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The NGK BCPR7ES-11 are apparently matched for the design of the car.

The "R" means the plug is a 'Resistor' plug, which is fundamental to limiting the current through the plug, relative to the applied voltage produced by the DI Pack! If resistor plugs are not used the DI pAck burns out. If wrong resistor plugs are used then the DI functionaility could be impaired.

The DI unit is a very clever device which not only fires the plugs as standard, but cleans the plugs after ignition off - AND - also measures which cylinder is on compression stroke in order to determine the firing order when the engine is first turned over before ignition takes place.

So stick with the specified NGK's!
 

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It turns out that NGK has both a part number and a stock number. Most of the places I called won't be able to find stock on their computer if you ask for the part
number - you need to ask for the stock number instead. The first digit in the NGK part number indicates the heat rating. Lower numbers are hotter, higher numbers are colder.

Without trying to describe the whole NGK part number system, part numbers break down as follows, from first letter/digit to last:

B - 14mm thread diameter
C - 5/8" hex size construction
K - 5/8" hex size construction, projected tip (ISO)
P - Projected insulator type
R - Resistor type
(heat range 2 through 11)
E - 19mm (3/4" )thread reach
P - Premium platinum
VX - High-performance platinum
Y - V-grooved center electrode (14mm only) 2.5mm insulator
A - Special Design

For plugs with a flat seat and gasket,NGK recommends torquing 14mm plugs to 18.0-25.3 lb-ft in cast iron heads and 18.0-21.6 lb-ft in aluminum heads. If you don't have a torque wrench they say to give it between 1/2 and 2/3 of a turn after finger tightness.
 

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I have always liked Bosch plugs so your info was very good for me. Out of curousity I looked in my manuals and my '94 9000 CSE manual states NGK BCPR 6ES. My '95 9000CS manual states NGK BCPR 7ES for the 4cyl US version and Bosch FR8 LDC for the V6. Does any one have any more insight as to the differences?
 

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Alix,

The only difference between the two plugs you mention is down to the electrode. 7's are a cooler plug than the 6's.

Main reasons for switching to these cooler plugs might be if you're running slightly higher boost on a Turbo model or if the compustion of fuel is somewhat more than in your first car you mentioned.

Sorry for the delay & hope this answers your question.
 

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NB: Some Torque Wrenches don't have settings 'low' enough to do a spark plug.

If the plug is new, and the gasket is uncompressed, tighten plug to finger tight, and then turn 1/2 to 3/4 of a turn more to compress copper gasket on plug. If retightening plug, screw down finger tight and then just a very slight turn of 5 - 10 degrees should be sufficient.

It's very hard to snap a plug as the hexagonal part which the plug socket sits on is made of metal. Much more likely to nacker the thread in the alloy head though if overtightened.
 
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