberty, throw on some 235/85-16 smoothies, like a Michelin LTX M/S, or a preferred Cooper equivalent, heheh, this will give you the best return for the money spent regarding mpg, and it wil be noticable. Just swapping the ST's for a smoothie in the same size will be noticable, he 16x7's and 235/16's will be even more.

No other change will net you better mpg return
 
#36 ·
Anything Jerry says = THE JEEP GOD HAS SPOKEN.

:laugh: Seriously tho, I listen to everything he says. It all makes sense and is almost guarenteed to be the end result of a certain modification. :bowdown:
 
#39 ·
Double Dog said:
If you drove your Jeep 100K miles and had a 2 mpg improvement, my calculations reveal you would save about $2,700 with $4 gas.
The dollar saving in driving 100k miles is dependent upon your miles per gallon before the modification. The lower the average MPG, the higher the savings for a 2 MPG improvement and vice versa.
 
#40 ·
Exhaust

Really it's like most other mods.. Smart mods will get you something; possibly not cost effective to everyone, but something. Don't be fooled by the auto makers; they couldn't care less about the Wranglers MPG. They only want our money guys and we'll buy the Wrangler anyhow, right. Why would they invest in something like that, for no return? Nobody really thinks that the 07 was redesigned to make a better Jeep do they? It may be better, but that's not why they did it. It's cheaper... That's the only reason they do anything.. Ron

bairy said:
OEMs try very hard to get the most MPG they can. This means, making the engine run more efficiently and reducing mass on the vehicle. Aftermarket headers do both. But who trusts the OEMs and their dyno numbers. I am sure they purposely did not make them as efficient as they could

I am sure the aftermarket headers do flow more and weigh less. But at how much of a difference? The money you spend on those will get you a long long way in gas. If you have money to blow, and you might want a coupe extra HP on the butt dyno, then go for it. Otherwise you will gain much better mpg and hp by never filling your gas tank over 1/4 for weight savings.
 
#41 ·
rljsrubicon said:
Really it's like most other mods.. Smart mods will get you something; possibly not cost effective to everyone, but something. Don't be fooled by the auto makers; they couldn't care less about the Wranglers MPG. They only want our money guys and we'll buy the Wrangler anyhow, right. Why would they invest in something like that, for no return? Nobody really thinks that the 07 was redesigned to make a better Jeep do they? It may be better, but that's not why they did it. It's cheaper... That's the only reason they do anything.. Ron
Damn, I am soooooo upset. Here I thought they were cranking out Wranglers to be NICE to us....Do you mean those capitalistic dogs in Toledo are just out to make a buck? ;)

Moon
 
#42 · (Edited)
mdm said:
Have you noticed that the '07 has a different engine?
No kidding. Didn't I mention that? I'd said they changed nearly everything. That would include engine, frame, and nearly everything (like I'd said). It always gets me when someone talks down to me because they didn't accurately read what I'd posted. With all due respect, please read more carefully; and use/give some diplomacy and respect so that you may receive it in return.
 
#43 ·
Yes. That is why I said that I sometimes miss owning BFG ATs. They're smoother enough, and yet rough enough to still get some traction. A good compromise, and looking better all the time as gas prices go up.

Gas costs $3.50 a gallon here right now, and still climbing. So drastic measures to gain 2 or 3 mpg might be reasonable.

However, I've already paid for those Cooper STs and I'm going to use 'em up (at least they're quiet on-road and good off-road, even if mpg sucks). If gas is still uber high in a few years, then next time I'll buy another set of BFG ATs. I might also look for narrower tires next time. Like some 10" or 10.5" wide in a 33" tall, if I can find 'em in a tread I want.

hoseclamp said:
The biggest gains to be had for the money, drum roll............

...........Run smoother tires, less rolling resistance. Find yourself some 16x7 alum wheels spec'd for a Liberty, throw on some 235/85-16 smoothies, like a Michelin LTX M/S, or a preferred Cooper equivalent, heheh, this will give you the best return for the money spent regarding mpg, and it wil be noticable. Just swapping the ST's for a smoothie in the same size will be noticable, he 16x7's and 235/16's will be even more.

No other change will net you better mpg return
 
#44 ·
edzakory said:
The dollar saving in driving 100k miles is dependent upon your miles per gallon before the modification. The lower the average MPG, the higher the savings for a 2 MPG improvement and vice versa.
That is correct. The lower the initial mileage the greater the impact. It is still tough to justify all the little toys we can add to the Jeep to improve only mileage. They do also improve performance and pump up bling.
 
#45 ·
Hey CB3, all I'm going to say is for the amount of money you could throw at the Jeep trying to save a mpg or two could probably be better used to buy a cheap import car to drive when the weather isn't as much fun, thusly saving you money on fuel. lol

I've tried a couple of things and nothing really helps. I don't get much freeway time in, some, but not much. The best way to get decent fuel economy (or at least what passes for it with a Jeep) is to try to no exceed the speed limit when you're over 45mph and leave stops smoothly, but I'm sure you already know this. Just wanted to offer up what I've tried and played with. HTH. Jerry is pretty much dead on on this subject.
 
#46 ·
It's sort of a pattern on this forum. The original question "Do aftermarket headers and exhaust systems really improve fuel economy?" gets lost and the pack mentality clicks in. As soon as one of the pack leaders states that your question and/or response is BS, the rest of the pack pile on. They appear to pay more attention to the pack leaders comments than to the original question. The question evolves from a "does it" question into a "is it enough to justify it in someone's opinion". Any opinion is relatively subjective and none anymore valid that another really. One can say that 37" tires are superior to 31" for this or that, but what does it really mean. I can say that it's not worth the cost and one should just not do this or that. Both are just opinions, neither better then the other. MPG and related threads/questions are the same. It doesn't matter whether anyone else thinks it's "worth it" or not. Ron

CB3 said:
No kidding. Didn't I mention that? I'd said they changed nearly everything. That would include engine, frame, and nearly everything (like I'd said). It always gets me when someone talks down to me because they didn't accurately read what I'd posted. With all due respect, please read more carefully; and use/give some diplomacy and respect so that you may receive it in return.
 
#47 ·
rljsrubicon said:
It's sort of a pattern on this forum. The original question "Do aftermarket headers and exhaust systems really improve fuel economy?" gets lost and the pack mentality clicks in. As soon as one of the pack leaders states that your question and/or response is BS, the rest of the pack pile on. They appear to pay more attention to the pack leaders comments than to the original question. The question evolves from a "does it" question into a "is it enough to justify it in someone's opinion". Any opinion is relatively subjective and none anymore valid that another really. One can say that 37" tires are superior to 31" for this or that, but what does it really mean. I can say that it's not worth the cost and one should just not do this or that. Both are just opinions, neither better then the other. MPG and related threads/questions are the same. It doesn't matter whether anyone else thinks it's "worth it" or not. Ron
As a tech forum, I prefer opinions based on experience or facts. This provides a baseline by which the OP can make an informative decision. By matching the variables associated with another's experience or facts, the OP can compare his needs to their baseline.

The header question is a little easier to qualify. If one is able to claim, with some merit, that they saved 2 MPG by solely changing headers, then the OP could be able to make an informed decision about the amortized cost of the headers over the projected mileage of the JEEP vis-à-vis the gasoline cost savings.

I think this same principle can be applied to tire size. However, when you get into spark plugs, oil, tire brand, etc., objectivity is much more difficult to qualify and you end up primarily with opinions.

Not that opinions are bad; they just lend themselves to controversy.:(
 
#51 ·
MPG is more driving style, gear and cam dependent, with cam being the big killer. If you have a fuel injected unit, you are already getting the best burn you can with your cam. Adding an aftermarket exhaust may hurt your MPG. A higher flow unit will usually reduce mid torque numbers but increase upper RPM HP numbers.

Scavenging exhaust at the exhaust port is what you try and increase for torque and power. Increasing flow rates in the exhaust system can reduce that scavenging effect in the mid RPMs. It all has to do with the velocity of the exhaust pulse, larger exhaust systems reduce veleocity in the mid RPMs plain and simple.

Adding larger tires reduces your gear ratio, you may get better MPG but that's going to be driving style related. If you have a heavy foot, add larger tires and an higher flowing exhaust, my moneys says your MPG will go down.
 
#52 ·
Update:

About 6 months ago I had installed a highflow muffler called a Hush Power. I haven't noticed any change in power or gas mileage. I miss my quieter stock LJ muffler and plan to put it back (I did save it).

I don't notice any difference at low RPM. I never drive high RPM.

If I notice any power difference at all, it seems like there might be a slight decrease in torque at mid-range RPM like Dryseals was talking about. That's frustrating because the mid-range RPM is where I already needed more torque/power.

The most noticeable thing is the literal headache it gives me when cruising down the freeway. I hate it because it's to loud, even with windows closed. In summer, with windows open it really is miserable.

From my experiences with a high flow muffler on my LJ, it's best to leave the stock muffler in place. Heck, the whole stock exhaust is great. Fooling around changing it won't help, but might hurt, IME. At least in regard to pipe, cats, and muffler. I don't know about changing header or head since my are stock and I have no experience with those.

My feeling (now that I have some experience) is leave the stock exhaust system stock. It's much quieter, and at least as good as aftermarket stuff IMO. In fact, the stock exhaust system might even be better than aftermarket stuff.

That's because it's low-end and mid-range RPM I care about. I don't think aftermarket exhaust makes any difference to low-end, and I think Dry Seals is correct about aftermarket exhaust reducing mid-range RPM.

If an aftermarket exhaust helps the high-end (and it might), it really doesn't matter because I don't windup my 4L engine past 3000 or 3200 RPM. Usually it's running below 2500 RPM.

I'm looking forward to putting my stock muffler back on.
 
#53 ·
I ran the stock exhaust for a few years then put a cheap sports muffler on for some noise. After a few years it became too loud, droned at hwy speeds and gave me a headache so i put a stock exhaust back on. After 15 months that exploded/popped and the only reason i noticed was due to lack of power and because i was getting 10.5mpg, even when taking it easy. So i decided to bite the bullet and get a new 2.5" cat back system with a high flow aluminium cat and high flow muffler (for a mitsubishi 6cyl sedan) for about $450 ($500au). Since then i have noticed that as the exhaust has been wearing in the power has increased and so has economy. With the power curve change from the exhaust there's more power throughout the rev range so i can change at lower revs but it now doesn't sound like it's got asthma in the upper revs and ithe 4.0L loves it. The new exhaust doesn't drone at hwy speeds either.

If i take it real easy and change gears at 2100rpm up to 4th and 2400rpm to 5th (wind resistance) i can get the economy to 21mpg+ which is almost double the fuel economy but a big chunk of that was probably because the TJ had a stuffed stock muffler.

Here's a video of the new exhaust just after it was fitted:



even if it didn't improve my economy all that much, it was worth it because the engine now sounds great throughout the entire rev range. When stock and above 3000rpm, the 4.0L didn't like it at all.

cheers
 
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