Kingtal0n

ok so, this is one of my specialties. Because I am so poor, I have to find ways to improve my fuel economy, otherwise the car is not practical. I cannot drive anything that averages below 25~ mpg that is for SURE.

First clarification about the word average, When I say average I mean when driving the car like a normal daily driver out of boost, with 50% highway commutes.
Now, on to the gory details,
To achieve this kind of economy requires patience to say the least. There are several factors affecting fuel economy on all cars;
First let us tackle the tuning. My average air fuel ratio while cruising is 15.4:1, and I have developed a sort of "checker board hypothesis" whereby the fuel map gradually dips from high 14's (14.9:1) to mid 15's(15.7:1 max) in cruise situations, and to ensure engine longevity the fuel map resolution in those areas has been enhanced (a typical feature of many stand-alone ecu is you can decide what sort of resolution you would like by changing pressure/mass breakpoints) such that a slight movement outside of the cruise range (even just a steep hill while cruise control is set) will drop the air fuels quickly to about 14.5:1 which is much closer to the average closed-loop air fuel ratio you would see when using a narrowband sensor (they tend to flip from 14.3 -> 14.9 quickly). In the past I have used a simulated wideband analog output to keep my ECU in closed loop at these air fuel ratios ( 15.5:1 @ .002volts, 14.9:1 @ 1.002 volts) but I have found open loop to be just as effective when the engine is mostly stock (mainly because of the great vacuum a stock engine will produce, makes each load point more well defined)

Now, all of that is fine and dandy, but it does not have that great of an effect on fuel economy as you might expect. And I have discovered this because I data-log everything for hours of driving for years and years on different cars. The best way I have found to measure fuel economy is by comparing injectors duty cycle, engine vacuum, and road speed all at once. If you also include the injector flow-rate, you can write an algorithm to generate a real-time fuel economy display from this data, but it is un-necessary to simply find out if your changes are saving you gas. The more important tuning aspect of fuel economy is ignition timing. Finding the best timing for your highway cruise at different load points. And here is my method.
Load your car with luggage, full tank of gas, passenger, weight it down as heavy as it can be. This will ensure your load cell is just about as low-vacuum as possible for a highway cruise, this will ensure that if you tune your timing then later on decide to add all of this weight, you do not run outside of your intended cruise load cell and into the part throttle acceleration zone.
Now, set your cruise control to eliminate the movement of the tps to keep the acceleration enrichment out of the picture as much as possible. In my case, I simply disabled my TPS enrichment feature for this tuning session. Cruise along at a speed low enough that wind resistance will not factor in (yet). I usually start at 65MPH. Find your load cell, remember the vehicle is heavy, on my car this cell is right about 10" of vacuum at 65 MPH. Set your timing to a low number, something like 30* that is much too low to be the final result, and drive for 20~ minutes while logging your fuel injector duty cycle and engine vacuum. In my case, injector duty was about 8%. Now, advance your timing. I used 35* next. And repeat the above proceedure. My injector duty cycle dropped from 8% to 7.6% average, and my air fuels became slightly richer in fact, allowing me to remove even more fuel. If I had an EGT gauge I would have also noticed the temperature drop at the exhaust manifold around 50*F~. This is all a very good sign that the additional timing was a welcome change. You can now see where this is going; repeat the proceedure, adding timing and logging fuel injector duty cycle, and look for the signs of a welcome change, that is, reduced injector duty cycle, lower EGT, increased engine vacuum. At some point you will encounter diminishing returns, and then the application of the vehicle will tell you what to do next. For me, safety is number one, so I never run off into the deep end for that extra .2% (it took another 12* BTDC of timing to drop the injector duty only .2% so clearly the additional timing was unwelcome). My final timing is right at 37* btdc for this engine, some have appreciated as much as 45* btdc (big cam(s), big manifolds, large displacement engine usually)

Now, it is important to realize that before you start playing with the engine's tune, there are several other factors to consider when trying to get the best fuel economy, they should be taken care of first.
1. Rolling resistance. Do your brakes drag? grease the backs of your pads. Grease your wheel bearings. Spin your driveshaft by hand and feel it, does it feel rough or notchy? Push your vehicle by hand, often, get a feel for how easily it rolls. Update and maintain all of the aspects of driving straight, such as the alignment, toe and caster. Consider the tire compound.
2. rotating weight. Use the lightest wheels you can find. I also have a light weight flywheel (but not too light!). Anything in your drivetrain you can afford to have lighter is a fuel saving benefit. You do not want the rotating assembly too light on a street car (no knife edged crankshafts) though.
3. ride height / wind resistance. Speaks for itself, is your car suitable for high speeds? Get it lower to the ground if possible.

and finally, the way you drive is very important. use your brakes as little as possible. Every time you brake, you waste the energy that was extracted from the fuel you burnt and send money out the window. Engine braking for long distances pissing everybody off behind you that wants to speed up to the stop light is essential. My car will engine brake with zero fuel input from 60mph roll for about 1/2 mile, including every gear on the way down to crawl and then it can crawl a little or I Jump out and push it to finish the gap.

zdave87

You forgot to add in your key fob.

Kingtal0n

"A fob, or more commonly called a key fob, is a small security hardware device with built-in authentication used to control and secure access to network services and data. The key fob displays a randomly generated access code, which changes periodically, usually every 30 to 60 seconds. A user first authenticates themselves on the key fob with a personal identification number (PIN), followed by the current code displayed on the device.
Key fob is also a word used to describe a key chain and several other similar items and devices. The word fob is believed to have originated from watch fobs, which existed as early as 1888. The fob refers to an ornament attached to a pocket-watch chain. Key chains, car starters, garage door openers, and keyless entry devices on hotel room doors are also called fobs."http://www.webopedia.com/TERM/K/key_fob.html

better?


I love all cars, if I needed to I would build one from scraps and drive it. The difference between a random vehicle for transportation and what we drive is that we are enthusiasts, and wish to enjoy our time driving, whether it is in a truck or a race car.

Driven

yep... it sat in his garage for a year or so. He was looking to gain some garage space back. Included a trailer too

AngryTurtle

This thread is like going to ferrari chat and bragging about your Supercharged C4 corvette.

rockville

I call BS on 200k reliable. Hell, I've had a number of Toyotas and Hondas in the family. Good cars but not 200k with just oil changes.

bgoetz

Yeah this may be one of the stupidest threads I have ever read, lol

Marioshi

Yeah, everyone knows you get to pick 2 out of cheap, reliable, and fast. He might be overstating things a bit...

RedCelica

And here I was gonna guess the OP was driving an Eagle Talon

shifter kart ftw

blkwidow

Ha but then it wouldn't be reliable (kidding).