Jump to content
SAU Community

Boosting Problems with RB25

sprinterboy
 Share

Recommended Posts

sprinterboy Enthusiast

sprinterboy

Posted
Posted

Hi, i'm new to this so any help would be great.

I just bought an R32 with an RB25 conversion done to it, and it seems to be hitting boost cut to easily and i would like to know if there is a nice simple (ha nothing ever is) soulition to fix it. The car has a "stage two" turbo on it, apexi AFC, big fmic, k&n pod filter. and the boost guage read's in Bar and gets very close to the 1.0 mark, so i'm guessing around 10-11psi. do i just need to tune the AFC or just go all out and get a new computer.

Thanks, Justin

Link to comment
https://www.sau.com.au/forums/topic/43830-boosting-problems-with-rb25/
Share on other sites
sprinterboy Enthusiast

sprinterboy

Posted
  • Author
Posted
What do u mean by 'stage 2' turbo

Well, i was told a stage two is TO4 internals fitted to the stock turbo. Anyway i found out the can be fixed by a new computer or a boost cut defender and nothing else(unless i turn the boost down)

But the turbo does searge alittle when i'm not driving it hard. is this common in skylines with aftermarket turbos and stock computers?

sprinterboy Enthusiast

sprinterboy

Posted
  • Author
Posted
!!!!!DO NOT BUY A BOOST CUT DEFENDER!!!!

They are a ripoff. I bought one before i full understood what they did. Not good.

OK, explain, i just thought that i was a comp bypass allowing the turbo to run higher boost, so how is this a bad thing? Anyways, i'd prefer to buy a full computer and have it tuned to the car, i'd also gain a few kw too if i was lucky!

skyr31 Enthusiast

skyr31

Posted
Posted

I'm not overly mechanicaly oriented but i'll give you the best explanation i can.

A fuel cut defender is actually a device that when installed will 'trick' the computer into thinking that the car is running less boost than it actually is.

In the case of an RB25 skyline, the fuel cut defender is wired up to your airflow meter. When air flows through the airflow meter, it sends a message back to the computer via a voltage level to let the computer know how much fuel it must inject into the motor for the given boost level that the car is running.

Just before the factory boost cut is activated by the stock ecu, it holds the airflow signal coming through the airflow meter at that point so the computer only thinks its running say 10psi of boost. Therefore, no matter what psi you turn the boost up to, say 14, it is only injecting enough fuel for 10psi. The car won't hit boost cut but it will make the engine lean out very quickly...you will end up pushing your engine home in a shopping trolley.

Just for an example, i had mine installed and dynod it to be safe, with only 2 extra pounds of boost the engine went from running filthy rich to dangerously lean. (It had now been removed!!)

Moral of the story, get a computer.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • MBS206
      Rb26/30 build

      By MBS206 · Posted

      And if you want more power, more reliably, and cheaper, go get the Aussie RB... The 4L Barra and put that in instead.
    • MBS206
      Nismo rear spats

      By MBS206 · Posted

      No cats will keep discolouring the rear bar. Sends white paint a weird yellow stain. Cut and polish normally gets it out, but you'll be doing that every fortnight I found.
    • Butters
      Rb26/30 build

      By Butters · Posted

      Both heads will be equally reliable or unreliable depending on what you do to them.  Stock the RB26 head will flow more. You have access to the stock intake ITB manifold on the RB26 cheaply which flows really well(1000hp+).   Arguably more aftermarket support for RB26, though in Aus we love our RB30 SOHC heads too.    The only downsides to the RB26 head is if you have a VL commodore and want to keep the SOHC look.  Where you may have an issue is drilling out the rb30 block for the bigger head studs but if you are building a big power motor you'd probably put bigger studs on the SOHC head too.  This is just about finding a good machine shop, sometimes easier said than done.  RB30 head worked can make big power just like a Rb26 head, so really it actually more comes down to what your preference is for your car.  People now even making billet versions of both.
    • GTSBoy
      Rb26/30 build

      By GTSBoy · Posted

      2630s work perfectly well. There is something to be said for just using the 30 head, as it saves all the pain of the conversion, still makes tons of power, still sounds cool, etc etc. 2630 will obviously make more power again, but the differences are not stupidly big. It really depends on whether you're racing for sheep stations or not. If it's dead serious, then it's a 26 head. If it's just for fun, it could go either way. But the 26 head and the effort to get it set up, etc etc, is part of the fun.
    • lilley's gtr
      Rb26/30 build

      By lilley's gtr · Posted

      I've been building a 26/30 for a few years now. I've had the head built with all the good stuff. I had a 32 gtr but blew it up and yes its all going into a vl but im looking for some advice from some RB nuts on pros and cons on putting a 26 head on a 30 bottom end is it worth it Works are as follows Head -Extensive porting 1mm oversized supertech valves Supertech double springs Supertech valve guides Supertech titanium retainers Tomei solid lifters Tomei 270 x 10.25 cams Head drain Bottom end series 2 rb30 block Cp ceramic coated pistons Eagle rods Romac balancer Oil restrictions  O ringed blah blah spent a fortune And will get a girdle because the 30s arent used to handling that much rpm Nitto billet oil pump Hypertune plenum 6boost mani Refurbed astra pump thats the cover for it in the boot I did have a precision 6262 but sold it because drag car life. Currently building the ass end full 4 link floater rear end with a 2 speed  But the dilemma i have is my mate rekens I should just stick with the 30 head for reliability. Has any one had any issues with mounting the 26 head ie compression blowing gaskets etc. Just looking for some advice from people who have gone down this route. Here's some photos. Blew the oil pump in the gtr and decided to rip the motor out at the time and do a full build only to find it had been a repairable write off so went down this path.     
×
×
  • Create New...