Fuel economy 'how-to' thread

[RallyBob]

The timing for this seems appropriate. Not looking for your mileage claims, but rather what things you've mechanically done to the car to improve your car's fuel economy.

List 'em here folks.

Bob

[73Manta72gt]

I was surprised to see how low some of the MPGs were...I checked mine on the highways 60-70mph. 72 gt with a 32/36 carb. everthing else stock 34mpg 73 manta with a 32/36 and a 5spd getrag always gets 31.8 when I check it.

Has anyone used an exhaust gas analyzer to check the mixture and adjust the
carb leaner?..

how about a mixture control like airplanes have..at a steady state speed on the highway you should be able to lean the mixture. I think the one on my plane is just a needle valve in the fuel supply line to the carb...

[sleeper]

The only things I have done is put on a weber 32/36 and run my tire pressure very high (tires are rated to 51psi!) on my 74 manta-I average ~32mpg on the hwy. I'd love to see what kind of improvement could be had from a full belly pan, retractable antena and any other aero optimization might achieve. Also, would there be an efficiency gain from going to a sprint exhaust manifold and a slightly bigger exhaust system?

[namba209]

I'm gonna guess that you meant a model airplane engine on having a mixture control, in actual real aircraft carbed engines, the mixture is controlled, as you suggest by a needle valve arrangement, but it meters the fuel coming out of the main jet. In order to be able to adjust the mixture, you would need a method to measure cylinder head temperature for all cylinders, to insure one cylinder doesn't run too lean and hole a piston. That is one of the cautions/warnings in all carbed aircraft air-cooled engines. As far a using an Exhaust Gas Analyzer, I borrowed one from a friend many years ago when they were available from Sears. I adjusted all my motorcycle engines to 16:1 air-fuel ratio and never had a problem. All the analyzers I've seen lately are permanently attached to the exhaust and not easily moved from car to car. It appears that the only way to get a mobile unit is to purchase a very large analyzer that runs into the thousands of dollars. Plus, the ones I've seen available for permanent installation only go to a max of 15:1, which, IMHO, doesn't have the range I would like. Here's a little story told by my A & P engine instructor. The US Navy was going for a record for non-stop flight in a four turbo-engined aircraft, Leaving Austrailia, they started leaning out the carbs. Keeping an eye on the cylinder head temp gages, they increased the turbo boost pressure as they leaned out the carbs and eventually had the excess turbo air cool down the cylinder heads. They did set a record flying from Austrailia to the States, landing somewhere in mid-continent. The air-fuel ratio was somewhere in the 20:1 range, if I remember correctly. Todays cars are set up for 14.7:1 ratio which makes the EPA happy, but, from what I was told many years ago is too rich, optimum being supposedly at 16:1. Now if all the cars were set up using 16:1, that would be an across the board savings in fuel of 3%, world wide, plus the same percentage of emissions not going out the tailpipe. Of course that would be compounded by the numbers of MPG increase too.

Again, many years ago, and experiment was made with full belly pans of cars and vans. Cars had a modest increase in MPG but the vans had a substantial increase in MPG. Probably because of all the disrupted air flow going under the vans creating turbulance and holding them back. Smooth airflow over, under, around, and through was the key back then. The key for an aerodynamic antenna shaft is to have it teardrop shaped. This was used, again, in the aircraft sector on fixed landing gear aircraft. There was a very noticeable gain is speed and distance using a teardrop shaped airfoil over the round landing gear struts used at the time.

[RallyBob]

Ron, 16:1 ratio would be a tough call in an Opel! They like fuel ratios on the order of 12.6-13.2:1 to make any kind of power. I will dial them in to 14.2-14.5 at idle, higher numbers usually create a lean misfire and emissions goes through the roof!

For a turbo car engine on pump gas, anything leaner than 11.8:1 is usually asking for holes in pistons! I have heard severe detonation on the dyno with some cars when they get up to 12.8-13:1 ratios with a turbocharger.

But I realize aviation fuel and aircraft engines are another thing altogether!

[baz]

acetone @ 2 oz /10 gall giving 12-22% improvment for the cost of 30cents a time

[namba209]

Baz, I'll try that next time I gas up the motorhome, that much of an increase in MPG would be very nice.

Bob, you have the dyno expertise, so of course, I will bow to that expertise. I just related to what I have done on my bikes with no ill effects, and the story was told by my engine instructor who has a wealth of knowledge on aircraft engines, akin to your expertise on the CIH. Absolutely, AVGAS burns much more slowly than automobile gas, the aircraft engines are usually redlined around 3750 RPM, so the fuel has more time to burn in the combustion chamber. Another story on burning AVGAS. While stationed in the Phillipines, I was heavily involved in bike racing, one of my competitors filled his tank with 115/145 AVGAS. After a half a lap at approximately 8-9000 RPM his engine siezed. Teardown revealed the piston expanded and scored the cylinder badly. It seems all he did was change the fuel and not the carb jetting. Also, at altitude the air temp is cooler and less dense, the actual reason for a turbo to begin with. I'm amazed the AFR was so low in the CIH motors, especially since the computer controlled engines are scheduled to run at 14.7 through all throttle settings. Thanx for the info, it should help those who would like to use an EGA in their cars. The Master of the CIH has spoken again.

[madhatterpdc]

As far as I am aware, there is only one way to significantly improve acceleration, handling AND fuel economy...

Reduce weight.

I've seen too many people throw money, time and magic at a car and be disapointed with the results with no regard for the fact that the amps, subs, rubberized undercoating, neon lights, chrome rims, "spoiler" and fat chicks have over laden their car by an additional 200-300 pounds.

That's a 10% increase in weight for most cars, which would require a 20% boost in power to achieve the same performance. In other words, you are going to need a lot more than a fancy air filter and a carbon fibre shift knob to regain performance.

A perfect example is the new Lotus Elise. That car weighs just under 2,000 lbs and *only* has 190 hp. It is also regularly nipping at the heels of Ferrari 360's, 911 Turbos, and even F50's on road circuits. It is also rated at 23/27mpg. That is simply amazing for a car of this calibre. In a similar fashion the Ultima GTR weighs just under 1 ton as well and with a 680 hp SBC, can rip the 0-100-0 in 9.8 seconds, that's a full second quicker than a Ferrari Enzo that has about the same power, and the GTR has no electro-wizardry like launch control or paddle shifts.

Another physically sound way to improve gas mileage is by keeping the rpm's as low as possible. Try to stay in a taller gear and dip deeper into the throttle, the engine will only draw as much air as it needs and fuel will be metered as well to only meet the needs of the motor. I'm not doing this philosophy any justice, Patrick Bedard of Car and Drive did a decent write up on this topic several years ago in the context of an early review of the first Honda hybrid.

[namba209]

To amplify the thread by madhatterpc, in a couple of things he stated, I increased my MPG and performance in my 71 Dodge van by changing engines. The cam gear broke on the original 318 cu. in. and trashed the engine big time. I found a NASCAR built 340 cu. in., and dropped it in. My mileage went from 17 MPG on the 318 to 21 MPG with the 340. The reason was simple. In order to move 3 tons of van I had to use a higher throttle setting with the original engine and a lower setting with the 340 with a lot more horses available. Performance between the two engines was definately noticeable. Prior to changing the engines, I had already installed a 426 Hemi auto tranny, and the van came with a 4.10 Trac-Lok rear-end. I do believe, by seat of the pants technology, the van is much quicker than my monza, up to a point, then the frontal area of the van comes in to play somewhere above 45 MPH. The point here being more horses can do the same or more work with less fuel consumption.

[PROPEL]

Originally Posted by madhatterpdc Another physically sound way to improve gas mileage is by keeping the rpm's as low as possible. Try to stay in a taller gear and dip deeper into the throttle, the engine will only draw as much air as it needs and fuel will be metered as well to only meet the needs of the motor.

I've found that this driving technique does result in better mileage. I also read it in a book (How to Drive Your Car Forever, I think). Have to be careful not to "lug" the engine though... instead exploit momentum.

[RallyBob]

Originally Posted by madhatterpdc Another physically sound way to improve gas mileage is by keeping the rpm's as low as possible. Try to stay in a taller gear and dip deeper into the throttle, the engine will only draw as much air as it needs and fuel will be metered as well to only meet the needs of the motor.

This doesn't always work. In fact I've found that certain engines (especially 'tuned' performance engines), tend to have better economy at or just below their peak torque rpm. My first Opel got 24 mpg @ 65 mpg. It got 32 mpg @ 92 mph (the 'sweet spot'), with a 4-speed and 3.67 rear axle.

Worth noting is the 'sweet spot' on an Opel is usually the accoustically loudest point in the rpm range while cruising.

My Toyota truck with the supercharger on it got better mileage with a 3.73 axle than with the 3.07 axle I swapped into it. Higher top speed too with the 3.73's. With the 3.07's, I was always deeper into the throttle, and mileage suffered, plus it never really got into the power band in top gear so it shortchanged the top speed.

As always, your results may vary!

Bob

[Geek]

I wanted to back up one of the points that namba made. I have a 2003 Ford Contusion (Excursion), with the 7.3 Power Stroke. I was attempting to find ways of improving the mileage (currently around 16mpg), and found myself at the website of Gail Banks. Banks specializes in raw power, and produces a string of ECU plug-n-play controllers for diesels. What was surprising is, they claim an increase in mpg with an increase in hp. When I called, I found out that the increase (with no 'lead foot'), should be in the neighborhood of 15-20%. That's a pretty respectable neighborhood. Reason for the increase is less time spent in lower gears. It's a lot more of a difference with the turbo charged engine because higher RPM's mean more boost, but you've got to figure the principle is going to remain the same.

As for my best method of increasing mileage - sensible driving. I don't practice it a whole lot , but I've found that I get far worse mileage traveling at 80 mph (in my truck), then I do at 75 - it's a really surprising amount of difference.

[Wolf Spyder]

O.K. all you gurues, is the below harmful to an Opel 1.9? For that matter, what about a current model car? This sounds real good and cheep to do.

Originally Posted by baz acetone @ 2 oz /10 gall giving 12-22% improvment for the cost of 30cents a time

[namba209]

I've got a complete Banks system on the motorhome, it was installed before we got it so I can't compare before and after. But we did install a GearVendors unit on it shortly after getting it. For those that don't know the GearVendors is an over/underdrive unit that goes in behind the tranny. Before it was installed we had a standard heavy duty Ford auto tranny with 4th gear being an overdrive. Now I have an 8 speed sem-automatic tranny, I had to convince the techs I wanted/needed the 4th gear overdrive overdrive, normally the unit is locked out of top gear overdrive. Now instead of turning 3500 RPM at 70 MPH, I turn 2000 RPM, which is right at the bottom of the power band with the Banks unit. I can say that just with the GearVendors unit my mileage on the motorhome has increased 62.5%. Now that may seem to be a whole bunch, but in reality it's the difference between 5 and 8 MPG, but with an 80 gallon gas tank it's the difference between 400 miles and 640 miles between fill ups. Not too shabby, having more HP and being in a taller gear at highway speeds. The only problem I have with the unit is trying not to hot rod a 20,000 lb. 38 ft. go fast. It's a real chore.

[West Coast GT]

My feeling is the the best tool for optimizing gas milage (best meaning affordable, yet effective) is a vacumn gage. Inexpensive. Reliable. Easy to install. Easy to use. It surprises me new cars don't come with them already installed.

For highway driving, my gut reaction is that the 5-speed transmission is going to give us the most "milage" bang for our buck for highway driving. And improving the breathing characteristics will do it for driving around town.

Other areas for improvement (my guess):
- electric cooling fan
- small stock alternator
- higher thermostat setting?
- electric fuel pump
- electronic ignition
And keep those headlights on the GTs in the down position until it gets dark.

Again, these are my guesses. Comments welcomed.

[PROPEL]

http://www.fuelvapors.com/

[GoinManta]

Well my Mantas always seem to get in the 25 mpg range. I havent checked since I went to the 32/36 Double Pump though.. I have a feeling it will be down a bit from that.

That said. I have a mean right foot.. seems to be about 2x as heavy as the Left..

It probably doesnt help I leave the tires on the softer side for grip (Usually 33 on a H rated tire that can handle 45)

I am going to be REAL curious what the Mantissan gets once I get it ready.

Charles

[Gumby]

Originally Posted by PROPEL Welcome to the home of high-mileage fuel vaporizer system information!

Has anyone here actually tested anything like that?

[CoriolisSTORM]

Higher compression ratios in some cases can result in better mileage since in some cases that is more efficient, but then you offset it with higher fuel costs as well. That being said, you guys' GTs are very aerodynamic and such as it is, and fuel mileage should be pretty good with a stock 1.9L with a 5 speed in it. I want a GT so bad I can taste it. For what its worth, I have found if the motor is built for torque down low then it is best to keep the RPMs down low. I've actually averaged about 25MPGs once in my 2.5L 5 speed brick Wrangler. The drag coefficient of the Wrangler is .55-.58 whilst you guys GTs are at .36. If I keep the motor down in the <1k sections and really lug it, it actually does get pretty decent mileage. Pretty sad I know, but its a sad motor in the first place. So, as stated above, the sweet spot of the motor is a definitely good place to keep it. Not really sure about your 1.9s or 1.1s though, just my experience with an ancient 2.5L.

[baronbors]

Originally Posted by Wolf Spyder O.K. all you gurues, is the below harmful to an Opel 1.9? For that matter, what about a current model car? This sounds real good and cheep to do.

I've read evaluation reports and the claim seems to be close to accurrate- just don't spill it on you paint or it will get really expensive, really fast