Had an interesting discussion about what could be the cause/fix on a common Z failure, aka leaking turbo seals.

 

Damage to the turboseals and bearings is very often caused by compressor surge.

Compressor surge occurs during boost and when you let of the throttle, the air in the system has nowhere to go, while the compressor is still spinning at extremely high speeds.

This causes the pressure in the boost lines to dramatically jump and as an effect of this it puts a severe load on the compressor wheel, bearings and seals.

 

This is where the recirculation valves come in, they

are there to reduce this compressor surge.

They release the pressure from the boost lines and lead most of the air back to the inlet side of the compressor.

THAT IS...if they are working as they should !

The recircs are mechanical and when I recently replaced the 10 year old recircs on my car for BOV's, I noticed they sort of had seized and were probably not fully working anymore.

 

I also noticed that since I have the BOV's installed, my car stopped smoking. (It used to smoke a little after a gave it a good thrashing)

 

After some digging into the archives of tt.net, I discovered that more people have noticed this positive effect of BOV's and that the stock recircs on the Z are actually not really up to their job, since their diameter is too small and the 'reaction' is too slow...especially if boost has been increased above stock levels

 

So I'm interested to hear if someone on here also had a similar experience or what your opinions are on this ?

If this appears to be the case for more people, the blow off valves or aftermarket recircs may actually be a much better alternative to protect turbo-seals then that crappy piece of shit breatherkit, which only prevents that oil isn't sucked into the inletside of the compressor through the carterventilation (if I understand it's design correctly)

 

-Eric

 

[This message has been edited by lymon (edited 24-04-2002).]

Hi Eric,

 

Excuse a question from a novice but where would you get the aftermarket recirc valves, how much are they appoxiamately, and are they hard to fit?

 

Thanks,

 

Mark

I know TurboXS make aftermarket recircs for our cars.

I'm not sure about the price...I think the fitment shouldn't be any harder then fitting blow off valves.

 

 

Eric - thanks for posting that, I feel I have a much better understanding of recirc vs BOVs and can now way up the pros and cons based on something other than the sound they make!

Are there any signs that you can look for to assess the state of the recirc valves, running about .8 bar and from what you posted I can understand that this is putting serious pressure on the system.

 

Cheers and rezpect

 

Marj

 

Eric, do you reckon BOVs would solve the recirc 'honk' from an earlier post??

 

Please expand on 'shouldn't be any harder than fitting BOV's' - Does this mean engine out to get to the turbos?

 

Cheers,

 

RobH

Rob,by fitting bov's you will no longer have the 'honk', since this sound is caused by the stock recircs. (long story)

Fitment of bov's is fairly easy (and doesn't require engine removal)

You'll need to remove the stock recircs (located next to the AC-fan, under the airfilter), which is timeconsuming, but it isn't hard...definately a DIY-job

 

Mark, as far as I know it's very hard to tell if the recircs are not working 100% anymore, even if you remove them and look at them there's not much to see.

I opened up one of my old recircs and noticed a lot of oxidation and traces of sludge/oil on the inside.

 

-Eric

 

[This message has been edited by lymon (edited 24-04-2002).]

I have BOVs and believe they are the correct method for venting the excess pressure caused when releasing the throttle.

 

I cant see how the recirc can help matters by transferring the excess to the inlet side at the Throttle flap will be closed. This can only cause back pressure on the turbo on the compressor.

 

This in turn slows the turbo, whereas the excess on BOV is vented into the air, and hence no pressure on the turbo, so it can maintain its speed.

 

Leigh.

 

 

I thought the idea of the recircs is that they vent from the pressurised side of the turbo (that would slow it down if the air has nowhere to go) and release it to the inlet or low pressure side in order to keep the turbo spinning ready for when you next boot the throttle. Made sense to be at the time but I must admit I'd not given it much thought or interrogated the schematic.

Originally posted by lymon:

Fitment of bov's is fairly easy (and doesn't require engine removal)

You'll need to remove the stock recircs (located next to the AC-fan, under the airfilter), which is timeconsuming, but it isn't hard...definately a DIY-job

 

Mark, as far as I know it's very hard to tell if the recircs are not working 100% anymore, even if you remove them and look at them there's not much to see.

I opened up one of my old recircs and noticed a lot of oxidation and traces of sludge/oil on the inside.

 

-Eric

 

[This message has been edited by lymon (edited 24-04-2002).]

 

my recircs were gleaming inside, no traces of anything.

not sure if that was a good or bad sign....

 

the apexi bov's fitting was very time consuming for me, and i think it might have been easier if i had removed the engine even though its completely unnecessary.. lol

The pro's and con's of blow offs versus recircs on the Z32 is a complete other story.

I had my doubts about blow offs, until I fitted them myself and sofar I really like them.

They seem to prevent boostloss between shifts, but this could also be because you're distracted by the sound they make

 

Only negative thing I found out sofar is that if you drive at high speeds (>120mph) and you slightly let of the throttle, the car/engine starts to develop a very severe stumble...which doesn't occur if you let go of the throttle in one go (hope this makes sense)

 

 

[This message has been edited by lymon (edited 25-04-2002).]

Originally posted by lymon:

The pro's and con's of blow offs versus recircs on the Z32 is a complete other story.

I had my doubts about blow offs, until I fitted them myself and sofar I really like them.

They seem to prevent boostloss between shifts, but this could also be because you're distracted by the sound they make

 

Only negative thing I found out sofar is that if you drive at high speeds (>120mph) and you slightly let of the throttle, the car/engine starts to develop a very severe stumble...which doesn't occur if you let go of the throttle in one go (hope this makes sense)

 

 

[This message has been edited by lymon (edited 25-04-2002).]

 

Eric... I removed my BOV's for this reason. I found them irritating to live with becuase of the hesitation at high speed. I think it is because they vent boost if you lightly release the throttle and the ecu can't compensate for airflow that is measured through the MAS but not arriving at the combustion chamber. If that makes any sense

 

Steve