Compressor Surge, good or bad?

[subsonic]

I think you should use these!
 :twisted:        :twisted:           :twisted:

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[zagarus]

So Zagarus what is your rpm, boost , and engine size , also what turbo do you have. We can figure it out from there provided that the map is available. Cheers Dan

1.6l, garrett T3, as for boost at rpm is hard to say as it varies if im on a hill or not, but next time on level ground ill take some readings. any specific rpms you would like?  i can tell you right now cruising on level ground in 5th at say 110km/h im boosting about 1-2psi, if i goto 125km/h its about 3-4 psi.  90km/h and the boost gauge isnt showing anything.

[bigblockchev]

Now I have opened my big mouth I will have to try to get an answer for you. It is a lengthy calculation with several equations involved. I am going to pick one of the maps supplied by subsonic and try to plot. To start with there is no way that you are having compressor surge at that low level of boost. 3-4 psi translates into a pressure ratio of around 1.27 which is below the surge limit of any of the T3 maps provided (14.7 psi+ 4 psi / 14.7psi). I will retire to the Batcave to see if my aged brain can get a precise answer for you. Cheers Dan

[zagarus]

thanks a bunch  


but full boost in say 3rd with the pedal mashed is about 23psi, then i go to shift and get that oh so sweet sound.

[jtanguay]

try to stick to around 20-22 psi.  andy2 did some backpressure measurements, and the turbo is most efficient at that level... anything beyond means more turbine backpressure, which means that you can cook your motor pretty good if you spike your EGT's up.  not sure if there are any mods to the turbine housing to try and reduce the backpressure though.

i suggest you try water/meth injection  :twisted:

why did you choose AAZ nozzles? i bet merc nozzles would make your car fly!

[bigblockchev]

Here for the edification of all is what I am working from. It is taken from an old book of mine Turbochargers by Hugh MacInnes which I haven't used in twenty years or more.

[zagarus]

hey jtanguay the car usually is only boosting around 22psi, its the really good nights when it max's out at 24psi, never hits 25 but i seriously think i should get an EGT gauge. I just want to do it properly and put the probe in the exhaust manifold, but i want to take it off to do it. if i didnt have to worry about that i woulda had one in a loooong time ago.  And i got the AAZ nozzles cause they were the ones on kermatdi. Im sure one day ill upgrade them again...when i go 1.9TD  

[bigblockchev]

I used subsonics maps but was not sure which a/r ratio the turbo has do I did all three. There is a mix of celsius and farenheit temps  and psi pressures but these are mostly ratio calculations so it doesn't matter. I assumed 70 deg F as air temp and .65 as the compressor efficiency for calculation. The black dot is the point on the map at the theoretical 5000 rpm and 23 psi shift point. As you can see on 2 of the maps that point is close to the surge line and on the third it is in the surge area. You can go through the calculations yourself for different points & pressures. Cheers Dan





 (Took me 4 times as long to get the pix in here as it did to do the calculations)

[zagarus]

thanks a lot!! so really i am not getting to the point of compressor surge, or at least not all the time to the point its gonna kill my turbo very soon.  I dont go hard on the engine often anyways, but i drive spiritedly  :lol:

[vwmike]

That turbine chop sound is nromal. Often I find compressor surge isn't found just to the left of the surge line but trust me when I say you will hear it when it happens. I stayed safe on boost for a while but recently started pushing for more pressure down low. I found I never hit surge until I was coming up this big hill in 6th. With that much load it hit about 24 psi at around 2300 RPM on the GT22 causing the typical compressor surge sound (sort of a chattering) and made the needle on the boost gauge bounce.  I turned that down a bit after so that can't happen again  

I never heard anything of a sort on my 1.6TD.