What hurts a RB25DET motor? Boost or Power

[qwikky]

im running 270rwkw on a standard engine. running 20psi and racing at wsid every month. revs kill engines not bost.

[INASNT]

A 2530 running 1.4 bar will be pumping the same amount of air into the engine as say a GT30 running 0.9 bar boost. So its the airflow into the engine not the boost that can kill an engine.

[Roy]

A 2530 running 1.4 bar will be pumping the same amount of air into the engine as say a GT30 running 0.9 bar boost. So its the airflow into the engine not the boost that can kill an engine.

:confused: That doesnt sound right. More airflow means you need more fuel, so more air/fuel equals bigger bang. Now this bigger bang means more power, higher loads on rods, bearings etc etc.

With boost though, the increase in cylinder pressure to get the same amount of air into the cylinder increases the loads. Or thats at least how i understand it.

If RB25s were spinning bearings, throwing rods etc, then id say your asking too much of the engine. The fact that many kill pistons tells me you want to be mindful of A/Fs and the boost level your running to make the power you are after.

I dont own an RB25 so dont listen to me, im just dribbling:)

[Sydneykid]

If RB25s were spinning bearings, throwing rods etc, then id say your asking too much of the engine. The fact that many kill pistons tells me you want to be mindful of A/Fs and the boost level your running to make the power you are after.

Exactly Roy, by far the most common engine failure I see in RB25's is pistons, and that's a tuning problem. The second is valves and guess what, that's a tuning problem as well. Bearing damage is not all that common, mostly in RB26's and that is related to oil surge more than rpm.

[cameron]

A 2530 running 1.4 bar will be pumping the same amount of air into the engine as say a GT30 running 0.9 bar boost. So its the airflow into the engine not the boost that can kill an engine.

Finally,

You guys are saying that a bigger turbo is better because you'r runing less boost, as i said before if you do get a boost spike and you are really pushing you'r internals you have a greater chance that the smaller turbo will run out efficency eg not being able to produce more air their for no power. As a bigger turbo will.

[HCR32]

I dont own an RB25 so dont listen to me, im just dribbling:)

lol aye roy dont worry about these boys, we both know the rb20 is the best motor;)

[teejay]

Finally,

 

You guys are saying that a bigger turbo is better because you'r runing less boost, as i said before if you do get a boost spike and you are really pushing you'r internals you have a greater chance that the smaller turbo will run out efficency eg not being able to produce more air their for no power. As a bigger turbo will.

1 a properly set up car will not get boost spikes

2 id rather a spike from a big turbo - at least the air wont be 100000 degrees because the turbo will be waaaaaaaaaay out of its effiecency range

[R31Nismoid]

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2 id rather a spike from a big turbo - at least the air wont be 100000 degrees because the turbo will be waaaaaaaaaay out of its effiecency range

in a split second spike your gonna have a massive rise in temps?

i dont think so

[Abo Bob]

Why not? If you compress air it gets hot. Compress it more it gets hotter.

[cameron]

']1 a properly set up car will not get boost spikes

2 id rather a spike from a big turbo - at least the air wont be 100000 degrees because the turbo will be waaaaaaaaaay out of its effiecency range

If a properly set up car won't get boost spikes then a properly set up car should have a decent cooling system, so you won't be getting temps of 100000*

The inlet temps should not vary much from running 18psi and getting spikes to 23psi, as nis said, the only real variation you'r going to get is from the outside weather temperatures.

[teejay]

i know of a turbo set up that would make excellent power at 18/9 psi

at 21 plus it would literally melt engines

it popped at least 5 rb20's in the hands of 3 owners. we never got to check the exact difference in heat but they where massive. why? because it was outside its efficency range.

a cooler can only do so much , it a turbo is roasting air its roasting air.

a spike in boost is more likely to damage an engine due to afr issues rather then heat anyhow.

[cameron]

You said: We never goto check the inlet temps when it was breaking motor's

Then you said: Heat is less likely to dammage the motor?

Anyway its all down to tuning, You can only tune to an extent intil you'r standard internals become un-safe.

You make it you break it.

[bigcarl]

thats what im trying to say, if my turbo is still making reasonable power gains as the boost is being screwed into it and my support systems are on par , air fuel ratio is spot on, inlet and exhaust temp not excessive ,how far can i go on stock internals if the tuning and support systems are spot on??? 18 psi? 20psi? 22psi? 25psi?

[Slide]

low performance drivers and poor tuning = trouble

[Sydneykid]

thats what im trying to say, if my turbo is still making reasonable power gains as the boost is being screwed into it and my support systems are on par , air fuel ratio is spot on, inlet and exhaust temp not excessive ,how far can i go on stock internals if the tuning and support systems are spot on??? 18 psi? 20psi? 22psi? 25psi?

In the real world it simply doesn't happen like that. If you have spent enough money on the outside of the engine (bolt ons) to make what you describe possible, then you have enough money to upgrade the internals. You will have spent something like this;

Exhaust manifold ------ $1,500

Exhaust system ------ $1,400

Hi flow cat ------ $500

Turbo ------ $3,000

POD, AAI, heat shield ------ $400

Inlet manifold ------ $1,500

Camshafts ------ $1,400

Valve springs ------ $600

Adj pulleys ------ $500

Radiator ------ $700

Oil cooler ------ $800

Clutch ------ $2,000

Power FC ------ $1,100

AFM upgrade ------ $400

Boost controller ------ $500

Intercooler ------ $1,500

Injectors ------ $700

Fuel pump ------ $400

Head work ------ $1,000

Fitting labour ------ $4,000

Tuning ------ $1,000

Gauges ------ $800

Total ------ $25,700

So after spending $26K on the engine, what's another $1400 for a set of plstons? And finding that situation, plus one where nothing has gone wrong on the development path, is very unlikely. I have certainly never seen it.

[bigcarl]

whats the maximum boost have you used on an internally stock engine sk?

[The Mafia]

http://www.skylinesaustralia.com/forums/sh...201#post1261201

can you help me here? I'm asking for 250rwkw with a GT 30-40 with a .63ar exhaust housing, and an injector and fuel pump upgrade.

(and a unopened motor)

You think it will handle it with a good tune?

[BBQ]

whats the maximum boost have you used on an internally stock engine sk?

Its not about maximum boost, each turbo is different.

If you’re running a Stock r33 High flow turbo that can push 20psi,

And you’re running a T88 that is pushing 20psi.

Which one do you think is pushing more air? A T88 at 20psi is equivalent to the high flow pushing 38 psi.

You can run as much boost as your want on a stock motor, I will only last you a few days. Until things give way, Eg Head gasket, Piston ring lands, Rods... So on...

So their is no set limit on max boost for any motor. As each setup is different. And will have different effects on the motor internally.

It’s about reliability, insuring your motor lasts you longer then 1 week, and allowing good performance from it at a safe boost level.

Which all comes back down to tunning.

[R31Nismoid]

You said: We never goto check the inlet temps when it was breaking motor's

 

Then you said: Heat is less likely to dammage the motor?

 

Anyway its all down to tuning, You can only tune to an extent intil you'r standard internals become un-safe.

 

You make it you break it.

i was gonna say a not much different thing.

i would very much doubt a turbo would go from fine @ 19psi, to motor killing @ 21psi without something dreadfully wrong with the tuner.

[teejay]

funny you say that..

all popped on the same dyno

all the same tuner

no need to name names (and please dont assume i mean bad by that)

the thing was a filthy air baker, that was the call of one of turbo techs best technicans... but im sure he has no idea, right?