Spark plug modification
 

Hi team, I have been talking to a neighbour about general mods of rotary engines and he mentioned the modification of the spark plug mod to stop the chrome from splitting but I couldn't understand what he meant....... Anybody out ther have any info on how the mod is done????????

Re: Spark plug modification
 

what i think he means is taking off all the grounds on the spark plug except one, so it'll look like a normal spark plug. the older style rotary plugs had 4 distinct grounds that gapped the electrode instead of one like a 'normal' spark plug. supposedly when the plug fires, the spark will contact all grounds simultaneously. in theory cutting off 3 prongs would open up the spark plug like a normal one, so that the spark isn't shaded from the mixture. the plug on a rotary doesn't reach all the way into the combustion chamber so i think any performance gained from it would be negligible. if im correct, the plugs that the rotaries use were specifically designed for the engine. if using a single ground plug was beneficial, i think mazda would have put it as at least an option as a replacement for the OEM plugs. Thats just my opinion.

to answer your question, i would pick the best looking ground, and leave it be. bend all the others upwards, and either cut them off and/or file them down until they are flat. another reason why people might do this is because these plugs cant be gapped, but if you actually look at one it doesn't look like they were meant to be gapped like a normal plug. you could try it, but i don't think it'll do much.

Re: Spark plug modification
 

Mazda rotaries and aircraft engines share a problem. Controlling tip temperatures in their spark plugs. The range of temperatures these engines see is beyond the normal range available by just altering cone lengths and diameters. So both Mazda and aircraft plugs have rather
large multi ground shields to keep the combustion process off of the ceramic on the center electrode.

So the ground electrodes are also shields to limit over heating the plug. So the plug heat range can be hotter to keep cludge burned off of the ceramic at low speeds and still not melt the center electrode at high power settings.

Removing ground electrodes would defeat the shielding effect and the plug would over heat during the first high load, high RPM pass. Very bad MOJO.

For racing NGK 11.5 heat range is used. That is a retracted tip single side ground electrode plug style.
This is an ice cold plug and any plug that croses to that style and heat range works just fine in a rotary. The down side is of course, you must run a CD style ignition system to avoid fouling at low speed low load.

Lynn E. Hanover

Re: Spark plug modification
 

hmmmm, you learn something new everyday. definitely makes sense. good thing you answered Lynn, i didn't realize how potentially bad un shielding the ceramic could be.

Re: Spark plug modification
 

For more on spark plugs from me, Leon Promit (Australia)
and the Sky Ranch manual, a technical manual about airplane engines, go to:

http://www.knology.net/~rv7rotary/Sparkplugs.htm

Lynn E. Hanover

Re: Spark plug modification
 

I think a major cause of the housing split at the plug hole is not warming the engine up gradually/completely before hard pulls. Especially with forced induction. Dissimilar metals which expand at different rates, combined with restriction of the coolant passages in the housings around the plugs. If your worried about splitting housings, just warming your car up properly and especially avoiding boost until it's at operating temps will be way more effective than jacking-up a set of plugs.
Just a thought....if you have turbos, AI can also help to carry more heat out of the combustion chamber without having to disassemble the engine for coolant passage mods.

Re: Spark plug modification
 

thanks fellas for the info on that side of things, but i should have been more specific in my question, apologies.

to re-frase my question, what the old guy was trying to tell me had something to do with modifying the housing in or around the spark plug area... he used to do specifically to his pereferal ported 13b. id go ask him myself but hes about 80 years old and seems to sleep alot so its hard to catch up with him, top guy tho hes from greece and still has a 12a blow through turbo setup in his imaculate rx4... rather stolked having a neighbour that doesnt mind my rotary:)

Re: Spark plug modification
 

He's talking about modifying the internal coolant passages in the housing around the area of the spark plugs. A dremel is used to create grooves in the walls of the coolant passages. Just have to be careful not to weaken the walls of the housing too much. Doing so increases surface area exposed to the coolant. It also increases turbulence which increases time of contact between the coolant and housing. Never tried it myself...never felt the need. I think it's mostly for tracked cars, but it probably does help.