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Bolt on power adders: Fuel Economy vs Power - input wanted!

21K views 28 replies 14 participants last post by  01_OffRoad 
#1 ·
I put my muffler back on my truck last week, and I gained nearly 2 mpg.... I had virtually zero backpressure while I was on the freeway, which pretty well kept the gas pedal pegged to the floorboard while on an overpass to maintain speed. Forget about it with a head wind. :) Now I'm up to a whopping 12 mpg. The wife's Expedition gets about 15 mpg or so....

So that got me to thinking (scary, I know)....

Maybe some of these "bolt ons" out there could help out fuel economy, in addition to a few extra ponies. Maybe something like a Cold Air Intake, throttle body spacer, new throttle body, etc.... Which got me thinking even more.....

First..... I'm not 100% sure that a throttle body spacer does anything. I've heard mixed reviews on them, and I don't know anything about the "technical" side of them. What good does adding a 1" spacer do? If anything....

The Cold Air Intake seems like a proven "power adder." I wouldn't mind having one for the day to day drive, and keeping the factory unit for when it's time to get dirty. I'm not sure how much they improve MPG.

A new throttle body.... There's a guy on another site that does nothing but Dodge throttle bodies, but that seems more along the lines of something that would add power, but not really save me any gas.... Also the most expensive option that I've looked at.

Which leads to another question / thought.... Most of these bolt on power adders seem to be based on the "more air = more power" theory. However, it's my understanding that with more air, more fuel is required.... Kinda seems like it wouldn't be helping my gas bill at all... Maybe even hurting it.... Or is this something that goes with the thinking that 'If I've got more power on tap, I won't have to have my gas pedal all the way to the floor to maintain speed.'

I'm totally lost and confused on this stuff. The other thing to consider is the money involved in throwing these bolt on's on. Consider a CAI cost $180, that translates into nearly 3 tanks of gas. Throttle body spacer $80, about a tank and a half. New throttle body, about $300.... that's a lot of gas, especially when you add 'em all up. And it seems like the most gains will be had if I were to "group" these bolt on's together.

I need the added power from 1500 - 3500 rpm. 1500-2000 rpm is my freeway cruising RPM. I've got plenty to get me off the line, but my mid range power is certainly lacking. Should I consider a new cam "pointed" at that RPM in the powerband? A new cam isn't that expensive, but forget about me putting it in myself... That means $$$ to pay someone else to do it. Worth it???

I'm not looking to win any 1/4 mile races, and I don't expect 20 mpg. But a few more ponies, and with any luck, match the 15 mpg that my wife gets, and I'll be a happy camper.

Thoughts? Suggestions? StrongWind's technical advice? :D
 
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#2 ·
01_OffRoad said:
'If I've got more power on tap, I won't have to have my gas pedal all the way to the floor to maintain speed.'
That's pretty much the jist of it. Throttle body spacers, or modded TB won't do much in mileage, it has to be a combination of things from the intake, heads and exhaust. As for cold air intake, there is already one installed from the factory. It draws air away from the engine heat. Any heat from the air intake will = less horsepower.
Anyways, this is just the way our 318's are, gas guzzlin pigs.
 
#3 ·
360 / 5.9L - but you're right anyway... Gas guzzlers. The 41" tires and 5.38 gears don't help any.
 
#4 ·
Throttle body spacers do nothing on our engines.
 
#5 ·
From the standpoint of power vs fuel economy, there are certain modifications which do yield better MPG as well as more power. But there are other mods which also require more fuel to get that power. If you do a mod that does net you better mileage as well as more power, more often than not, the driver also has their foot in it more - making the engine work harder. Since fuel economy is a function of work done by the engine, little to no gains are seen at the pump.

As for which mods get you better mileage and power without the expense at the pump? My initial guess would be CAI, electric fans (since they rarely run), and probably a throttle body (which would yield smaller gains I'd imagine). This is only my personal guess, and only holds true if the driving habits don't change!

Continue discussion.
 
#7 ·
Iv got the Throttle body spacer on mine and i seem to have noticed a small difference. There is a small stretch of road before i come to my driveway and test the acceleration there. I usually got to 50 before braking for my driveway. After the throttle body sapcer i actually got up 52-53. And the whistling is not as bad as the chevys.
 
#8 ·
360ram14 said:
Iv got the Throttle body spacer on mine and i seem to have noticed a small difference. There is a small stretch of road before i come to my driveway and test the acceleration there. I usually got to 50 before braking for my driveway. After the throttle body sapcer i actually got up 52-53. And the whistling is not as bad as the chevys.
And I bet it had nothing to do with the TB spacer :D
 
#9 ·
Sooooo....

Anyone out there using the Fastman TB? What kinda milage difference did you notice (assuming you were able to keep your foot out of it)....

Anyone have anything to add here... besides the TB Spacer?

C'mon folks... I know some of you have tried different things to up the MPG.... let's here it!
 
#11 ·
When I got my 97 5.9L Ram i had a plugged cat and stock exhaust the first thing i did was make it straight pipes. << That was dumb then i got dual flowmaster 50 series 2 mufflers not poo mans dual i allso added gibson headers and a K&N cold air intake along with a hypertech chip I now get about 18-19 mpg on the highway. I would like to get the fastman TB next because it is still a little slow 2500 lol But that is what i did and it made a huge diffrence was prob getting about 10 before with clogged exhaust.
 
#12 ·
here is what I have done, the price, and the results - this is with a 5.2 so should be about the same gains:

edelbrock ProFlow 1002 open element air filter assembly - $28 for filter +$5 for misc parts needed
Gains over stock air box were much more acceleration from 3500 rpms up. There are some ney-sayers that claim you don't gain any due to hot air from under hood...as long as you are moving at 10mph or faster there is sufficient air circulation to negate this.
Bottom line is it's a LOT cheaper than a CAI and has equal to or better gains than most. MPG gains were maybe +.5 - 1 mpg highway.

F&B 52mm TB - $300 - most gains from 3500 - 5500, no noticeable off the line improvement or loss.
MPG suffered more when driving hard, about the same when driving easy.


Magnaflow stainless steel high flow cat & y-pipe setup - $160 - most gains were again in the mid to upper rpm range. Retained enough back pressure to keep the low end power on tap off the line, but outflowed stock setup by far.
Gains MPG-wise were +2 highway, maybe +1 city.

Flowtech Shorty headers - $230 - by far the best MPG improvement. Gains in the upper rpm range were decent. MPG went up by 1 city and 1 highway.

B&G custom PCM flash - $375 to $400 depending on options - no real change in MPG, tire roasting power-o'-plenty off the line thanks to torque management removal.

Yukon 4.11 gear set - parts $350 labor $300 - best city MPG gain of a solid +2 and highway mileage went up by maybe 1. best effect of this install was being able to hold O/D when going uphill thanks to engine being closer to powerband (2500 @ 70 with 33" tires)

So with the above I currently average 13-14 city and a steady 16 on the highway, when I swap the 33" mudder for the street tire I expect a +1-2 gain highway.

Hope this helps some.
 
#13 ·
chizzle1 said:
here is what I have done, the price, and the results - this is with a 5.2 so should be about the same gains:

edelbrock ProFlow 1002 open element air filter assembly - $28 for filter +$5 for misc parts needed
Gains over stock air box were much more acceleration from 3500 rpms up. There are some ney-sayers that claim you don't gain any due to hot air from under hood...as long as you are moving at 10mph or faster there is sufficient air circulation to negate this.
Bottom line is it's a LOT cheaper than a CAI and has equal to or better gains than most. MPG gains were maybe +.5 - 1 mpg highway.

F&B 52mm TB - $300 - most gains from 3500 - 5500, no noticeable off the line improvement or loss.
MPG suffered more when driving hard, about the same when driving easy.


Magnaflow stainless steel high flow cat & y-pipe setup - $160 - most gains were again in the mid to upper rpm range. Retained enough back pressure to keep the low end power on tap off the line, but outflowed stock setup by far.
Gains MPG-wise were +2 highway, maybe +1 city.

Flowtech Shorty headers - $230 - by far the best MPG improvement. Gains in the upper rpm range were decent. MPG went up by 1 city and 1 highway.

B&G custom PCM flash - $375 to $400 depending on options - no real change in MPG, tire roasting power-o'-plenty off the line thanks to torque management removal.

Yukon 4.11 gear set - parts $350 labor $300 - best city MPG gain of a solid +2 and highway mileage went up by maybe 1. best effect of this install was being able to hold O/D when going uphill thanks to engine being closer to powerband (2500 @ 70 with 33" tires)

So with the above I currently average 13-14 city and a steady 16 on the highway, when I swap the 33" mudder for the street tire I expect a +1-2 gain highway.

Hope this helps some.
Good info right here.
 
#14 ·
I think that some power adders can actually net both a power increase and a mpg increase. I think this happens because they make your engine more efficient. If it is operating without any restrictions, you will get better mpg, but you will feel as if you have more power too. This may not be more power then what the engine was capable of out of the factory, but it feels like more because you had some restriction or issue that was robbing you of that power. But then I think there is a point were you no longer can be any more efficient, so you start to see mpg go down as your performance goes up. This is just because that is the only way you will make more power - more fuel and more air.

Everone comes on here and asks how much mpg gain they will see with a certain mod, but really there are too many variables to accuratly say. For example, I saw over 2 mpg increase when I did a Fastman TB followed a week later by a Flowmaster muffler. This was the first two mods I did. Someone else who already has a cat-back and other mods like maybe headers or a programmer may not see any gains like I saw from the Fastman. Or, they might see even better gains. Plus, I live at about 7000ft elevation. The gains I see will be differnet then what someone at sea level might see.
 
#15 ·
01_OffRoad said:
360 / 5.9L - but you're right anyway... Gas guzzlers. The 41" tires and 5.38 gears don't help any.
Even though you are helping offset the tire diameter by re-gearing, that is still a LOT of rolling resistance. Those tires are what's killing your mileage.

When I bolt-on the 35"s I lose about 3 city and atleast 3 highway, I get about 9 city and 11-12 highway.
\It takes a lot more pedal to keep the larger tires moving due to all the wind resistance, larger footprint, and added weight.

Get a set of cheap-o wheels (or use the stockers) and some all terrain tires. You'll see a big improvement in the MPG & performance dept.
 
#16 ·
chizzle1 said:
Even though you are helping offset the tire diameter by re-gearing, that is still a LOT of rolling resistance. Those tires are what's killing your mileage.

When I bolt-on the 35"s I lose about 3 city and atleast 3 highway, I get about 9 city and 11-12 highway.
\It takes a lot more pedal to keep the larger tires moving due to all the wind resistance, larger footprint, and added weight.

Get a set of cheap-o wheels (or use the stockers) and some all terrain tires. You'll see a big improvement in the MPG & performance dept.
Ya, I agree that there is way more rolling resistance. I used to have 33" (285's) BFG AT's and now have 35" Toyo M/T's. There are hills that I used to coast down, and would have to apply break to keep under the speed limit. With the 35's now, I never have to hit the break at all. Even have to speed up to maintain speed sometimes. The aggressive tread and larger size make a big difference in rolling resistance. I also lost about 3 mpg going from 33's to 35's, but I also have a blown plenum at the moment, so I think some of it is that. I have 4.10 gears. Planning to change that to 4.88.
 
#17 ·
On the SpikeTV power block's Horse Power they tested the Fitch Fuel system on there dyno. It dropped there fuel consuption by 2 gallons per hour.
 
#18 ·
chizzle1 said:
Even though you are helping offset the tire diameter by re-gearing, that is still a LOT of rolling resistance. Those tires are what's killing your mileage.

When I bolt-on the 35"s I lose about 3 city and atleast 3 highway, I get about 9 city and 11-12 highway.
\It takes a lot more pedal to keep the larger tires moving due to all the wind resistance, larger footprint, and added weight.

Get a set of cheap-o wheels (or use the stockers) and some all terrain tires. You'll see a big improvement in the MPG & performance dept.
Yessir... 100% correcto. 41" tires = hella rolling resistance. Show me a set of 40" all terrains or street tires, and I'll show you a smiling face.
 
#19 ·
chizzle1 said:
here is what I have done, the price, and the results - this is with a 5.2 so should be about the same gains:

edelbrock ProFlow 1002 open element air filter assembly - $28 for filter +$5 for misc parts needed
Gains over stock air box were much more acceleration from 3500 rpms up. There are some ney-sayers that claim you don't gain any due to hot air from under hood...as long as you are moving at 10mph or faster there is sufficient air circulation to negate this.
Bottom line is it's a LOT cheaper than a CAI and has equal to or better gains than most. MPG gains were maybe +.5 - 1 mpg highway.

F&B 52mm TB - $300 - most gains from 3500 - 5500, no noticeable off the line improvement or loss.
MPG suffered more when driving hard, about the same when driving easy.


Magnaflow stainless steel high flow cat & y-pipe setup - $160 - most gains were again in the mid to upper rpm range. Retained enough back pressure to keep the low end power on tap off the line, but outflowed stock setup by far.
Gains MPG-wise were +2 highway, maybe +1 city.

Flowtech Shorty headers - $230 - by far the best MPG improvement. Gains in the upper rpm range were decent. MPG went up by 1 city and 1 highway.

B&G custom PCM flash - $375 to $400 depending on options - no real change in MPG, tire roasting power-o'-plenty off the line thanks to torque management removal.

Yukon 4.11 gear set - parts $350 labor $300 - best city MPG gain of a solid +2 and highway mileage went up by maybe 1. best effect of this install was being able to hold O/D when going uphill thanks to engine being closer to powerband (2500 @ 70 with 33" tires)

So with the above I currently average 13-14 city and a steady 16 on the highway, when I swap the 33" mudder for the street tire I expect a +1-2 gain highway.

Hope this helps some.
FANTASTIC info! Exactly the kinda info I was looking for! A HUGE thanks!
 
#20 ·
01_OffRoad said:
FANTASTIC info! Exactly the kinda info I was looking for! A HUGE thanks!
No problem.

Merry Christmas from sand land :tup:
 
#21 ·
or you can spend 8 grandish building a 408 and get a whopping 7 mpg.
 
#22 ·
All good info here. From reading this site over the last 2 years, if you free up the restrictions, you will get a better power and better mpg. examples would be a cold air intake that flows better, and an exhaust that also flows much better.

bigkuntry72 said:
or you can spend 8 grandish building a 408 and get a whopping 7 mpg.
I am not an expert at what you did with your 408, but i think there is something wrong here. I heard from other guys that did a 408 that they get similar fuel mileage. I would double check with your pcm that it is programmed correctly for the new cubes and your m1. Are you using the stock injectors? Did you check the air/fuel ratio when you started the engine? did you install a new oxygen sensor?
 
#23 ·
greg- i know there is something wrong. my size 14 1/2 boot is too heavy!!! no seriously i think it running real rich, my stall converter( without shift kit installed yet, which should help the initial slipping feel), and the fact that i usually let it warm up 10 min for a 7 min drive to work every day( and home to) and those 7 miles usually see 5000+ rpms a couple times.
 
#24 ·
http://home.insightbb.com/~jbenner/mods/intake/abs_intake.htm
This is a site someone gave me a while back, there are diff. variations to this, but all are pretty much alike. The filter is most of the money, but you never buy one again, and it's DIY. (do-it-yourself) Just another thought! ;) IMO Every 2nd gen. dodge could use some type of better air intake?
 
#25 ·
slambony said:
http://home.insightbb.com/~jbenner/mods/intake/abs_intake.htm
This is a site someone gave me a while back, there are diff. variations to this, but all are pretty much alike. The filter is most of the money, but you never buy one again, and it's DIY. (do-it-yourself) Just another thought! ;) IMO Every 2nd gen. dodge could use some type of better air intake?
Thanks for the link.

For day to day driving, an open element, CAI (cooler air intake - there's no "cold" air in an engine bay) could be benificial. If you took that set up in the link provided off road, you may be looking into a stroker set up after you rebuild the engine from the Hydro-lock. :D For off road, the stock set up actually works pretty well. And believe it or not, the stock paper filter works better than the K&N types at stopping massive amounts of crap from entering your engine if you happen to have an "oh shit" moment while off road.

It's just going to come down to money "invested" in the improvements vs MPG / power gained.... Something we'll probably all have to figure out for ourselves.

Thanks again for the links and info!
 
#26 ·
I can say that my '95 Dak, 5.2 3.9 posi rear with 27" tires, ported heads/kegger, fastman TB, Cam of some sort, Mopar Perf SBEC, Gibson Headers (single 3" exhuast with high flo cat), MSD 6A Ignition etc... Got like 12 MPG.

My '93 Dakota with all the above minus cam/head work got 22 *highway ofcourse*

My Ram returned my 18.8 MPG yesterday almost entirely on the highway around 80-90. The biggest thing I've found to increase the milage was going to a stock height / narrower tire. My 20's have 275/45s I got Dakota tires on my 16s 255/65s and they are ALOT better on gas. when they wear out I am really thinking of some stock (per door sticker) 225/75s. Not only are they cheap, but a narrow tire like that should have VERY little rolling resistance.

I think the 3/6 drop helps alot too. Every new truck has a big ol spoiler under the bumper to try to help with milage... I just moved the whole damned truck closer to the ground. Wind resistance KILLS your highway milage.

I should soon be trying Long Tubes with a true single 3" exhuast. I'll let ya know how that helps.
 
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