Metro owner mulling over swap to XFi transmission and 1-ring pistons
 

A visitor to metrompg.com sent me this email recently:

My feeling is if you're going to go to the trouble of swapping transmissions to get a taller final drive, you might as well go big or go home. The 3.52 is where the biggest gains are to be found.

Just a guess, but I bet that individual change is worth a very small improvement. Not saying it's not worthwhile, but it probably won't show up at the gas pump, over the usual noise of variation between fills.

That I can't answer. The XFi was never sold in Canada, so I've never actually seen one in person, much less spoken to anyone who drove one for any length of time.

Maybe some of the other members will chime in on that one.

I don't think I would bother with the piston/ring swap unless I had to take the engine apart already. It might be a 1mpg difference at best and nearly impossible to measure.

The xfi trans is better than the base model but swapping it is up to the person doing the work. If they have done things like that before swapping it is not hard and I say go for it. But if they don't plan on swapping again if they ever find a 3.52 I would say wait a bit. But if they use the xfi trans and 13 inch tires they will get a pretty close ratio to 3.52 with 12 inch tires so that might also be an option.

As far as reliability, the engines don't seem to have any issues that make them have problems earlier than normal. At most they might need rings replaced a bit earlier than the base model but really I don't think it would matter much at all. Mine has 150,000 miles on it now and it seems to be about the same as any other 150k 3 cyl. It looks like pretty much all of them could use rings at around 175,000 miles to bump the compression back up. Some might make it longer and some less but that seems to be what I would expect out of a set of rings on any of the G10 engines.

If I saw an xfi drivetrain available I would probably grab it even if I didn't plan on swapping it right then. It would be good to rebuild everything and have it ready to just swap the entire drivetrain over some weekend, or if nothing else just to have the spare parts and the xfi cam.

That's a good point about rebuilding, Coyote. Plus you could get the computer as well if you take that route.

Is it worth getting the computer from an XFi (it's a 1992 in case that matters)? I've read somewhere that the difference between the XFi and the base Metro computers is minimal, but I might just be imagining that. Is the 1992 XFi computer a direct plug-in replacement for the base 1995 (airbags and all)?

Thanks.

Sorry, I don't know the answer to that one (XFi computer into a 95).

As long as the distributors are both electronic they should swap without any problems. I am not sure of what year they went from mechanical advance to electronic advance but that is pretty much the only difference in them.

Hmm, I don't know about the distributor. That's one of the things missing from the wrecking yard car. But, supposing the 92 XFi and the 95 base both have electronic advance distributors, it it worth the cost of replacing the computer? That is, I'm looking at buying an XFi camshaft from Delta Camshafts on the other side of the mountains (in Tacoma) and I estimate that it'll take ~11000 miles of driving to pay for itself (gas at $2/gal). So, is spending $75, or whatever the wrecking yard folks want, going to be justified? That is, if it's only a 1% increase, that would be similar to getting the XFi pistons - of course, swapping computers is a whole lot less work than swapping pistons/rings.

Does anyone have data on the actually difference in fuel economy between the XFi and base computers?

It was just one of several differences. I don't think anyone has quantified any of those things because it's nearly impossible to do a proper A-B-A comparison:

- lighter curb weight (1621 vs 1650 lbs for the LSi)
- no passenger side mirror (OK, that one's easier to estimate)
- different engine computer
- different cam shaft & sprocket
- different piston design (2 vs 3 rings)
- taller final drive
- 49 hp / 58 lbs-ft vs 55 / 58

I found a web site forum (View topic - 1992 GEO METRO Convertable to XFI Status • 3Cylinders.com) with reference to using the XFi computer in a base Metro. Assuming the information is correct, it would seem that the computer by itself will improve economy and is therefore worth getting.

Now on to transaxles again... What's the drivability like with a 3.52 transaxle with 13" wheels? I've read that some people are fine with it being dog slow, but some people opt to go with 12" wheels. Is it comparable to anything else on the road or that I've driven (the small cars I've driven are: '79 Mazda GLC, '80 VW diesel Rabbit, '83 Nissan Sentra, early '80s Plymouth Horizon automatic, early '90s Geo Metro automatic, '95 Geo Metro)? The reason I ask is that I found a 3.52 transaxle at a local wrecking yard but it's $125 more than the XFi transaxle.

Does anyone know the economy difference between an XFi with 13" wheels and a 3.52 with 13" wheels? Would it be worth an extra $125 or should that money be saved and when my tires wear out (which may be a while since they're new), go to 14" rims and get close to the same effect?

Also, would I possibly be hurting my economy by going to a 3.52 when one considers that most of my longer distance driving is on long hills where I routinely have to downshift to 4th just to maintain 50-55 mph (the speed limit is 70 mph). I imagine that with a 3.52 I would probably have to downshift to 3rd (which would be lower than base 4th, right?), the end result being that I would be burning more fuel.

The only way to truly figure that out is to run the numbers of those cars using an RPM/tire size/gear ratio/final drive calculator, and compare engine power.

It'll be less than the 5.2% top gear steady state improvement I measured by going from stock to the 3.52 final drive. I don't know anyone else who has tried to systematically figure out the improvement from an XFi tranny swap, so the best you can do is estimate.

Only you can answer that - do the calcs based on how much you drive, how much you reasonably expect to improve fuel economy (you can only estimate), and what you think fuel is going to cost in the future.

Also keep in mind that when you go to taller tires, you'll be increasing ground clearance and frontal area, which have aero penalties.

Again, you can answer this definitively by using a calculator, eg:

Calulators from www.4Lo.com

And compare to what RPM you're currently using in 4th to get up those hills.