Jeep 4.0L engine mods - what mechanic told me, need opinions...

[KDOG]

I have a 2004 Jeep Grand Cherokee Laredo 4.0L I6 with the 4spd Auto and SelecTrac TC. Supposedly its a pretty good setup. Today at the shop where I was getting my oil changed and diff/TC fluids checked etc., I asked him if there are any legit mods that could be done to increase power/efficiency. He stated that if it was him he'd put a Flowmaster exhaust on it with a Summit "airbox". He said it would give me a boost in both HP and milage.

What say the gearheads at AT?

 

[thecoolnessrune]

It would sound better and feel good to the "buttdyno" but the difference in power wouldn't be noticeable nor would the improvement to mileage.

 

[Vette73]

It will give a little boost but more at higher end than lowwer.

That and don't use any foam/K&N type filter. They let in a lot more dirt for very little to nothing in return.

If there was a easy was to increase milage/hp (let alone at the same time) the maker would have done it. The 4.0L is known for good torque but not great gas milage.

Just keep up on the basic like most cars filters (air and fuel), clean throttle body and MAF sensor, tire pressure, etc...

 

[MikeMike]

i heard Chuck Norris in the oil won't even kill the 4.0l

 

[Throckmorton]

It's an inefficient old engine no matter what you do. Although Cherokees with the manual transmission seem to get up to 25mpg by some miracle.

But on the bright side it's a really tough engine.

Just leave it alone

 

[JulesMaximus]

I have a 2004 Jeep Grand Cherokee Laredo 4.0L I6 with the 4spd Auto and SelecTrac TC. Supposedly its a pretty good setup. Today at the shop where I was getting my oil changed and diff/TC fluids checked etc., I asked him if there are any legit mods that could be done to increase power/efficiency. He stated that if it was him he'd put a Flowmaster exhaust on it with a Summit "airbox". He said it would give me a boost in both HP and milage.

What say the gearheads at AT?

That's a load of horsepoo. While you MIGHT notice a slight miniscule increase in power or in certain areas of the powerband (you might actually notice a decrease in areas though too), you definitely won't notice any difference in fuel economy.

Every car/truck I've done exhaust/intake mods on only changed the sound the engine made and in most cases fuel economy stayed the same or suffered a bit.

 

[Throckmorton]

That's a load of horsepoo. While you MIGHT notice a slight miniscule increase in power or in certain areas of the powerband (you might actually notice a decrease in areas though too), you definitely won't notice any difference in fuel economy.

Every car/truck I've done exhaust/intake mods on only changed the sound the engine made and in most cases fuel economy stayed the same or suffered a bit.

Well a lot of people report better gas mileage with a snorkel. I have no idea why... it's more restriction and cooler denser air, so gas mileage should go down.

 

[JCH13]

You might see slight improvements in fuel economy and HP, but in no way would it be earth-shattering. Probably a few percent in each category.

I would find a jeep with a similar exhaust and ask for a ride to see if you can tolerate the increased noise. Like others have mentioned, steer clear of K&N and foam filters when it comes to the intake.

I'd go for it if I had the extra money kicking around because I like playing with my cars. If you're looking to save money on fuel costs, don't do it.

 

[fbrdphreak]

+1 on waste of money

Save the bucks to keep that 4.0L in good maintenance and running forever.

If my 97 Subie wagon ever died, a 4x4 4.0L Cherokee would be on my short list to own. Cheap, reliable, plenty of people & cargo room, etc.

 

[LTC8K6]

If you haven't been to WJJEEPS, it's a great site for all things WJ.

 

[T2urtle]

Every car/truck I've done exhaust/intake mods on only changed the sound the engine made and in most cases fuel economy stayed the same or suffered a bit.

its mainly sound yes. But in come cars removing a stock exhaust setup that weights 100lbs and replacing it with a 30lb exhaust and the fact that it MIGHT be better flowing could work. But yes its still like 1mpg difference and MAYBE a few ponies more, nothing you can feel but you can hear the noise.

keep it stock and enjoy it for what it is like most of us are saying. But if your exhaust starts to rust out i would almost always look into the aftermarket stuff.

 

[Bignate603]

Somewhere laying around here I have a copy of JP magazine where they did some things to the 4.0L and ran it on a dyno. There are some things you can do but for the most part people just leave them alone because they've got enough low end torque to be fun and are reliable as long as you keep it's fluids topped off. I'll see if I can find the magazine though to see if they thought any were worthwhile.

 

[LTC8K6]

http://www.moparproshop.com/inc/sdetail/5042

 

[KDOG]

http://www.moparproshop.com/inc/sdetail/5042

Oh would I like to! LOL!


I also just heard someone on one of the jeep forums state that as far as the air filters go, a study showed ( he didn't say who or where ) that the stock air filter can allow more air than the engine would ever need but its the box and intake pipe design that can be modded to allow better flow.

 

[Throckmorton]

BTW, Petersen's 4 Wheel Drive And Off Road 4x4 Four Wheel Drive SUV Magazine 4x4 Monthly by Petersen's did an article on boosting efficiency, and they had a lot of success. Too bad I can't find the article.

I can't even remember the actual stupid name of the magazine.

 

[Bignate603]

Ok, I started looking through my old copies of JP to see if I could find an article about pepping up the 4.0L. They actually did a few articles over a few months about building something they called the "insane inline", a 4.0L with 600+ hp.

Here are a few things they said worked in their November 2009 article where they discussed different things people tried to increase power:

Cold air intake - like Kdog said, they found getting rid of the convoluted factory airbox netted 5-10 hp and around 1 mpg on a '91 and later MPI 4.0L

After cat exhaust - 5-15 hp gain, which they've seen through dyno testing

Exhaust header - 5-10 hp gain and fuel economy improvement IF your exhaust manifold has cracked like almost every single factory one will on a 4.0L. You might see some gains going from a non-cracked manifold to an aftermarket header but if it's not cracked now it probably will be later.

Their recommendation was to do all three to get a noticeable gain. However, be aware that not all aftermarket parts are created equally. They didn't recommend specific brands (the point of the article was just to confirm or disprove different power adding myths for the 4.0L) but putting crap on your car could very easily harm performance and fuel economy more than it helps.


Things they said did not work:

Throttle body spacer
Piggyback programers - found very limited benefit on '96 and later 4.0L engines and not possible to reflash factory computer
Bigger diameter throttle body
Ignition improvements
Swapping to '91 to '95 heads for better flow - only beneficial if you are moving to a camshaft with higher lift and/or duration to make use of that extra flow
Swapping to a '99 and up horseshoe style intake - They tried this one on a cherokee and it actually reduced the power by 5 hp

 

[Throckmorton]

I think it was the JP article I was thinking of

 

[KDOG]

Ok, I started looking through my old copies of JP to see if I could find an article about pepping up the 4.0L. They actually did a few articles over a few months about building something they called the "insane inline", a 4.0L with 600+ hp.

Here are a few things they said worked in their November 2009 article where they discussed different things people tried to increase power:

Cold air intake - like Kdog said, they found getting rid of the convoluted factory airbox netted 5-10 hp and around 1 mpg on a '91 and later MPI 4.0L

After cat exhaust - 5-15 hp gain, which they've seen through dyno testing

Exhaust header - 5-10 hp gain and fuel economy improvement IF your exhaust manifold has cracked like almost every single factory one will on a 4.0L. You might see some gains going from a non-cracked manifold to an aftermarket header but if it's not cracked now it probably will be later.

Their recommendation was to do all three to get a noticeable gain. However, be aware that not all aftermarket parts are created equally. They didn't recommend specific brands (the point of the article was just to confirm or disprove different power adding myths for the 4.0L) but putting crap on your car could very easily harm performance and fuel economy more than it helps.


Things they said did not work:

Throttle body spacer
Piggyback programers - found very limited benefit on '96 and later 4.0L engines and not possible to reflash factory computer
Bigger diameter throttle body
Ignition improvements
Swapping to '91 to '95 heads for better flow - only beneficial if you are moving to a camshaft with higher lift and/or duration to make use of that extra flow
Swapping to a '99 and up horseshoe style intake - They tried this one on a cherokee and it actually reduced the power by 5 hp

Thanks for the info! Decisions, decisions!

 

[iGas]

IMHO, the best modification that you can do for it is to buy a used fuel miser car.

Cost of total modification ++ fuel consumption of the Jeep vs. cost of fuel miser car ++ fuel saving.

Jeep fuel economy average is around 15~16mpg.

Honda Fit/Scion xD average consumption is 34mpg.

Pending the mileage that you do a year a fuel miser car could save you $1200 a year. It would take you 4 years to break even if you used fuel miser car costs 10K, if the mod cost 5K to save 1mpg on the Jeep.

 

[JulesMaximus]

Ok, I started looking through my old copies of JP to see if I could find an article about pepping up the 4.0L. They actually did a few articles over a few months about building something they called the "insane inline", a 4.0L with 600+ hp.

Here are a few things they said worked in their November 2009 article where they discussed different things people tried to increase power:

Cold air intake - like Kdog said, they found getting rid of the convoluted factory airbox netted 5-10 hp and around 1 mpg on a '91 and later MPI 4.0L

After cat exhaust - 5-15 hp gain, which they've seen through dyno testing

Exhaust header - 5-10 hp gain and fuel economy improvement IF your exhaust manifold has cracked like almost every single factory one will on a 4.0L. You might see some gains going from a non-cracked manifold to an aftermarket header but if it's not cracked now it probably will be later.

Their recommendation was to do all three to get a noticeable gain. However, be aware that not all aftermarket parts are created equally. They didn't recommend specific brands (the point of the article was just to confirm or disprove different power adding myths for the 4.0L) but putting crap on your car could very easily harm performance and fuel economy more than it helps.


Things they said did not work:

Throttle body spacer
Piggyback programers - found very limited benefit on '96 and later 4.0L engines and not possible to reflash factory computer
Bigger diameter throttle body
Ignition improvements
Swapping to '91 to '95 heads for better flow - only beneficial if you are moving to a camshaft with higher lift and/or duration to make use of that extra flow
Swapping to a '99 and up horseshoe style intake - They tried this one on a cherokee and it actually reduced the power by 5 hp

So that's anywhere from 15hp to 35hp using those numbers. No way all that would net you 35hp increase. Maybe all those things together MIGHT get you 15 more hp but not 35. 15hp on a heavy vehicle like that won't make much of a difference if any.

 

[LTC8K6]

Plus, he has a 2004 vehicle...so it seems really unlikely that any of the mentioned mods would do much.

 

[Bignate603]

IMHO, the best modification that you can do for it is to buy a used fuel miser car.

Cost of total modification ++ fuel consumption of the Jeep vs. cost of fuel miser car ++ fuel saving.

Jeep fuel economy average is around 15~16mpg.

Honda Fit/Scion xD average consumption is 34mpg.

Pending the mileage that you do a year a fuel miser car could save you $1200 a year. How much the modification is going to cost just so that you can get and additional 1mpg?

You're saying he should spend >$10k to buy another car to save $1200 a year?

The OP is asking about something to increase both hp and mileage of his current vehicle. Presumably he likes his Jeep, and wants to keep it. Suggesting that he spend thousands more than he'd save to replace a car he likes is insane. He's just trying to take something he likes and make it even better.

 

[Bignate603]

So that's anywhere from 15hp to 35hp using those numbers. No way all that would net you 35hp increase. Maybe all those things together MIGHT get you 15 more hp but not 35. 15hp on a heavy vehicle like that won't make much of a difference if any.

The 4.0L in the Grand Cherokee only had 195 hp. He'd be in the ballpark of a 10% increase in hp and some improvements in throttle response. The change would be noticeable.

Plus, he has a 2004 vehicle...so it seems really unlikely that any of the mentioned mods would do much.

I fail to see how that would make modifications suddenly not have an effect. It's not like the 4.0L is a crappy engine that wears out after 6 years. If anything, that would make the benefit of an aftermarket exhaust header even greater because it increases the chances that his already manifold is already cracked.

 

[iGas]

You're saying he should spend >$10k to buy another car to save $1200 a year?

The OP is asking about something to increase both hp and mileage of his current vehicle. Presumably he likes his Jeep, and wants to keep it. Suggesting that he spend thousands more than he'd save to replace a car he likes is insane. He's just trying to take something he likes and make it even better.

I'm saying keeping both. The Jeep for the weekends.

 

[Bignate603]

I'm saying keeping both. The Jeep for the weekends.

Again, you're suggesting a $10,000 purchase to get $1,200 in savings on gas. That $1,200 savings is going to be much less, possibly close to zero, once you factor in the cost of insurance and maintenance.