Boost Cut Rb25det

[familiaturbo]

ok iv got an rb25det onevia i had an accident and swapped the running gear into a new shell bigger turbo external gate ect

but now i cannot put my foot down without it lagging and feels like its hitting a massive fuel cut .

i need to know if there is a boost cut , what psi it kicks in at .. iv never had this issue with any of the other rbs iv played with soo yeah im lost

if anyone knows could you please pm me as i dont get on here much

[Craved]

standard ecu has a air flow limit - std turbo its up to 16 psi

so it really depends on the ECU your running, and turbo your using as its related to air mass flow not boost level.

[familiaturbo]

standard ecu has a air flow limit - std turbo its up to 16 psi

so it really depends on the ECU your running, and turbo your using as its related to air mass flow not boost level.

well im running a series 1 rb25 , for some reason my ecu says series 2 but it wouldnt run if that were the case

anyway im running a larger turbo similar specs to a t3 . at about 12psi ..

pretty much feels like i hit an ignition cut and the car shits .. it doesnt start pinnging so its definantly not a fuel cut its just driving me insane as its all thats holding me back from putting the car on the dyno to be tuned and selling it

[R33S2]

The ECU is saving your motor by flooding it, an AVCR will get you running but a AM ECU would be best.

[bumble_bee]

yeah, most rb25det boost cut is around 14psi..

the stock ecu was designed to stop people from boosting to high..

so they put in a boost cut...and becoz the stock turbo can only take so much pressure..esp. the wheels!!!!!!!!!!!!!

mine felt like i was going really fast..then wen i hit 14.7psi..it felt like i drove into wall and it was like if i was pushing it forward!!!!!!!!!!!!!!!!!!!!!...lol

so like ur only using 70% of ur power but it feels lik u can go way faster!!!!

i think every car would feel some sort of cut etc..

but depending on modifications done to ur car aswel..

and its not a fuel cut, as mentioned above..

and a air/fuel controller wont fix it...

i know coz i got an apexi neo afc..

and im 100% max on the stock afm..depend on how much fuel enter my engine...and i only got 250rwhp..

the only thing you can do is get an new afm and a new ecu!!!!!!!

but doesnt mean ur stock turbo can take it lol

but u aint got a stock turbo do ya???

Edited May 12, 2008 by bumble_bee

[Legumis]

the only thing you can do is get ... a new ecu!!!!!!!

Is this something that people like Toshi or Dr Drift could reprogram out of the stock ECU?

[TTT]

RB's don't have a boost cut.

the cut is Rich and Retard.

it describes what the computer does the the mixture and timing.

it does not happen at any particular psi.

stock turbo seems to make it happen at anything above 10 psi and more so at about 4500rpm as this is where max torque is produced.

a larger turbo will make the same torque figure at a slightly higher rev and different boost reading due to how much air it can move.

The larger turbo doesn't need as much boost to ingest the same amount of air that the stock turbo does with higher boost.

Long story short, you'r ecu needs to be tricked, modified or replaced.

take your pick.

tricked is via a signal bender like SAFC etc.

modified is re-flashed/tuned/chipped (Yes Toshi in sydney or Dr-Drift in melbourne can do this)

replaced is well just that. replaced totally with an aftermarket stand alone ecu - eg Apexi Power FC, Wolf V4, Haltech, Autronic etc etc.

[**RB2530**]

Stock ECU has both 'Rich and Retard' PLUS 'air flow cut'.

1. Rich and retard is triggered by excessive cylinder knock only. When knock level threshold is exceeded the ECU richens AFR and retards igntion. Once R&R has been triggered the ECU then will attempt to reinstate AFR and ignition advance back to normal until it detects knock again. It is designed to protect engine against bad or incorrect fuel and internet mechanics.

2. Air flow cut is triggered when AFM voltage exceeding threshold voltage. Air flow cut starts at 4000rpm and threshold increases as a function of rpm up to about 5000 rpm. When it triggers, it cuts fuel and ignition...It is designed to protect against boost control failure...overboosting from broken WG actuator etc...also provides protection against internet mechanics...

So there you go...a bit of truth for you amongst the fog...

[TTT]

also provides protection against internet mechanics...

[WhatBrake]

Stock ECU has both 'Rich and Retard' PLUS 'air flow cut'.

1. Rich and retard is triggered by excessive cylinder knock only. When knock level threshold is exceeded the ECU richens AFR and retards igntion. Once R&R has been triggered the ECU then will attempt to reinstate AFR and ignition advance back to normal until it detects knock again. It is designed to protect engine against bad or incorrect fuel and internet mechanics.

2. Air flow cut is triggered when AFM voltage exceeding threshold voltage. Air flow cut starts at 4000rpm and threshold increases as a function of rpm up to about 5000 rpm. When it triggers, it cuts fuel and ignition...It is designed to protect against boost control failure...overboosting from broken WG actuator etc...also provides protection against internet mechanics...

So there you go...a bit of truth for you amongst the fog...

RECENT POST 8/3/10

Did a search as i'm quite sure my series 2 RB25det from a stagea is giving me the old AFM bs. I'm gona wind it back again and see if it hopefully fixes it. I'm still thinking my ecu is playing a bit of silly buggers. When I have the spare cash its getting aftermarket, and that afm is getting pissed off. bane of my existence, afm issues with my 32! =P

Also what the original guys issue was, mine is quite similar. RB25det ser2 from stagea into 32 gts4, got a 25 ecu, not thinking its running it properly? difference between ecus? (didn't think so) or over boosting (which im gona wind back looks like i can only get away with 0.5 bar? this seems a little low? Stil gona wind it back and see. Any more ideas? would be very very much appreciated!

Cheers guys!

[SKiT_R31]

Does anyone know at what airflow percentage the ECU starts to crack the shits? I'm currently on 10PSI peaking 90% airflow (according to my SAFC), I have a wideband o2 air/fuel mixture + RPM datalogger which I'm using to tune my air-fuel mixtures.

Currently my AFR's are around 10.5:1, so if I remove 15% of airflow on my SAFC to bring it to a more suitable 12:1 AFR, my ECU should see ~ 76.5% airflow, is this correct? I have leaned it out about 10% so far and have a massive improvement through upper midrange and at peak power, which I am unsure whether its from moving back into the ECU's more tolerant maps, having more ideal fuel mixtures, or a mixture of both.

Anyway, what I'm asking (to try and save myself some work, since I’m really tuning by feel) is what is the ideal airflow to tune for? I could get away with upping the boost another psi or so (willing to take the AFM to about 95% flow, as I monitor it, have an alarm plus it is very consistent and reliable), but don’t want to then lose power from the ecu pushing me into R & R maps - obviously I’ve got the fuel under control, but I don’t want to take the ign hit.

Also, I've had to add fuel down low to fix a massive lean spot (so the ECU see's another ~ 10% airflow) so another question is, does the ECU get upset only about maxing the airflow meter, OR does it get also upset about higher air flow at a lower RPM (say 50% at 3000rpm).

Ta in advance if anyone has the info .

[mad082]

the ecu throws a tantrum at lower rpm if the airflow is more than what it thinks is acceptable/safe.

as for what airflow to aim for, you want an AFR of around 12:1, however because you are just using a signal bender (safc), you may find that you start getting pinging before you reach that point, because as you bend the signal to alter the fuel map you are also indirectly altering what point of the ignition map the timing is reading. so you may just want to keep an ear out for any signs of knock while you are tuning it.

[larlok]

Stock ECU has both 'Rich and Retard' PLUS 'air flow cut'.

1. Rich and retard is triggered by excessive cylinder knock only. When knock level threshold is exceeded the ECU richens AFR and retards igntion. Once R&R has been triggered the ECU then will attempt to reinstate AFR and ignition advance back to normal until it detects knock again. It is designed to protect engine against bad or incorrect fuel and internet mechanics.

2. Air flow cut is triggered when AFM voltage exceeding threshold voltage. Air flow cut starts at 4000rpm and threshold increases as a function of rpm up to about 5000 rpm. When it triggers, it cuts fuel and ignition...It is designed to protect against boost control failure...overboosting from broken WG actuator etc...also provides protection against internet mechanics...

So there you go...a bit of truth for you amongst the fog...

if the skyline ecu is similar to the Z32 ecu then Air Flow Limiter it tripped when the AFM voltage exceeds 4.08Volts the only way around this is to get an after market ecu or tune the STD ECU i recomend Nistune great for self tuning but one can easily destroy a motor that way.

Joe

[KnightRiderR33]

Stock ECU has both 'Rich and Retard' PLUS 'air flow cut'.

1. Rich and retard is triggered by excessive cylinder knock only. When knock level threshold is exceeded the ECU richens AFR and retards igntion. Once R&R has been triggered the ECU then will attempt to reinstate AFR and ignition advance back to normal until it detects knock again. It is designed to protect engine against bad or incorrect fuel and internet mechanics.

2. Air flow cut is triggered when AFM voltage exceeding threshold voltage. Air flow cut starts at 4000rpm and threshold increases as a function of rpm up to about 5000 rpm. When it triggers, it cuts fuel and ignition...It is designed to protect against boost control failure...overboosting from broken WG actuator etc...also provides protection against internet mechanics...

So there you go...a bit of truth for you amongst the fog...

hey man sounds like your onto something i have the same problem im new to the turbo scene so hear me out. I get the cut of problem around the 4000RPM - 5000ROM mark i watch my boost gauge and it cuts at 15psi i went to Autotech in granvile and they told me to adjust the acctuator i had a look at it today and it doesnt seem adjustable. U reckon i should source out a new acctuator??

[Moodles2]

Wastegate actuator has nothing to do with the ECU R&R boost cut. I reckon you should source out an aftermarket ECU and get a proper tune.. or a piggyback to tune around the factory R&R if the AM ECU options are too expensive.

12psi+ through the stock turbo? What you really need to be sourcing is a new turbo, because you're going to blow that one putting 15psi+ through it.

[SKiT_R31]

I think he wants to wind his boost back...?

"KnightRiderR33" Are you sure you dont have somesort of boost T in the vauum line for the wastegate? And/or are you sure that the vacuum line is properly connected? To trouble shoot, try running a fresh vacuum line directly from the wastegate to the compressor housing (bypassing the factory 2 stage boost controller). If that doesnt work then a new actuator is a good option as yours could be leaking/seized, if you pull the circlip off the wastegate flap and disconnect the arm your car will drive around on a couple psi (hopelessly slow) but it will same your turbo and your motor in the meantime.