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Old 07-26-2010, 09:03 AM   #1
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4.0l headers and exhaust worth it?

does anyone have any real world hp gain numbers for a good set of headers and free flow exhaust for the wrangler 4.0l .

i am looking into my next big mod and i am thinking full exhaust but would like to know what gains the 4.0l gets.

i have already done k&n cold air intake and ff dynamics electric fan conversion and picked up some nice gains in mpg and seat of the pants power gains that i was impressed with. now looking for next step and i think the full exhaust might be it but before i drop a 1000.00 i want some opinions.

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Old 07-26-2010, 09:09 AM   #2
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Have you done a gear change yet?

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Old 07-26-2010, 09:15 AM   #3
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Just wondering where you got the electric fan. I can not find one anywhere.
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Old 07-26-2010, 09:53 AM   #4
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no gearing change yet, stock 3.73's, dont plan on doing it until these gas prices decide to come down some,the gearing seems fine for now as i only run 30 inch tires.in the future i plan on 35's and 4.88's as my choosen combo

i got the electric fan kit from ffdynamics.com,it comes with cut off switch and adjustable fan control, i gained 1.7mpg with this mod and there is a definate gain in take off power that i felt,this is a really good mod for the money.

as for the k&n i wish i would have gotten a no name brand for 50.00 instead of 250.00 i spent for the k&n because i didnt gain any mpg and i didnt feel hardly anything of a power increase

i am told the intake will give me the most when i get the exhaust and headers so maybe its not a total loss.
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Old 07-29-2010, 04:01 AM   #5
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Wow nobody on this entire forum has any real hp numbers for full headers back system on the 4.0l?

Anyone can chime in,I don't want to waste a 1000.00 if its not going to do anything but make it louder.Help me out here guys
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Old 07-29-2010, 05:30 AM   #6
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I'm at the same point you are, i know a good header adds @ 15 hp / 25 ft/lb of torque. The best headers for the 4.0 in my opinion are Dougs, Banks, JBA, and Borla. Couple a header with new, bigger piping and a free flow muffler and you should pick up even more. I'm gonna build a stroker this winter to drop into my Jeep in the spring, i'd love to see real dyno numbers from before / after your exhaust upgrade to estimate my gains.
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Old 07-29-2010, 05:35 AM   #7
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I'm at the same point you are, i know a good header adds @ 15 hp / 25 ft/lb of torque. The best headers for the 4.0 in my opinion are Dougs, Banks, JBA, and Borla. Couple a header with new, bigger piping and a free flow muffler and you should pick up even more. I'm gonna build a stroker this winter to drop into my Jeep in the spring, i'd love to see real dyno numbers from before / after your exhaust upgrade to estimate my gains and choice of components.
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Old 07-29-2010, 08:13 AM   #8
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I don't know about the Jeeps but the best reason I had to put on headers for my Camaro was that it turned a 6 hour spark plug change, where I had to take some out from the bottom and some from the top, into a 20 minute job where I could get them all from the top. I'll put headers on anything I have after that.

Like I said though, I don't know about the Jeep yet (probably buying an 06 LJ this weekend, which is why I'm trollin around here)
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Old 07-29-2010, 10:02 AM   #9
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According to many on this and every other Jeep forum I've found intake/exhaust mods are pretty worthless. (power wise). Luckily, the Jeep has quite a bit more room under the hood than that of a F body, so changing to a header won't impact your spark plug change...(its easy already)

IN theory you may gain a slight amount of HP, and maybe even improve the gas mileage by a cpl points, but its not widely done b/c those that have done it were disappointed with the results (unless they lied to themselves).

I haven't seen any dyno proof for any "bolt on power mod" so I won't waste my pennies on them. Most people I've found that changed over to a header did it for one reason - the OEM manifold cracked.

OP - if I were you I'd trash the K&N. (or sell it to some other unsuspecting fool)

If you do decide to swap exhaust/header, please dyno before and after. PLEASE!
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Old 07-29-2010, 10:28 AM   #10
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The TJ comes with headers, not an exhaust manifold, right from the factory. So far as the exhaust system goes, buying a cat-back is not going to make any difference you'll notice. I had to replace mine due to a major suspension modification and the so-called "low restriction" muffler the shop used made zero performance difference except it was louder.

And X2 on the recommendation to get rid of the K&N which is one of the most potentially damaging things you can install onto a TJ engine. Tests show two things... 1) the K&N was the worst at filtering air of all the air filters that were tested. 2) The TJ's OE air intake system was designed specifically to not be restrictive and it can easily flow more air than the engine is capable of consuming even at wide-open-throttle and redline engine rpms. I got rid of my K&N years ago when I discovered how much gritty grime was getting past it. My K&N ended up with TWO prefilters on it before the inside of my air tube and throttle body stopped getting coated with gritty dust.

This is a photo of my K&N that now just takes up room on my garage shelf with those pre-filters (Outerwears and foam Unifilter) pulled back so you can see them...
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Old 07-29-2010, 10:31 AM   #11
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Something else to consider is the noise level which you may or may not like. One of the Jeeps I test drove had after market headers/exhaust & a stage two performance chip. It sounded cool on the outside, but when I drove it with the full top on the rumble got old real fast. All conversations I had with the owner & my wife were near shouting level at any speed.
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Old 07-31-2010, 07:48 AM   #12
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So drop on a 100.00 flowmaster muffler and save the other cash for lift kit?
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Old 07-31-2010, 08:03 AM   #13
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Quote:
So drop on a 100.00 flowmaster muffler and save the other cash for lift kit?
Bingo! You wont get much (if any) noticeable power and mpg gain from a new muffler, but if you want a more aggressive sound, a new muffler/exhaust is worthwhile.

I have the Banks Cat Back exhaust. It sounds good, but definitely no noticeable power or mpg gain.
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Old 07-31-2010, 08:20 AM   #14
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Bingo! You wont get much (if any) noticeable power and mpg gain from a new muffler, but if you want a more aggressive sound, a new muffler/exhaust is worthwhile.

I have the Banks Cat Back exhaust. It sounds good, but definitely no noticeable power or mpg gain.
Yep, I put in a Mello tone muffle rin there... like it a lot.
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Old 07-31-2010, 08:55 AM   #15
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This is what I Installed: Banks Headers (new design),4" Ultra High flow Cat (might not be legal in your area),Magnaflow High Flow Through Muffler. Coupled with my Airaid Intake. I wasn't looking to gain any MPG because it's a brick and I accept that, But I did notice a large gain in available Torque at at the low and midrange rpm's, high rpm's torque are also better as I no longer had to drop from 5th to 4th on some local roads where I had to previously. As for the exhaust note, I haven't heard a jeep that sounds anything like it yet around here, gnarly and barky when you get into it but low and rumbly when driving normally. So in my opinion it was a good investment.
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Old 07-31-2010, 09:24 AM   #16
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I agree the cat back exhaust will do nothing for power, but does sound nice. I put a Flowmaster on a couple months ago with a 2.5" mandrel bent tail pipe.
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Old 07-31-2010, 10:28 AM   #17
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JP magazine did a real life myth buster story on many of the popular performance mods that people do to their Jeeps. They did before and after dyno and mpg comparisons. The story covers cold air intake, cat back exhaust, throttle body spacer, and some other mods I had never even heard of before. Here's the link: Jeep 4.0L Myth Busting True Lies - Jp Magazine
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Old 07-31-2010, 10:39 AM   #18
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i have yet to see an engine that didn't benefit from a tuned header swap. tuned meaniing specifically designed for that particular engine. since the 4.0 is fairly unique, most reputable brand headers will make some power. you have to decide if the cost is worth the likely 10hp you'll pick up. same goes for a good cat-back exhaust, you will pick up a few hp and likely a mpg or two, so it's up to you to decide if the price is worth it.
with other airflow mods or head/cam work, headers will become almost a necessity to realize your full potential. typical stock exhausts are designed to be cheap and quiet, not make power.
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Old 07-31-2010, 11:22 AM   #19
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I hate to play the Devil's Advocate, but seat-of-the-pants dyno testing is useless to those of us who can't drive your rig. Unless a person can provide real life dyno numbers (from a REAL dyno) before/after their intake/exhaust mods, it's pointless to try to sway some of us towards your way of thinking.

You can spend a ton of money chasing horsepower and torque on a 4.0L, but in the end, the cheapest and best money spent is on gears.
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Old 07-31-2010, 01:32 PM   #20
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^^ True dat.

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Old 08-03-2010, 09:25 AM   #21
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ok ordered a flowmaster from summit racing. not really wanting to go with gears yet because of the gas prices. going to hold off on anything that will chew up my mpg because this is also my work car and I drive over 400 miles a week.

any thoughts on a msd ignition system?
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Old 08-05-2010, 10:05 PM   #22
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All the coin I spent still wouldn't get me gears,axles and lockers.Cause you can't upgrade the gears and expect the shafts/housing to last.
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Old 02-23-2011, 12:34 PM   #23
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I have a 93 wrangler 4.0. I ripped out the carpet inside and had it rhino linered. I ripped out the entire exhaust system and replaced it with magna high flow cat, magna high flow muffler, cermaic header, and an aftermarket cool air intake (not the k&n). I also cut out the resignator underneath and left the cat and muffler only coming straight off the header. And for the last kicker i added a fuel chip (also aftermarket). I have a 4' roughcountry lift and 33's. I am right now getting about 18 to 22 to the gallon and i travel around with and without the top on. When i changed up, the engine ran sooo much smoother,and climbing with the extra torque was a really good bonus. Also when goin thru mud or sand, i don't scare. Since jeeps are so easy to work on and not too expensive to fix up, if your gonna keep it, build it to it's limit that way u never question "what if".... I did and glad i did. As a result i did the same to my 06 tundra with a small v8. Its now a mustang eater...... and damn good on gas....
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Old 02-23-2011, 04:56 PM   #24
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I did intake testing on the dyno and there are no gains to be had.
http://www.wranglerforum.com/f5/jeep...ing-77391.html

I would expect something very similar for the exhaust.
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Old 02-24-2011, 07:43 AM   #25
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I did headers into a flowmaster all with 2.5 piping,felt definite gain in power,not huge gains but noticable,mpg stayed about the same tho,I figured i would have picked up some mpg with a system that free flowing,if your doing an exhaust for mpg don't waste your money,none to be had here with the 4.0l
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Old 02-24-2011, 07:57 AM   #26
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One thing to keep in mind about the 4.0L engine is that it already comes with headers right from the factory. It does not come with the less efficient cast exhaust manifold like most car engines do.
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Old 02-24-2011, 08:24 AM   #27
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I got the headers off ebay,they were cheap and stainless steel so iIscooped them. if I had it to do over again I think I would keep the exhaust factory,I now have two choices when driving,radio loud or radio off and listen to exhaust loud.
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Old 02-24-2011, 11:29 AM   #28
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when my header cracked on my 8 4.0 I replaced it with a cheap one from quadratec paired with a magna flow cat and a cheap cat back. I didn't notice any performance gains, but it does sound really nice now. Every time I am at Rausch creek I get complements on the exhaust note... I know you guys are looking for dyno numbers, but I don't think the header back exhaust is worth it if you are expecting noticeable power gains. In my past experience I had a road race car and I was constantly changing computer tunes, and every time I made a plus/minus 10 hp change on the dyno i could feel it on the street... so I am assuming that IF I gained any power in my jeep it was minimal.
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Old 02-24-2011, 11:37 AM   #29
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Remember not all "headers" are created equal. You get what you pay for.
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Old 02-24-2011, 11:44 AM   #30
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I used a dynomax superturbo on my 03 and it sounded really nice. The stock muffler was starting to burn out anyhow and Dynomax makes a direct fit in the superturbo series so I figured why not. No pwer or mileage gains but a nice little rumble at idle and more aggressive sounding when opened up. Not too bad as to be annoying inside.

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