Rather than welding the multiple ground electrodes onto a steel shell, the entire outer shell and ground electrodes on racing plugs are machined from a single piece of steel. That is really the only difference besides them being hand made. I am running W3CS plugs now with no fouling even idling at 12.5 AFR. Dark dry brown ceramic insulators.

F= 14mm X 1.25 pitch thread and a 16mm hex
2= heat range
C= Reach 19mm
S= Silver

W=14mm X 1.25 pitch thread and 21mm hex
3= heat range
C= Reach 19mm
S= Silver

Thanks GJF. Should the electrode and everything else at the top of the plug be brown too?
Do you run the w3's at the track? What kind of HP are they supporting?

I prefer the insulator to be mocha brown and the strap should see a slight dis-coloration at the end to the bend and then stay consistant to the base of the plug. Some may like it cleaner than that but I am safe and I like the cruise to be in the high 13's and on boost in the extreme low 12's. On my car I have a EFI 3.4 with twin Garretts, big valves and ported heads running a little over 770HP @1.5 and typically run a hair over 650HP @ 1 bar.

Holy Mother Of God! :eek:

Thanks. I'm with you. Run a bit richer and keep it safe.

Here is a link to the reference data provided by GJF:
http://www.boschautoparts.com/NR/rdonlyres/C77B3446-232B-4AEC-AFA9-AD05F2A0A2AD/0/DesignationCodes.pdf

As he mentioned, his AFRs are spot on and his plug heat range is perfect for his application. Your application is different and the plug characteristics will not be the same so the comparison is for information only.

Your mechanic has recommended 7's for street. I think that is a good start.

You mentioned "track". What does this mean? If you are speaking about autocross, I would stay with 7's. If you are talking the 24 hrs of Le Mans, then 9's are appropriate.

BTW, Spuggy was right about the history of Porsche turbo plugs. They spec'd Bosch WR3DP0 for the 930. It is an ice cold plug. The thought was that it is better to use a top grade cold plug than a lesser grade warm plug because, after all, we are just silly American drivers.

For the 964 turbo introduction in 1991, they spec'd the Bosch WR6DP0. This is the plug that should have been in the 930. It is expensive, but it will not foul except in the worst conditions and it will outlast standard plugs in the turbo application.

As you can see the WR6DP0 breaks down as:
W= 14mm X 1.25 thread pitch and a 21mm hex
R= Resistor type
6= Mid range in the heat scale
D= 19mm reach and 3mm tip projection
P= Platinum electrode and ground
0= No deviations from original design

Thanks,
Mark

If the plug is sparking, it's not fouled (although it might be dirty). If it's fouled, there's no flame path to clean it, because the motor isn't running on that cylinder.

Raising the temperature of the flame path can perhaps clean a plug that's borderline dirty and going to get fouled if you don't do something with it.

But that's a plug that's too cold and has no tolerance for running out of the temperature range.

Whilst I'd love to tell you that my daily driver gets wound up at full throttle to redline in at least 2 gears every time I take it out, that would just be a fantasy.

Traffic and short (15-20 miles) journeys with a maximum speed limit of 35 tend to preclude winding out 930's.

And weather. With 255/40/17's out back, I've noticed that damp conditions make abrupt throttle opening quite pointless. So now I just drive like there's a brown paper bag full of doggy-do on the throttle pedal in the wet.

I will tell you that I've driven the car in (re-)freezing slush, and on mornings where I had to use an ice chisel on the windshield to get the frost off before de-icing the door locks and using the demister to the point where I could see through it before driving off.

Car had no thermotime switch connected (and thus no CSV operation) during this time, but always started well, and, despite sometimes months of being driven with a healthy amount of respect (read: fear) for the lack of traction available, has never fouled a factory W3.

In 30 years of motoring, I've never changed the heat range of a set of plugs because ambient temps changed. The combustion temperature is kind of fixed by physics, in my view. YMMV.

Higher Compression Ratios/Forced Induction
will elevate spark plug tip and in-cylinder temperatures!

Compression can be increased by performing any one of the following modifications:

a) reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, milling heads, etc.)
b) adding forced induction (Nitrous, Turbo charging or Supercharging)
c) camshaft change

As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage!


Advancing Ignition Timing

Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C


Engine Speed and Load

Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed


Ambient Air Temperature

As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures.

This creates higher cylinder pressures/temperatures and causes an increase in the spark plug's tip temperature. So, fuel delivery should be increased.

As temperature increases, air density decreases, as does intake volume, and fuel delivery should be decreased


Humidity

As humidity increases, air intake volume decreases

Result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power.

Air/fuel mixture should be leaner, depending upon ambient temperature.


Barometric Pressure/Altitude
Also affects the spark plug's tip temperature
The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature de-creases, so does the plug tip temperature

Many mechanics attempt to "chase" tuning by changing spark plug heat ranges

The real answer is to adjust jetting or air/fuel mixtures in an effort to put more air back into the engine

But to add to this it is also recommended to use the manufactures base line spark plug. From there for every 100HP over stock it is recommended to change 1 heat range. It all depends on the particular engine combination. I think if you have a factory car with modifications the spark plugs used would be close to the factory recommended. But when you create a engine with drastic performance modifications that is creating twice or even three times the original power output. The requirements will change for that combination.

Hi Doug,

Great thread about plugs for turbo engines. I think the biggest problem here is lugging this engine. I believe a slightly hotter plug would only help in this particular situation.

I wish the car was still here in NY.

Bill

I think you have to be careful when you check the plugs. If you just dawdled over to your mechanics(or house) in low speed traffic in a bogged down rich running turbo car, I think they will always look like crap. Try checking them after the normal spirited driving that you probably usually do. I bet if you pulled over after a nice highway run, they would look much better and much of the crud would be burned off???

Thanks gang. This has been the most informative plug thread I've seen. I'll post results soon.

ressurecting an awesome info-packed thread.

Here's some more info:

On my supercharged 3.2 race car running 11 lbs, twin-plug, 98RON and EFI I have been fouling plugs. We did quite a lot of troubleshooting on the car today for a non-starting issue and it was indeed fouled plugs.

I have NGK9EIX on the tops and NGK8EIX on the bottoms. Both fouled.

I am replaceing these with NGKBRES tomorrow (hotter on the tops and same at bottoms but both sets standard-type rather than Iridium) and hope to overcome the fouling issue. Will tell more tomorrow.

Subscribing

Japanese plugs know when they are in a German car, they get uncomfortable. They start talking to each other whispering from #4 to #5 "Hey how cold are you?" And then #1 chimes in from the other side "Man it's fricken' cold in here, let's foul out and get outa here!"

Fouling is the carbon trail from the tip, down the insulator, to the base where the spark is grounded. Wire brushing makes the plugs worse. The only thing I found to fix some of these plugs is sandblasting. But it damages the soft platinum, so there you go.

Put in some Bosch plugs, I recommend WR6DP0, and you should have no more fouling problems. There IS something about that platinum stuff.

Unless your AFRs are out to lunch this should help. (You didn't say what your AFRs were.)

Good Luck,
Mark

What about ignition? Would a weak ignition cause fouling problems as well?

John, what ignition system are you running?

We popped an oscilliscope on the coil grounds, the coil is definately trying to fire but actual spark is intermittent. We then pulled each lead individually and verified each of the 12 leads will fire a clean, new plug.

I am running 2x Accel EDIS-6 coils (new) by a pair of Haltech triple-channel ignitors. Driven by Adaptronic ECU.

John:

I only have experience with NGK's and can tell you this: NGK 9:s are really cold "snowmobile" plugs which are 99% overkill on the street and will foul quickly. I would start with 7:s and maybe go up to 8:s if driven on the track. (Don't mix up NGK and Bosch numbers, they aren't compatible).

I haven't experience any drastic improvements with rare-metal plugs over ordinary ones, so I still run with 2$ NGK's and they work fine. There is probably difference in longevity though.
I switched from 2$ NGK's to 15$ platinum Bosch's on my Audi S4 and there wasn't any discernable difference.

Also, wastefire EDIS coils aren't powerful and will be sensitive to plug gap.