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Boosting Problems with RB25

sprinterboy
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sprinterboy Enthusiast

sprinterboy

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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

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https://www.sau.com.au/forums/topic/43830-boosting-problems-with-rb25/
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sprinterboy Enthusiast

sprinterboy

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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

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!!!!!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.

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