R33 Gtr performance issue

[Dose Pipe Sutututu]

I don't think it's a fuelling issue, if you look at his AFRs they are more than safe.

Also with his power levels on 98RON, there's not a lot of fuel demand.

[BK]

yeah fuel SHOULD be ok with enough head room on 98Ron. My 33 with GT-SS on 22psi boost is around 70 -75% duty with Denso 700cc injectors, stock rail, stock fpr, Nismo 280lph in tank pump and twin 80mm Z32 afm.

[KiwiRS4T]

2 hours ago, Dose Pipe Sutututu said:

I don't think it's a fuelling issue, if you look at his AFRs they are more than safe.

Also with his power levels on 98RON, there's not a lot of fuel demand.

I have reread the thread and can find no reference to his  AFRs. I have seen a lot of flow charts for Walbros and the drop off in flow with an increase in boost is dramatic with 12v or less. The stock set up (not sure how a GTR is different from my C34 Stagea) will often deliver less than 12v to the pump when running.

https://www.efihardware.com/products/2065/800HP-EFI-Submersible-E85-High-Flow-Fuel-Pump-F90000267

[TXSquirrel]

I'm only suggesting the fuel data should be look at if the pump is not directly wired to chassis for ground and battery for positive.

When I was only getting 12V at the pump, the most fuel pressure I got was 51psi with 570cc injector.  Would be even lower if injectors were bigger.  After directly wiring positive I got 12.8V, and after also directly wiring negative I got 13.8V. 

Surprisingly all I need was 12.8V and fuel pressure was back to normal.  But then looking at the fuel flow curves for various pumps there really is no surprise, just half a volt would make a huge difference.

[Dose Pipe Sutututu]

Trust me it's not fuelling issues, I have a data log off his car but his tuner was smart and didn't log timing and locked the map.

AFRs are pretty much like this:

[KiwiRS4T]

6 hours ago, Dose Pipe Sutututu said:

Trust me it's not fuelling issues, I have a data log off his car but his tuner was smart and didn't log timing and locked the map.

AFRs are pretty much like this:

You may be right but all that chart shows is that tuner was keeping afrs safe - he may have limited power in order to do that. I would like to know if the fuel pump has been directly wired. It would be interesting  to see pressure before and after the intercooler rather than just change it on spec.

[TXSquirrel]

Right, my AFR was fine too but injectors were completely maxed out.  OP's 800cc injectors seem big enough, but if fuel pressure were at say 45psi they could still be maxed out.

[Dose Pipe Sutututu]

His motor wasn't taking anymore timing, it's not fuel related guys.

His injectors were not maxing out either.

[TXSquirrel]

I agree it's quite possibly not the fuel.  But wiring issue is something fairly easy to eliminate so he can move on to the next possible cause.  That's all I'm suggesting.  

Coincidentally my car also couldn't take any more timing.  I recall 17 was the most my tuner could push at the top.  And coincidentally my tuner also said it could be the cooler and coils, so I bought a Plazmaman and new Splitfire. 

A couple months later I went back to get the Plazmaman installed and a retune, but as my tuner tried to set another baseline we saw my car had lost a lot of power.  AFR looked fine but duty cycle was showing 108% theoretical pulse on Nistune, so he hooked up a fuel pressure gauge and we both saw it would go up to 62 psi but as RPM climbing pass 5000 it would drop to 50 psi.

After sorting out the fuel some months later, on went the Plazmaman and Splitfire and timing came back, so did power.  However I honestly can't say what was the true cause, coils, fuel, or cooler.  Maybe the Plazmaman and Splitfire were completely unnecessary, and the issue with timing first time around was really the wiring going half way out.  Or maybe it really was the OEM cooler and coils, but they were replaced together so I would never know.

[BK]

Look, if afrs are fine, they're fine. It doesn't matter if injectors are maxxed or fuel pressure is not ideal, whatever. 

14 hours ago, TXSquirrel said:

Right, my AFR was fine too but injectors were completely maxed out.  OP's 800cc injectors seem big enough, but if fuel pressure were at say 45psi they could still be maxed out

And, so what. If there was not enough fuel to achieve correct mixtures, because of a low pressure situation, the base fuel map would have to be run higher than expected, and expected duty % would be higher, which you would see you are doing in the tuning software. If the system can achieve say 12:1 afr at full load and that's what your tuning to that's what it is. You are somehow implying that you can have spot on air / fuel ratios but still be not delivering enough fuel, which is not possible.

Logging the fuel pressure and the injector duty % will give the answers to how maxxed pump is.

[Chrisko33]

Hey guys thought I’d give a update the car has gone back in for a touch up tune I have since changed exhaust to 3.5inch,changed the cooler 100mm trust, coil pack wiring harness  and put a single bov  car put out 305kw on 20psi. With previous setup it was at 282kw on 21psi. Its still running stock cams and stock valve springs cars at its limit now.