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Overboost On Stock Turbo

skysthelimiter

By skysthelimiter,
in Engines & Forced Induction

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skysthelimiter Apprentice

skysthelimiter

Posted
Posted

So a bit of a background on the issue I'm having.

I have a 95 manual r33 gtst which was completely stock when I bought it and for the most part it drove pretty well however I did notice a little bit of a surge or slight miss sometimes after 4500rpm but put it down to a possible boost leak.

I later added a 3" turbo back exhaust with bell mouth dump, just jap fmic and a gizzmo boost controller. Since doing these mods the car will now continue to overboost even with the boost controller disconnected and the wastegate actuator disconnected from the flapper. The flapper also seems to have a nice range of motion so I dont believe it is fouling on the dump.

I have done some reading around however this doesnt seem to be a common issue with these levels of mods and mostly seems to be related to bigger turbos however mine is stock so I am a little stumped as to how it is still building boost.

I have since tried

- cleaning the maf

- checking for boost leaks

- Installed a nistune ecu with stock S2 maps

Is it possible the stock wastegate port is too small? Anything else worth checking? I would like to be able to get the car back to stock boost levels before having the nistune tuned.

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https://www.sau.com.au/forums/topic/450782-overboost-on-stock-turbo/
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skysthelimiter Apprentice

skysthelimiter

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Car was hitting boost cut anywhere from 8.8 psi to about 11.5 psi at around 4500rpm. Even with the actuator arm disconnected it is still building boosting and hitting boost cut although a little higher in the rev range and only when I'm hard on the throttle.

GTSBoy Grand Master

GTSBoy

Posted
Posted

There's no such thing as boost cut on R33s. All right, so it cuts. But it's not a boost cut. It's essentially purely a result of there being higher AFM signal for that engine speed than the ECU is happy with. It is an "overpower" cut.

So having said that, your car shouldn't make much boost at all with the wastegate held open. If by "disconneted" you're simply letting it flap around in the breeze, perhaps you need to go back and wire the thing in the open position to ensure that it is open and try again.

If the thing is in fact pretty much jammed shut, regardless of your statement that the actuator arm can move freely (see my earlier post) then you will get enough boost to trip the ECU out.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

try this, plug the boost sense hose directly into your actuator and drive the car.. it should not see more than 0.6bar of boost...

The boost sense hose should not be a vacuum hose.. as it's the worse possible source to use.. It needs to be pre throttle.

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