The spark plugs in my K6 have been there for years and I decided to replace them. The OEM plug was the NGK CR9E or Denso U27ESR-N. A simple upgrade would be an iridium plug like the CR9EIX or IU27. I like Denso's .4 mm center electrode, which provides less quenching and allows a bigger gap. However I've been aware of the IU27D, which projects further into the combustion chamber and should be better yet. It additionally has an inconel ground electrode and I'm a sucker for exotic materials. It and the NGK CR9EIA-9 were the OEM plugs on the K7-up 1000 and were also used on some YZF-R1's. Yet the Denso plug is impossible to find in the US - even with the Suzuki pn. I contacted Denso USA and they said that they've never imported them. Go figure. However they're available from overseas sellers, notably in the UK. So I bought some from gsparkplug.com and will shortly be installing them.
The Denso specs indicate that the IU27D extends 4 mm into the combustion center. That's much further than the OEM K6 plugs, though when asked, Denso wouldn't provide me with the specs of the common U27ESR-N (thanks again Denso USA!). It was enough that I was worried about the ground electrode to piston clearance, so I built a tool to measure it. It's shown here and you can see the clearance, 7.95 mm. That should be plenty.
Here's a comparison of the IU27D, CR9EIA-9, OEM U27ESR-N and the IU27. The IU27, the standard iridium replacement, is similar to the U27ESR-N except for the smaller iridium electrode. The CR9EIA-9 extends further into the combustion chamber and the IU27D extends even further. That puts the spark significantly closer to the center of the compressed charge.
I don't expect a big horsepower increase but, if nothing else, they ought to improve my mileage.
The Denso specs indicate that the IU27D extends 4 mm into the combustion center. That's much further than the OEM K6 plugs, though when asked, Denso wouldn't provide me with the specs of the common U27ESR-N (thanks again Denso USA!). It was enough that I was worried about the ground electrode to piston clearance, so I built a tool to measure it. It's shown here and you can see the clearance, 7.95 mm. That should be plenty.
Here's a comparison of the IU27D, CR9EIA-9, OEM U27ESR-N and the IU27. The IU27, the standard iridium replacement, is similar to the U27ESR-N except for the smaller iridium electrode. The CR9EIA-9 extends further into the combustion chamber and the IU27D extends even further. That puts the spark significantly closer to the center of the compressed charge.
I don't expect a big horsepower increase but, if nothing else, they ought to improve my mileage.
