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Gap size has nothing to do with a plug's heat range.
Decreasing the gap size is a way to increase the energy of the spark kernel which makes it harder to "blow out" under the greater cylinder pressure of forced induction.
The .035 range is a typical gap to start with.
2000 SVT #674
13.47 @ 102 - All Motor!
It was not broke; Yet I fixed it anyway.
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OK good sound slike we got it straight now. So I will set the plugs for .035 to start with. I just picked them up from the dealer today. 1 range colder and copper instead of platinum.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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Took a look at the intercooler again, there is no way its going to work as a side mount due to serious unibody in the way which would sacrifice crash strength. So I am going to mount it in the bumper under the license plate and a friend of mine can weld aluminum so he is going to modify one of the endtanks. This will hopefully not be too obvious or ugly when done. I had the turbo manifold surfaced today and added mounting studs for the turbo to ease installation.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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You want as wide a gap as you can get to help burn all the fuel properly, the wider the gap, the longer the spark. Mainly for efficiency when you're out of boost. Most Focus people recommend .045, but that's dependent on a lot of factors. Even .040 is a pretty narrow gap and should be good for 5-7psi. Most would say if you have to run under .040, you should look to upgrade your ignition or wires.
Right now, I'm running .040 at 9psi and it feels fine. I don't push the car hard though, especially now that gas is so expensive.
2000 Rio Red I4 Cougar
200whp & 210wtq at 9psi
254whp & 276wtq with NX 35shot
WRX TD04 Turbo, Cut Short Shifter, Strut Tower Bar, 17" ZN Wheels, Roush Springs, Starion Intercooler, NX 35 shot, HKS SS BOV, Full 3" exhaust,StreetFlight Chip
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Originally posted by DemonSVT:
Gap size has nothing to do with a plug's heat range.
Decreasing the gap size is a way to increase the energy of the spark kernel which makes it harder to "blow out" under the greater cylinder pressure of forced induction.
The .035 range is a typical gap to start with.
Correct on the first point but.......
Here's my take on the whole thing:
Reducing the gap doesn't increase the energy of the spark, it only allows the dielectric effect to be reduced enough for spark to form again. It actually decreases the ability of the spark to ignite the charge due to the reduced area and will eventually reduce the energy of the spark when you shorten the gap too far. The closer the anode is to the cathode, the less voltage required current to jump the airgap. An extreme example is to bend the prong until it touches the electrode. When it touches it is considered a short...lots of current flows but no spark.
The ignition system can produce some theoretical maximum energy, we'll call it TE for total energy. In this example
TE= Egap + Epres.
Egap varies with distance and Epres (or dielectric const) would vary on charge density in the cylinder.
If you drop one without raising the other you get a lower spark energy. IF you drop Egap too far and raise Edieletric to far, you have too little area for the spark to ignite the charge.
A wider gap is best when possible!
Wider gap requires lots more potential for the current to jump the gap. Air is an insulator (so is fuel) so that also makes it harder for the spark to jump the gap. If you increase the boost you are increasing the insulation effect, added more dielectric material between the anode and cathode. This also requires more voltage to jump the gap. The extreme example in this case is you pack so much air and fuel into a cylinder that it would be the same as sticking a piece of insulation between the electrodes.
Conclusions:
Spark isn't "blown out", it fails to jump the gap. The gap is decreased to compensate for increased dielectric effect under the new cylinder pressure. This in turn results in a smaller area for the spark to ignite the charge and eventually results in a lower energy spark when the gap gets too close.
Best to leave the gap stock unless you misfire, then only decrease it by a few thousandths each time until the misfire goes away.
OR, get higher energy ignition and leave the gap stock.
I have run .045-.050" almost the whole time I have been turbo with the exception of when I first put it together. AT that time I ran .035-.040" under other peoples advice because I had no first hand experience then.
It worked well enough when warm, but a few misfires on cold mornings taught me the lesson that the gap was too short to properly ignite the fuel on cold mornings.
I run .045" now as a rule since our ignition system is quite strong stock. No issues with misfires related to spark.
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black
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Thats an awesome explanation  Makes perfect sense to me.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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OK I got an OBX BOV today while I was in portland OR for $50. Its easily adjustable by just rotating the top and is suppose to produce 115db.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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Finally got the intercooler installed. I went with my original plan and did a side mount like a mitsubishi does. It required cutting of the subframe and lots of reinforcement. But there should be plenty of air flow now as the part of the fender well has been removed and air is directed in from underneath and through the factory fog lamp area that has been enlarged. probably not as great as a front mount but I am sure it is within 90% of that. For the most part it still appears to be 100% stock from the outside even with my 2.5" exhaust I also found a way to bolt the fuse box back down now that the battery is in the trunk. Now I need to really start looking at the intercooler piping. Can anyone reccomend a flexible piping for some of the more difficult areas, besides radiator hose?
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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CHeck out this article http://www.nissanperformancemag.com/february05/qg/thats the kind of intercooler I have. So yes it flows less but cools better then a comparible tube and fine intercooler of the same size. Which is good because there isn't much room for a big intercooler on these cars.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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OK I got the intercooler piping installed to the intercooler. I also got the BOV installed. I used all aluminum mandrel tubing and a 16" section of steel pipe so that I could weld the BOV flange on. It looks really nice. I also used high torque clamps.
ATX MTX swap, rear drum disc swap, drilled rotors, ported intake, optim throttle body, CAI, 7.5L MAF, adj. fuel regulator, longtube headers, underdrive pulley, no EGR, low inpedence bigger injectors, 2002 Focus Swap
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