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Unread 05-19-2007, 09:57 AM   #46
rljsrubicon
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Do aftermarket headers and exhaust systems really improve fuel economy?

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


Quote:
Originally Posted by CB3
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.


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Unread 05-19-2007, 10:54 AM   #47
edzakory
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Quote:
Originally Posted by rljsrubicon
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.
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Unread 05-19-2007, 11:34 AM   #48
jfondren3
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How about this then, buy a fuel atomizer and let me know if it works. I don't know anything about them and don't really care about the gas anyway but it looks like something you could check out.

Here is one but there are hundreds out there.

http://www.wyominginstruments.com/gas_home.htm
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Unread 05-08-2010, 03:30 AM   #49
Maverickxeo
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Originally Posted by halfmoonclip View Post
Because gas is $3 @ gallon, and we are looking for miracles!

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.
Moon
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.
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Unread 05-08-2010, 04:45 AM   #50
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Originally Posted by gargyle View Post
$3 a gallon.

Lucky you.

Try living in Canada.

$1.14 per liter X 4.5 liters per gallon = $5.13

and we make the stuff.

Canada has enough oil in the tar-sands up north to fuel this continent for a hundred years.
Tell me about it I put 600-700 bucks into mine every month. Thats why I'm looking for a DD right now
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Unread 05-08-2010, 08:45 AM   #51
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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.
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Unread 05-17-2010, 07:25 PM   #52
CB3
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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.
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Unread 05-17-2010, 08:16 PM   #53
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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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Unread 05-17-2010, 09:16 PM   #54
Bubba3200
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All you guys have to do is get the "Tornado" and slide it into your intake tube and get 25 more mpg and at least 50-100 more hp. And the best part is that it is only 65 hard earned dollars...........
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Unread 05-17-2010, 09:48 PM   #55
SupaJosh
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Quote:
Originally Posted by Jerry Bransford View Post
The Jeep already has headers. Jeep is under IMMENSE federal pressure to up their CAFE (corporate average fleet economy) mpg averages and if they could further improve on them by a simple exhaust system design change, they'd be all over it.
I know for certain when you have 160K on your Jeep and never changed the factory clogged Cat and Rusted...holed muffler with a High-flow cat and High-flow Muffler and a K&N filter in the factory box that you get the lost horsepower back and the gas mileage goes back to normal if not a couple better... I have done this with 3 Jeeps and have been successful everytime!
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Unread 05-17-2010, 10:00 PM   #56
SupaJosh
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Quote:
Originally Posted by Bubba3200 View Post
All you guys have to do is get the "Tornado" and slide it into your intake tube and get 25 more mpg and at least 50-100 more hp. And the best part is that it is only 65 hard earned dollars...........
I do have to say the tornado is a Joke!!! I bought it and it was a waste of money... I bought a 1998 Jeep TJ 4 banger and it was only getting 15mpg with 235x75x15 tires and I put a $20 K&N filter on it bought a Magnaflow high-flow cat for $65 and $25 Dynomax Super FLo muffler on sale. All for $95...
That is not that much money for my power back and better mpg.
I just checked my mileage and I got 377 miles off 15 gallons.
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Unread 05-17-2010, 11:08 PM   #57
rubidriver
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Quote:
Originally Posted by Jerry Bransford View Post
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. 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.
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Unread 05-19-2010, 01:37 PM   #58
CB3
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Quote:
Originally Posted by SupaJosh View Post
I know for certain when you have 160K on your Jeep and never changed the factory clogged Cat and Rusted...holed muffler with a High-flow cat and High-flow Muffler and a K&N filter in the factory box that you get the lost horsepower back and the gas mileage goes back to normal if not a couple better... I have done this with 3 Jeeps and have been successful everytime!
Maybe so - when your Jeep has 160K miles on it, since by then the stock cats might be clogging. do muffler's clog?

My Jeep only has only 27K miles on it, and my stock muffler has only about 25K miles on it. So in my case, putting my "almost new" stock muffler back on would be fine, IMO.

BTW - do mufflers clog when high miles? I know cats can clog, but I never heard of a muffler clogging. I'm not saying you're wrong about your muffler clogging, but I never heard of that before.

Last edited by CB3; 05-19-2010 at 02:57 PM..
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Unread 05-19-2010, 02:55 PM   #59
CB3
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Though I would like to ask, are there any high performance cat back systems that are as quiet as stock?

How about aftermarket mufflers that are higher clearance than stock and just as quiet as stock?

I like the better ground clearance my aftermarket Hush Power muffler offers, but I hate the noise, and I suspect it might be losing me a bit of mid-rpm torque.
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