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Old 02-09-2009, 03:09 PM   #1 (permalink)
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,376

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.07 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 50.04 mpg (US)
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Dumb Idea of the Day(TM)?: removing a compression ring to mimic the XFi 1-ring piston

Whenever someone asks if it's worth swapping in the XFi 1-ring (compression ring) pistons in place of the garden variety 2-ring style, the opinion seems to be: probably not worth (it in terms of fuel economy gains), unless you're taking the motor apart anyway to do something else.

The implication is that the gains are probably pretty insignificant.

Then Peter7307 posted some interesting figures about the relative amount of friction from bearings, pistons & valvetrain for a Mercedes 2.0L gas engine operating at 2500 RPM and medium load (in the thread about valve spring strength as a possible efficiency mod).

Total engine friction losses were estimated at 1.5 kW:
  • 42% - piston assembly contributing
  • 39% - bearings
  • 19% - valve train
(Source: Engine friction lubricant sensitivities: A comparison of modern diesel and gasoline engines)

(Anybody know approx how much power a 2.0L gas engine would be making in those conditions?)

Anyway, the relative amount of piston drag got me thinking about the XFi pistons again, and thus the Dumb Idea of the Day(?) TM:

Would removing the bottom compression ring be feasible for non-XFi owners?

Here's the XFi piston. Anyone got a pic of a regular piston to compare to it?

Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown

has launched a forum for the efficient new Mitsubishi Mirage - fuel efficiency info for Geo Metro owners - electric car conversion on a beer budget
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