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Technical & Safety: Spark Plugs, Trouble with CATs, Installing Late Gauges in Early 911s, Buying New Tires

Pelican Technical Article:

Technical & Safety: Spark Plugs, Trouble with CATs, Installing Late Gauges in Early 911s, Buying New Tires

Lee Rice


0 hours0 hrs





Applicable Models:

Porsche 911 (1965-89)
Porsche 912 (1965-69)

Parts Required:


Performance Gain:

General tips and knowledge on spark plugs, catalytic converters and tires for your classic 911.

Complementary Modification:

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.

     In the near future, I've been told that we may not see the large inventory and range of spark plugs in our favorite auto parts store anymore, as the new generation of plugs will be reduced to only a mere dozen or so types. It seems these new plugs have such a wide range, that one spark plug will work perfectly in dozens of different engine types.

Trouble with CATs

     I got involved with an interesting problem this summer. The owner complained of a rather sudden loss of power with his 911SC. The owner had the engine worked on elsewhere and there were lots of new parts installed. Nothing really helped the problem. I started with the basics: ignition timing, coil output, ignition cable & connector condition and resistance, fuel pressures and fuel flow quantity, mixture sensitivity. etc. All was perfect. Now troubleshooting the fun stuff: EGR valve, Aux. air regulator, friction drag (Alternalor), fan, air pump. Nothing there. However during the EGR check I did disconnect the exhaust line as the exhaust header that supplies hot exhaust to the EGR itself.  This line was removed and with the engine running it positively removes a source of power robbing exhaust gas from entering the induction system. Well that didn't help anything but that open line certainly shot a lot of exhaust out. In fact it made quite a blast under the car.  I also noticed that when the car was started the engine caught right away and seemed very healthy except when loaded down and labored.

     I got a tip that the early catalytic convener cars have had problems with the 'CAT' coming apart. The honeycomb material incIting and breaking apart and restricting the exhaust flow. I removed the 'CAT' and cranked it over: Blat. Roar !! No hesitation.  No lagging. Just like a little RSR. It ripped around the block a few times just to make sure. A good cat was installed and this SC is as sharp as a tack.

     The CAT had big pieces broken inside and the honeycomb material was melted so thanks to Allen Faraballah I came out looking good. Remember, a good engine should have a good blast from the exhaust pipe.

Installing Later Instruments in an Early 911

     The early 911 and 356's secured their instruments to the dash panel with 'U' brackets and hand tightened screw nuts. This was an excellent method until the area behind the dash was all filled up with ducts and other components. The factory started installing instruments from the front in 1969 as access was impossible without removing the whole ventilation system. You wouldn't want to do that! The '69 cars had a rubber sleeve that slides over the instruments and then the item would slip nicely into the dash.

     For the early cars there have been all kinds of methods used to install the later instruments. Mostly duct tape wrapped around the instrument until the right fit could be made. The problem is the duct tape does not always hold the instrument flush with the dash and removal to replace a bulb becomes a mess when the tape rolls up and the instrument is half in and half out of the dash. Frustration!

     Relief is on the way. VELCRO kits with a roll of black fuzzy self sticking velcro. I use the 1/2 inch stuff cut into small . about 2 inch pieces. Place the velco on the instrument about 1/8 inch from the outer ring. You should trial fit the instrument without the wires connected to get the fit right. If the fit is too tight trim off some of the velcro and if it isn't snug enough add some more.

     This idea came to me while browsing in a hardware store. I've been wondering why on earth it took so long to finally solve the problem. I have been using this method since last winter with great results and it is much easier than anything I have tried in the past.

Trouble with Buying New Tires

     After a great Tire Tech last fall I would like to remind all serious Porsche owners to recall the words of George Lugo from Yokohama Tire Company concerning being a good customer by knowing and reading tire data of the tires that are going to be installed on your car before they are installed on your car.

     I have a good friend who ordered some new Yokohamas for his RUF car and became alarmed at what was attempted to be installed on his new RUF 8 & 10 x 17" wheels.  I am impressed that this wise customer took his curiosity a step further and stopped the installation because something didn't look right while the tires laid out before him in this San Pedro tire store

     To save you a long story, he had ordered four new Yokohama tires with the rim protector on the side wall.  What he got was hard 10 believe.  First the next day delivery took two weeks to arrive. Then the two front tires did not have the rim protectors and the tires themselves looked old. The rear tires looked old also so he took them out in the sunlight for a good look. He saw that the paint rings that encircled the outside diameter were nearly gone. The rubber flashing and whiskers were all gone from the tread and most of the sidewall. The sidewalls had ozone cracking and there were two small nails in the tread from use. To cap it all off someone had stuck new tire stickers on the tread!

     After his blood pressure receded my good friend regained his composure and asked for an interpretation of the date of manufacture code. What was to be installed was over four years old. There was an admittance of some display use and maybe a prior mounting. An offer to knock off $30 from each tire was as made. My friend was on his way to another --- any other tire store.  A day later this tire store wanted the prospective customer to pay for shipping the tires to the San Pedro store. That did not happen.

     This RUF owner is now rolling on a real NEW set of Toyos and has exactly what he needed.

Lesson:Just because it looks new and is round and shinny, black and smells  like a new tire, it does not mean it is one.

     You are the person with the wallet full of hard earned money, so take the time.  Ask how is the tire you are buying rated for wear, wert & dry traction?  Ask the sales person how you can locate and understand the date of manufacture.

     I always go to the store and ask  for a copy of the data sheet for the specific tire I want.  These are very helpful when determining the real WIDTH and diameter of the installed tire, espeically if you are upgrading to a new wheel size.  A 225 45 x 16 of one manufacturer is very different in actual size than another manufacturer'st tire.  After you pay for the special order and install them on your wheels, it is too late to return them.

     Ask the representative tire retailer how you can interpret the data codes.  If they do not know how to or show no interest in helping, go somewhere else.

     Lastly, the haunting thing that Yokohama's Georgre Lugo reminded us of is that a brand new high performance tire that has been stored too long will never perform well and may be unsafe.  Tires are life limited as the rubber ages and deteriorates with time.

     My good friend with the RUF car had a 930 with tires that looked new, but were over nine years old.  His airline job and family took most of his time, so the tires aged-out before they wore-out.  One afternoon while acceleratirng past 60 mph on I-10, the left rear tire exploded.  Big Time.  The driver thought the car would flip as he fought to control it.  When he got off the freeway, he found the tire in shreads.  He eventually discovered all four tires were weather cracked through the sidewall and showed signs of tread separation.   His concerns should be a warning to all of us.

Lee Rice writes the monthly Technical & Safety column for the Orange Coast PCA(zone 8) Newsletter.  He has generously allowed Pelican Parts to republish these articles here for the benefit of everyone who visits the site.

Comments and Suggestions:
Quentin Comments: I just bought a 1978 911SC and had a similar experience. The car had nice high performance Pirelli tires all around that looked brand new from the bits of extra rubber still hanging off. The problem was that these tires were cracked all around the sidewall and between the tread. The problem was quite obvious. Examining the date code, the tires were 13 years old! I rushed drove very slowly straight to a reputable tire shop.
August 3, 2009
  Followup from the Pelican Staff: Whoa, glad you didn't have an issue. - Nick at Pelican Parts  

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