If you wire up a knock sensor to your stereo and play with your timing you can see there is a lot of economy to be had under 3000 rpm on a Metro. The factory tuning is not really tuned for economy at all it seems like. I can actually drive 45mph/5th gear with the timing 20 degrees advanced without knock steady state. My vacuum readings with that much advance are a lot higher than normal so I know it is getting much better mileage. It knocks under load real bad like that though so it isn't drivable other than to experiment.
Sadly the only people that know the timing and fuel maps for a metro ecu want to sell chips and are not interested in letting anyone know the map locations in memory so there is no way for me to tune the stock computer without a lot of effort to decipher the maps. The factory computer is pretty limited anyway so for a metro to get better tuning you need a megasquirt computer and a wideband O2, EGT, and knock sensor. Then you can run lean burn 18:1 ratio all you want
Which of course makes me want to adjust my timing more too. I think I had it pretty far, then backed it off this fall.
Thing that's holding me back is: exactly HOW bad is a little ping now and then? I never went "marbles in a paint mixer" bad, but something lighter than that I could hear once in a while when I *had* to step on it.
As some of you here know, I had some work done on the head of my DOHC Saturn. It was shaved .050" which raised the compression ratio to around 10.5:1; stock was 9.5:1. It also had Singh grooves cut into the combustion chamber to promote a more efficient burn and had Power Lynz cut into the intake ports. We also machined the locator slots for the cam gears and changed the cam timing. If I remember correctly, we advanced the intake 4* and the exhaust 2*. The effect of changing the cam timing was incredible! According to the butt dyno , hp was significantly increased. More importantly though, peak torque occured much closer to the 2500 rpm level instead of the stock 3500-4000 range. These mods allow me to run 87 octane with no noticeable ping even in 5th at speeds as low as 20 mph. Also, according to the SG2, the timing runs at just over 40* advanced while cruising at around 60 mph under light throttle. The guy who did the work on the head has driven numerous turbo-Dodge cars that are rated at around 150 hp stock and said that my engine now feels much stronger than that. All this to say that timing-cam and ignition-can have some very dramatic effects on performance and FE.
Horsepower is how hard you hit the wall, torque is how much of the wall you take with you.
Good stuff. I'm aware that I would need to run different timing setting for summer and winter.
From Matts article:
"Over-advanced timing may not only damage engine components, but may also negatively impact fuel economy. Many technicians mistakenly believe that advancing timing beyond the factory specified range can improve mpg. This is inaccurate and a misconception. Some also believe that advancing the timing and burning high octane, premium fuel improves mpg. This is also a misconception. To burn high octane fuel efficiently, engines must have sufficient compression ratios. The timing advance profiles for premium fuels are different than those for regular octane fuels. This lesson attempts to bring these points home by getting the student technician to investigate the three types of timing."
This seems to go against what I've read and what most are doing here.
Also form the article:
For too many years, technicians have taken liberties with engine timing to correct minor, local engine performance problems. Taking these liberties can result in reduced fuel economy. A general accepted rule of thumb has been a ? mile per gallon loss for each degree of off-standard static timing. However, off-standard centrifugal and vacuum timing negatively impacts engine power and fuel economy.
If that is correct than getting the timing setting could make a difference of 2 MPG or more if you get it right on. Of course that timing is set up for the whole power band and not the area must FE nuts are operating in. This is intresting stuff.
The ideal timing gets the peak pressure at 14 degrees after top dead center. Whatever timing you run needs to get that ideal. you can get the peak pressure at like 5-10 degrees atdc and it won't knock but you are not getting peak power or economy. Same thing if you run to little timing you can get your peak later than 14 atdc and you are getting less power and economy.
So the way I usually do it when tuning a timing map is to tune it till I get knock then back off about 4 degrees for low rpm and 2-3 for higher rpm. This gets you pretty close then you can adjust from there depending on if you have a dyno to tune with.
One thing I have been playing with with is the idea of hooking up a vernier cable to the distributor so I can adjust the timing while driving to find the ideal timing for highway use. Using a vacuum gauge adjust the timing till you get the highest reading and you are pretty much good. A scangauge would also do to see the effects of timing.
And if you have a tape player in your car still you should really try the setup I did with the knock sensor hooked to the stereo. You can learn a lot about what is going on in your engine with that. Plus it is cheap to do and very simple to hook up.
I should add you can clamp the knock sensor to the engine with a pair of vise grips or whatever you have handy to keep it very tight to the engine and it works just as good. Saves from drilling and doing any real work to test it out.