On my old Volvo 245 (LH 2.2 system) the spark plug gaps were set at 0.028 inches. I figured that Volvo used a weaker coil than I was accustomed to. Most engines that I had experience with used a gap somewhere between 0.035 and 0.050 inches, unless the engine was supercharged, then you decreased the gap so that the increased cylinder pressure did not blow the spark out. My GMC blown Big block Chryslers and Chevys often use a gap as tight as 0.025 for this reason.

Now with this 2.4 normally aspirated engine in the V70, Volvo still calls for a gap of 0.028 inches. Are our coils a tad on the weak side or what? Any thoughts on this?
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Obama, One and Done!

For those of you who don't like the idea of spark blow-out, see

http://www.superchargersonline.com/index.php?main_page=page&id=27

Unfortunately they do not really explain how this happens.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks

Larger plug gaps - with a stronger coil and a resulting larger spark probably were needed to fire a wide range of fuel mixtures resulting from chokes or other enriching systems used for cold engines - did these engines rev up when started?

With proper mixture and ignition computers and better designed combustion chambers perhaps a smaller spark is plenty.

All the bricks that I have owned ran fine, and their plugs looked great when tune-up time came.

BTW I do not think that you can blow a spark out - higher levels of fuel and air in the cylinders may have made the smaller spark adequate.

The above is just my thoughts on the topic - I would love to read anyone's else's thoughts.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks

Has anyone experimented with plug gaps?
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Obama, One and Done!

How would you measure small changes in power or mileage?

Volvo probably could and did. Besides, their goal was an engine that ran well on that gap.

Besides, Volvo, like the old Beetle used LONG runs for many of their parts - for instance, the power seat controls in my 2012 look just like those in our "95 854 base.

I don't know, but perhaps they are still using the same plugs as in the 850.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks

30,000 miles is not a long time spark plug. Most modern engines require a plug change every 100,000 miles.
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Obama, One and Done!

Click and Clack on NPR say - If you only touch your plugs after 100K - you will NEVER change them, you won't be able to get them out !!!

They recommend that every 2 years having a mechanic pull them out, inspect them and if they are OK, reinstall them.

Keep in mind that some Volvo drivers are old ladies that need frequent checks to keep their cars safe.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks

30k spark plugs change? Are we talking about 240's here? The new Volvo's (such as the 2007's and 08's) scheduled replacement is much higher. Plus there is nothing to change except the plugs.

Personally, I've found that Volvo schedules the tune-up parts replacement way early. For example, the wires on 850's can outlast the car. The rotor, cap and plugs all last much longer than scheduled. I'm about to tune-up my car just because I don't know when it was last done, not because it needs. Even on my 240 I found that the tune-up parts lasted much longer than 30k.

My owner's manual calls for plug changes at 30K. 2001 V70 2.4 NA engine.
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Obama, One and Done!

The 2.3 - 2.5 5 cyl engines are not like big bore American iron, with coffee cans for pistons. The plug gap is designed for a very small compressed space and all of the fuel burns. No need for a hand granade if all that is needed is a spark.

The ignition coils are hardly weak. Just grab one with your fingers and turn the engine over!!

No, sparks never 'blow out', unless you visit a shyster NJ mechanic.
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My name is Klaus and I am a V♂lv♂holic

Klaus - As you can see, I was very skeptical about loss of ignition under boost, Perhaps blow out is not a good term, but two supercharger sites and two Mustang sites told very similar stories about spark problems under boost. Usually starting at 10 puonds of boost and 3000 RPM.

Using colder plugs and smaller gaps were mentioned many times.

Actually, I remember reading about the phenomenon in the 60s, but I don't remember which magazine(s) it was in - as a teen I did read Road & Track, Sports Car Graphic, Hot Rod, and Mechanics Illustrated off and on.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks

James, when you mention the RPM range and being under boost, I'd speculate that you are talking about exhaust driven superchargers (Turbos). I'm referring to a crankshaft driven high displacement Rootes type supercharger. These produce boost at idle. I've owned several, and they actually do require a cold plug, low compression, and a small gap. Depending on the amount of cylinder pressure, this can require plug gaps down to 0.020 inches. These superchargers can eat up to 30% of the total horsepower produced by the engine. Some of them use more horsepower than your normally aspirated engine produces.
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Obama, One and Done!

Sparks don't blow out? You have obviously never tried running a big block with something on the order of a GMC 8/71 huffer running 10% overdrive. Yes, you can actually cause the spark to die with excessive cylinder pressure. If the spark gap is too wide, the spark will not bridge the distance on these engines.
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Obama, One and Done!