Denso sparkplugs

I noticed quite a few posts about driveability/starting issues. I've owned my XJ750 Seca from the beginning and lived through the leaded to unleaded to reformulated gas issues with non-adjustable carbs. One thing that helped mine a lot was using the old ND Hot-U(W22EPU) spark plugs and indexing them so the electrodes point generally toward the center of the cylinder. The theory with these was the U-grooved part of electrode can better fire a lean mixture with a stock ignition. They've worked well in my bike as the current ones have over 12K miles on them and despite being due for a change, it still runs reasonably well with no high-rpm miss.

The Hot-U's have been off the market for a number of years, but I recently saw an ad on TV for Denso Performace sparkplugs. I haven't been able to find any, but has anyone tried them or know if these are similar to the oldies?

 

Well - knowing what I know about electrical engineering, and spark plug design, most of these plugs have been marketing gimmicks.

V-Groove, U-Groove, split ground electrodes, multiple ground electrodes, etc.... these are all gimmicks. None actually provide any better spark performance.

The only things that will provide better and more reliable spark are:
A - higher voltages
B - finer & sharper electrode point

A is covered by replacing the stock coils with aftermarket units like Dyna's or Accel's.
B is tougher - platinum tips were a step forward and offered smaller and tougher electrode tips than the old copper or nickel. The current use of Iridium has allowed the smallest and strongest tips yet - 0.7mm

So without replacing the coils, from an electrical engineering standpoint, replacing with iridium plugs is your best bet.

Oh - and orienting/indexing the spark plugs is a myth.

 

Use Google to search for these key words "Denso Performance spark plugs" any you'll get lots of hits, including the manufacturer's Web site. Search for "Denso Performance sparkplugs" and you'll find lots of places that sell them.

Be forewarned, they are "iridium" plugs. That is supposed to equate to high performance, likely is simply marketing hype, and definitely means big $$$.

 

I would agree with Altus however, one other factor for a better spark is resistance. Different metals have a higher conductivity than others. Likewise, different alloys or combinations of metals have different resistances.

I'm not fully up to speed on which metals would perform best but iridium may have better conductive properties than steel. The same can be said about plug wires and caps and their respective conductivities. The less resistance, the more efficiently the spark can be transferred to the cylinder.

 

I'd have to agree and disagree about marketing hype. That's true to a large extent, especially claims about increased horsepower. However in the 70's and 80's when lean mixtures became the norm, auto makers increased the gap specification, sometimes doubling it in order for the spark to have a better chance of igniting some fuel vapor between the electrodes. In most cases they also increased the output of the ignition system to compensate and in that case different plug designs won't make any difference. I haven't tried any of the newer plugs, but with normal NGK'S the Seca's stock ignition won't fire gaps over .035" and I believe the tuneup spec is a very old-fashioned .028". I agree that changing the coils would be a better solution, but the ND plugs have worked well in my bike. I used to be lucky to get 2-3K miles out of a set of NGK's. Likewise indexing is an old drag racers trick that can make a marginal situation better, but is of limited value with modern 4 valve heads and high turbulence combustion chambers. I don't go as far as using copper washers, I just swap a set of plugs around to get a decent orientation.