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Dan M
Dodge Dakota
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5/15/2006
07:35:24
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 Subject: Exhaust and MPG
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The overall plan for my 2002 QC 4x4 auto 4.7L 3.55 LSD is to make it a nice off road capable truck while still making it a smooth (as possible) ride on the highway and keep the mpg as high as possible.
Now, my defination of off-road capable. I am doing more and more fly fishing for trout in the mountains of ga, nc and tn. I will be traveling/fishing in these ares year round. This includes winter and snow. Some of the areas I will be visiting on on property where some of the roads are dirt/mud/gravel. Speaking to others who have fished these areas before 4x4 is required and a winch is highly recommended.
My first modification will be to the exhaust in a couple of weeks. I'm hoping to get some input on how/what to do to get a nice sound and increase my mpg if at all possible. I want to at least keep it the same. I am not interested in doing anything that will make it worse. I'm NOT looking to get as much performance as possible. The stock 4.7L has enough hp/torque for what I would need it to be as I'm not making an extreme off roader nor a rock crawler. I may in conjunction with the exhaust upgrade also uprade the throttlebody. Thoughts on that?
Given my overall goal, what would be better? Single/dual or single/single. I'm pretty much set on getting a flowmaster unless someone can make a compelling case (proof needed) to go with another vendor.
I know there are other mods that will help in accomplishing my long term plans. These are listed on my cardomain website listed below.
http://www.cardomain.com/ride/2272232/1
- Dan M
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jpkomm
Dodge Dakota
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5/15/2006
09:30:25
| RE: Exhaust and MPG
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It sounds like you have a pretty reasonable plan laid out there, Dan. On my 00 Dak, I kept it as a single/single and just put in a Flowmaster Super 40 and a nice looking tip. My grandfather, who dislikes most loud mufflers, said that the muffler did sound aggressive, but not obnoxious like straightpipes or just plain annoying like fart-cans. You can go with a Delta-Flow if you want it to be a wee bit quieter. Right now, my engine is all stock. With the Airaid intake I had on it, it did make it quite a bit louder. However, I just wanted to go back to the simplicity of a stock engine. No muss, no fuss. With just the exhaust upgrade, you should notice a slight increase in your mpg.... that is if you can keep your foot off the petal after hearing it. ;)
Like you though, I would like to upgrade my throttle body to something a bit bigger. I think it is a good investment, but I'm not sure how much of a difference it will make on a stock engine. Perhaps you can try to port it yourself?
I live up in the NE GA mountains and if there was any upgrade I could do on my truck right now, it would be to swap out my 3.55 differentials to something bigger. Even if it were just to a 3.92 LSD gearing. Mountains and 3.55s don't get along real well. Other than that, at 31.6k miles, the truck runs like brand new. I'd have to say that changing to all-synthetic fluids made one of the biggest impacts on my mileage.
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Shatto
Dodge Dakota
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5/17/2006
02:43:01
| RE: Exhaust and MPG
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Gibson says their systems are designed for performance where you drive. My 98 3.9 does so at around 2,000 RPM, where it lives.
I guess you don't spend too much time redlining it on logging roads and trails........
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crow318
Dodge Dakota
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5/17/2006
09:25:51
| RE: Exhaust and MPG
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Dan,
I would have to agree with jpkomm. I have a delta series flowmaster on my truck and it sounds great. If you will be off road quite a bit, I would keep with the single in single out. Also, don't change your pipe size. Going larger will only help way up in the rev range and it will work against you on the low end torque.
You should toss the 3.55's and either find a used set of 3.92's or a new set of 4.10's
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truck guy
Dodge Dakota
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6/04/2006
18:08:23
| RE: Exhaust and MPG
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As for the exaust size, go with the bigest thing you can afford. A motor is an air pump, the better you can bring air in and out the better power you make. Some people say that you need some back pressure, that's wrong. Any back pressure you have will rob you of power. Think like this, try to put a garden hose on a fire plug while it's open. when you chock off the flow of anything you lose power. Also if you've got the motor mods for it then go with true duals. Once you make the motor breath better you will gain MPG.
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.boB
Dodge Dakota
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6/04/2006
18:42:46
| RE: Exhaust and MPG
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A new exhaust won't gain you any worthwhile power. It might get you 1-2 mpg, but don't count on it. Unless you're adding a full header and dual exhaust system to a modified engine, there's not enough power gain to make it worth the trouble. You won't increase gas mileage enough to make it pay off in less than 50-60K miles; if it increases at all. Likewise changing to huge pipes behind the cat.
The only reason to change the muffler and pipe is for a better sound. Which I think is an excellent reason.
More power for hills and mud bogs can be obtained simply by changing the final drive ratio. Unfortunatly, there's a good chance that will cost you fuel mileage on the highway if you over do it. I have 3.92's on mine. This is an excellent all around gear for me. Good torque around town, tows easily, just gets into the power band at 70mph. I would not go with anything smaller, like 3.55 or 3.25. And if you really need some extra torque, drop it into 4Low. That will change your FDR quite a bit. It's like instantly switching to 4.56 gears.
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Obio3
Dodge Dakota
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6/04/2006
18:53:22
| RE: Exhaust and MPG
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BINGO>>>>>Truck guy just gave you the currect answer. Nice going. Saying it simple,Better breathing = better HP and better HP, with in reason, = better fuel milage PROVIDED you can keep from using it unless absulutely needed. The dakota intake system isn't that great. But the Dakota exhaust is top quality stock but geared toward the intake and engine tuning as delivered. Before i get jumped, The last statement doesn't include the poor quality converter.
So many problems .... So little time
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truck guy
Dodge Dakota
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6/10/2006
14:42:41
| RE: Exhaust and MPG
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Thanks obio3, It's nice to know that I've helped. It seems that most time you try to give out info on this site some people get offeneded if what you say doesn't go with the group.
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Obio3
Dodge Dakota
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6/10/2006
16:29:49
| RE: Exhaust and MPG
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Ttuck guy...... Seems to me there's a lot that have wrong info NOT because there dumb but that they hear it so often from so many other wrong guys here and other places they deside it's true. I'm not perfect myself nor is anybody else but unless I type something incorrectly, the info I pass on came from actual experiance or trusted reading information NOT connected with the selling company.And just because I think my way is best doesn't mean it's best for everybody.
So many problems .... So little time
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Dan M
Dodge Dakota
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6/10/2006
17:01:11
| RE: Exhaust and MPG
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As I pointed out, i'm not after horse power. I'm after milage. The sound is a good side effect.
All modifications have been put on hold for the time being. We're looking at buying a new house. I'll take a 1 acre yard and 2 car garage over better sounding exhaust any day.
I think I will give the halo's a try in a few weeks.
- Dan M
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shatto
Dodge Dakota
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6/10/2006
21:47:15
| RE: Exhaust and MPG
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Obio3,
I was told, by the guy who installed my noisy Flowmaster, that the stock cat on the 98 3.9 was a pretty good free-flowing unit.
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ricardcapecod
Dodge Dakota
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6/14/2006
09:44:51
| RE: Exhaust and MPG
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The biggest is not the best period.
Being simple, what really counts is the scavenging power created by a combo of factors.
Headers are most responsible for a good scavenging power, and will vary according w/ the speed of the exausting gases.
The perfect exaust is a matter of where you want the power to be, lower or higher rpm, more tork or more hp. Length and width are the terms of the equation.
I`ve got Gibson headers and single 3in cat back and i love the sound of it.
If i needed to be on high rpm frequently, i`d get some duals or else.
2000 cc 4.7 2wd 3.92 lsd 5 manual K&N fipk 68 fastman TB HO intake and cams etc.
I get 20 mpg normally and 22 to 23 ave when i want.
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N56629
Dodge Dakota
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6/14/2006
10:41:59
| RE: Exhaust and MPG
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Mufflers do little or nothing to increase either hp or mpg. Mufflers are to far back to contribute to any scavenging effect.
Spend your money on the intake side first unless having the right sound is more important to you than performance.
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shatto
Dodge Dakota
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6/17/2006
19:32:43
| RE: Exhaust and MPG
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N56629 is right.
My noisy Flowmaster allowed me to get the same MPG at 70 as 65. So what? I drive 65.
Much later, in time and miles, I discovered Gibson makes headers for the V6. Immediately, I picked up almost 2 Miles Per Gallon, what I wanted in the first place.
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truck guy
Dodge Dakota
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6/18/2006
13:47:10
| RE: Exhaust and MPG
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Ok here it is in a nut shell. If your motor has trouble removing the spent exaust gases and it doesn't expell all of it then you get left over spent exaust gases in the chamber. So when your motor takes it's next breath for that power stroke you lose power because the new fuel air mix comming in is mixed with the spent gases still there and it takes the punch out of the new mix comming in. Also back pressure forces the motor to work harder to get it's next breath of fuel and air. The harder the motor has to work the more fuel you use to make power.
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4.7 guy
Dodge Dakota
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6/21/2006
09:53:25
| RE: Exhaust and MPG
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"But the Dakota exhaust is top quality stock" "Before i get jumped, The last statement doesn't include the poor quality converter"
look at the Y-pipe on the dual cat 4.7's. seems like a major restriction to me. Two 1 7/8 pipes crushed into one 2 1/4 pipe. Converters are the least of this exahusts concern. Even the older 5.2, 3.9 cats were'nt that bad. "As for the exaust size, go with the bigest thing you can afford" Richardincapecod has the right explanation of what you want in an exhaust. Effective scavenging at the rpm you most use. = Bigger pipes are not always better.
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