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Juanito84
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Joined: March 17, 2012
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Location: Colorado Mountains
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 Posted: Sun Dec 08, 2013 8:44 pm Post subject: |
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| bugguy076 wrote: |
The most important thing to remember is not to overspend when building a mileage engine. Any savings on fuel is waisted on a high priced engine that will take 10 years to offset the cost. |
Defenitley true, unless you expect fuel prices to raise high enough. But that's just speculation.
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Juanito84
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| Posted: Mon Dec 09, 2013 7:42 pm Post subject: |
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So let’s just recap here.
Aerodynamics
Aerodynamics are affected by shape, size and speed. The easiest way to improve aerodynamics is to just drive slower. Extras, like roof racks, will increase aerodynamic drag so it’s best to leave them off. A front spoiler, or lowering the vehicle might help. Also wheel skirts will help mainly since a lot of drag is caused at the wheels because the tops of the wheels are moving twice as fast into the wind as the rest of the vehicle. Plus the fenders tend to grab air. Losing the front louvers will help some too.
Rolling resistance
Rolling resistance is affected by the wheels, wheel bearings, driveline and brakes. Narrow tires, high tire pressures, drum brakes, well kept bearings and a good alignment will help. Stock tire widths were usually 5.6” or 145mm. Disk brakes tend to constantly drag. Also by keeping the drive line as flat as possible so there isn’t much bend at the CV joints or swing axle joints will help.
Weight
A heavy vehicle might increase rolling resistance a little, which usually is compensated for by increasing tire pressure. But the main loss due to weight is the extra energy needed to accelerate that is then lost during braking. Both acceleration and hill climbing will need more energy. That energy would not be lost if you didn’t have to brake. This is because acceleration is transferred into momentum which will push a heavy vehicle farther as you coast. But then you come up to a stop sign and you have to turn that momentum into heat, which is where you lose the initial energy spent during acceleration. You could take off as much weight as possible. Or always coast to a stop as much as you can. Or try to adapt some sort of hybrid regenerative braking system to your car.
Fuel homogeneity
We want to burn fuel in the cylinders, not let it find its way out the exhaust. And the better it is mixed with air the better. Drops of unmixed liquid fuel will not burn. Carburetors mix fuel through vaporizing it with heat so heated intakes, heat-risers and thermostat with flaps help. The closer the fuel inlet is to the cylinder, such as in port fuel injection, the less time fuel has to vaporize and must rely more on a fine spray to keep fuel atomized. With stock fuel injection, smaller valves are used to help increase turbulence and break up drops of fuel and mix fuel more evenly. Turbulence can also be created by a good quench which benefits both fuel injected and carbureted engines. Some feel single port engines mix things up better than dual ports. Rough or golf ball intakes may help too.
Air/Fuel ratio
Rich air/fuel ratios put more fuel in the system than what can be burnt. The result is that some fuel is wasted out the exhaust. Lean air/fuel ratios of between 15 to 16:1 seem to give the best fuel mileage for low loads, but air/fuel ratios no leaner than 13:1 are necessary at high loads to prevent detonation. More vacuum advance and a strong induction ignited spark will help you reap the benefits of a lean air/fuel ratio.
Equal cylinder air/fuel ratios
Some have noted that single carburetors and throttle-body injection systems don’t always send the same amounts of fuel and air to each cylinder. This can cause some cylinders to run rich while others run lean. This not only makes the rich cylinders lose fuel but also makes finding an optimal timing curve impossible since some cylinders will want to ping long before others are advanced as much as they could be. Dual or quad carburetors supposedly will allow adjustments that are more accurate for each cylinder. Port fuel injection can be tailored to do the same. Also timing each cylinder individually could help. Of course there are always pros and cons to each set up.
Compression ratio
The higher the absolute compression ratio (usually referred to as cylinder pressure) the higher the efficiency. The absolute compression ratio is not the static compression ratio, nor the dynamic compression ratio, but rather it’s the actual ratio between the air volume before it entered the engine and its volume when it’s compressed at TDC. You could say the absolute compression ratio is the dynamic CR multiplied by the volumetric efficiency of the entire intake system, including the volumetric efficiency lost at the throttle, minus any loss due to blow-by. (That’s why most engines tend to run more efficiently the higher the load, short that of high load enrichment, although usually running around at a high load means you lose more fuel mileage through aerodynamic drag or incessant braking than you gain through high throttle driving.) The more the air is compressed before its fuel is ignited the more energy that can be extracted from that fuel.
Two easy ways of increasing the absolute compression ratio while cruising is by using and/or shifting into higher gears; and/or using a smaller displacement engine. EGR systems can also increase the absolute compression ratio. That’s because all these make you open up your throttle more which in turn increase cylinder pressure.
Other changes to the absolute compression ratio can be made by increasing the static and dynamic compression ratios. Increasing the static CR and decreasing the dynamic CR with a higher profile cam does not count. Of course too high and you will cause detonation. Engine quench, increased cooling and a few other detonation resisting techniques and systems may allow for a higher compression ratio. Or if you could switch to diesel injection you could increase the compression ratio considerably.
Compression loss
As air is compressed it heats up. If that heat could be removed while it’s being compressed then it could be compressed with less energy since it will push back with less pressure. The only engine I know of that can do this is the Miller cycle engine. The Miller cycle engine uses a supercharger to partially compress the air. The air is ran through an intercooler which takes out some of its heat. This causes the engine to be able to compress the air with less energy and therefore increases efficiency. The cooling effect also allows for a higher compression ratio.
Decompression ratio
Ever wondered why we need mufflers? Because when the exhaust valve opens the cylinder contents are still under pressure, which force their way out in a loud POP! Theoretically, it would be best if that pressure could keep pushing the piston until all of its energy were used. The Atkinson cycle engine’s intake and compression strokes are shorter than the combustion and exhaust strokes which loses less energy during the combustion stroke. This can also be mimicked by increasing the open duration of the intake valve.
Ignition timing
One of the greatest fixable losses is due to ignition timing. Optimal timing would place the end of the burning fuel at around 10° ATDC crankshaft rotation. Any sooner and the pressure really isn’t doing anything except possibly provoking detonation. Any later and you lose out on having full pressure from the top of the combustion stroke, which translates into inefficiency. The problem is that the flame and piston speeds are constantly changing causing the ignition timing system to keep having to correct itself. The old school style systems usually include a mechanical advance unit to make up for changes in piston speed and a vacuum advance unit to make up for changes in flame speed. New technology systems use crank position sensors, manifold absolute pressure sensors, mass airflow sensors, throttle position sensors, temperature sensors and oxygen sensors along with an engine control unit.
Flame speeds
Fuel is ignited in the cylinder several degrees before top dead center. Before it reaches top dead center the piston is actually pushing against the increasing pressure caused by the advanced timing. We call this back pressure. A slow flame will also continue to burn long after the piston starts on its way back down. This causes another loss since full pressure is not achieved during the beginning of the combustion stroke. Because of these factors the faster the flame burns usually the better the efficiency that can be achieved. Well tuned ignition timing curves, higher compression ratios, higher gears, smaller displacement engines, narrower bores, longer connecting rods, more compact combustion chambers designs and centrally located or dual spark plugs all increase flame speed. If possible, a stratified charge will also increase flame speed. Wide semi-hemi head designs will decrease flame speed.
It would seem to me that quicker flame speeds should tolerate higher compression ratios since pressure at TDC can be lower from retarded timing and will build up to tops still by the 10º ATDC goal.
Heat adsorption and loss
Heat is what causes the gasses to expand which create the pressure and therefore power to push the vehicle down the road. Some of this heat is absorbed into the engine and must be removed by the cooling system. It would seem that polished or ceramic coated cylinder tops and combustion chambers would keep more heat in the combustion gasses and out of the engine.
Besides the heat lost through adsorption, a lot of waisted heat energy goes out with the exhaust. A six cycle engine can recover part of that lost energy and can even cool the engine making engine cooling unnecessary.
Other engine losses
Bigger than necessary oil pumps and fans will use more power. The fan will use more power exponentially with speed so reducing engine speeds leads to an increase in efficiency. A thermostat system, especially the old ring type, should reduce fan losses during cold running. Using electrical systems as little as possible may help a little since the alternator or generator will use less power when less electricity is needed.
Driving skills
If you could drive around at a steady 35mph in top gear on flat pavement theoretically you should get over 40mpg (US measurements) in any stock Beetle setup. At stops it would be best to be able to coast to the stop; of course that’s not always practical. Using the highest gear possible will help, even during acceleration. That means shifting whenever you can hit 1600RPM in the next gear. If you have a vacuum gauge or oxygen sensor with a gauge it’s best to accelerate, not with as little throttle as possible, but with as much throttle as possible without activating the power circuit(s). Usually that happens at about 10” or 8” Hg. Contrary to an old myth, turning off the engine when it will not be in use for several minutes will actually help save fuel. This includes not letting it idle to warm up but rather driving it immediately after start up.
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Boolean
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Joined: January 19, 2012
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Location: Stockholm
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| Posted: Tue Dec 10, 2013 4:44 am Post subject: |
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| Juanito84 wrote: |
| bugguy076 wrote: |
The most important thing to remember is not to overspend when building a mileage engine. Any savings on fuel is waisted on a high priced engine that will take 10 years to offset the cost. |
Defenitley true, unless you expect fuel prices to raise high enough. But that's just speculation. |
We are all into hot rodding because we like different aspects of it. I think that noone has caught this bug because it saves money. I would love to have a six stroke 1000 cc turbo engine running super lean combustion just because. It would cost more to build and tune than I could ever regain, but still extremely cool.
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Juanito84
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Joined: March 17, 2012
Posts: 2436
Location: Colorado Mountains
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| Posted: Wed Dec 11, 2013 9:14 pm Post subject: |
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| Boolean wrote: |
| Juanito84 wrote: |
| bugguy076 wrote: |
The most important thing to remember is not to overspend when building a mileage engine. Any savings on fuel is waisted on a high priced engine that will take 10 years to offset the cost. |
Defenitley true, unless you expect fuel prices to raise high enough. But that's just speculation. |
We are all into hot rodding because we like different aspects of it. I think that noone has caught this bug because it saves money. I would love to have a six stroke 1000 cc turbo engine running super lean combustion just because. It would cost more to build and tune than I could ever regain, but still extremely cool. |
I guess that's true. If your only goal is to save money then that's one thing. But there are guys out that have modified cars, not necessarily ac VW's, but have modified perfectly functionable cars to get over 90mpg. It would be cool to do that in an ac VW, or any car perhaps, just to say you did what manufacturers just cannot seem to do. After all, how many hotrod their engines and really expect to get anything more out of it other than the feel and pride?
It seems strange to me when someone pulls up in a new car bragging about how it gets 30 to 40mpg. I plan to get that in my 1971 Bug and already get over 50mpg in my 1985 Golf non turbo diesel. The technology is out there and the math points to +100mpg being quite possible. But why they still use the same otto cycle piston arangement and call it progress when they put on a finer spraying injector nozle is beyond me.
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vwkirb
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| Posted: Thu Dec 12, 2013 3:44 pm Post subject: |
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One thing that should not be forgotten in this discussion, is that how the engine is running effects what comes out the tail pipe. The point of this thread is one thing mpg, and the basic answer to that is run leaner.
Why is it though that car manufactures aren't doing this?
It's not a conspiracy. It is because they can't. Legally they cannot pass EPA regulations doing this. The leaner you go, the types of pollutants become different and considerably worst. This is why we have catalytic converters on contemporary vehicles, to control the type and amounts of pollutants. If it was simply 02 and gas in c02 out, that would be great (well easy at least), but its not, its more complicated than that. |
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Juanito84
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Joined: March 17, 2012
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Location: Colorado Mountains
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| Posted: Thu Dec 12, 2013 8:48 pm Post subject: |
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| vwkirb wrote: |
One thing that should not be forgotten in this discussion, is that how the engine is running effects what comes out the tail pipe. The point of this thread is one thing mpg, and the basic answer to that is run leaner.
Why is it though that car manufactures aren't doing this?
It's not a conspiracy. It is because they can't. Legally they cannot pass EPA regulations doing this. The leaner you go, the types of pollutants become different and considerably worst. This is why we have catalytic converters on contemporary vehicles, to control the type and amounts of pollutants. If it was simply 02 and gas in c02 out, that would be great (well easy at least), but its not, its more complicated than that. |
This is only half true. Yes, leaner makes more NOx emissions and most cats can't controll NOx un less O2 is nearly zero and there's some left over unburned ffuel. But NOx traps do exist and can filter it out on lean burn technology. The problem all along has been the cost. The same reason manufactures don't make cars out of titanium and platinum with turbine engines.
That being said it seems that several manufacturers are going torwards lean burning, direct injection, stratified charge engines with NOx traps, including VW. The results are a jump in fuel economy.
But there are still many technologies I don't understand why manufacturers don't use. Porsch invented the hybrid system before he designed the Beetle and finaly 90 years later is it being used in some cars. The Atkinson cycle engine has been around just as long yet it hasn't been but less than 10 years ago when Toyota put an Atkinson engine on the Prius, and viola! 50mpg! No one I know of puts a Miller cycle engine on any of their vehicles, nor a 6 cycle engine. The Stiriling engine boasts both high efficiency, emmisions and simplicity, yet no one uses them except in antique generators. All these engines boast some 40% efficiency or more. Steam engines were about 5% efficient when the 10% efficient otto cycle car became popular. But nowadays there are steam turbines running at some 50% efficiency. And even some otto cycle internal combution engines, the least efficient of them all, have reached the 50% mark. Cars have improved in aerodynamics some. But then there's that Aptera car that gets 130mpg on gasoline alone due mainly to it's aerodynmic design. The real problem is money and actual desires. Drivers want power, style and speed. Manufacturers are only going to make what makes them money. The possibilities for a 300mpg emmisions friendly car do exist. But it won't happen until drivers realize that 33mpg in a 2014 VW is not really that great and demand something better.
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morymob
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| Posted: Fri Dec 13, 2013 5:13 am Post subject: |
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| Don't forget the newer eng big boost with direct inj they up the compression , close to and maybe exceeding 15 to 1.Always wondered what a 1.6 diesel on gas would do, wouldn't have any means of lube 4 inj pump. Very cold areas add gas to fuel to help starting,maybe a separate tank? |
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Juanito84
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| Posted: Mon Jan 13, 2014 9:03 pm Post subject: |
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Perhaps the easiest way to lower aerodynamic drag is to lower your speed.
This doesn't include rolling resistance.
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[email protected]
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| Posted: Mon Jan 13, 2014 10:40 pm Post subject: |
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See that, you drop to 10hp (33% reduction) at 55mph.
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Juanito84
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| Posted: Mon Jan 13, 2014 10:54 pm Post subject: |
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Yep. Of course that's power and not energy per mile (aka fuel mileage). The amount of energy per mile doesn't drop 33%. You have to divide power by speed in order to determine energy per mile. So it would be closer to a 25% drop in energy needed. It's interesting because you do the same equation to determine force. I'll post a speed vs. force later for a better comparison.
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modok
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| Posted: Mon Jan 13, 2014 11:11 pm Post subject: |
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| Juanito84 wrote: |
Perhaps the easiest way to lower aerodynamic drag is to lower your speed.
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Exactly. That was waht the 55MPH national speed limit was about back in the day........saving fuel.
Of course, besides rolling resistance your vehicle also has to be able to go up hills too, and accelerate eventually, and deal with wind, so you need more power than just what is needed for cruising. But even today I think you'll find that 55-60 MPH is what you'd want to design for if making a super MPG car. In fact, i think they knew that from the beginning 
you need 40 HP! |
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Eaallred
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| Posted: Tue Jan 14, 2014 7:56 am Post subject: |
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I'm seeing tons of theories being thrown out there. Lots of great info on paper.
What are people getting real world out of their setups?
I've dattalogged high 30's doing 65mph so far in my car that has run 10's in the quarter. New trans that will be more streetable is going in this spring. I want to get solid 40mpg numbers out of it this year and hit a 9 in the quarter. On 91 octane, no water/meth injection. Pump gas, baby!
I see no reason why a purpose built Bug couldn't get 60mpg at 60mph.
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JoeCormier
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| Posted: Fri Feb 07, 2014 1:21 pm Post subject: |
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I just pulled my 1600 after 6 months of service for the job and 20,000 miles and this engine with a 110 cam and dual baby dells got consistent 33-34 miles per gallon. I just installed my new 1955 cc with dual 40 mm dellortos and I was hoping for 25-28 mpg. I topped it off in Ramona and went to pacific beach 37.5 miles pulled in and topped it off and I was shocked! 1.05 gallons which is 35.7 mpg . Totally impressed and this engine has torque to get me back up the mountain in high gear with ease at 1/4 throttle. FUN mid sized engine for daily driving and don't think I will EVER have None stroked engine in my car again. Build on my friends! |
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AlteWagen
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| Posted: Fri Feb 07, 2014 1:42 pm Post subject: |
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| JoeCormier wrote: |
| I just pulled my 1600 after 6 months of service for the job and 20,000 miles and this engine with a 110 cam and dual baby dells got consistent 33-34 miles per gallon. I just installed my new 1955 cc with dual 40 mm dellortos and I was hoping for 25-28 mpg. I topped it off in Ramona and went to pacific beach 37.5 miles pulled in and topped it off and I was shocked! 1.05 gallons which is 35.7 mpg . Totally impressed and this engine has torque to get me back up the mountain in high gear with ease at 1/4 throttle. FUN mid sized engine for daily driving and don't think I will EVER have None stroked engine in my car again. Build on my friends! |
That is GREAT!! What combo did you end up with?
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[email protected]
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| Posted: Fri Feb 07, 2014 1:52 pm Post subject: |
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What distributor and 40 DRLA jetting Joe? The MPG will improve as the engine loosens up too.
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JoeCormier
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| Posted: Fri Feb 07, 2014 5:26 pm Post subject: |
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Here is what's in it! 76x 90.5 with a 4062 bugpack cam
9 to 1 with 40 thou deck 1.1 rockers , 40x 35 revmaster heads unported with 40 mm dellortos with 50 idles, 145 mains 180 air and a sidewinder exhaust .
It has around 300 miles so oil change and just adjusted the valves and had two that were a little loose. Now I wish I would have put this engine in a long time ago if I knew it would get this kind of mileage ! I love the torque it puts out and it enables me to crack the throttle to get around and cruise 70 at 3500 it just purrs and the straight cut gears are quieter. At idle it's loud and the wify says what did you do to your car it sounds like a grinder!))
FUN STUFF! |
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JoeCormier
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| Posted: Fri Feb 07, 2014 5:28 pm Post subject: |
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| Distributor is 009 with points and no vac advance. |
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AlteWagen
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JoeCormier
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| Posted: Fri Feb 07, 2014 5:51 pm Post subject: |
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32 vents 1 1/2 exhaust
I have never heard of that distrib but if it would do that I'm on it! Thanks
I'm running a 4.12 stock gears and 205 65 rear tires and my car weighs 1690lbs and running a stock weight flywheel to keep it really smooth shifting. |
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AlteWagen
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