Volvo - LPG spark plugs

[volvobaggen]

I don´t think it will be expensive. The BP7ES are 1£ each on ebay, and what could go wrong with the carburetted Volvo 245?(If these plugs fit that is)

I have been trying to read up on this topic on different foras, and people seem to be divided on this topic, but my very much uninformed mind tells me less resistance means stronger spark, which is good for a rather weak old fashioned ignition system running on lpg. Modern cars have a very high energy ignition system, so no need for it there I guess.

[classicswede]

You have not read my post properly.

for a 240 the start of the plug number will always be BPR the the heat range number 5,6,7 etc and then E and then S at the end is the code for supressed.

[volvobaggen]

Thank you again for clearing this up, its very much appreciated.

The reason why I was asking is because I´m ordering a whole lot of plugs so I wanted to be absolutely sure I was ordering the best plugs. The NGK chart can be somewhat confusing when you are new to it.

[Pete_c20]

Originally Posted by volvobaggen

Bumping this thread.
Would there be any issues with using non-resistor spark plugs for older carburetted volvos without ECU´s? Instead of NGK BPR6ES using the BP6ES?
Theoretically this should give a better spark right?

I would guess that a non-resistor plug would give you a more intense spark as there is less resistance in the circuit, and for as long as the spark lasts, a higher peak current. I would also guess that the spark will last for less time as the coil energy is dissipated faster due to the higher peak current.
A possible downside I can think of is that the plugs are eaten away faster, but on the upside you might see a performance gain.

In a resistor based plug, at the point just before the initiation of the arc the voltage is high but current is zero, so the resistor plays no part. As the gas/air mix in the plug gap is breaks down due to the high voltage, an arc strikes. With more resistance in the circuit the peak arc current is lower for a particular voltage and this in turn will mean less damage (less erosion) to the metal surfaces where the arc starts and ends. Would it mean inferior burning? Maybe not as for the resistor to play a part you must already have an established arc. After that the resistor can/may play a part in limiting the damage caused by the arc to the plug itself. And plus they're known to suppress RFI better, again due to lower peak currents.

But, with all that craziness going on, in an explosive atmosphere, and so quickly, who knows what's going on there. I'd be very interested to see a comparison between resistor and non-resistor plugs.

I'd say plug type and operating temperature is much more critical. Plug temperature is a complex balance between heat coming in (energy in the arc, gas/air mix, revs) and heat being dissipated (materials used, geometry of the plug, gas/air mix, revs). For a given gas/air/pressure/voltage mix a hotter plug will arc more readily than a cold one. But if it's too hot then it could be arcing before its time. With plug choice, part of it is optimal operating temperature. An acquaintance used to race 2-strokes and they were plug crazy. The overall plug colour would tell them fuel mix, tip colour would tell them tip temperature.

I've often read threads where people are saying they don't like the Volvo triple prong plugs.
Well, doubt there will be be 3 arcs. I'd say they'd be one. I would expect a plug that would wear less if the sacrificial part of the plug is the triple prongs. The arc will wander from prong to prog as the plug wears. Maybe these plugs are inferior due to other factors rather than the fact they have 3 prongs? In my S40 I never had a problem with them for its first 70K miles. Since then I've used single prong LPG specific plugs as 99.99% of the time its on LPG. I haven't noticed difference between them.