Compressor surge, Is it really that harmful ???

[neil_jdmr]

That\'ll do me
 
Thanks gent\'s

[Grizzly]

The compressor wheel does NOT STOP SPINNING or Stall.

Would you say it puts more load on the shaft between the Hot and cold side? i.e. the extra pressure in the Inlet tract physically trying to stop the the Compressor wheel or pushing air back past the wheel while its still spinning causing the Chirp noise.

I think i ment to say it starts to stall (as you say it doesn\'t actually stop) but it does slow quicker due to the extra Force created by the pressure in the Compressor/inlet.

[Carl]

The compressor wheel does NOT STOP SPINNING or Stall.
Exhaust gas is still turning the Turbine BLade!! it will not rotate in the other direction!

The other man use of the recirc valves was to do with emissions

Hi Mark,
I beg to differ,if the throttle is shut then there is no longer any exhaust gas driving the turbine,then you do indeed get air rushing back over the compressor which can slow it down,it makes a chirrupping noise and it tries to do this in a cycling fashion.
You are right that certain setups are fine without,but it does depend on the type of turbo,and also it\'s end use.
Also if dump valves were not needed then manufacturesrs would not put them onto production cars as it would save them money,and we all know that if they think a corner can be cut then they will cut it.
Regards
Carl

[BlitzBoy]

sure there is some type of load on the shaft but its negliable on a big single, it wont see anywhere as much as the engine sees, eg say you running 10 psi you wont get 10 psi passing back over the blades probably 2-4psi, you can read all the different theories on that Ausrotary thread.

[Carl]

sure there is some type of load on the shaft but its negliable on a big single, it wont see anywhere as much as the engine sees, eg say you running 10 psi you wont get 10 psi passing back over the blades probably 2-4psi, you can read all the different theories on that Ausrotary thread.

Quite right.
Hows your new bridgeport going?
Regards
Carl

[RemarkLima]

I was just thinking what carl said, with no throttle, there\'s no exhaust gasses and hence no boost per se.

But tell me this, while we\'re on the subject, if I\'m gently accellerating, and making zero pressure on my boost gauge, then the turbos are still "doing work"? Just nto made it to +ve pressure right?

So to cool down you really need to be very gentle ont he throttle?

[BlitzBoy]

I think we are talking in msseconds here lol once you snap the throttle shut im sure there is still some exhaust gas and heat still turning the turbine wheel, and im sure the wheel is still turning at still some rpm, you see what we need is a high speed camera in there to tell us lol
Turbos are always working when gently cruising

[Grizzly]

I was just thinking what carl said, with no throttle, there\'s no exhaust gasses and hence no boost per se.

in a nut shell the amount of time from the 10psi (e.g.) passing through the throttles going round the Rotor Firing and out the exhaust is the time the Turbo will see Surge.

Out of intrest, if you rev your engine with the outlet of turbo blocked off how much pressure will you see in the Comp housing?? will it be 10psi if the waste gate is set to 10Psi? i guess it all depends on how much of a damper you have.

[Grizzly]

So to cool down you really need to be very gentle ont he throttle?

Ideally cool down should see no + boost.

[Timmy]

Look at it this way the throttle closes and the air hits the closed throttle and bounces back through the system normaly finding it\'s way though a dv. In this case it has no where to go but back through the turbo. On hitting the turbine which is spining still it pushes against the fins in the opposiet way to usual slowing it down. Theoreticaly this puts a twisting force on the shaft also cud bend the fins of the shaft very bad for ceramic turbines as they will just shatter. Also the forces probably push the bearings in an odd way maybe causing a metal on metal contact for 1/10000th of a second.
In other words only bother if you have a large turbo as the shaft will be thicker and also the finns.
The bearing damage will probably take a long time to become a problem so even on a big turbo you will reduce the life of it. You could just buy a hks ssqv the old tyoe thats adjustable and adjust it nice and stiff and your get a little bit of stall along with a dump. Probably just stall at low boost levels.

[BlitzBoy]

no way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts

[Carl]

no way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts

They don\'t shut the throttle though the run and between gear changes either,so it won\'t be a problem for them anyway,that is why they don\'t run them.
The compressor does slow down on clutched manual shifts,so a slight amount of time maybe can be gained by keeping the turbo rotating by using a dump valve,rather than it having to respool even slightly after each manual gear change.
Regards
Carl

[BlitzBoy]

I beg to differ I believe you lose time with a dump valve as you have to repressurize the intercooler pipes so you slower building boost.
Thats why WRC cars run without BOVs as they do many many gear changes per rally time is lost building boost with a DUMP valve.
I done back to back drag runs when I run the the T04R turbo and I disabled the bov i had at the the time and my quarter miles were better

[Grizzly]

no way would compressed air bend the fins in the boost levels we are talking about, hell top end turbo drag cars that run 40 plus psi dont run BOVs and they dont break fins or shafts

Ok, what other reason is there for blades to come off a Garrett turbo?? i was only told it was Due to Surge.

We aint talking top end best you can buy turbo\'s, lets face it most of the T series are x truck?

[Carl]

If you run a recirculating dump valve then you don\'t lose any boost at all.
Regards
Carl