Ok I've been searching on the forum about running colder plugs for higher single turbo output with upgraded ignition. I already know about that but I just noticed that some members (Athiun and Mono4lamar) were saying to use the colder B10EGV in the leading and the hotter B9EGV in the trailing. But then I read on and I see Chuck Westbrook recommend using the colder plug in the trailing postion and hotter plug in the leading. What does everyone think? I know everyone mentioned is realiable. I'm bored at work so I decided to dig around.

 

Colder in the trailing first then in the leading. The colder plug land is shrouded (presumably to prevent fouling) therefore the area retains more heat than the leading. If you want evidence of this, take a peek at some used rotor housings, especially 3rd gen ones, and look for lateral cracks next to the trailing plug hole. That's from heat.

B

 

Small port for the trailing plug is there to help retain combustion pressure.

If you run 9's all around you will notice the ones in the trailing position will run a nice tan (hotter/cleaner) than the leading. This indicates that we should run trailing one heat-range cooler.
Barry

 

Being that the leading plugs perform the majority of the combustion, I've always ran the colder plugs in that spot.

 

Mazda reasoning...
1) Smaller trailing spark plug hole due to losing less compression, because the apex seal hits the trailing spark plug hole first versus the leading as Barry Bordes has already mentioned, and
2) colder trailing spark plug to supress pre-ignition, since the combustion charge does hit the trailing spark plug first when the rotor sweeps around.

All documented in SAE papers.


-Ted

 

ok that's what I was talking about. I also noticed Steve Kan as well as Rich recommend running the colder plug in the leading position. I guess it might be a preference thing. I am running a ignition amp and TII coil to the leading plugs. But I did notice that my trailing plugs which are non-amped seemed to be more worn then the leading plugs especially in front housing. so I might just try the egv10 for the leading and the egv9 for the trailing.

 

Heya,

Actually Steve recommended to run the 10's in the leading and 9's in the trailing for tuning; not just for me but for a few others. I switched them on the dyno.

From what I remember, his take was that since the opening for spark was much smaller you can use a 9 in that location because the heat dissipates easily from that location. Under high load the leading fires first and takes the brunt of the heat therefore a colder plug would dissipate heat faster from that area.

And since most people run 9's all around on 400 rwhp without problems, does it matters that much?

Maybe Steve can chime in here...

 

It's not a preference thing, guys. Why would the factory run a colder plug in the trailing from the get-go if it were both preferential and unnecessary? Ted's correct on the compression loss point but there's more to it. It's not preferential by any means.

B

 

ok I guess I worded it incorrectly, I guess it would be better worded as there are different theorys as where to use the colder plug.
I'm starting to lean towards using the b10EGV for both trailing and leading positions. Just going to have lean out the water temp. correction table on the PFC. There is some good info in this thread. thanks guys..!

 

Anyone else..?

 

Ted is right on.

The hole size is minimized to reduce gas leakage across apex seal. And trailing plug is colder due to potential for extreme engine damage if it preignites at that point.

Of course, this is 1970-1980 mazda research, so maybe things have changed a bit since then(although even their modern engines use the colder trailing). Could be why some tuners have found in some situations that other things are needed.

 

Simply use the plugs with the highest heat range number (coldest) you can find in all plug locations and IF you encounter fouling from lack of self cleaning in your vehicle as you intend to operate it switch to the next lower heat range number (hotter) until you have no fouling.

Any other way of determining spark plug heat range required is contrary to the whole system of spark plug heat ranges.

On a high performance turbo rotary with upgraded ignition I predict you will almost always end up with the coldest plug manufactured.

 

I have always ran 9's in the leading and 10.5's in the trailing when running 21 lbs boost on 110, anything over 25 lbs I ran 10.5's all the way around. Others over 700 whp on here are running 11.5's all way around.
It was explained the same reason as BDC and REted have said.
In fact, I have two brand new NGK racing 10.5 plugs for sale....30 bucks for BOTH. PM me. I also 4qts amsoil 20W50 series 2000 race oil for 20 bucks.