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Trying to diagnose a disappointing lack of power

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Hi guys, got a tuning related question.

First, the car: a 1996 Nissan Primera, 4WD running a GTiR gearbox. Engine is an SR20DET from a W11 avenir.

I am running a GTiR manifold and a T28 ball bearing turbo from an S14. The downpipe is stock but the rest of the exhaust is 3".

-Nismo 740cc injectors


-Link G4+ Storm with knock control

My tuner is currently as stumped as I am as to why I can't make any power above 5000rpm -- see the attached file. For some reason the power drops massively, for no obvious reason.

AFRs are good at around 12:1 at the top. Timing is around 20 degrees there. Apparently that dyno pull was 13psi until redline.

Feel free to fire any suggestions or ideas as to what my problem is!!

Attached Files

Hey man, I am a diesel mechanic by trade with not a huge amount of high performance experience (But learning fast :) but just my thoughts on things I would be checking.

What is your fuel pressure? is your fuel pump able to keep up with the injectors (or it could be on its way out)? maybe at that rpm the amount of fuel flow is to much for the pump to keep up enough pressure? but then you should be seeing that in the fact that you would start to lean out...

Either that or maybe you have a restriction in your exhaust pipe... check if you have any flex joins that they have not folded (have seen this before on a nissan)

interested in finding out what is causing this :) keep updating what you find!

Looks like a restriction in your intake or exhaust or a boost leak.

Appart the obvious lack of power, does the engine run smoothly ?

No jerkiness, no weird noises, that kind of stuff.

What did the boost curve look like?

Thank for your replies. My tuner says there is a "slight intercooler restriction, but nothing too bad." Car still held 13psi according to the Link.

No jerkyness or weird stuff, in fact the car ran like factory on another ECU before I installed the Link.

Fuel pressure is good. Boost leak UV test was good. Leak down test 5% - 7%, I.E. very good.

I initially thought cam timing, however car still makes good vacuum and run smoothly.

Exhaust pressure was apparantly good as well. However, the previous owner also had problems with the SR20VET he had in there, in that he was running 20 - 22psi and barely making over 260wkw. This makes me think it's something sinister with the car (he sold it to me minus the engine, turbo setup, downpipe, ecu, intercooler piping). If this were the case, it could be something weird with the exhaust (some strange harmonics?), or perhaps even the drive train?

However, he did manage to make 197wkw on the standard SR20VET T28 turbo. So that's unlikely...

Could it be a worn coil pack? Could it be my intercooler is not efficient enough? Turbo worn out?

Another thing is that I didn't have very much wastegate preload when I put the turbo setup together, hence why I'm currently limited to 13psi... could this somehow be causing the issue? Still holds 13psi steady so I assumed not. Although I haven't actually seen the boost curve - I'm just going on what my tuner told me!

To eliminate the exhaust then dyno it disconnected.

Is there any chance you could post a copy of your map for us to look at, it could even be something in the settings they're missing

a detailed log file might also help

Sorry for the delay.

I checked the fuel and ignition maps after receiving the car back, and they look fairly normal, ad the AFRs are good. What is NOT good is the boost trace. See the attached picture.

A friend of mine and I also did some touch up road tuning and played with the boost control settings. Even setting the boost table to 100% duty cycle didn't help with a). Controlling the boost better or b). Aiding the spool up. As you can see, it is still fairly laggy for an S15 T28 ball bearing turbo.

I've come to the conclusion that I must not have set enough wastegate preload when I assembled the turbo assembly. As it's a transverse setup, the whole turbo/manifold/front pipe assembly as well as the radiator must be removed to rectify the supposed problem.

All thoughts welcome.

Attached Files

Which camshafts do you use? Are you sure about camshaft timing?

~4000RPM to see a bar of boost on a T28? that is very lazy, I'd test your actuator and pre-load as your thinking, is there no way of cracking the locking nut and turning the rod in place?

Cams are standard W11 SR20DET cams, which according to my research, are identical to S13 SR20DET cams. I've checked the cam timing too, which is fine.

There really isn't a way to get at the locknut as it's essentially sandwiched between the manifold and engine block. Unless I had some angle nose pliers that happened to be *exactly* the right shape, that is. One thing I can be thankful of, at least, is that the turbo is at the front of the motor, rather than the back...

The best I can hope for is to undo the exhaust bolts and manifold bolts and slide the assembly forward, in the hopes of being able to adjust the nut through the gap.

The intercooler should be ok, because in case of cooler restriction you would see a smoother power line with torque going down.

The problem may be the wastegate leak, i had that issue and the turbo was getting on boost very lazy and 1 bar was taking from 1700 to 4000rpm. I had no fire ring in the wastegate.

Also if there any other leak before the turbo - it wont work good as well.

Also check your diafragm of WG, it should hold vacujm/boost without leaks - else it'll leak exhaust gases and turbo wont get its meal ;)

Please update us

I am in a similar situation with a 4g63. The engine is full built with the usual modifications. Peak power is 400whp at 20 psi and the curve is essentially flat from 7000 to 9000rpm holding 400whp. The torque curve is also flat. The turbo is a 6765 and at 37 psi only produced 530whp. There aren't any obvious boost leaks I have whoever discovered that the intake cam is off timing by one tooth.

Fuel is q16.

Attached Files

Fix your cam timing and try again, what modifications are done to the car?

284/280 degree cams and required valve train components. Forged bottom end. 1650cc injectors. I intend to fix the cam timing but I can't imagine that it would have such a dramatic effect on the peak power.

What about intake, intercooler and exhaust?

Intake is a 4 inch pipe routed to the rear of the head light. Exhaust is 3 " straight pipe exiting out of the side of the front bumper. I can't confirm the make/ model of the ic core, but it's 3 " thick. Iat's are stable throughout the dyno pulls with a delta t of 3 or 4 degrees. Ignition is mw pro14 with motorbike coils. Clutch is a twin plate compclutch.

I've had a closer look at the mechanical timing, it doesn't appear to be off by one tooth on the intake cam as i originally thought. Any other suggestions would be greatly appreciated.

Try a pressure test pre and post cooler, whats the torque curve like?

I will try the boost leak test. Have a look at the image I posted the torque curve is laggy and flat.

I couldnt find any boost leaks, the only thing i have identified is that the turbo's bearings appear to be in pretty bad shape now, lots of shaft play. Can you make any suggestions Andre?

I never seen the torque, yellow on white isn't the clearest.

If the bearings are in bad shape the chances are you're suffering bearing drag

Check to see if the fins on your turbine wheel are damaged

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