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Old 01-08-2006, 14:50   #1 (permalink)
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Spark Plugs and Leads

I was considering putting the 'direct hits' ( www.directhits.com ) spark amplifiers onto my EF futura but was hoping to pick someones brains first as to whether it would be worthwhile.

The first thing is, I am assuming I have 'resistor' type spark plugs, as would most (all?) efi vehicles. Was looking at the BoschUSA website at their Platinum +4 plugs and the FAQ, which explains that there is a glass membrane which acts as a resistor in the plug to reduce/dissipate the RF Interference.

Without this, some RFI "MAY" interfere with other electrical signals. "MAY"

Elsewhere I read that it is only a major problem if you have solid core cables, and that a 'non-resistor' can be used in conjunction with a helical wound glass core cable ( like Eagle 9mm leads ) and that it shouldn't be a problem.

My workshop manual doesn't explain a lot about the ford EDIS module, but I would like to think it is shielded and has optocouplers in the output to protect it from such things.

I just don't want to spend a couple of hundred dollars on improving the spark and ignition setup to find it won't work, or that it will cause electrical/electronic problems. Does anyone have any information on using 'non-resistor' plugs on an efi engine, and/or any information on using direct hits?

Thanks
Craig
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Old 01-08-2006, 17:21   #2 (permalink)
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Re: Spark Plugs and Leads

I've just had a look at these peoples website. It's all well and good that they get 500 amps of current flowing through the spark plug (10,000 times as much current as normal) but that will just cause the spark plugs to wear out 10,000 times as fast. You don't need a huge current to ignite the fuel air mixture- what you need is huge voltage, and that is supplied by your cars ignition coil/coils. (on the order of 30-60 thousand volts) Adding a capacitor in line with the plug and lead will do nothing to increase voltage...maybe current, but that doesn't matter anyway.
What they fail to mention is how the capacitor affects the timing of the spark. In an AC circuit (which is what a car ignition circuit actually is) a capacitor will alter when the current flows in relation to the voltage- it actually advances it. So while the voltage may rise at the spark plug, the current will already be flowing, thus altering the ignition timing. (research AC impedance on the net for more info)
Notice also that several of the vehicles in their 11 vehicle test had interesting results. 2 of them had "radio interference problems"- supposedly being correctable, which isn't necessarily true. Three units withdrawn due to some problem, one wouldn't work with CNG. Two had no change in fuel economy whatsoever which indicates no change in engine behavior and two had "no change" written as their result. Frankly these results are sh!thouse.
If you really want to increase your cars ignition performance, then what you need is more voltage supplied from the coil so you can run bigger spark gaps without worries. I ran the gaps on my mums EL falcon up to 1.7mm and I actually noticed an increase in performance and a decrease when i closed them back up again. This was after months of driving around and testing 0-100 times etc, so it should not be attributed to different petrol or weather etc.
Take note also that a pointy object will discharge a current better than something less pointy. This is why we see the new Iridium fine electrode spark plugs on the market nowdays. They could probably be safely run with an even wider gap again and outperform regular spark plugs, but you have to ask whether $23 per plug is worth it in the long run.
You have to consider that these engines run a relatively low compression ratio in the grand scheme of things and you're unlikely to NEED better ignition untill some serious mods have been done.
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Old 01-08-2006, 18:45   #3 (permalink)
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Re: Spark Plugs and Leads

Now that's the kind of response I was after.
I thought it was one of those things that is too good to be true. While I did realise things would wear out faster, it was more the RFI that I was worried about. At some point I will mount the supercharger I have, and thought I would need to improve the ignition.
But like you say it is the high voltage I will need and so maybe just a decent set of MSD coils good for 45kV+ will suffice, and leave the Ford EDIS module to do its thing.
I don't mind paying $23 per plug if they are going to last, and guarantee a decent spark, but then again I am sure every company is going to blow smoke up their own ass to a certain extent to convince you they have the best product.
Thanks for the comments.
Craig
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Old 02-07-2006, 02:12   #4 (permalink)
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Re: Spark Plugs and Leads

Hey this is what i have been looking for too....I have found that one my JMM(Autolite non resisted) plugs has burned it's electrode off after just underr 10.000k's causing a missfire.....I was also after that exact info as i'm not sure what plugs to repalce them with and I now realise that non res plugs will only wear out quicker anyways......Now i'm thinking about low res plugs and playing with bigger gaps as i'm running lpg...thanks anyways!!!
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