To much boost?

[krystalized_jdm]

Hi gtrc,

I will be upgrading to full 3" exhaust this winter, but I have heard full exhaust on a stock rb20 turbo makes it boost to high?

Is this true? If it is true, is there a way of turning the boost down say...via boost controller? (Unsure if boost controller can turn DOWN boost)

To add, I currently already have an apexi intake, and a fmic w/ catback exhaust (Says to be boosting around 10 psi on boost gauge)

If I do require a boost controller, what do you guys recommend? Electronic, manual? I have 0 experience with them, so your input is appreciated!

[Alak]

Its whats called boost creep. The wastegate cant keep up with the increased flow of having a free flowing intake and exhaust. A boost controller won't fix this.

However if you decide to get a boost controller, you can start with a manual, but my advice is to surf car forums. Greddy Profec B spec 2's sell for under $200 and they are great boost controllers.

[krystalized_jdm]

Does this hurt the turbo then? How much boost will I run with full exhaust 3", fmic and intake? Do I need a boost controller then? I don't want to turn boost up.


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[frankydodo]

Stock rb20 turbo can take 14psi if it is in good shape. Before changing mine i was running 15 psi on stock turbo and when i pull it out the shaft play was so little i was impressed! With intake/exhaust and fmic i thinm its 12 psi +/-

And you say you don't want to raise up the boost. I was thinking the same when i got my first skyline and now its my second one and i'm hoping to get 300+whp next summer ! Its really a drug :P


For boost controller

-a mbc is a cheap and good option if you are running a little setup but in my experience they always create boost spike and they not really hold high boost well.

A cheap and good ebc is the HDI ebc-r . It doesn't have alot of feature but it uses the same solenoid as aem, greddy, they all use MAC solenoid. Easy installation and easy setup( knob that turn in front of unit . Cw= more boost Ccw = less boost ) and its holding the boost very well! And at 150$ shipped brand new , you can't go wrong with it!
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[Alak]

Most guys run 12 to 14psi as standard. I wouldnt worry too much.

To solve boost creep you can port the wastegate. This involves enlarging the hole and placing a larger valve on the flapper arm. This is very common mod in FC rx7s so if you search wastegate porting FC3S then you get an idea of whats involved. That mod with a boost controller will give you absolute control.

[Skym]

Rough guide -

Podfilter = +0.1 bar

3" exhaust from turbo dump pipe / outlet pipe = +0.3 bar

Turbo dump pipe / outlet pipe = +0.08 bar

FMIC = +1-1.5 psi

1 bar = 14.5 psi. That depends on if it's at sea level or not. Some say 1 bar = 14.7 psi at sea level.

Also boost level probably won't be as high due to stock BOV can leak after 10psi and ECU can pull ignition timing, run engine richer, etc due to detecting knock.

I would be worried about fuel system, ECU tune mods. Stock fuel map is quite lean at lower rpm when up the boost level. ECU tune can be the difference between engine lasting, failing with boost levels above stock boost level.

You can't drop boost level lower than internal wastegate actuator spring pressure. On bench tested 2x RB20DET internal wastegate actuators and they were around 12psi when the arm started to move (spring pressure). When the internal wastegate actuator spring inside the bulb part is on the way out (wears out) it will be closer to 11psi or lower when the arm moves. When lower than 11psi you would replace the internal wastegate actuator.

If want to drop boost level lower, would suggest fitting a auto (from a R33 with RB25DET, autotransmission) R33 RB25DET internal wastgate actuator that is around 5psi with spring pressure.

The small wastegate port on stock exhaust housing can cause boost creep at higher rpm.

Stock turbo fails due to age / wear with bearings + higher boost levels (higher rpm on turbo). If turbo is out of balance due to age (bearing wear) it will get more out of balance the higher you rev it. Basic test is wiggling the compressor or exhaust wheel. More extensive test is using proper testing equipment that a turbo specialist has to see if play is within specs (there's a tiny bit of play which is normal).

Also high oil temps (need a engine oil cooler to lower oil temps) is the other cause of failure due to oil breaking down, which creates excessive bearing wear and turbo goes out of balance and compressor wheel or exhaust wheel touches housing (creates a whistling sound on compressor side).

Sometimes it can be exhaust wheel which due to turbo being out of balance, touches housing and shatters. The ceramic pieces go into engine when backing off throttle when exhaust wheel shatters or goes down exhaust (exhaust wheel ends up in middle of exhaust or can't be found).

Cheap boost controllers don't have filters to stop oil getting into boost control solenoid, map sensor. More expensive Japanese boost controllers have these filters. Top of the range HKS or Blitz boost controllers are the ones to buy if can afford them (control boost level better over 1 bar and can drop boost level if turbo overboost's, car wheelspins, etc). Can buy the cheaper HKS boost controller, but the 3 port solenoid is not as good at controlling boost level if boosting over 1 bar. Similar aftermarket boost controllers run the cheaper 3 port solenoid.