Just After A Quick Answer, Max Psi Recomended For Std Int Rb25

[DaveO74]

Hey people,

Im just after a quick answer to the above question, Im currently running 18psi with standard Internals head gasket. would I be wise to run much more boost later on if I upgrade the turbo or am I asking for trouble without a buit engine and cometic head gasket etc?

I have heard of people running 23odd psi but Im not sure if thats with forgies or standard internals

Mods are:

S2 R33 GTST

Hybrid FMIC

APEXi Super Suction Kit with pod

Custom Air box with CAI(Home Made)

Split Dump and Catco Race Cat

3.5" HKS Cat back Silent High Power exhaust

Exedy 5puk Clutch

Greddy Ex Cam Gear

EMU

Hypergear HighFlow (ATR28 G2 Profile)

Nismo 555 Injectors and Walbro fuel pump

Z32 AFM

Yellow Jacket Coils

[Moodles2]

Without more info on the turbo, you need to find out the pressure where it starts losing efficiency, or else you're needlessly generating alot more heat than you really be needing to out of the turbos efficiency range.

[R31Nismoid]

No such thing as a quick answer.

Too many unknowns, too many variables.

Its not really a question of PSI in many cases.

[DaveO74]

Ok maybe I should re-phrase my question. We all know that if you rev an unbuilt engine to say 10,000rpm day in and day out it will at some stage let go right?

So does the same thing happen when large amounts of boost is pumped through the same engine?

The max boost my current turbo can run is about 20-25psi but that's not my question.

Let's say hyperthetically I go out and buy X super turbo which has a max efficiency range of say 50psi, now surely if you pump 50psi through a standard internaled engine it will fail as it would revving it to 10k all day.

Does that make make more sense?

[tridentt150v]

Knock levels will be your limiting factor, without lowering your compression or WMI you will get knock.

The combinations that can run more than say 18psi without big knock numbers on a std motor are rare [not impossible]. The more you ask for the worse it will get.

You can wind up the boost, but then you'd have to wind back the timing, so you could be no better off and probably worse than if you hadn't bothered.

But as the others have said - too many worms in the can to say for sure, its not a general rule.

[DaveO74]

Ok thanks guys

[crack]

as a very general rule the standard rb25 is reliable for between 250 to 280 rwkw. pick the power you want and choose a turbo to suit. no good having a big laggy turbo for 250 rwkw. if the turbo is sized right for the power and application you want then you only need to run the minimum boost required to get you there.

[Cjmartz2k]

OP--it sounds as though you think there is a boost number that will pop your motor. There isn't. It's cylinder pressure which if effected by horsepower and knock (and a bunch of other things, but those two pertain to your question.) Like trident mentioned, if it knocks enough, your motor goes pop. Many things can cause knock including to much boost for a given octane of fuel/CR/timing/etc. The other is hp. You try making 1000hp on a motor with stock head bolts, the insane cylinder pressure is going to lift the head and the head gasket will go pop.

Think about how many psi of cylinder pressure you have when the air/fuel mixture goes bang compared to a measly little 30psi of boost. Nothing in comparison. I remember reading a lot of internet "fact" when I first started researching skylines online saying headgaskets go out on RB's at 1.2 bar. Those people had NO clue WTF they were talking about.

[DaveO74]

Cool that's pretty much what I was after, so long as it's a "safe" tune so to speak there is no majic number.

Thanks for the advice guys.... And not treating me like a dumb dumb, just one of those things I've always been curious about