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Old 07-23-2009, 01:03 PM   #1
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article on spark plugs and the fit

interesting article on spark plugs, i wonder if the yaris has the same issues. 2 whp for a spark plug change NA is pretty amazing.

on a side note, i looked up plugs for the yaris on the Denso website, and they list a platinum plug as our OEM replacement. I know i have heard people say we have OEM iridium plugs before, but i don't know if thats true.

Denso part look up:
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Old 07-26-2009, 10:58 PM   #2
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Possible to gain wheel HP just from getting NEWER, FRESHER plugs. I've seen as much as 5 wheel HP gain on the dyno, but on an Evo with a big turbo and stand-alone ECU although there was no tuning done (yet) with the old spark plug run vs the new spark plug run. Overall the tuner picked up something like 10 wheel HP gain across the board but insists it could not have been possible without new spark plugs.

On my end, I got rid of a lot of detonation in my Yaris by going one plug colder. The detonation has been there since BNEW, probably because my Yaris throws a lot of crazy ignition advance.
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Old 07-27-2009, 08:18 AM   #3
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Isn't dyno error around 2hp per run? In other words, can't the readings go up/down 2hp every time they run the car, with no changes made to the car? I don't doubt fresh plugs make a difference, but I don't think it's huge on our level of car.
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Old 07-27-2009, 02:22 PM   #4
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I'd take all of that with a grain of salt. There isn't a lot of info to be had there, and schleppy is right about the dyno accuracy.
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Old 08-01-2009, 11:50 PM   #5
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ok, this is my undestanding about plugs! i know their main function is to produce an ignition source to ignite the gas and air mixture in the cynlinder. for some reason some plugs hinder this operation. one can argue the differences of the materials used and metal thickness make a difference to the outcome of horse power and gas usage. some go as far to follow accepted universal rules as denso good and autolite bad for japanese cars. or, ngk's good and so on and so on bad. i know that copper cores and grounds have different ressistances compared to platnum or iridium plugs. and, these differences yield different performing out comes. i know that platnum is a much harder material than copper and iridium is harder than platmun. so, in terms of the internal stress due to the combustion, the gapping on iridium plugs will remain much much longer rather then the eroding softer copper material. thus, your iridiums plugs will last longer and gapping remain constant. but! the stresses in the cylinders and heat will, of course, in time damage your plugs reguardless of the type of plugs used. while your gapping in the i-plugs will last longer the rest of the plug is subject to stress fractures and material deterioration. so, regular inspection and replacement of your plugs my be necesseray. i know my yaris came with denso iridium plugs, so your car's plugs might also be i-plugs. there are numerous types of plugs, such as copper, platnum, a fusion of platnum and iridium, and iridium plugs. now, you are going to do your homework and decide what type of plugs to use. you may want to go with the fusion type rather than the i-plugs. remember that some plugs my say iridium on them but the center electrode may contain a smaller amount of iridium in them. look at the amount of material used and thickness in comparing plugs. the key is to get what you want out of you plugs because engines, believe it or not, are picky! i went with ngk's i-plugs because i didnt want to wait for the denso. but, i almost went with the fusion type. plugs are a mess and even the oem plugs dissatisfy you during the life of you engine because as your car gets older you dont get the same performance you did when your car was newer. sooo, you will find yourself looking at others instead of i-plugs.
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