I clipped the following from HONDA TUNING magazine:

It was brutally hot the day I arrived at the Kraftwerks dyno. The kind of hot that makes you wish you'd stayed at home, soaking in a tub filled with ice, eating a chocolate frosty. Not one to ever back down from a dyno session, Oscar braved the heat and got the dyno session started as soon as I arrived. I had installed the factory air box back in the car to get a baseline. Horsepower peaked around 102. Trading out the stock filter for the Takeda cold-air unit earned us a bit more peak horsepower, but more importantly, provided a nice useable kick in the midrange, where the car spends the majority of its time. This is far more important than a peak number when dealing with a street car.
The Spark Plug Theory
If anyone else had told me I might pick up a few horsepower with a different set of plugs, I would have probably laughed and moved on. But I've learned not to doubt Oscar Jackson very often, as he has a funny way of delivering on every claim he makes. Since changing the plugs on a GE was a first for him, as well as me, we started pulling parts out of the bay until we found the proper route.
With the new plugs installed, Oscar let the car get hot at idle. That's not a mistake, he let it get really hot. Instead of trying to cheat the dyno by running the car much cooler, or covering the intake manifold with cold towels, he prefers a real world test. He states "I could run the car right away, before it gets really hot and probably pull a better number, but what good is that? In the real world, your car gets hot, REALLY hot. Why not measure something realistic?" After a few pulls, the average number is 104.5 at peak. It might not sound like much, but think about the motor we're dealing with. His theory proves that for the price of a set of spark plugs, you can make as much power as an exhaust or an intake on your Fit.
Here is the full article: Project 2009 Honda Fit - Mugen Front Grill - Honda Tuning Magazine

 

Old news buddy.

 

Sorry if it's an overpost. I tried searching for iridium plugs and couldn't find any threads. It just seems like an inexpensive, must-do mod that I felt obligated to mention. Funny thing though.... Why wouldn't someone do this first, to see if the Extra HP is worth spending hundreds more (on exhaust/intake mods) for another 2-3 HP?

 

What are the plugs they suggest?

 

 

I put some in my car with the high boost kit and some other modifications.... I guess they do as they are said to but all of the stuff together is amazing.

 

been running that for the last year dude ....
gone through 3 sets already good sh***t for sure !

 

There are a few varying opinions about why the Denso IK22 spark plugs show a power gain on the dyno... 1. Because they are replacing old plugs with wear on them.... 2. The smaller electrode is less disruptive to air flow during the intake stroke.... 3. They are a lower heat range spark plug that allows for more heat dissipation from the combustion chamber allowing the ECU to respond by increasing the ignition timing advance without needing to increase the fuel to air ratio...... I have noticed that my engine runs 3 to 6 degrees cooler than before even though ambient temperatures are 16 degrees or more warmer and I have gone from 5PSI to 10PSI boost..... I believe the power increase is due to the effects of lower combustion chamber temperature allowing for more advance.... I spent a lot of time when I was younger tuning motorcycles for street and track and dialing in the most ignition advance and lean A/F ratios always meant using colder plugs and resulted in better performance when you got it right..... As small as the valves and combustion chambers are on the L15 engine I can also see where the tiny electrodes on these plugs could be beneficial to flow characteristics.

 

Have these shown a performance increase in the lower HP 07-08 Fit?

 

About a year and a half ago Oscar Jackson Sr. dyno tested a few GD3s before and after changing from the stock plugs on stock and supercharged Fits.... Fit Freak member Koi was one of the guys that had an increase in power on his car.

 

That's good to know, thanks. I've been looking at prices. They seem to average around $50 for a set of IK20s.