R34 Gtt, What's The Max Boost With Uprated Turbo?

[DeanR33]

I've fitted a hybrid turbo to my Series 2 Stagea RB25det neo engine. It's from a well known supplier over here in the UK and is basically the std turbo with the hot and cold sides machined to take a larger Garrett core. I also have a FMIC, induction kit, de-cat, cat back exhaust,one grade colder 0.8 NGK Iridiums,Walbro fuel pump and Gizmo EBC fitted. Oh and it's had brand new genuine coilpacks.

I've been running on various boost settings, the lowest 0.67 and the highest 0.8 bar up until now. Today I tried upping it but I think I hit the fuel cut at 1 bar. It wasn't a misfire, just an immediate and complete loss of power for a split second.

I know that the Neo engine has it's own boost sensor to the ECU, but in my searches I haven't been able to confirm if this is definately just for a boost cut signal or the ECU uses it for it's map, so I don't want to disconnect it at this point until I can confirm without a doubt.

I know that I am at the point of moving onto new injectors and a Nistune and Z32, but I just want to run it as it is for a while.

[trel]

you are hitting fuel cut due to the stock ecu limitations. you either need a piggy back, something like an s-afc, or new management ie. nistune to overcome this and run higher boost. until then run 11psi or so and your stock ecu shouldnt have a hissy and freak.

it's been covered quite a few times dude! "fuel cut" in search and you will find many results!

good luck.

[mad082]

yeah you are hitting the limit that the ecu will take and it is throwing a tantrum. only solution is to lower the boost. there isn't really a safe or easy way around it until you get the nistune.

i had the same thing happening to me in my 33

[GUN_METAL_GTR32]

y would u change the turbo with out changing the ecu?

i dont get y flamin mongrels do that for u could be causing detrimental damage to ur engine.

[lachlanw]

yeah a bit stupid really . i would not give it anthing over half throttle untill you get it tuned

yes the boost sensor affects tune about 1 and a half afr's

yes the ecu will cut fuel at 1 bar

[DeanR33]

Thanks for all the answers. I did do a search, but I couldn't find what I would call a definitive answer because many posts were referring to the R33 ECU which I know uses the AFM readings for fuel cut and what I needed to know was if the R34 was different in as much as it has it's own dedicated boost pressure sensor for the ecu as opposed to the boost guage.

The decision to fit the turbo was all mine and I fitted it myself as I have done with all the mods on my Stagea. From my own research I knew that I would be able to run lower boost for the same power as a std turbo, which is exactly what I have done most of the time. I was just experimenting with upping the boost because my afrs are down to 10.5 ish on full boost at 0.67 bar so I thought I could put some more boost in and let that lean it out a little. I know that there are many skylines running hybrid steel internal turbos like mine on std ecu's withoout problems, though of course they can't take full advantage of the available extra boost without further modifications.

I must admit to being surprised at the comments suggesting that it will expire and not to use it over half throttle, AFRs are fine, in fact a little rich, so I would have thought safe. I've driven it, shall we just say in a very spirited manner for some time with this set up. I won't pretend to be massively knowledgable on tuning, but I do have what I believe to be a pretty good basic understanding of what's happening since I have been working on vehicles for over 20 years, though the ones I'm on now are trains !

I will be uprating my ECU, it's just a case of organising a nistune since I can't go the route of power fc with mine being a tiptronic.

Anyway, rather than disconnect the boost sensor as I was tempted to do, I will run it at 0.8-0.9 bar boost on high and continue using the lower settings on my Gizzmo for normal use until I organise the extra mods.

[lachlanw]

oh yeah fair enough . didnt know you were keeping an eye on afrs and what not . do you have a wideband ?

there was a thread somewhere bout someone tuning a stagea with a safc and how he blocked the line to the boost sensor once going over 14 psi

i think "status" made the comment about it affecting afrs bu 1 -1.5 points

[DeanR33]

oh yeah fair enough . didnt know you were keeping an eye on afrs and what not . do you have a wideband ?

there was a thread somewhere bout someone tuning a stagea with a safc and how he blocked the line to the boost sensor once going over 14 psi

i think "status" made the comment about it affecting afrs bu 1 -1.5 points

Yes, I have a wideband in the car. I do also have an SAFC2, but I haven't used it to tune anything on boost because I know that if I lean out I will advance too. I noticed that the AFRs were quite lean before boost comes in and I tried richening up a little between 1600 and 3000 rpm on high throttle, but I'm aware that I'm probably retarding the timing a little going down that route, so it's swings n roundabouts.

Thanks

[mad082]

i tried disconnecting the boost sensor once, made no difference to my boost cut issue because it is based off the AFM voltage.

as for people saying that it is stupid to run higher boost without getting it tuned, it's pretty safe to do so. the AFR shouldn't lean out unless there is an issue with the fuel pump or something like that as the stock ecu is tuned from factory pretty rich. you will have more chance of doing damage with a tuned ecu than with the stock one. my 33 when running a fraction under where it would cut out (so about 12psi) was running about 10.5 or 11:1 AFR, so there was no issue with it leaning out.

unlike a tuned ecu where you can put as much boost through it and it will just lean right out if you go off the mapping, the stock ecu will pack it in if you go off the mapping.

[DeanR33]

i tried disconnecting the boost sensor once, made no difference to my boost cut issue because it is based off the AFM voltage.

as for people saying that it is stupid to run higher boost without getting it tuned, it's pretty safe to do so. the AFR shouldn't lean out unless there is an issue with the fuel pump or something like that as the stock ecu is tuned from factory pretty rich. you will have more chance of doing damage with a tuned ecu than with the stock one. my 33 when running a fraction under where it would cut out (so about 12psi) was running about 10.5 or 11:1 AFR, so there was no issue with it leaning out.

unlike a tuned ecu where you can put as much boost through it and it will just lean right out if you go off the mapping, the stock ecu will pack it in if you go off the mapping.

Thanks for that but are you talking about a 34 boost sensor here though? I believe that the 33's only use the boost sensor for the gauge, not an input to the ECU and the boost cut works on the 33 as you say thru the AFM. In fact that was one of the things that I was trying to clarify with this thread.

[Randon_I_Am]

there is another dedicated boost sensor on the neo, at the back of the block near the firewall.

It is used to trigger boost cut (usually at around 1bar i think) And I'm led to beleive that the ecu also uses this sensor to adjust fueling. but at 0.8bar could it just be you're hitting r&r?

when i put my new turbo in i hit this boost cut at around 15-16psi. was able to tune the boost cut out with nistune.

Also it brings on the engine light when i boost past 18psi...