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Help Me Tune This Car, Won't Make Power

BoostdR

By BoostdR,
in Engines & Forced Induction

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BoostdR Mentor

BoostdR

Posted
Posted

I have offered my tunning services to a good friend of mine, however I am not getting the results expected. Unfortunately the engine was not built very well, was returned for warranty rebuild once and has had many problems since. The car previously has the same HKS GT2835 turbo and made 200rwkw. It also made the same power with a RB25 turbo. I attemped to gain some more power by increasing the boost on the previous RB20 and it resulted in minimal improvement. So the choice to install the RB25/30 was chosen.

Specs are:

RB25 Head

Rb20 Cams

RB30 Block

Unknown comp forged pistons

HKS GT2835

STD manifold

3" exhaust

Trust turn flow FMIC

RB26 Apexi PFC

RB20 loom

So my experience so far is.

-RB26 PFC is used on the RB20 loom and rewired to suit. I have corrected the Airflow correction and curve as the 'Shop' decided to just change the airflow correction to 50% as the GTR expects two air flow meters inputs. The output from the single VG30 AFM has been bridged into the PFC which is fine, However I modified the Air Flow Curve to actually represent the amount of air entering the engine as I like the A/F ratio on my Datalogit to reflect what it is in relality. So now the Air Flow correction is back to 100%. I have rescalled the Maps to 400-8000rpm instead of 800-9200rpm(GTR). Injectors are std RB25. Fuel pressure has be raised to emulate an output of ~444cc so injector correction remains at 100%. Injector lag has been changed to 0.04ms (diff between std GTR and RB25 injectors).

-Tuning the AFR was resonably straight forward and 11.8-12.0AFR was acheived at full load and 14.7AFR at cruise. 0 boost was 13.0AFR so no reason for concern there. The car was experiencing missing, so I pulled the plugs to find they were gapped to .4mm.. I regaped them to .75mm. No change in missing as expected or felt. I have ordered some NGK PFR7A plugs but have not installed as yet.

I was able to tune out the miss with AFR's richer than 10.8....The car will not be tuned to this as there is obviously a problem.

-Timing was adjusted however there was a rythmic rattle heard when accelarting in 3rd or 4th for long periods. The noise does not show up with knock. Response is amazing with 1 bar @ 2900rpm and 1.3bar @ 3100rpm. Power is way down on what I would expect however with this turbo. Similar power can be made with half the boost(inicating at restriction). It has adjustable cam gears so I checked the timing in regards to TDC. I found the inlet cam retarded 10 degrees(crank) and the exhaust advanced 5 degrees. I have dialed them in as best I can so would hope them to be much closer than previous. The car ran almost with no noticeable difference after adjustment, maybe alittle more response. The car still hesistates and misses, is low on power and drops off quickly after 6000rpm.

-I have blanked off the BOV to see if it was leaking but this is not the case.

-I haven't checked but am planning on.

-Exhaust/Cat for restriction

-Intercooler for restriction

-Injectors for even flow

-RB20 Resistor box(is in the engine bay) have to check connectivity and suitablilty with the RB25 high Impedance injectors

-turbo compressor condition, check GCG rebuild specs.

-compression test

-RB20 Camshaft suitabilty

Any help, thoughts and guidance would be valued. I don't want this one to beat me.

Matt

blind_elk Grand Master

blind_elk

Posted
Posted

My first guess - and I'm no expert - would be that a 3L engine wouldn't breath too well through RB20 cams, in standard form, let alone with a huge turbo pumping stuff in. Lift is only 7.8mm (GT-R is 8.3mm lift). Both are a 240 duration (In & Ex).

And which RB20 cams (DE, DET)?

Also, the specs for the RB20 and RB25 cams are different:

. In Open In Close Lobe Centre Ex Open Ex Close Lobe Centre O/Lap LSA

RB20DET 5 BTDC 55ABDC 115 60BBDC TDC 120 5 117.5

RB25DET TDC 60ABDC 120 57BBDC 3ATDC 117 3 118.5

Maybe a set of adjustable cam gears might help.

RB20s don't run a resistor pack on the injectors. (although I recognise that it might be needed for the PFC to not poo its drivers)

BoostdR Mentor

BoostdR

Posted
  • Author
Posted (edited)
My first guess - and I'm no expert - would be that a 3L engine wouldn't breath too well through RB20 cams, in standard form, let alone with a huge turbo pumping stuff in. Lift is only 7.8mm (GT-R is 8.3mm lift). Both are a 240 duration (In & Ex).

And which RB20 cams (DE, DET)?

Also, the specs for the RB20 and RB25 cams are different:

. In Open In Close Lobe Centre Ex Open Ex Close Lobe Centre O/Lap LSA

RB20DET 5 BTDC 55ABDC 115 60BBDC TDC 120 5 117.5

RB25DET TDC 60ABDC 120 57BBDC 3ATDC 117 3 118.5

Maybe a set of adjustable cam gears might help.

RB20s don't run a resistor pack on the injectors. (although I recognise that it might be needed for the PFC to not poo its drivers)

I was told they where DET cams, but will check as the DE have less duration(232 inlet) and lift(7.3). I have tried changing the lobe center on the cams to mimic rb25 cams closer but it made minimal difference. It has adj cam gears which I used to correct the initial cam to crank/TDC alighnment issue.

So the resistor pack I saw must be unrelated... If the PFC is expecting low impedence injectors and you connect high impedence RB25 injectors I would not expect it to cause an issue as the output current required to operate the injectors would be less. I will still have a look however..

Thanks for your thoughts, keep them coming

Edited by BoostdR
BoostdR Mentor

BoostdR

Posted
  • Author
Posted
dont waste your coin on those platnium plugs either. BKR7E do the job just fine.

It had 6's in it. They were NGK R with the split earth strap and V groove electrode. I'm not a fan. The owner of the car also wanted plugs that have a longer life span.

I myself don't mind the extra labour and use the cheap ones.

BoostdR Mentor

BoostdR

Posted
  • Author
Posted (edited)

No graph as yet. All road tunning at this stage. I may be able to get you a graph using Copilot software.

Cheers.

The car had uprated springs fitted, so most likely not the issue.

Thanks for the idea, however much appreciated.

Edited by BoostdR
BoostdR Mentor

BoostdR

Posted
  • Author
Posted

update.

Did some more investigation after work tonight. Found the car picked up ~50rwkw with no missing with no changes. The weather here is 16 degrees. I tuned the car to the point it would step out in second so was happy at the improvement. Some 7 degrees were added to the map. What has got me re thinking the problem is after we sat on the side of the road for 5min to up load some data(after a few runs) and relieve me of feeling sea sick the car again felt very lifeless and lost the previously found power. Heat soak is my first thought. I'm going to look at the ignitor, CAS, Camshaft CAS drive keyway next. I think disregard looking at the

exhaust,

intercooler,

camshaft duration and lift

Resistor box (doesn't have one for the injectors)

Turbo compressor

My first point of call will be checking the ignition timing with my light when the engine is cold and hot. I will also check the voltage at the ignitor at both temps. Thirdly, check the adjustable cam wheels haven't move.

here's to hoping

cheers

blind_elk Grand Master

blind_elk

Posted
Posted

Doesn't the GT-R run an inlet air temperature sensor? The others don't. Maybe lack of sensor is causing problems for the PFC.

And do you have real cold air induction (not running un-shielded pods)?

BoostdR Mentor

BoostdR

Posted
  • Author
Posted
Doesn't the GT-R run an inlet air temperature sensor? The others don't. Maybe lack of sensor is causing problems for the PFC.

And do you have real cold air induction (not running un-shielded pods)?

Yes the GTR runs a Air temp. It has been bridged to the water temp sensor from what I can see. Both read the same temp. I must say water temp seems very low, sitting between 55-62 degrees.

It does have an airbox with cold air induction.

BoostdR Mentor

BoostdR

Posted
  • Author
Posted (edited)
So the PFC thinks that the air going into the inlet plenum is the same temperature as the coolant. I don't think so!

Yes thats exactly correct. I have adjusted the ign and fuel air temp correction to negate this. Maybe worth my while picking a an air temp sensor and wiring it in. Some thing is fishy which the low temp coolant reading it is giving me however. Maybe the fact the inputs are bridged/parallel, the overall circuit resistance changed and has skewed the value....or the rb26 coolant temp sensor works on a different resistence to the rb20. Never the less it is not the cause of the engines troubles from what I can see.

Edited by BoostdR
MBS206 Grand Master

MBS206

Posted
Posted

R32, R33 and R34 all run different temperature senders for the dash and ECU... Becareful.

Also, you have the readings in parallel, this will most likely cause issues, as the ECU is reading the resitance of it, by varying voltage...

BoostdR Mentor

BoostdR

Posted
  • Author
Posted (edited)
R32, R33 and R34 all run different temperature senders for the dash and ECU... Becareful.

Also, you have the readings in parallel, this will most likely cause issues, as the ECU is reading the resitance of it, by varying voltage...

Agreed,

Will split them up.

Edited by BoostdR
swanny180 Proficient

swanny180

Posted
Posted

You can't just copgyback another signal off the factory water temp sender, as it works off resistance which is being influenced by the addition of another sensor.

My car ran like a cop when I tried to wire up my old water temp gauge off the factory sender. As soon as I removed it, problem solved and it was running as normal.

Definitely get an air temp sensor ASAP and DONT run the car with both signals from the water temp sensor.

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