Tuning Rb25, Power Drops Off At 5000Rpm

[Sparky206]

I'm in the process of getting my R33 S2 Rb25 tuned with nistune on a std R33 ECU. When we put it on the dyno yesterday, the graph showed a sudden loss of power at about 5000 rpm or 160km/h in 4th, with the car reving noticeably slower and occasionally backfiring. We wern't able to tune it out, the best we could get it was to stay flat from 5000rpm onwards, but this required a noticeable jump in ingnition timings around that rpm i.e. 17-18-18-21-23-24 ect. Highest power reading we had was 210KW

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The car has the following modifications

FMIC

3" exhaust

Hi flowed hypergear turbo @ 14psi

Z32 AFM

GTR fuel pump

Spark plugs are R5671A-7 gaped to .7 . I have investigated the coils before while experiencing rich and retard and have coated them in high temp silicon, but i could never find any cracks, or see any sparks in the dark.

Boost started at 14psi and gradually dropped to 12psi by redline.

Any ideas for whats causing this drop off in power?

[6boost.com]

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

My problem turned out to be soft valve springs on the exhaust side...not cool.

Matt

[R31Nismoid]

What cat?

Done a run without exhaust?

Double checked base timing etc?

Cam belt isn't out a tooth?

Boost drop means actuator might not be setup right?

Are the plugs iri? You sure they are ok? (in future use coppers please!)

That's enough to start.

[zebra]

I'm in the process of getting my R33 S2 Rb25 tuned with nistune on a std R33 ECU.

This.....

Cannot be

[MrStabby]

This.....

Cannot be

Correct.

OP, your options are;

1. R32 CPU without VCT, or with an external VCT controller

3. Z32 CPU

Nistune does NOT support the R33 ECU. So which ECU do you really have?

[zebra]

I could be Wayne Besanko tuning it?

He can do anything!

[AngryRB]

Had a similar problem , boost started at 14 and was 10 by redline, apparently its the wastegate actuator but im no expert

[hypergear]

Looks like this sort of behavior:

Above was from worn valve springs and valves. That dip could not be controlled by timing or fuel, the depth of the dip is random.

Also you are likely to need high pressure actuator to hold boost steady up top.

[Sparky206]

The car is being tuned using an ostrich emulator on the R33 std ECU which will then be burned to a permanent chip once finished. Tuned by toshi who has done many cars on here this way

I believe the cat is a high flow, but it was there when i purchased. I've had it off before and its definatly 3" and you can see through it with a spiral type alloy fins inside

I did not do a run without the exhaust

Base timing was checked and is correct at 15 degrees

Have not checked cam belt, but have not touched it either

The plugs are copper, and have only done about 5000km, but this will be the first thing i change.

As for wastegate problems, the boost drop is very gradual, and i cant see this accounting for a sharp drop in power and noticeable slowing of reving. It was so sharp that on some of the runs the dyno would stop recording after 5500rpm as it thought peak power had been reached.

Also forgot to mention that the car would backfire once on some of the runs. Also the tuner said that the ignition timings we were running would usually cause pinging, but he was surprised that it was not.

Thanks for the replys so far

Edit: My KW graph looked a lot like the torque graph above, but staying flat through the 6000-7000rpm range

Edited May 3, 2011 by Sparky206

[6boost.com]

Add boost/timing just for one dyno ramp to see if power increases...if it does it'll elminate a valvetrain issue at least.

[Sparky206]

While setting the boost, we did do a run at 15psi and it did make more power

[jjman]

had a similar problem myself. It was the stock rubber intake pipe distorting/sucking shut.

my symptoms led me to find this out as it was doing it more when the conditions were warmer (therefor rubber is softer and more able to be sucked n distorted).

I put in a metal intake pipe n that sorted it perfectly.

if you are only every going to go for about this power (famous last words) then one of the cheaper silicone intake pipes may suffice but otherwise i highly reccomend a metal one.

It also means more power is possible in the top end due to the better air flow.

I went from 290rwhp @14psi(when the intake wasnt sucking shut) to 300rwhp @14.5psi (the intake allowed for a bit more boost) just by replacing the intake.

[simpletool]

Also forgot to mention that the car would backfire once on some of the runs. Also the tuner said that the ignition timings we were running would usually cause pinging, but he was surprised that it was not.

Consistent with exhaust valve spring issues ???

[Sparky206]

had a similar problem myself. It was the stock rubber intake pipe distorting/sucking shut.

my symptoms led me to find this out as it was doing it more when the conditions were warmer (therefor rubber is softer and more able to be sucked n distorted).

I put in a metal intake pipe n that sorted it perfectly.

if you are only every going to go for about this power (famous last words) then one of the cheaper silicone intake pipes may suffice but otherwise i highly reccomend a metal one.

It also means more power is possible in the top end due to the better air flow.

I went from 290rwhp @14psi(when the intake wasnt sucking shut) to 300rwhp @14.5psi (the intake allowed for a bit more boost) just by replacing the intake.

Did you have a similar power curve to the torque curve above with an almost instant abrupt loss of power?

[jjman]

Did you have a similar power curve to the torque curve above with an almost instant abrupt loss of power?

yep.

[mii11x]

hey mate,

when my car was tuned it did the same sorta thing.......simple problem and wondering whether or not you have checked to see if your air filter plumbing is sucking closed. this would probably??? show up on tune graphs (a/r ratios etc).

we reinforced it and hey presto everything ok.

hope you can sort it out

Mick

[Sparky206]

Here is the dyno sheet. This is the best we could get it with advanced ignition timings around the point where the power dropped. Other runs it would drop lower at around the 155KM/h mark then flatten out

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[hypergear]

If that is a final run with correct dyno settings on full throttle I would suggest to check the factory actuator adjustments or it’s in need of a better actuator or a leak from some where.

else it was very similar to mine when I discovered the valve issue, I could initially get away from that dip by patching up timing and till it stopped responding and the depth of the dip became random. The R33 Rb25det would generally give a small dip after 6800RPMs while Neo engines don't.

[Rolls]

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.

Edited May 8, 2011 by Rolls

[caaraa]

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