[kismetcapitan]

After getting my injectors sorted, I've now been retuning my map in earnest. I've upped the boost to 1.3bar and after dialing out knock with a bit more fueling and retarding the timing 1 degree in the upper reaches of the (power fc) map, I started to get an interesting/annoying/cause for concern effect as my on-road tuning session went on. At WOT, at 7000rpm on up, I'd start to hear backfiring noises (little pops) from my tailpipe, and the car didn't seem to pull as hard (but was still going). Knock sensors didn't indicate anything over 23.

The only thing I can think of is, am I somehow blowing out the spark, sending an unburnt fuel charge down the exhaust pipe? Or is it something else? Backfiring when letting off the throttle I've gotten (hope to get??), that's normal and if we're lucky we get a nice pop and a meter-long shot of flame, but getting rapidfire little pops at WOT high in the rpm range...what is that??

 

[Marky_GTSt]

What plugs/gaps ? Though with all your work im guessing you got them sorted

 

[kismetcapitan]

What plugs/gaps ? Though with all your work im guessing you got them sorted

haven't looked at the plugs to be honest. My engine builder gave them the thumbs up and the car has only been back on the road now for a month or so. But I really have no idea what type of plug, or how cold or hot it is, or the gapping or anything.

The problem only surfaced today as I raised boost from 1.2 to 1.3.

 

[Marky_GTSt]

I think you need to check out the plugs before going much further, Its an easy job to do and it might just cure this... (well I hope it does for you anyways)

 

[kismetcapitan]

right, will do, they could all be fouled something fierce. If I need to get a new set, recommendations? NGK or Denso? what heat range, and what gap seems to be the recommended spec for a GTR?

 

[Marky_GTSt]

I dont know about the GTR (Im sure plenty of folk here will tell you) but Im a big fan of NGK plugs, So I got some iridium ones in my RB25DET, I didnt notice the power/economy gains that they claim, but they seem to stay clean for a lot longer... I gapped them at 0.8mm IIRC.

 

[kgleeson]

Plugs

Many use the NGk / Denso and here have been a few negative threads on the HKS plugs.

Denso IQ24 seem popular

I know a few are using NGK BKR8EIX. Just getting some of these for mine they work out at £5.70 per plug + VAT. Get them From Partco or the like.

Note
The BKR8EIX is slightly shorter than the standard plug. This is ok so long as you have a good spring in the cap or new splifires etc..

Kev

 

[kismetcapitan]

I'm going to go in for a plug checkup - if I'm super-lucky all they'll need is a good scrubbing, if I'm lucky a new set of plugs will do it, if I'm not - will probably have to install an ignition amplifier (any recommendations?). If I'm super unlucky I'll require Splitfire coilpacks too...but I really didn't think that 1.3-1.4bar boost required such extensive ignition upgrades...

 

[ExScoobyT]

All your threads, none state that you`ve checked AFR behaviour. You need to check this. Misfire could be too rich OR too lean. Lean misfire on full throttle is not a good thing.

If it is the plugs, decreasing the gap will help - try 0.6mm and see.

 

[kismetcapitan]

that's true, but I've been having a bugger of a time tracking down a wideband lambda to borrow. My knock readings are ok so at least I know I'm not running suicidally lean. The car boosts fine up to 1.15bar, anything past that and it starts to miss. Plugs will be done tomorrow (regapped or replaced), and if the plugs in the car now are anything like the plugs that were in before (which I also have), the gap is the issue - the last set (used by the previous owner in Japan) are grade 6 and have a 3-4mm gap!

 

[ExScoobyT]

Your knock reading is not directly related to the AFR. You may be running lean and hence have retarded timing, which of cource further increases EGT and the chance of melt-down.

 

[kismetcapitan]

Your knock reading is not directly related to the AFR. You may be running lean and hence have retarded timing, which of cource further increases EGT and the chance of melt-down.

my timing is retarded 2 to 4 degrees from the base map. But I hear you on the EGT thing - I'm waiting on a set of gauges but I definitely am painfully aware that I can't monitor my EGT. My map runs are in the chill of November at 3am and go about ten minutes, so I haven't been pushing it.

But yes, the critical tools a tuner needs to see are A/F ratios, EGT, knock, injector duty, and timing (on top of the basic vitals - oil pressure, water temp, etc). I need those last two to finish my map, even though I'm certain that I'm blowing out the spark at high boost.