RB20DET Boost Cut???

[VLRB20DET]

can anyone tell me why the rb20det seems to have a boost cut as mine hits 15PSI then falls back to 12PSI, how do i get rid of the boost cut, can you buy a defender to remove it or is it just the ceramic turbo running out of air/power??

[RaseR]

Doesn't actually sound like you've hit the cut as yet as in my experiences with boost cut on my R32 GTSt, it's quite violent....ie. you'll know when you've hit it.....Forget falling back to 12psi, you lose all power until you take your foot off the accelerator!! You can get a fuel cut defender to stop this, Turbosmart make one specifically designed for the R32 RB20DET:

http://www.turbosmart.com.au/fuel_cut_defenders.htm (see bottom of the page, I have one and can verify that they work...bit touchy to tune tho!)

Sounds more like your boost control setup and/or the wastegate not being unable to hold all the way up the rev range.....For reference, I used to run 16psi through my steel wheeled R32 turbo without any falling back even at 7000rpm, but that was using a solenoid controlled bleed valve.

Also bear in mind the ceramic turbo tends to fail fairly quickly at these kind of boost levels.

[doglet]

You're damn right about that boost cut RaseR! First time it happened to me it scared the c**p out of me.

[VLRB20DET]

so all i will need when i put on my bigger steel wheeled T3 is a fuel cut defender to get rid of the boost cut??, will this still apply as I have the motor in a VL commodore???

[RaseR]

Hey guys,

doglet - You're telling me mate!! I thought I'd f**ked the car right up first time it happened!!

VLRB20DET - Presuming you're using the R32 RB20DET ECU/Airflow meter and not a custom setup, you will be able run the Turbosmart fuel cut defender I gave a link for earlier, worth about $200 if I recall correctly.

Some useful info about FCDs from my personal experience - the boost cut occurs on the RB20DET when the voltage coming from the air flow meter to the ECU exceeds a particular value (5.05V?), what the fuel cut defender does is clamp the voltage seen by the ECU from the air flow meter to an adjustable amount, usually just below the cut voltage....So just be careful if you do get one as they can lean out the fuel mixtures too much in the upper rev range if not adjusted correctly, many tuners view them as a bit of a band-aid solution and prefer to modify the ECU to remove such cuts....more expensive though!

[VLRB20DET]

so at the end of the day to get the engine to work reliable, i should just ditch the stock ecu and go aftermarket eg Link or Microtech etc..........., then i can do away with the air flow meter and the boost cut(and rev limiter) alltogether??

[RaseR]

It's up to you man, the FCD was okay on mine until I started fiddling around with new mods, at which point - like I said, it was touchy to readjust. With a different turbo bolted on, you're likely to see more decent, reliable power gains from either a modified/dyno tuned RB20 ECU or an aftermarket job such as those you mentioned, and yeah another major benefit is then you can set boost/rev limits wherever you want, but it all depends on what you can afford.