Spark Plug indexing

[Creeper9]

Please excuse me if this is a dumb question, but I got to thinking about this and thought someone might know.

Way back when I used to race cars, we always used small copper washers on the spark plug to "index" it so that the open part of the electrode faced down in the cylinder (wedge type combustion chambers). It was a trick that was suggested in Hot Rod magazine back then that was supposed to ensure more complete burning of the charge. I can't really admit to being able to tell a difference, but it seemed logical.

What I'm wondering is, would there be any benefit to doing this on a bike? If so, do you think be able to notice it outside of a dyno, which way would be the best for electrode orientation?

I'm kind of thinking that it really doesn't matter on the bikes, since most (or is it all) are hemispherical chambers, but I was wanting a fresh opinion on the subject.

What do you think..?

-Kurt

 

[Rich Rohrich]

Modern four-stroke race engines with narrow valve included angles have combustion chambers that promote high degrees of mixture motion and leave the sparkplug eseentially unshrouded. Old style high compression wedge cylinder heads had shrouding and clearance issues to contend with which made indexing a necessity in many cases to keep the ground strap from being hammered.

I've never seen any properly controlled test results published that would lead me to believe indexing plugs provides any advantage in a modern engine and I've never personally been able to measure a difference on a modern fourstroke. The same held true for me in air cooled RD350s at the drag strip.

 

[Creeper9]

Rich,

I had never seen any real official test results or an SAE paper on the subject either. It was just one of those tip of the month type things in Hot Rod magazine. I don't even think they provided test results. I suppose I funded one of the editors buddies retirement? I got to thinking about it recently (usually a dangerous thing), and was wondering how it would apply to a modern off road motorcycle. I figured if anyone had tried it, it would be you.

-Thanks :thumb:

On another note, those RD 350's were (still are in my opinion) fun to blast around on weren't they? Do you remember the TZ 700 by chance? Quite the bike for the early 70's!

-Kurt
P.S. sorry for posting this in the wrong forum originally

 

[Rich Rohrich]

Originally posted by Creeper9
Rich,

I had never seen any real official test results or an SAE paper on the subject either. It was just one of those tip of the month type things in Hot Rod magazine. I don't even think they provided test results.

In a wedge chambered engine with a tall dome there might be some power advantage in specific indexing due to the rather bizzare path combustion has to take, but it always looked to be application specific.

Originally posted by Creeper9

On another note, those RD 350's were (still are in my opinion) fun to blast around on weren't they? Do you remember the TZ 700 by chance? Quite the bike for the early 70's!

I remember them well. I was even fortunate enough to take a quick blast down the street in front of Eric's old shop in Elk Grove on the TZ750 that piloted the first privateer to an AMA national win. One of our friends stopped by the shop on his way to Road America to do a little work and we had to TEST the engine before he loaded up and headed North ;) Yep that's my story officer and I'm sticking to it. :eek:

Originally posted by Creeper9
P.S. sorry for posting this in the wrong forum originally

Don't worry about it :thumb:

 

[cujet]

I run a turbo Miata with generally around 17PSI boost. The OEM ign coil is not really up to the task. So the use of NGK extended reach plugs (vs. stock) helps, but the mixture still won't ignite properly at high RPM under certain conditions. A switch to Bosch Platinum +4 plugs will work well and they last more that 20K miles before the problem returns.

So, I have guessed that the proper ign coil would solve the problem. However the +4 plugs (the best I have found for my app) seem to be able function well. Certain engines are sensitive to gap issues and that is probably a function of getting the spark to the mix. Maybe a +4 type of plug would work well in these engines.

Chris