Reference threads:
Plug Change (see post #76)
http://www.smartcarofamerica.com/for...-ixuh22-24065/
Not listed for Smart yet, but from the above threads and specs off the Denso site, these are correct for the 451.
Why you want them:
http://www.globaldenso.com/en/produc.../features.html
Where to buy:
$11.99 each at
www.sparkplugs.com. For comparison, factory XU22HDR9s are $6.15 each.
Install:
Not the easiest plugs I've ever changed, but doable with a decent socket set. About a 30 minute job. Possibly not recommended for beginners.
Initial impressions:
As advertised. Quicker starts -- less cranking. Smoother idle. Definite power increase -- not huge but it's there -- at least a couple hp. Would compare it to how the car feels on a cool morning when air density is greater. Even sounds different, maybe slightly deeper tone.
Mpg:
Will report after a couple tankfulls. Could go either way, I've been putting my foot in it, newfound power is fun.
Negatives:
Not "long-life" plugs, ground electrode isn't exotic metal. 0.4mm electrode and u-goove optimize fuel ignition not plug lifespan. Long-life option is the SXU22HDR8 (also available at sparkplugs.com.)
Conclusion:
Improved driveability and a couple hp for about the same $$ as a drop-in air filter. IMO a no-brainer.