Tuning Rb25, Power Drops Off At 5000Rpm

[Sparky206]

Thanks for the replys. From what I've read on coil packs, when they cause backfires, it sounds like a machine gun going off, for me it was only ever one backfire. I have also coated the coils in high temp silicon to insulate them, and when i tested them in the dark, i couldnt see any arcing

AFR were between 11.6-11.8 . If the intake was sucking shut, would this show up in the AFR? Plugs were gapped to .7

Also another symptom that needs to be factored in is how much slower the car rev'd through the 4500-5500 range. It rev'd A LOT slower through this range, almost as if it was on half throttle, then would speed back up from 5500-redline.

I've ordered a new set of plugs and a metal intake pipe

[Rolls]

Sounds very much like a problem I had with a recent RB25 powered SIL80.

cool post bro

[DVS JEZ]

And how did u fix it caaraa

[AngryRB]

hey so did you guys find the problem, cause ive just had mine tuned , new coilpacks, plugs, different actuators used, and it loses bout 15-20kws after 6000rpm,

was told the dump pipe is a bit average, what do you think???

Mods-walbro pump, hiflow turbo, pwr fc, splitfire coils, pod, fmic

[Toshi]

Did everyone miss where he said it backfires? Backfire sounds like it is missing, for it to miss it sounds almost certianly like an ignition issue, old shagged coilpacks almost always cause a miss around peak torque (4500-5500rpm). There are loads of threads about this issue, surely this has to be the problem?

Check the spark plug gap as well, 0.8 is the largest I would go. Toshi is in Japan, most japs tune the cars very rich around 10:1 from what I've seen, this exaggerates any weak spark problems massively making any misses due to poor spark even worse, you don't have to see cracks/etc for the coils to be stuffed, mine looked perfect and were stuffed, fixing the tune up from 10:1 to 12:1 completely removed the misfire in my situation as well.

The only other thing I would bet money on is the intake sucking shut, but I can't see how this would cause a misfire.

edit: You say you have an R33 ecu but these cannot be nistuned, the most likely option is an R32 ecu, however these can't control VCT, how is your VCT being controlled? If it isn't switching off at 5000rpm correctly and is keeping the exhaust cam retarded you will see a big dip in power over 5000rpm, make sure the VCT is switching on and off correctly at the right rpm, this could also be your issue, I can't see it would cause any backfires though.

edit2: just saw that it wasn't nistuned, ignore my first edit.

Im in Sydney.

R33 ecu is able to remap by nistune software.(nistune do not have board so Im using daughter board.it imported from Japan)

Im using R33 ECU so cost only from $550 realtime road or dyno tune.

[rollex]

have you checked the coilpacks and spark plug gaps?

[AngryRB]

has new plugs and splitfire coils, tuner set the gaps so i havent checked, i noticed that the avcr is only set up to 6500... so not sure why they'd stop it there

i take it 1bar is safe using a standard head gasket up to 7000rpm.. or is that leaning on danger???

[Rolls]

i take it 1bar is safe using a standard head gasket up to 7000rpm.. or is that leaning on danger???

it is heat and peak cylinder torque that will destroy head gaskets not rpm imo, though rpm will contribute to heat.

[AngryRB]

so what is the safe limit of boost on standard head gasket, and also i was told not too use octane booster, is that bull or good advice??

[JonnoHR31]

never use octane booster oter than as a temporary fix to a bad batch of fuel as it ruins sensors very quickly.

18-20 psi is usually considered the safe limit for standard bottom end stuff, including head gasket. although sometimes you can get away with more, its all in the tune.

[AngryRB]

Thanks for that info,