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Improve Fuel Economy on 360 |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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Just because you're running as much ignition timing as you can without ping doesn't mean the engine is running at peak power and efficiency.
Ping is caused by the spontanious ignition of the fuel charge set off by heat and pressure. The cylinder pressure spikes rapidly and this is the sound you hear. Since the cylinder burn event is shortened, power is reduced greatly. Early ignition lead can raise cylinder pressures high enough to cause ping or detonation, it's technical term. Early ignition lead creates ping in the same way preignition does, the engine doesn't know the difference.
It is possible to lose power through early ignition lead by another way without abnormal combustion characteristics. In most low to moderate compression engines operating at proper temperature with proper grade fuel, detonation will not occur even with early ignition of the fuel mixture. Cylinder pressure will gradually increase then decrease as normal without the shocking spike of detonation. The problem with this is cylinder pressure increases high enough before the piston reaches top dead center, and tries to force the piston backwards back down the cylinder bore. The other pistons and the inertia of the rotating crankshaft assembly keep the engine turning forward, but that doesn't get around the fact that the engine is internally fighting itself. Not only that, but cylinder pressure after TDC is reduced, further lowering power output.
And this whole time, the engine is not pinging. In severe cases, the engine will run rough, but in mild to moderate cases, the driver is unaware.
The key to maximum power output is for cylinder pressure to peak at the point durring the piston stroke after TDC that the connecting rod has the most leverage on the crankshaft. To calculate this point requires college level calculus involving the connecting rod length and piston stroke relating to the crankshaft moment arm. For most engines with a rod to stroke ratio of 1.6:1, maximum leverage occurs around 20* ATDC. After some more calculus and analysis of cylinder burn rates, the proper ignition lead can be determined. That is how the engineers find it.
For street use, any change in engine compression ratio, intake charge temperature, fuel brand, fuel mixture, ignition system for spark intensity, etc. changes the cylinder burn rate and the required timing of the spark. The only real way the average car owner can set their ignition timing "by ear" is by trial and error on a dragstrip or on a dyno. Without expensive test equipment to anayize cylinder burn rates, it becomes alot harder.
Hence why I tend to stick with stock specs for everything, as a change in one thing can throw everything else off.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7949 |
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smills61074
AMC Nut Joined: Feb/05/2011 Location: savanna, il Status: Offline Points: 270 |
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This is the first I have seen anyone mention calculus on the forum. I am an engineer and have had calculus, physic, statics and dynamics,thermal dynamics, fluid dynamics, etc. You are correct about the piston firing after TDC and having the best leverage. The same with fuel combustion.
Factory setting are generic. Consider them a baseline. All engines are different. Whether it is the carburetor, plugs, wear on the timing chain and engine, or even changes in temperature. I for one have always base lined my engines and then carried a timing light with me in the car. I try adjusting the timing a degree at a time. Once I hear pinging (usually going up a hill) I back off the timing. Then I back off a degree at a time until I feel I have hit a sweet spot. You can do this over a few tanks of gas and get a real feeling or where your cars runs well. You will definitely loose performance to gain a little bit of mileage. But, there is a few miles per gallon to gain. By driving you car right an having a good tune on your car. |
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68 Blue AMX Perfect California Body going for 401/6 speed
1 1/4 ton Power Wagon Ex Colorado Brush Truck 2006 Caddy CTS V with LS2 and manual trans Corsa Exhaust Beater car (daily driver) |
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16611 |
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16611 |
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16611 |
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Just my opinion...............advance the initial to anywhere to 8-12 BTDC. make sure your choke opens quickly. and make sure your choke pull off is working as well. and make sure the power valve in the carburator is working. put some good plugs and wires on it. (my preference is no champions) get a distributor cap and rotor from blue streak. they are a set, and the cap will have copper terminals. put a vacuum gauge in the car and try to keep it above 15 inches at all times. also a tach, and try not to go over 2500 RPM. If you do this, I believe you can increase your MPG by 1-2 MPG.
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nda racer
AMC Addicted Joined: Nov/28/2009 Location: Ohio Status: Offline Points: 2591 |
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X2 |
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Buzzman72
AMC Addicted Joined: Sep/15/2009 Location: Southern IN Status: Offline Points: 2725 |
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I think the original premise in the original post is wrong. You don't make an ENGINE get better mileage, unless you put it in a lighter car. But you make a CAR get better mileage by using the steps that everyone has mentioned in this thread.
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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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gwryder
Supporter of TheAMCForum Joined: Jun/30/2009 Location: Michigan Status: Offline Points: 710 |
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Years ago, for a project with one of my electronics classes, I made a poor fuel economy minder. Mine used comparators, a vacuum can to turn on a red, yellow or green LEd depending on the manifold vacuum. A simple one can be made with a vacuum can, micro-switch and LED. The idea behind this is to have the LED turn on when the vacuum drops to the level the carb's power enrichment system comes into play (~ 8-10"Hg). I put mine on a 1980 Pontiac Phoenix and it worked really well, but was hard to drive without the LED coming on.
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John
70 AMX |
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BassBoat
AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1719 |
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OK, let me say this another way. Increase the timing. No other change will make as much improvement in efficiency and driveability. Its easy to do, costs nothing, and is readily reversible. Advance the timing until you either do not see an additional improvement, based on your driving, your fuel, and keep advancing the timing until you observe one of these three things: You don't see any further improvement, the car is hard to start when hot, or you get ping. If you get ping, put in better fuel because fuel is so bad today that you will reach the limit of the fuel long before you reach the optimum conditions for driving and the increase in fuel cost will be offset by the increase in mileage.
If you don't see an improvement, that you can feel in the seat of your pants and in your wallet, by all means put the timing back. Tuning tip here is if it runs better retarded keep retarding it. It won't, because in thousands of instances I have seen this happen only once, but that is how tuning works. Try it, evaluate the result, and follow the data where it leads you. I am a "rocket scientist", and have maybe 40 years of combustion engineering and engine development experience, and frankly could not do calculus anymore on a wager. But recollection of calculous or ferver in conviction as exemplified above is not what you need in your case for tuning your car. Just a little common sense and trial and error.
BB
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