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R33 Boost Cut & Ecu


adikt
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Im trying to get a decent straight answer here, everyone i ask has something slightly different to say.

Im wondering if R33 GTS25t's have a boost cut? If so, where?

I have been told that yes they do, but ive also been told that the ECU does NOT detect the boost at all?! (by the same people, at different times).

This kinda confuses me, as I dont understand how there can be a boost cut if the ECU cant actually tell what the boost is.

If someone can help clear this up for me it would be good.

Im getting a headache trying to work this all out.

Cheers

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From everything i've read, most of the factory ECU's go spastic past 10psi...Some people say there's went fine at whatever boost they were running over 10psi so maybe there's some 'freak' ECU's....

When my car was dynoed just before the pfc was installed and tuned, they set it to 12psi...the dyno graph looks like a rollercoaster, and it certainly didnt drive like that with the stock ECU, and running 10psi....

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The factory ecu does not measure boost, only airflow. The program in it is set so if the airflow exceeds normal operating parameters, the timing is retarded, and the mixture is enrichened. Also if the rate of airflow increase is too high, or it exceeds a certain point for a preset time, there is a safety feature built into the computer which wil cut the fuel. The boost sensor only operates the boost gauge.l

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No, it doesn't have boost cut, it has Rich and Retard...

e.g. dump a heap of fuel in and retard the timing if you exceed the airflow threshold as said above (this happens when a turbo comes on boost to say 12 + psi with the stock ECU )... Result is massive loss of power

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hrmm, ok, that makes sense.

my car went crazy on the dyno after about 10psi, so i guess thats why.

i guess ill be buying a pfc for xmas (if i can find one) and an external wastegate after that if i cant sort it out with the pfc.

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cos my car is overboosting atm, to close to 1bar, the standard gate cant control it properly - exhaust is too free flowing.

ive got another thread about it somewhere, apparently its a fairly common problem.

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yer nah dont think an internal gate is your problem.

dont see how a hiflowing exhaust would cause problems controlling boost seeing as the less restriction means the exhaust gases driving the turbinw wheel are 'getting way' nice and easy and there is no backpressure 'holding' the gases in the turbine housing.

using the standard 5psi rb25 actuator is probably more of the problem. i used one of them on my rb25 turbo on my 20 and boost was random so i used the 10psi from the rb20 and it was sweet

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cos my car is overboosting atm, to close to 1bar, the standard gate cant control it properly - exhaust is too free flowing.

ive got another thread about it somewhere, apparently its a fairly common problem.

The stock turbo doesnt not suffer from creep, or any other problems.

It will be your boost controller. A free flowing exhaust has nothing to do with it.

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no. its not my boost controller, ive been over that in my other thread.

and the rb25 actuator is actually about 7psi, as thats what it goes to without the boost controller in the loop.

and it boosts quickly & cleanly to about 7psi, then creeps up to about 12-15.

and according to nearly every performance shop/tuner ive talked too - it is definitely possible to have too free flowing an exhaust - it causes the turbo to spool too quickly, and the wastegate cant dump enough gas to control the boost.

im starting to think it might be the seperate pipe for the wastegate being too much of a restriction, so i might have to have a go at it with the die grinder and see what happens

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adikt is correct, the stock gate is too small for the turbo, once exhaust and other mods are introduced. It is easier for the exhaust gas to go through the turbo then the gate, and hence you get creep. I am in the process of porting my stock gate 2.5mm either side, enlarging the area by 38%. This will be a big difference. and the stock gate is DEFINATLY the problem. It's more of a problem on the R33 the R32.

As for boost controll, if you wire teh gate fully open, it will still creep, this is because the gate is too small.

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because it comes down to the design on the exhaust, if the exhaust is such that the cat and the bends and the dump, cause sufficient enough restriction in the system, the gas will want to flow through the gate, or to put it more presisly, it is forced to go that way, as it it easier to do so then to go through the turbine with has restricted flow. When the exhaust is so efficient, that it is easier for the exhaust gasses to go through the tubine and not the gate, as there is no restriction, that is when problems occur.

THIS IS A VERY COMMON PROBLEM, especially on SUBARUS and EVOS, when you change the dumps and get high flow or run no cats at all.

Not only is the exhaust a colprit, but if you run a FMIC, then the problem is worse. As cooler air means more dense air, esspecialy on cold morning, the turbocharger does not have to work as hard to compress the exhaust gases, and boost is made eaven easier. On such cold days with an FMIC, it is not uncommon to see a 5psi boost creep. This is to do with the fact that eaven though the gate is fully open, the gas is not going through it to regulate boost.

Now ther are things you can do, like getting an aftermarcket BOV, and regulating some of the boost that way, adding a restrictor plate in the exhaust, commonly done on RX7's. But the true fix is the internal gate, this is providing that you have tested things like the actuator and the arm and the gate for damage.

To port the standard gate, is no biggie, just a pain in the ass, as the whole turbo needs to come out, but seing as i can make nearly

210-220rwKw with a stock turbo, and the other mods i have, i am happy with keeping it as is.

Hope that anwsers some of the questions.

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External wastegates are typically for turbo's that don't have internal wastegate. If you think you have a wastegate issue, then you probably need to modify the one you have, i.e. increasing the flow through it by porting it, and a new actuator.

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ive been ringing around today trying to find somewhere that will port my internal gate.

they all say they wont do a rb25 turbo, but do lots of others - evos/wrx/mazda/etc.

have to keep ringing around, unless anyone happens to know anywhere in NZ that will do it?

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