Is there any benifit to modifying the spark plug hole? When I look into the trailing spark plug hole especially, there is a hole only a few mm in diameter. This is not the best for flame propagation. I don't see it working that well at all.

I have heard of people drilling this hole out so that the spark would be more exposed to the combustion chamber, but there was a loss of power due to the loss of compression when the apex seal passes over it.

My idea was to make a slot, width wise, making the slot as thick as the holes diameter. Maybe 10mm wide x 2mm thick?? This will make the flame from the spark plug much more exposed to the combustion while still being able to keep compression when the apex seal passes over it. Good idea or not?

Could probably do the same with the leading hole as well. I dunno. what do you guys think?

 

Go and get some good books and read frist, this small hole size is for a reson, one most imported is to keep the plug from fowling on cold start ups thus you can start and the other plug if it fowls will self clean and start to fire. Dont contest me on this I've played with these plugs to see how they work.

 

Even making the spark plug hole into a slot like you suggest would have a lot more leakage... and that leakage is *really* important, because the fuel/air mixture is still burning as the apex seal passes over the trailing plug hole. Increasing the area in any way may help flame propagation, but it will hurt torque.

The R26B added a third plug, as we all know. The burn efficiency was higher, so economy and whatnot ended up increasing something like 3-4%, but because of the leakage it didn't end up making any more torque. And this is with an additional hole the size of the trailing plug; increasing the size farther would have hurt power even more.

Tradeoffs.

 

You're thinking with pistons on the brain. You know that a piston engine needs as much spark as it can get for every plug. A rotary only needs attention paid to the leading plugs. The trailing are just there to clean up emissions, and as gambone said, to keep the engine going until the leading plugs can self-clean. They don't really add any power to the engine.

You can try an experiment before and after you upgrade your leading to direct fire. Hook the trailing up to a switch that you can access while driving. Turn trailing on and off under all sorts of conditions and feel how much power trailing actually adds to the engine. I've gotta tell you with DLIDFIS, I couldn't tell a difference because the extra leading spark took care of the trailing edge of of the rotor quite handily.

 

Mazda has already tried that, and their findings show the loss of compression from a larger trailing spark plug hole does not increase power from the unshrouded spark.  The engine actually LOSS power from the drop in compression.


-Ted

 

Die grind a tranverse ellipse, same height as hole, 2 - 3mm deep at hole and tapering off to nothing 8 - 10mm away from hole centre. So you will have an ellipse 16 - 20mm wide. Sorry I don't know how to post pics or I would show you. 5hp increase(engine dyno).

 

Totally fill the trailing hole and run three sparks per rotor face on the leading plug. 0, 90 and 180. Huh, huh?

 

Re-engineer an MSD to spark over 90 degrees of engine rotation. Hoo boy, who needs single sparks when you have a 90 degree long bolt of lightning?

Might be hard on plug life, and there might be hellacious RF noise. (What am i saying, might?)


Trailing was good for 10hp on a 110hp engine. Whether that is 10hp outright or ~10% is up for debate.

 

Detonate that and you just punched a larger hole...


-Ted

 

I learned the hard way.

Why not experiment with the tralining hole size ?So i did it,and opened it up.

Not enough compression ,and the huge overlap resulted in a no start.Only way it started was by run starting it.Starter couldnt turn it fast enough.

So i would advise against doing anything to the hole.

I had to throw away some nice rotorhousings because of my stupidity.

Karis

 

2 - 3mm at deepest point for the above reason amoung others.

 

you didn't lose that much comperssion not to be able to start unless you had a poor motor to start with. most likly some of that metal shaveing got in and under a apex