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Old 01-25-2011, 11:04 PM   #1
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Cool Mods leads to better mpg says a friend, what u think, true or false?

A friend told me that he is planning on doing some mods on his jeep. He said that he will get installed the following items:

Better headers

Better pipe and exhaust system

Better air intake system with better filter

He claims that by doing so his jeep will get maybe an additional 30HP. I'm ok with that as I know is suppose to get more HP with those mods. However, he claims that he will also get his mpg improved because his jeep will be more powerfull and requires less energy to move the vehicle. That's were I'm not getting it!!!

In physics, work = power, work is the jeep moving, power is the jeep HP. To get power you need energy, so the energy comes from the gas.

If you are still here, you might already understand that to move an object you need X amount of power which will consume Y amount of energy. So, if you need more power, you consume more energy.

If the jeep gets an additional 30HP and at the same time reduces his energy intake (mpg)....WHERE THE HELL IS THE OTHER REQUIRED ENERGY COMING FROM!!!!?????

Can someone explain me, or am I just going nuts here!?!?!

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Old 01-25-2011, 11:10 PM   #2
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You're not nuts, your friend is completely full of sh!t.

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Old 01-25-2011, 11:12 PM   #3
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Sounds like a classic case of rationalization.
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Old 01-25-2011, 11:44 PM   #4
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He will gain a little power on the top end and loose some on the bottom end [the exhaust and intake will change the rpm in which the engine puts out power] and "may" see a 1-2mpg increase at best. Power gain will be at a minimal due to the engine not being a performance engine like in a Mustang.
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Old 01-26-2011, 12:16 AM   #5
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The reason he gets better mpg with these mods is because it puts less stress on the engine meaning it doesnt have to work as hard, heres your physics for you to make it easier to understand.

Person A runs 10 miles

Person B attempts to run 10 miles except he has a rag covering his mouth and nose. He can only run 7


Everyone here should agree that This makes sense? Am i right?!
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Old 01-26-2011, 12:17 AM   #6
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I spend years and multi thousands of $$$ pursuing those kind of theories.

In the end, what I found, was my own driving habits affect my mileage a lot more than any of the mods I ever made.

I also found that every rig I've bought since my bank account become more important than my testosterone level, they all had enough power to accomplish what they were intended to do.

I have had rigs I increased the horsepower. Then came unexpected costs, in wear and tear, in maintenance, in unexpected break downs, and a constant cycle of continual expensive upgrades to overcome the last cycle of performance enhancing trinkets.

But it is fun trying.
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Old 01-26-2011, 12:22 AM   #7
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re: "heres your physics for you to make it easier to understand.

Person A runs 10 miles

Person B attempts to run 10 miles except he has a rag covering his mouth and nose. He can only run 7"

Person B is running through a volcanic induced dust storm. His rags prevents his death from psilicovolcanokoniosis due to rupture of the lung sacs.

Person A dies on the way to the hospital.

Person B has to tow Person A's Jeep home for his grieving widow.
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Old 01-26-2011, 12:23 AM   #8
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You know if your gonna worry about mpg's i think its time for a second car?
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Old 01-26-2011, 12:25 AM   #9
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If you're going to worry about 30hp get a bigger engine.
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Old 01-26-2011, 12:33 AM   #10
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Quote:
Originally Posted by makotoshishio View Post
A friend told me that he is planning on doing some mods on his jeep. He said that he will get installed the following items:

Better headers

Better pipe and exhaust system

Better air intake system with better filter

He claims that by doing so his jeep will get maybe an additional 30HP. I'm ok with that as I know is suppose to get more HP with those mods. However, he claims that he will also get his mpg improved because his jeep will be more powerfull and requires less energy to move the vehicle. That's were I'm not getting it!!!

In physics, work = power, work is the jeep moving, power is the jeep HP. To get power you need energy, so the energy comes from the gas.

If you are still here, you might already understand that to move an object you need X amount of power which will consume Y amount of energy. So, if you need more power, you consume more energy.

If the jeep gets an additional 30HP and at the same time reduces his energy intake (mpg)....WHERE THE HELL IS THE OTHER REQUIRED ENERGY COMING FROM!!!!?????

Can someone explain me, or am I just going nuts here!?!?!
It should help the MPGs some but not enough to overcome the cost of the Mods.


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Old 01-26-2011, 12:44 AM   #11
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I spend years and multi thousands of $$$ pursuing those kind of theories.

In the end, what I found, was my own driving habits affect my mileage a lot more than any of the mods I ever made.

I also found that every rig I've bought since my bank account become more important than my testosterone level, they all had enough power to accomplish what they were intended to do.

I have had rigs I increased the horsepower. Then came unexpected costs, in wear and tear, in maintenance, in unexpected break downs, and a constant cycle of continual expensive upgrades to overcome the last cycle of performance enhancing trinkets.

But it is fun trying.
Very well stated. This is exactly why I plan to keep my Jeep virtually stock. It's so damn capable already for it's intended purpose.
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Old 01-26-2011, 06:35 AM   #12
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You're correct in your statement that it will take extra fuel to make 30 more HP. If your friend's mods made the engine more efficient he may be able to make some slight HP gains (probably not 30) and not use more fuel. Your friend may see some slight MPG gains and some horsepower gains, but he probably won't see them at the same time. If he runs his engine about as hard as he did before the mods he may be able to pick up some MPGs; if he guts his engine trying to take advantage of his HP gains he'll lose MPGs. JeeperJake hit the nail on the head; driving habits have a huge influence on fuel economy and extra HP usually induces us to modify our driving habits at the expense of MPGs.
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Old 01-26-2011, 09:02 AM   #13
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Quote:
Originally Posted by JeeperJake View Post
re: "heres your physics for you to make it easier to understand.

Person A runs 10 miles

Person B attempts to run 10 miles except he has a rag covering his mouth and nose. He can only run 7"

Person B is running through a volcanic induced dust storm. His rags prevents his death from psilicovolcanokoniosis due to rupture of the lung sacs.

Person A dies on the way to the hospital.

Person B has to tow Person A's Jeep home for his grieving widow.
LOL! I like the way you think.....
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Old 01-26-2011, 09:18 AM   #14
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I did all that stuff and went from 17 mpg to 14 mpg... more power = heavier foot, otherwise, why change it at all, you'll get there eventually...
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Old 01-26-2011, 09:35 AM   #15
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You'd see some modest gains, but the 30 horsepower estimate is very--very--generous. Overall, your friend will be paying a lot of money for just a few ponies. Plus this:

Quote:
Originally Posted by Peepers View Post
I did all that stuff and went from 17 mpg to 14 mpg... more power = heavier foot . . . .
is generally correct. Up to him though. Plenty of folks do all, or some, of that stuff.

Does your friend have an automatic or manual transmission? If he has an automatic, I'd say the most warmly received dollar-for-dollar performance improvement on this forum is a Superchips Flashpaq, which you can see here.
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Old 01-26-2011, 09:36 AM   #16
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Quote:
Originally Posted by JeeperJake
re: "heres your physics for you to make it easier to understand.

Person A runs 10 miles

Person B attempts to run 10 miles except he has a rag covering his mouth and nose. He can only run 7"

Person B is running through a volcanic induced dust storm. His rags prevents his death from psilicovolcanokoniosis due to rupture of the lung sacs.

Person A dies on the way to the hospital.

Person B has to tow Person A's Jeep home for his grieving widow.
What if your not near a volcano?! Rofl
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Old 01-26-2011, 09:49 AM   #17
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Originally Posted by sheetsd66 View Post
You're correct in your statement that it will take extra fuel to make 30 more HP. If your friend's mods made the engine more efficient he may be able to make some slight HP gains (probably not 30) and not use more fuel. Your friend may see some slight MPG gains and some horsepower gains, but he probably won't see them at the same time. If he runs his engine about as hard as he did before the mods he may be able to pick up some MPGs; if he guts his engine trying to take advantage of his HP gains he'll lose MPGs. JeeperJake hit the nail on the head; driving habits have a huge influence on fuel economy and extra HP usually induces us to modify our driving habits at the expense of MPGs.
Right! When he told me all this I was like "What for???" I mean, the jeep is brand new, and as it comes is very capable. I would go around such mods after maybe 3 years if ever required.
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Old 01-26-2011, 10:03 AM   #18
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I did the air intake and cat-back exhaust mod to my 2nd Jeep (02 TJ). Promises were more HP and better MPG. I didn't notice either. I did notice that I stood on the pedal a lot more to hear the Cat-back. Sounded sweet. So MPG went down. When I put the 33's on it helped with acceleration (3.73 gears)...but not that much.

Overall opinion with air intake and cat-back exhaust was, it was a waste of money. Unless you just want your jeep to sound better when you floor it. Doesn't do anything for Mudding/Rockcrawling...IMHO. Any MPG or HP is negligible, b/c you could just change your driving habits to save MPG.
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Old 01-26-2011, 10:09 AM   #19
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I would bet on 10-15 real world horsepower. You're just not picking up a honest 30hp with only airflow mods and no added fuel on the 3.8. Peak horsepower means nothing in a typical Jeep, it's a flat power curve you want. An extra 15hp at 5000rpm is practically useless in a Jeep, but any torque you might lose down low you will definitely miss, which is quite possible when upsizing the exhaust and intake.
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Old 01-26-2011, 10:18 AM   #20
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With all the generations of design engineers slaving to put out a competitive product that performs well under a wide variety of uses over a long period of time using a huge amount of data point inputs to arrive at the most reliable, powerful and economical package available, I found I needed neither volcanoes nor rags stuffed in my various orifices, to benefit from their 70 years experience in building Jeeps.

I have come to the point I like the sound of a quiet reliable power plant that doesn't require endless investment in time and costly gadgets to occupy my speculative notions.
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Old 01-26-2011, 10:43 AM   #21
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I have come to the point I like the sound of a quiet reliable power plant that doesn't require endless investment in time and costly gadgets to occupy my speculative notions.
It seems the most of us evolve even though it takes some time and money. LOL

Been there done that.
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Old 01-26-2011, 12:17 PM   #22
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I spend years and multi thousands of $$$ pursuing those kind of theories.

In the end, what I found, was my own driving habits affect my mileage a lot more than any of the mods I ever made.

I also found that every rig I've bought since my bank account become more important than my testosterone level, they all had enough power to accomplish what they were intended to do.

I have had rigs I increased the horsepower. Then came unexpected costs, in wear and tear, in maintenance, in unexpected break downs, and a constant cycle of continual expensive upgrades to overcome the last cycle of performance enhancing trinkets.

But it is fun trying.
Mirrows my experience exactly.

You will probably experience a slight power increase at WOT. What you will get is more engine noise. You might like that but it's of no benefit in the power department.
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Old 01-26-2011, 12:42 PM   #23
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If your planning on getting larger tires then I would recommend Superchips FlashPaq. I got 2 mpg increase from the tune on it but at $350 the claim of 10 HP and 2 MPG is not worth the investment unless you do plan on larger tires were you can make the changes to correct speedometer.
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Old 01-26-2011, 01:52 PM   #24
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Originally Posted by Cleric73 View Post
I did the air intake and cat-back exhaust mod to my 2nd Jeep (02 TJ). Promises were more HP and better MPG. I didn't notice either. I did notice that I stood on the pedal a lot more to hear the Cat-back. Sounded sweet. So MPG went down. When I put the 33's on it helped with acceleration (3.73 gears)...but not that much.

Overall opinion with air intake and cat-back exhaust was, it was a waste of money. Unless you just want your jeep to sound better when you floor it. Doesn't do anything for Mudding/Rockcrawling...IMHO. Any MPG or HP is negligible, b/c you could just change your driving habits to save MPG.
A pet peeve of mine is when people throw around the term "cat back exhaust" as if it's something magical. All it means is the catalytic converter wasn't replaced. Only things from the back of catalytic converter.
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Old 01-26-2011, 01:54 PM   #25
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"cat back" is where the sound comes from. if you want to sneak around and not make any noise you cut the "cat back" off.
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Old 01-26-2011, 02:02 PM   #26
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A pet peeve of mine is when people throw around the term "cat back exhaust" as if it's something magical. All it means is the catalytic converter wasn't replaced. Only things from the back of catalytic converter.
True - but when you do happen to replace the ENTIRE exhaust system (from the cylinder head exhaust port to the tip), its nice to differentiate *begin snobbish aristocrat tone of voice* from those who only changed their exhaust from the cat back. *end snobbish aristocrat tone of voice*

Actually my bigger pet peeve is those who refer to a cold air intake as 'intake'. When I think 'intake' I think 'intake manifold'...not plastic tubing.
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Old 01-26-2011, 02:13 PM   #27
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Actually my bigger pet peeve is those who refer to a cold air intake as 'intake'. When I think 'intake' I think 'intake manifold'...not plastic tubing.
Hey hey now, mine's metal.

But while we're talking about "CAI" peeves, I don't mind calling it an "intake"--it's the suggestion that it's COLD that bothers me. To me, Cold = Snorkel. Anything else is just a new "air intake."

Still not sure why anybody switches an exhaust for "power" purposes.
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Old 01-26-2011, 02:14 PM   #28
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I'm running a cold air intake right now. It will probably remain that way until late May.
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Old 01-26-2011, 02:19 PM   #29
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Most of the ricer terms that have carried over irritate me. Using "system" to refer to a stereo or speakers is another pet peeve.
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Old 01-26-2011, 02:37 PM   #30
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"system" to me is a marketing term used to suggest superior technological aspects that are too esoteric for those without such personal enhancements meriting a "*snobbish aristocrat tone of voice*" to understand....

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