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nissan
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as far as i know all the releif valve(little chinamans hat looking thing) does is stop it from boosting past 10psi, is this what ya mean by blow off valve? if so it can be removed and plugged with a brass fitting or something, its a good place to run your boost gauge from :) There are other blokes on the forum that know heaps more about it tho.
Oh and their usually bunged up to run more boost :)
 

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Rust is just natural weight reduction.
1986 SD33T SWB
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You don't really need it of you have a boost controller and gauge, since the turbo has a wastegate anyway. Its more of a fail safe in the event of overboosting.
I've heard they vent at between 7 and 10 psi, can't confirm which as I've never tested it, but most guys run over 10psi anyway so it's redundant in that scenario.
 

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nissan MK
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Thanks guys for the info. Confusion on the BOV(relief valve) set-up as per pics.
Must have a BOV to control over boost, I thought?, or some form of control otherwise you run the risk of stuffing the turbo. Venting a BOV out of the system I thought is illegal on new cars but being as our models are older, the law is different. Thanks again.
 

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The Prodigal Child Has Returned
nissan
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It's not a blow of valve ,it's a relief valve 2 different thing. It's for emergency situation. Say the little hose that controls the waste gate falls off or cracks and does not allow the waste gate to open your turbo will boost right out to say 20psi, Obviously not ideal so the relief valve opens to stop the extra boost.
You will know when it happens and you would get it fixed asap.

Yes a BOV venting to the atmosphere is illegal, I believe it's due to changing the pollution gear on the car, so a car with a turbo that was pre pollution theoretically could run a BOV. so being that these old patrols running a sd33t had very minimal pollution gear it's not an issue for the relief valve to vent, As said it's not constant thing like a BOV, Its only in an event of over boost (rare event)
 

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nissan MK
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Thanks Coils, that clears it up.
Waiting for controller and gauge from evil-bay to set my SD33T up, it is an unmolested truck, so keen to see the difference between 7psi and 10-12psi.
 

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The Prodigal Child Has Returned
nissan
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You will certainly feel the difference. The best mod by far has been an intercooler. but exhaust and dump pipe should not be forgotten.
 

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Thanks guys for the info. Confusion on the BOV(relief valve) set-up as per pics.
Must have a BOV to control over boost, I thought?, or some form of control otherwise you run the risk of stuffing the turbo. Venting a BOV out of the system I thought is illegal on new cars but being as our models are older, the law is different. Thanks again.
It's Dave here.
I've got an MQ flat tray that I've put an SD33t with 550000km on it in and I have blanked off the bov and wired shut the waist gate on the turbo and was getting 10 pound boost. Now I have give it more fuel pressure ( 2 turns ) and screwed out the boost compensator 2 turns aswell and am now getting 13 pound boost and it's loving life
 
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