Help me understand cam timing, advancing or retarding a SOHC for mpg

[MetroMPG]

FYI, I changed the Firefly's cam to the XFi version (that trim was never available in Canada, so there's no emissions profile for it here) and advanced the ignition timing quite a lot and the car always passed emissions (sniffer/tailpipe gas analysis type) with flying colours.

[California98Civic]

They check ignition timing here in Cali. So I would assume most if not all states that adopted the Cali law also check. I don't know about WI, but Canada is among the states exempt.

[Daox]

Wisconsin hooks your car up to an OBDII scanner and pretty much as long as there is no check engine light you're fine. Anything pre-OBDII isn't even checked.

[Madmanmax]

Hey, realize this is an old thread and probably not relevant to the originator any longer so I guess this is just a little FYI. I had an early Geo metro I wanna say it was a 1990 or 1991 and the cool thing about these older models was that Suzuki had an adjustable cam sprocket on that G10, if you pull the cam gear off and inspect it, you will find it has an extra notch that is if I remember correctly 3° offset. I don’t know if they still do but Suzuki used to race these three cylinders and the other notch is the setting that used for racing . As far as mpg I never clocked it, so I don’t know if it improved or gotten worse. Either way I was still getting killer gas mileage, and with the offset cam timing once that thing hit 90 did not want to slow down. I had a lot of fun with that car.

Now part two is that I arrived here in the first place, because I am trying to figure out the answer to that same question that started this thread. If I’m trying to increase my mpg, should I retired or advance from what I remember on the metro I believe I need to go 3°, but I can’t remember which direction or if it would improve gas mileage at all, but my assumption is that the more efficient burn That this adjustment I believe creates would increase gas mileage as well. So if anybody has the answer, let me know please. My current project is not a metro by the way, but a single overhead cam YJ so I’m assuming the results would be ballpark similar.

[Isaac Zachary]

When I rebuilt the 1972 VW Super Beetle engine I had the cam ground for a close to stock cam timing and lift that was also compatible with a 10:1 compression ratio running regular gas. I'm not sure how much power it made, but that Super Bug felt like it was quite a bit faster than the 1985 VW Golf I had that was suposedly more powerful even though everything else on the Bug was stock (carb, air filter, exhaust, pistons, heads except machining for higher CR) except the custom ignition timing. I could climb any pass at the speed limit in the Bug whereas the Golf wouldn't. I also got a rock solid 30mpg average in the Bug.

[cRiPpLe_rOoStEr]

Originally Posted by Madmanmax

I had an early Geo metro I wanna say it was a 1990 or 1991 and the cool thing about these older models was that Suzuki had an adjustable cam sprocket on that G10, if you pull the cam gear off and inspect it, you will find it has an extra notch that is if I remember correctly 3° offset. I don’t know if they still do but Suzuki used to race these three cylinders and the other notch is the setting that used for racing

Kinda like a manually-activated VVT? Interesting, even though it's often pointed out that DOHC valvetrains are better suited to feature VVT.

[freebeard]

I have no idea, but thanks for reviving the thread.

I know all about VW flat fours, but the Metro is allien technology [to me].

[cRiPpLe_rOoStEr]

Wouldn't the composite headlamps be supposed to be better suited to the XFi, as they're more aerodynamic than the recessed sealed beams? Well, at least until the FMVSS 108 is not repealed...

[freebeard]

It's a thousand-dollar car. [shrug]

I've got some good used side marker lights, have been thinking about stainless steel mesh covers.

[Madmanmax]

a cheap upgrade on the old metro would be a plexiglass cover over the headlight openings.