What hurts a RB25DET motor? Boost or Power

[nemz]

yeh if u run more boost with not enuf fuel ur in for alot of problems!!!

[Robo's]

So in summary, with a careful tune, i shouldnt encontour any problems. I think the best way also is to have a look at your pfc handcontroller and make sure timing is decreased and fuel increased past the tuned point of the power fc. This will help save your motor if ever there is a boost spike.

[slow13dude]

']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?

Looks like the tuner's the weak link there

[R31Nismoid]

']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

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

at 21 plus it would literally melt engines

one min its boost spike.

next its prolonged boost.

...........

[Sydneykid]

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.

A quick explanation;

*Boost is a measure of resistance to airflow.

*If you keep the resistance the same and increase the airflow then the boost MUST increase.

*But (there is always a but) by using a larger turbo you are decreasing the resistance. The turbine (and to a lesser extent the wastegate) are in themselves a fairly noteable resistance. So by going larger (or external) you are reducing the resistance.

*Hence you can have increased the airflow, decreased the resistance and held the boost at the same level.

However, I don't think 20 psi versus 38 psi is a valid example, perhaps an exaggeration to make a point.

A real world example, by sticking a larger exhaust on the car you have increased the power, even at the same boost. This is because you have decreased the resistance and increased the airflow. Increased airflow means more power.

Hope that makes sense:cheers:

[Butters]

Thats a top bit of text SK.

[Roy]

I think the best way also is to have a look at your pfc handcontroller and make sure timing is decreased and fuel increased past the tuned point of the power fc.  This will help save your motor if ever there is a boost spike.

What do you mean by tuned point? The power Fc measures the airflow in the engine, so a boost spike would just equate to more air. Do you mean get the car tuend at 22psi and then drive it at 18psi, just in the event that you get a boost spike its fueelign etc will be ok:confused:

My htinking is, rather then spend money and tune around a possible boost spike, you r money is better off spent on making sure all hoses/connections etc are sound. That way you dont have to worry about spikes at all:)

Does anyone know how you can make up an aftermarket ignition cut for when a certain boost pressure is reached? Something like a Hobbs pressure switch wired up to a relay on the ignition wiring form the ECU. I know it can be done... But i dont know enough about control circuits to set one up.

Something, with say a 2/10 th of a second kill for 3 seconds so as soon as the engine spikes it well and truly kills the ignition and let the driver know that a hose has let go, wastegate failed. LOL...my wastegate was installed incorrectly and jammed open after about 200kms. Imagine if it jammed close:)

I see that as a better way of going about the whoel spiking issue and hurting engines

[Robo's]

What do you mean by tuned point?  The power Fc measures the airflow in the engine, so a boost spike would just equate to more air. Do you mean get the car tuend at 22psi and then drive it at 18psi, just in the event that you get a boost spike its fueelign etc will be ok:confused:

My htinking is, rather then spend money and tune around a possible boost spike, you r money is better off spent on making sure all hoses/connections etc are sound. That way you dont have to worry about spikes at all:)

Does anyone know how you can make up an aftermarket ignition cut for when a certain boost pressure is reached? Something like a Hobbs pressure switch wired up to a relay on the ignition wiring form the ECU.  I know it can be done... But i dont know enough about control circuits to set one up.

Something, with say a 2/10 th of a second kill for 3 seconds so as soon as the engine spikes it well and truly kills the ignition and let the driver know that a hose has let go, wastegate failed. LOL...my wastegate was installed incorrectly and jammed open after about 200kms. Imagine if it jammed close:)

I see that as a better way of going about the whoel spiking issue and hurting engines

If you get your car tuned at 13psi, then that is the maximum it is tuned at (refering to the loads on the Power FC) If you cant place anymore load, how can you tune it? What i am saying is, that at 18psi my load points on the power fc reach upto 16, so there is another 4 to go, going by the 20*20 table. So i do put -a rough tune from loads 17-20. I do my own tuning anyway so thats my theory.

Im not worried about boost spike as i have never experienced it but some people worry about it.

[INASNT]

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?

A GT30 with 0.63ar will be useless just about everywhere.

[bigcarl]

we will see.

[Wazz]

why useless?

[INASNT]

we will see.

Theres nothing to see as it has been proven many times over to just cause wheel spin and then have nothing uptop.

Go 0.82 (thats what i am using) or even a 0.78 if they are still available

[Robo's]

Theres nothing to see as it has been proven many times over to just cause wheel spin and then have nothing uptop.

Go 0.82 (thats what i am using) or even a 0.78 if they are still available

I somewhat disagree, No matter what housing you get your still going to get wheelspin.

Say we have 2 turbos, one producing midrange and the other top end. Ok, both are going to produce wheelspin in first gear regardless. Now, second gear, one produces maximum power earlier than the other, say 500rpm?? So one spins or 7/8 kmh before the other, lets say 10kmh it is then, so one spins at 60kmh and the other at 70kmh, one has more power than the other so in my theory they would spin about the same. And the wheelspin you get at those speeds does not really slow you down. Now 3rd gear, if you can get wheelspin you have a mighty strong motor, so i would say the midrange turbo would jump the top end turbo initially and then the top end turbo coming over the top.

[INASNT]

I am basing what I wrote from actual happenings not theory

Search for a thread on steve from SA and his 3037 with the small housing threads.

[Roy]

One car with Ohlins shocks and unknown rubber doesnt make something law:)

If your running std head with std cams, id be very interested to see if the smaller housing makes any difference to top end. Stev had Poncams and Greddy Plenum from memory:)

A car with a Trust equivelant to the 3037 making 330rwkws used an 8cm housing which in Garrett talk equates to something around the 0.63-0.78 area. Perhaps someone else can confirm that Mitsubishi equiv to in Garrett talk, 0.63 = 8cm^2?

[INASNT]

not talking peak power roy but drivability.

[Sydneykid]

I somewhat disagree, No matter what housing you get your still going to get wheelspin.

Say we have 2 turbos, one producing midrange and the other top end.  Ok, both are going to produce wheelspin in first gear regardless.  Now, second gear, one produces maximum power earlier than the other, say 500rpm??  So one spins or 7/8 kmh before the other, lets say 10kmh it is then, so one spins at 60kmh and the other at 70kmh, one has more power than the other so in my theory they would spin about the same.  And the wheelspin you get at those speeds does not really slow you down.  Now 3rd gear, if you can get wheelspin you have a mighty strong motor, so i would say the midrange turbo would jump the top end turbo initially and then the top end turbo coming over the top.

What you are attemtping to describe is Average Power, if you do an Average Power comparison between the 2 turbo configurations it will answer your question.

[Roy]

not talking peak power roy but drivability.

LOL...yeh, but part of drvability is the driver. Mashing the loud pedal and complaining of wheelspin defeats the purpose. If you have Supercar power, lets face it a GT3 Porsche is lucky to have 230rwkws then you have to start to considering that like a Supercar you have to start using good quality rubber, not cheap Falkens etc etc.

Like a Supercar you need decent suspension setup that is balanced for tractions, handling and braking. To knowingly go bigger on the exhaust housing to dull response and help traction, well...i dunno. Just thinking out loud. I was in a RB25 powered GT30 car recently that had some serious mumbo, and it had no traction problems whatsoever running i think 245/18s. Which gets me thinking would the same turbo setup with a smaller housing therefore cause traction problems?!?!?!

My experience with my little RB20, is that the exhaust housing made 200-300rpm difference in 2nd gear, and the car hooks up really well. In 3rd gear the car makes 17psi 800-1,000rpm earlier:) with the smaller housing and makes the exact same top end. Actually with another tune it now makes better top end.

So one car with cams and inlet plenum doesnt to close the book on the matter, especially if the car we are talking about has std cams and plenum.

I dunno...just trying to show a few different poitns of view, who is right i got no idea:)

[INASNT]

whos gt30 rb25 did ya have a ride in?

[Roy]

Have a guess:) It was at Phillip Island, and since yours played up i had to go a for a scoot in a real Skyline, even if it cheats by using an RB25:)