Below is a recent dyno graph on my car. As you can see power starts to drop off between 5-7k rpm since I have increased the boost. The scaling of the graph makes it look worse. The car is currently running the HKS ST kit which has a GT3037. Based on the graph I'm assuming the turbo is running out of puff and seeking a replacement. Ignore the boost fluctuation as this has been fixed and the torque spike is to do with the rpm pickup of the dyno.

I spoke with GCG turbo and they recommended to upgrade the comp and chra to the GTX3076r and retain the existing hot side which has an AR of 1.12. Some have mentioned that since the turbo has a T25 flange this is part of the issue but reading this thread it alludes to otherwise. (within reason)

https://my350z.com/forum/forced-indu...flanges-2.html

I have confirmed timing at topend is okay

I'm satisfied with the power the car currently makes but looking for the power to be held to redline. I'm also concerned with the bigger comp and existing large AR I will lose some boost response.

Replacing parts is ok but I need to stay away from fabricating new exhaust components etc.

Typical engine build with a CR of 8.8, JWT C2 cams and mild porting of the heads

Some say that the current setup should hold all the way to rpm. I'm just at a loss on what to do or check.

 

Any update on this mate? Off topic, you ever considered E85 since E85 is becoming more available in NSW.

 

not really. I'm trying to find out if the comp side of the 76r is the same as the HKS unit. Both have a comp 60 A/R but with our setup there is less than 2mm clearance to the starter motor. Any change in frame size will not fit.

I reduced the boost to .75 and it made 312rwkw and flattened out the power curve a bit.

Not really interested in E85 as it will not solve what i'm after.

 

U need to measure you turbine back pressure and see what your ratio is, your boost is not dropping much what points to the ex side. Also check your cams at higher rpm you should have them retarded.

 

@racer59, Do you mean a typical exhaust back pressure test. ie: plumb tester into upstream O2 port and rev to 3000rpm?

Base timing is about 14 degrees and VCC is about 10 > 6 degrees in that rpm range. When on the dyno we noticed not much difference when moving the either timing value from the current setup.

 

You need to measure the pressure before the turbine, just get a piece of copper tubing about 500mm long then a boost gauge, if you are running 15psi boost u do not want to see more than 30psi of preesure at the turbine, measure at full load and rpm.
Our old engine curve looked like yours and it was due to backpressure.

 

hmm.. I get you now and the copper pipe to dissipate the heat before the gauge. That's going to be a pain to test