Nissan Fairlady 300ZX V6 Turbo 1984 model?

Question

Anyone driving a Nissan Fairlady 300ZX V6 Turbo 1984 model. There is a whistling sound from from turbo unit starting after 80 kph onwards. And the boost meter climbs from -7 to 0 but does not go beyond...is it worthwhile to fit a blowoff valve. How to enhance hp without much modification to the factory turbo fittings?

Answer 1

check for charge leaks in the turbo intercooler pipes...its loosing air..as for extra power a couple of turns on the waste gate actuator rod works wonders...

Answer 2

I would've thought your car isn't boosting properly.

I don't know what figures your boost meter reads in...? Either PSI or BAR usually... some of the built-in boost gauges don't have any figures though.  Just coloured zones to represent higher and lower boost levels.

But if you do have figures on the gauge that actually mean something then the -7 figure represents vacuum... this is the engine sucking air in (like a non-turbo car) and then the 0 that you are seeing later on means the turbo is providing some boost but not much.  Only enough to keep the inlet manifold pressure at 0.  This means no positive pressure so the engine is not being force-fed like a turbo motor should. The turbo is only producing enough boost to remove the vacuum from the manifold.

Your car (according to Wikipedia) should be making 6.7 psi or  0.4 BAR.  That should show as a positive figure above zero on your gauge.

The fact that you mentioned a whistling sound suggests to me that the turbo itself is the cause of the issue.  When you hear a whistling sound from the turbo it means the blades of the turbine wheel or parts of the bearings inside the turbo are rubbing on the inside of the turbo casing. This stops the turbo from spinning as fast as it should and then it can't produce as much boost as it should.

If it is a 1984 car then I reckon it is going to have an old Garrett T3. That's a nice and simple turbo but they aren't very robust.  I have broken loads of those.

I would recommend you take the turbo out of the car and then phone CR Turbos in Hampshire 01425 638426 and arrange for them to rebuild it.  They will probably charge around £200 for a rebuild but check with them for their current price. They offer an inclusive collection and delivery service so you don't pay any extra. They send a courier to collect from your house and then drop it back a couple of days later.

A simple way to check if the turbo is good or not is to take off the tube that connects to the compressor entrance. (this is the tube that allows the turbo to suck in air from outside) Then gently rotate the compressor wheel with your finger.  If it's notchy as it goes around then the turbo is knackered.  Likewise, if there is lateral play in the turbine shaft then (i.e. left to right or in and out - depending on how you're looking at it...) then that is also a pretty sure sign of a knackered turbo. Also, if you push on the shaft with one finger and gently turn the wheel with your other finger then this will show you how the turbo spins when it is pumping gas at high speeds.

The problems might not be bad enough to show any serious issues with the finger test. At the workshop they would spin the turbo up on a dedicated turbo balancing machine and see how it performs.  The tests often involve stressing the turbo beyond its design limits to see if it really is robust enough to put back into a car for another 10 years.  

A blow-off valve is installed to stop the compressor wheel from either slowing down, stopping or in extreme cases - spinning backwards. It won't actually have any effect on the peak boost you can reach in your standing start scenario.  

It helps a turbo system in two ways. It's function is to allow pressure in the pipe between the compressor outlet on the turbo and the cars throttle body to leak pressure if the pressure suddenly spikes.  The spike is caused by boosting hard and then snapping shut the throttle - for a gear change normally... hence the varooom, ppsssst... varooom, ppssst noise you sometimes hear from turbocharged cars.  If the pressure in the pipe hits a closed throttle then it rebounds and heads back towards the compressor in the turbo.  When it hits the compressor it either slows, stops or reverses the compressor wheel. That is bad for your turbo.  There are two ways for the valve to work.  It can either vent to the atmosphere (when you hear the loud ppssst noise) or it can dump the boost back into the compressors inlet side.  If it puts the boost back into the compressor inlet then instead of slowing, stopping or reversing the compressor wheel it can actually help it to spin faster... that is called a reticulating system and is what manufacturers usually fit to standard cars.  Boy racers usually decrease the performance in favour of more noise by using a vent to atmosphere system.