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Re: Plug gap once more
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 19 Mar 2002 08:45:03 Share Post by Email
In Reply to: Plug gap once more, Tapani, Tue, 19 Mar 2002 00:33:18
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I agree with Vikingman-
The Trionic system does not directly measure knock. Older systems had a knock sensor that actually 'listened' for knock acoustically. The Trionic 'sniffs' the combustion results. Full combustion produces one set of byproducts - knock or pre-ignition is the sign of explosion, not burning, and produces a different set of byproducts, with a different set of characteristics, notably conductivity. The nice thing about the Trionic system, in addition to having one less dedicated sensor and knowing exactly which cylinder is having problems, is that it can actually detect pre-knock conditions, so the engine doesn't have to knock.

Indeed, conductivity (the inverse of resistance) is proportional to the distance between the electrodes. So moving the electrodes away from each other will affect the conductivity measurement. However, if the spec says that 1.1 mm is OK, then the designers took that into account, and the knock detecting capability will still be there. I suspect that you can move outside the limit and still do effective knock sensing.

However, I don't see any reason why you would make the gap bigger instead of smaller. The bigger the gap, the harder it is to produce a spark under boost. If you've modified the car to run higher boost, the max gap may not work and the engine will miss under boost. In addition, the typical wear mode for spark plugs is for the gap to get bigger over time, so unless you're going to re-gap your spark plugs every week, just due to wear the gap will get bigger and drift outside the limit.

Increasing the gap doesn't increase the load on the coils. The spark either jumps or it doesn't. I'm sure there are some minor detrimental effects on the DI for making it 'work harder'. But if the plug gap is too wide, the spark will find some other path, and that may be through a grease mark or imperfection in a DI coil, and that could be damaging. But the biggest downside is the engine missing - the lack of a proper power stroke will unbalance the engine, which doesn't help the bearings any, and dumps raw gas into the exhaust manifold and catalytic converter, which is a good way to poison a cat, assuming it doesn't get blown off.

Stick with smaller plug gaps.

Good luck!

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