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BPU plugs, coil packs, & gapping what's the real answer?

1379 Views 9 Replies 4 Participants Last post by  ronrich

I already know this is a sensitive, opinionated, and greatly discussed issue, so if at all possible just the facts please ... I'm not looking to start a bunch of trash talking. And yes I have read many of the previous posts via the search routine and have run many types of plugs, as I am sure y'all here have.

I have a BPU with ~ 120k miles, it starting missing at high boost/revs. My boost level is currently dialed in at 17 psi max. I am running the BCPR7ES-11, which are BPU plugs pre-gapped to 0.034".

Here is my confusion: after reading all threads concerning plugs, gapping, coil packs etc. I was about to go out and buy 6 new coil packs @ $81.00 a piece from the dealership. If I understood the posts (sorry don't remember the individual) he stated the coil packs get weak or go bad over time and once you replace them you'll be able to run at BPU levels at the original hotter plug stock gap of 0.043".

But when I consulted some local performance tuners in town they told me to just re-gap to 0.028", and that they set up their cars like that. They also said the coil packs are strong components and they hardly ever see then needing replacement. And apparently there really isn't a good way to test them based on what I have read on this group. They also said if the plug gap is too large, the spark "blows out" due to the higher cylinder pressures. Needless to say before I drop +$500.00 on coil packs I gave this a try. When the plugs came out the electrodes looked fine with a black soot residue on them (running rich as all Supra's do I assume). Bit of oil residue on 5 and 6 probably another problem like valve cover gaskets. So I gapped them down to 0.028" and now the car runs smooth as can be with no miss at all and pulls strong.

But this raises the question as you gap down the plugs you have a smaller spark hence reduced power ??? So am I losing substantial power because of the reduced gap?

So are there folks out there that already have info from previous testing ??? i.e. post their DYNO charts for the following or similiar set-ups to put this issue to "bed" ?


BPU level car running 17 psi with new coil packs and plugs gapped to 0.043"

BPU level car running 17 psi with original coil packs and plugs gap lowered.

I guess my bottom line question is if I drop +$500.00 on all new coil packs how much if any RWHP am I going to see??

Sorry for the long message, but this is the only way I could explain my situation.

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the -11's are pregapped to .042 or so the NGK with out the -11 is pregapped to .032

Interesting, so with the single set-up you mention with new coils what plugs do you run and what is their gap without missing? I realize you're running higher than 17 psi boost and the set-up is different. But at least its a point of reference.

its the ignition coil pack. change it and you can run stock gapped plug without a problem. I'm talking from my own and 3 other BPU supras experience. those copper plug make your car run like shit.
trust me, I went thru the whole "plug" trial Im just running 1 degree colder iradium plug at stock gap and the car runs awsome. lower gapped plug is a temporary solution.

What do you think about buying HKS twin power and no new coil packs. Will it make sense? How much for HKS twin power?

Thanx in adance.
So would that cause an idle stumble? Gapping the plugs plenty low? I installed new coil packs and the difference was noticable immediately. The idle was smoother but every once in a while it would stumble. Just curious.

so you replaced all your coil packs? what noticeable performance improvement did you notice?? any RWHP numbers? what gap are you running the the new packs? I'm running at 0.028" with orginal (102k) packs and I don't notice any stumble.

Zerosoul said:
now Im just running 1 degree colder iradium plug at stock gap and the car runs awsome. lower gapped plug is a temporary solution.

Jonas, can you tell me what exact plug you are running? Is it the Denso Iridium Plugs ? Can you give me the exact plug number so I may purchase them also for my BPU? And what gaps are they set at ?

My car has 20K miles with 4K mile BPU on and it idles low after a cold start for 10-15 minutes and then settles down properly. I am thinking about changing all my plugs so your input is appreciated. Also I do not want to buy the NGK plugs since you have to change them every 5K miles. Thanks.
Yeah, I replaced them all when the car hit 150000 miles. The idle was smoothed out and I sometimes revved up to 3000 rpm and held it with a miss now and then before the coil pack change. It's smooth now now matter how high the rev. I'm not sure the exact gapping, but I want to say it's .032. The tuner shop may have changed it on a dyno run when I wasn't there, so I don't want to say it's that for sure. I'm not sure of the RWHP difference becuase my clutch crapped out on the dyno at 5200 rpm. It caught once at 6200 rpm and hit 463.3 then slipped again. The previous number 443 rwhp, then I added cam gears and coil packs. The inclusion of a lightened flywheel and RPS stage III w/sprung hub and electric fans might push it towards the 500 rwhp range.

that does make me feel too bad. see mine was missing at high revs 4k to 5k. the gap was set to 0.034". so I gapped them down to 0.028", maybe I went too far. but at least the car doesn't miss any more. someone was saying you could gap at stock (0.043") once you changed your coil packs and I thought I might be losing quite a bit of power because of the large gap difference.
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