hey, I just changed my plugs out yesterday to the NGK BPR8es 's and last night I gave a bud a ride home, she felt quite sluggish. They were gapped at .026. I noticed that my boost now tappers. Ive got the hallman mbc, and its usually rock solid at 20 lb, but it now tapered down a pound to 19 towards redline.... does this make any sense? I am out of my element here, cannot figure out the correlation... only thing I can think is that since theres not as much gap, the spark isnt as stable at higher rpm, and therefore I wont hold as much boost? On a side note, my exhaust tone sounds much smoother at idle, so I figure it has helped out some idle misfiring or something. Please give me your best insight. I dont want boost taper.

 

probably the weather. it was 30 degrees, now 40, and 50.

 

What you changed your sparks from..? stock..??
I think the gap is too close.. try re-gapping at let say .028 to.030 and test again...

Later,

 

malibujack had a post about when you change to Cu plugs and colder to gap closer (.026) and that you would need a higher powered ign. in order to use the factory sized gap on Cu's. I was thinking maybe the weather too... but that would only lower my boost alltogether, not make it taper.
keep em' commin'

 

just out of curiousity, i know most people hate them but did you replace with iridiums? i was in a pinch to replace my plugs ( some how broke the ceramic on the side that is in the block) and a friend had a extra set for his gt mustang, but before i get nasty replies, his stang is twin turbo'ed. i dont remember the plug # but they were ngk's and the work wonderfully in the evo.

 

bump for you 5 'oclockers

 

no.. Cu=copper. I'm using them because I want that extra saftety margin for high boost apps. I researched it well, and many on here are using these with much success.

 

how mod'ed are you? and do you have a beefed ignition system? alot more boost? just fyi if you dont have a boost controler and are letting the car control the boost, then the most you will see is approx 20 psi. and that is at like 3500-4000 rpms, at redline you should only have 14-16psi

 

dude, your not reading my first post.... I said I have coppers, and I said I have a hallman mbc, and I said I dont have an upgraded ign. so increasing the gap is not exactly what I'm hoping to do. Also said I am running in excess of 20 lb of boost.

 

Where are you gurus??

 

do you know how much boost you are running? im not looking for "20+psi" im looking for "at this rpm w/o a load on the engine, xxpsi"

 

i heard Mailbu_Jack got shot the other day,cause he knows to much about cars

 

Hahaha.. These posts drop off the new post lists pretty quickly without bumping..

Ok.. .026 is fine for a gap, any larger and cooler plugs and high boost will just misfire at over 19psi.. cooler plugs misfire a bit at idle so the .026 gap helps a bit.

I use NGK plugs BPR7ES plugs (if anyone needs to know) Depending on the health of your ignition system, you can gap from .026-.030 and if you index the plugs, you can get as much as .032 if your ignition system is powerful enough.

FWIW, the stock EVO coils are IDENTICAL to the coils used on the base lancer and most of the other 4 cylinder cars that Mitsubishi makes, with the exception of the plug boots and wires... They just don't produce enough power to spark consistently when the plugs begin to wear..

Anyway, a bad misfire can result in your boost tapering, however it sounds more like the wires/boots aren't making good contact or are fully seated on the plugs.

Normally I'd never attribute boost tapering or low boost with bad plugs, but in theory, a misfire means less ignition, less ignition means less expanding gasses, so it could result in your boost tapering... However I doubt this is the case.

first, recheck the gaps of the plugs, this will do two things, first it will allow you to verify the gap hasn't shifted, and of course to see if their not terribly fouled.. Cold weather and cold plugs will lead to fouling the plugs when you first start the engine. Second, by checking the plugs, you get the opportunity to remove them, retorque (reinstall them) and then reseat the boots to the plugs, wires to the coils, and coils fully seated on the head.

Oh.. and the reports of my death are greatly exaggerated..

 

hmmm... I'll check that out. you say your run bpr7's ey? but those are the stock heat range, aren't they? I was looking to go colder so I got the bpr8's. So if gap is where I set it, and the boots go back on tight, and I still see taper, do you think it is the plug? Lastly, I saw in another thread that you were attempting to create your own high powered ign. sys, with coils from a motor cycle? Let me know if/how that works/worked and if it did then what the specs are on the products you used.

 

In my experience with my 94 Talon Tsi Turbo, I always ran better with the stock heat range spark plugs gapped at 0.28-0.30. This is when the car had simple mods (15PSI, Exhaust, Intake). So I would stick to the stock heat range and conservative gaps until you really start to modify your engine. BTW when I added cams, mild porting, and more boost, my Talon responded very well to a step colder spark plug. When I added water/alcohol injection, I had to close the gap more to keep the spark from blowing out.