FAQ: Improving Bad Gas Mileage

charlieRobinson wrote:

That's all fine and dandy. But this is real.


This is how you get poor MPGs


This is how you get better MPGs

I track my MPGs and miles per fill. Numbers dont lie.

When I get another riv someday I'm not going to have whitewalls

Cool story, bro.

charlieRobinson wrote:

Cool story, bro.

Only because when I demo-derby it I don't want the whitewalls to get dirty!!

Quote :

That's all fine and dandy. But this is real.
I track my MPGs and miles per fill. Numbers dont lie.

What's "real" to you is what you are willing to convince yourself. Numbers can and do lie when taken literally, out of context. There are rules for scientific testing - if you don't follow them, you'll see incorrect results.

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think about it. If it affects traction, acceleration, etc.. its going to affect MPGs. The power is being put to use and not being wasted like it was when the weight was tipped in the back.

I've been thinking about it a long time - for many years in fact. I've researched ways to improve MPG, and I understand how to apply fuel saving methods to our cars. I don't know every way that works, but I know some. I also know that some don't work.

"If it affects traction, acceleration, etc..." means a front-heavy weight distribution results in better grip to the front wheels, better traction due to less wheel spin. No doubt that's true, but you're forgetting whenever you apply enough throttle to reach the threshold of spinning tires, you're getting about 1-3 MPG. The other 99% of the time, the weight over the front axle isn't helping you one bit. In fact it's hurting your cornering ability. Wheel spin ONLY becomes an issue at WOT on dry roads. Heavy throttle and MPG don't mix very well unless you're measuring fuel economy while drag racing or doing burn-outs.

The short of it is, putting more weight over the front wheels definitely helps WOT acceleration performance, but the slight improvement to MPG due to improved wheel traction is moot when you're burning that much fuel. For MPG in actual daily driving, even in the wet - I'm calling BS on this whole idea.

AA I think a couple factors in the high front end helped ruin Charlie's MPG -
1) Aerodynamics - It's like having a mattress on the roof with the front lifted up, scooping air under the car. Not exactly slicing it's way along.
2) additional frictions - This could be nothing/tiny/irrelevant but maybe the incorrect ride height had additional rolling resistance because the CV joints were not even close to the 'level' where they normally sit. Of course, if it did do anything there would have been additional heat and probably a screwed CV joint by now. So maybe this one's moot. Any other rotating parts affected by ride height?

Just tossing some ideas out there. I think 1) is a big factor.

Good points.

I think #1 makes a better case for impacting MPG , but we don't know for sure how much, because we didn't measure before and after, and because there are other variables to consider. Drag is real, but how much extra drag was created in Charlie's situation? We really don't know.

People have sworn for years rolling with the windows down increased drag and decreased MPG. It does have an effect, but depending on the car it can be minimal. It's also been said that running AC has negative impact on MPG, however I've found it makes little difference in a SC 3800 powered Riviera, from prior experience. I feel the same about having the windows down, even though it definately creates added drag.

I just returned from a 1500 mile round trip in the Riv at speeds between 75-95 mph. Starting in OH at 900 ft elevation, ending in SC at sea level. It took very close 2 tanks of fuel each way. First 1/2 it was hot outside, so we used AC. Return trip was mild, so for part of the trip we rolled with windows down, AC off:

First leg:

1st tank, all HWY driving, w/ AC on: 23.3 MPG
2nd tank, mixed HWY/CTY, w/ AC on: 23.3 MPG

Return trip:

3rd tank, all HWY driving, w/ AC on part way: 23.5 MPG
4th tank, mixed HWY/CTY, w/ AC off: 23.8 MPG

Looking at these figures, we could say a lot of things. We could say having AC off helps MPG. We could say having windows down doesn't hurt MPG that much. We can say driving downhill helps MPG, while driving uphill hurts it (even though it's not evident in these results). We could say MPG is better in hot weather than in cooler temps. Again, not evident here although it's known to be true.

My point is, just because in theory something should make an impact, doesn't make it so in practice. It's okay to hypothesize, BUT do controlled tests to eliminate guesswork, so we can see real proof. My tests were not controlled, and they don't prove anything other than my car gets very consistent MPG over long trips through mountainous terrain. I don't know how much of an impact the AC or windows down made; we can make some guesses.

I can't say how much of an impact tilting Charlie's 3º forward on its nose really makes. The only way to know would be to perform controlled tests with the car in both positions over a period of time, then examine the MPG figures. I believe Charlie logged his MPG accurately, but I don't believe the trips were controlled tests. My gut tells me I could drive to SC with the ALC fully raised, then back to OH fully lowered and see 23-24 MPG each way.

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2) additional frictions - This could be nothing/tiny/irrelevant but maybe the incorrect ride height had additional rolling resistance because the CV joints were not even close to the 'level' where they normally sit. Of course, if it did do anything there would have been additional heat and probably a screwed CV joint by now. So maybe this one's moot. Any other rotating parts affected by ride height?

True, the raised front end caused misalignment of the CV/axles, but now he has 1.5" lowering springs, also misaligning the axles. Oh, and then there's this CV joint you mention. Interesting that Charlie just replaced a failed one a couple weeks ago. Now he's seeing better MPG. Anyone think THAT might be a variable to consider? Of course not - it must be the change in F/R weight distribution. R-i-i-i-ght.

I have an idea.....buy a 4 cylinder

Before new springs: lucky to get ~250 miles on a full tank
After springs: EASILY hitting ~300+ miles on a full tank.

Nothing major changed but my springs and effectively the weight distribution of the car. Because this gave me more power at the wheels, I ASSUMED it increased overall efficiency and was the reason for my gain in MPGs. Maybe it was the aerodynamics. I dont know. I only know that my MPGs are doing great now.

Maybe Scott is right, maybe it was the wheel caps! shoot! 

Dont think it was the CV because I noticed the improvement before I replaced the CV.

Anyone thinking of adding lowering springs in their ride for MPG gains should read this first:

http://www.stangnet.com/mustang-forums/threads/mpg-from-lowering-springs.749720/

Who would lower their car just for MPGs? You lower your car for handling and to look sweet.

I didn't say "just for MPG", you did!

Coincidentally I just watched a Mythbusters episode last night on "hypermiling" using various techniques to maximize MPG.  It was very interesting.  Bottom line, "windows up" and "no A/C" were two of the six that in combination added 40-70% increased MPG.

Can't say for sure about Charlie's experience since there there are other variables in the mix, but I would surmise that his "nose up" body attitude before the spring swap probably did nothing to help MPG and would have to guess it could have had a significant effect.  Bringing the car back to level no doubt helped.  I doubt the overall "lowering" from the springs contributed to increased MPG though.  Hard to say without more controlled testing though   

Al, "40-70%" is quite a varied result. Do you know what kind of car they used to test? I've noticed many hypermiling tests are performed using lighter 4-cyl cars, not heavy cars with power. Turning on the AC in my wife's 1.8L Toyota Corolla causes a noticeable drop in power. Turning on the AC in my Riv causes no perceivable change. I once hypermiled 120 miles in the Riv (OD @ 48-55 mph) for 39 MPG with the AC on the whole time. Wish I'd tried a follow-up test with AC off, but it's hard to believe the car would do much better.

Regarding the nose up or down, I think one poster at the Stangnet link above nailed it squarely on the head:

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You can increase mpg by raising the rear end. Lowering the front at the same time may help increae mpg even more. Doing this puts the car in a position to always be running downhill! LOL!

deekster_caddy wrote:

AA I think a couple factors in the high front end helped ruin Charlie's MPG -
1) Aerodynamics - It's like having a mattress on the roof with the front lifted up, scooping air under the car. Not exactly slicing it's way along.
2) additional frictions - This could be nothing/tiny/irrelevant but maybe the incorrect ride height had additional rolling resistance because the CV joints were not even close to the 'level' where they normally sit. Of course, if it did do anything there would have been additional heat and probably a screwed CV joint by now. So maybe this one's moot. Any other rotating parts affected by ride height?

Just tossing some ideas out there. I think 1) is a big factor.

I agree, if the MPG stats are accurate (I'm not picking on Charlie or suggesting they are wrong, but sometimes the data is erroneous or generates outliers.  Hence control data and large samples over a long period of time is better.  Just say'in.  But hey, we don't always have the time for a full-on scientific method   ) ...... my first guess is also #1

The pre lowered springs "nose up" body attitude couldn't have helped, esp at highway speeds.

Whatever the reason, here's to the increased MPG

AA wrote:

Al, "40-70%" is quite a varied result. Do you know what kind of car they used to test? I've noticed many hypermiling tests are performed using lighter 4-cyl cars, not heavy cars with power. Turning on the AC in my wife's 1.8L Toyota Corolla causes a noticeable drop in power. Turning on the AC in my Riv causes no perceivable change. I once hypermiled 120 miles in the Riv (OD @ 48-55 mph) for 39 MPG with the AC on the whole time. Wish I'd tried a follow-up test with AC off, but it's hard to believe the car would do much better.

Regarding the nose up or down, I think one poster at the Stangnet link above nailed it squarely on the head:

Quote :

You can increase mpg by raising the rear end. Lowering the front at the same time may help increae mpg even more. Doing this puts the car in a position to always be running downhill! LOL!

They had two different cars with some varied approaches.  If I recall one had a 40% gain, and the other 70%.  You'd have to watch the episode for more details on the their techniques and testing methodology, I just don't remember all the details.  I was multi-tasking  The "aftershow" video is pretty fun to watch.

Preview and aftershow videos here:
http://dsc.discovery.com/tv-shows/mythbusters/videos/hypermiling.htm

Here's a source I put a lot of value in, mainly because all these guys try to do is squeeze more MPG from their rides. They are constantly experimenting to see what really makes a difference. Lots of them are hitting 100 MPG in smaller cars:

http://ecomodder.com/forum/fuel-economy-mpg-modifications.php

This is a link to 65+ mods that they feel can impact MPG. Each mod is ranked according to impact on fuel consumption (1. small, 2. medium, 3. large). For example, everyone agrees that a real-time MPG gauge (like the Aeroforce I use) offers a large positive impact to lowered fuel consumption. Aerodynamics is certainly important, but if you look down the list, most all of these mods rank as small gains, even the more radical body alterations. One that offers medium gain is a tear-drop boat-tail rear-end build. That's a ton of cost and work, but would be cool on a Riv!

If you take the time to read through these, you'll see what works and what doesn't. Interestingly, according to Ecomodder, an AC delete (ripping out the entire system!) offers only a small gain. I don't doubt them one bit - it agrees with my own experiences 100%.

AA wrote:

Quote :

2) additional frictions - This could be nothing/tiny/irrelevant but maybe the incorrect ride height had additional rolling resistance because the CV joints were not even close to the 'level' where they normally sit. Of course, if it did do anything there would have been additional heat and probably a screwed CV joint by now. So maybe this one's moot. Any other rotating parts affected by ride height?

True, the raised front end caused misalignment of the CV/axles, but now he has 1.5" lowering springs, also misaligning the axles. Oh, and then there's this CV joint you mention. Interesting that Charlie just replaced a failed one a couple weeks ago. Now he's seeing better MPG. Anyone think THAT might be a variable to consider? Of course not - it must be the change in F/R weight distribution. R-i-i-i-ght.

Ahh - I didn't remember the CV joint bit. The raised height could certainly have contributed to the accelerated wear on the joint. Good point!

So I try to keep track of my MPG every other tank or so. I'm usually seeing anywhere from 15mpg city to 20mpg highway. Well after swapping over to Dextron 6 ATF , getting new tires, replacing plugs, and maybe even the addition of the mufflers, I was hoping to see somewhat of an improvement in my mpg. well driving fairly conservative the past week I ran the numbers again and got 13mpg   . I am completely strict about  every maintenance action on this car and everything is up to date. And while I don't have a code for the O2 sensor im thinking this is my next step ( front sensor ) Any suggestions? maybe even my cat is plugged up?? would be a good excuse to buy a 3" ZZP unit.

Well im bought a O2 sensor, probably needed replacing anyway..

Change fuel filter, clean your K&N, and run some seafoam through it and see if that does anything.

Sir Psycho Sexy wrote:

Change fuel filter, clean your K&N, and run some seafoam through it and see if that does anything.

Like I said, I am strict with maintenance, all the above have been done recently. I just changed out the O2 sensor and noticed an immediate change in the way the exhaust smells. It used to be very strong and now I can barley notice it. I went and filled up and calculated another 13mpg. we will see what the next fill up yields.

What size tires are you running? Did you recalibrate your PCM for extra rolling diameter?

I was careful to select a tire / rim combo that did not change the overall diameter from stock. I went from a 16" to a 17" but also to a lower aspect ratio, the result is only a 2mm larger overall diameter.

It's also the time of year for "Winter Fuel" blends to hit the gas pumps. Not sure what they do for winter fuel blends in CA but it's known to affect MPG.