Interesting Spark Plug Article

[WydRyd]

Found this in the Tech Article section

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Spark Plugs

I have been using three electrode Bosch plugs for years. They are specified on the 911 3.6 liter Carrera and 911 Turbo. What is really surprising, is the increase to a warmer heat range. The early 911S and all Turbos used a ridiculous cold and expensive W3DPO spark plug. This little plug costs about $16.00 each and I have never removed one that wasn’t dark and sooty (indicating too rich or too cold of a plug!) Tuners of these expensive Turbo and early 911S cars were, and are, reluctant to vary from the factory specifications. This is a problem. as Porsche can not respecify the older cars without recertifying the whole engine emission certification all over again. Porsche is not likely to do this.

What is interesting though, is what has happened to the 911 Turbos. The trend became to increase the power output while meeting tighter emission standards. The compression ratios were increased to 7.5:1(from 7.0:1) and even without knock sensing using a much hotter spark plug, the FR6LDC. This is a copper core, double ground electrode mini spark plug. The fact that the Porsche factory specifies this very warm spark plug for the awesome 3.6 Turbo is not so difficult to understand. I have talked to Bosch, BERU, and NGK about their new applications for old W3DPO spark plugs, and have been told that those were really too cold — even for a street Turbo. The factory originally specified them in the same way they specified spark plugs for the special 356 Carrera 4 Cam, 911 S, 2.7RS and other higher performance "street" Porsches. The factory expected these owner drivers to run the daylights out of their Porsches and they did not want the engines to "ping" and detonate from using non-German gasoline. So they specified cold spark plugs. It worked. The 911 Turbo came along at first as a batch of 500 only, to be sold originally for "Friends of the Factory." They got the same treatment as the earlier specials. Nothing changed until 1992.

The 3.6 Carrera has used Bosch FR6DTC triple electrode since 1989 and these run great. I started using these 3.6 spec spark plugs in just about all 911’s and have had excellent results with them, especially in my own hard run Turbo motor. I will keep my pile of old "W3DPO", but only for competition events.

[Candelaria]

You can always try the W4DPO, a bit more hotter.,Candy.

[WydRyd]

Yeah, I already run the W4CS plugs and have been happy with them. I have a stack of new W3CS plugs which I'll try next, but I know they're too cold anyway. Got them at $2k ea, so it was a no brainer to stock up

[Randy Blaylock]

Can someone point me to a source for Bosch F4CS plugs please?

[WydRyd]

I think I'm going to give the FR5DTC triple electrode plugs a try in my street turbo for a while, once these W3CS plugs are completely fouled up (which won't take long by the looks of them). I suspect the FR5 will have a much longer lifespan than a 3 heat range plug in my car.

Also, considering the later model 3.6 twin turbo's run a FR6 range plug, the FR5's should perform admirably in my 3.3 EFI turbo

[mede8er]

Hey Merv...did you drop those FR5's in?????

[WydRyd]

Certainly have... been in there for a while now. Seem to be performing nicely for my daily street monster, even at 1.25bar. I'm going to pull a few of them this weekend just to gauge how well they are working by assessing their color.

If there are any signs of running too hot, I'll drop down to a 4 heat range. If they are still sooting too much, I may even go to a FR6LDC (993TT units).

[mede8er]

Well...I'm getting some whacked out cyl head temps...steady 500's...may be a faulty temp guage as my oil temps are below normal with the front mount cooler...if I verify the head temps with a seperate thermometer I'm checking the spark plugs next....A/F is not too lean as per my dash guage.....

[h20cooled7]

will this cheaper plug work in a 80 3.3l turbo?

[WydRyd]

Originally posted by h20cooled7
will this cheaper plug work in a 80 3.3l turbo?

Sure it would. Just keen an eye on them to make sure they aren't exhibiting any signs of running "too hot", but in my motor running 1.2bar of boost, they are working great.

My original post above suggests the author of the article was having great success even running FR6DTC's on his "hard run turbo motor", so the FR5's would be fine as they are a heat range colder than what he's running.

The later model twin turbo's such as 993TT's and 996TT's all run the FR6's

[patkeefe]

Let me drag this topic up again...
So, my SC turbo has been online for a week or so. I feel like the spark may be a bit weak. I have Clewett wires, and a stock 6 pin Bosch CDI. I installed a set of Bosch plain jane WR5 single electrode plugs ( a bit HOTTER than stock). Car runs good, but not as good as I think it should. I am running 5 PSI boost.

My plug colors are a greyish color, not very uniform. Not the chocolate brown I would prefer to see.I'll post some pics tonight. Being colorblind, and not recalling ever seeing this in a plug, I ask opinions.

Thanks!
Pat

[DonE]

Pull a couple of plug wires and check the resistance on the wires. I have Clewett wires, but the connectors got wet (possibly condensation) and rusted. On a couple of wires, the resistance tripled.

[patkeefe]

Thanks Don:
I had the same problem with my Clewetts. I had sent them back, and R Clewett gave me a new improved set.

I spoke to a mechanic ( the term mechanic does not nearly describe his skill and expertise), and I richened up my mixture a tad, and backed up the timing 5 degrees. I guess 930's have boost retard on the distributors? My distributor is stock SC.

I neglected to mention I also have water injection, which may explain the lean looking plugs. My AFR's are in the 12's, and I can get into the 10's on boost.

Pat