N12 Turbo Forums

hey people ...were would b a better spot for afm in front of turbo or in the cooler piping i want some flutter but if it no good in the cooler piping i will have to put it in front of turbo ?


cheers for any advice

if not in the bin then in front of turbo mate

In the cooler piping for flutter, Up close near the TB is best, I can show you a picture of my setup I had on the exa, It fluttered crazy, Infront of the turbo you will get less flutter, With it in the piping you can then fiddle with a "dose pipe" :\

Put your hand up if you know flutter is the sound of your turbo having its arse flogged out.

It's a bad sound... might as well say you like the chain on your bike to squeak.

Kimmo wrote:Put your hand up if you know flutter is the sound of your turbo having its arse flogged out.

It's a bad sound... might as well say you like the chain on your bike to squeak.

Whilst boosting, "surge is bad, mkay!'

Whilst backing off, surge is not as bad as having a restrictive exhaust (back pressure at the turbine exducer).



Damo

Damo wrote:Whilst backing off, surge is not as bad as having a restrictive exhaust (back pressure at the turbine exducer).

You mean excessive backpressure (like the standard dump would cause) is harder on the bearing than off-boost compressor surge?

Compressor surge is an ugly thing; if what you say is true, I'm surprised the standard dump is so bad.

who cares dosing sounds fucking awsome

Kimmo wrote:

Damo wrote:Whilst backing off, surge is not as bad as having a restrictive exhaust (back pressure at the turbine exducer).

You mean excessive backpressure (like the standard dump would cause) is harder on the bearing than off-boost compressor surge?

Compressor surge is an ugly thing; if what you say is true, I'm surprised the standard dump is so bad.

and why would it be harder on the bearing?? i think you mean harder on the fins on the shaft, the bearings are located on the shaft and free spin, if you were to have surge it would only slow the speed at most.

Kimmo wrote:

Damo wrote:Whilst backing off, surge is not as bad as having a restrictive exhaust (back pressure at the turbine exducer).

You mean excessive backpressure (like the standard dump would cause) is harder on the bearing than off-boost compressor surge?

Compressor surge is an ugly thing; if what you say is true, I'm surprised the standard dump is so bad.

Not the shaft bearings, but definitly the thrust.

That should have read "Whilst 'Backing off surge' blah blah blah.

But yes, any backpressure is a bad thing for turbo. Exhaust pressure (post turbo) pushes the shaft onto its thrust bearing, and loads up the oil control seals with exhaust gases trying to force their way to freedom anyway they can.

Post turbo backpressure basicly reduces the efficiency of the turbine as a whole, as it needs more pressure across it to generate enough force to drive the compressor to a certain psi level. Which also introduces more twisting force on the shaft (which isn't a problem with anything but a ceramic turbine wheel realy).

Post turbo pressure also forces up back pressure in the exhaust manifold increasing pumping losses through the engine, which requires the turbo to work even harder to generate a given boost pressure.

I would go as far to say that a T2 running 20psi on a E15 with minimal total exhaust back pressure would last longer than the same T2 running 12psi on a completely stock exhausted E15 engine.

The factory don't bother about it because at stock boost levels it isn't a biggy.
Which leads to the BOV argument. IMHO, factory BOV are for NVH 95% turbo longevity 5%.



Damo

Thanks for the info, man : )

thanks for all the info guys i have learnt a lot of this site thanks to all that give info its great





cheers josh

n12sumfin wrote:and why would it be harder on the bearing?? i think you mean harder on the fins on the shaft, the bearings are located on the shaft and free spin, if you were to have surge it would only slow the speed at most.

If you consider the bearing (which is a straight bushing with oil flowing through it), you can see that there's a built-in potential for radial backlash, simply because there has to be room for the oil.

And when you consider the compressor and turbine housings' inlets and outlets are tangentially oriented to the shaft (and act on it via the blades) at whatever angle you have your turbo rotated to, loads introduced to the turbine/compressor assembly will be passed on to the bearing, because the bearing is what allows the blades to translate flow to/from spin by preventing any other motion.

So if you have a chaotic situation like compressor surge happening, there are a whole bunch of forces making the shaft basically want to thrash around inside the bearing... and if this is happening when you're lifting off, presumably this nastiness will be accompanied by a corresponding drop in oil pressure.

I reckon I'd rather avoid it, and get a few hundred million more revs out of my turbo before it's junk.

Kimmo wrote:

n12sumfin wrote:and why would it be harder on the bearing?? i think you mean harder on the fins on the shaft, the bearings are located on the shaft and free spin, if you were to have surge it would only slow the speed at most.

If you consider the bearing (which is a straight bushing with oil flowing through it), you can see that there's a built-in potential for radial backlash, simply because there has to be room for the oil.

And when you consider the compressor and turbine housings' inlets and outlets are tangentially oriented to the shaft (and act on it via the blades) at whatever angle you have your turbo rotated to, loads introduced to the turbine/compressor assembly will be passed on to the bearing, because the bearing is what allows the blades to translate flow to/from spin by preventing any other motion.

So if you have a chaotic situation like compressor surge happening, there are a whole bunch of forces making the shaft basically want to thrash around inside the bearing... and if this is happening when you're lifting off, presumably this nastiness will be accompanied by a corresponding drop in oil pressure.

I reckon I'd rather avoid it, and get a few hundred million more revs out of my turbo before it's junk.

interesting way of looking at it.

so i was told flutter and serge are complete different ? flutter is harmless as it is cutting through the air ?and surge is air pushing against the blades on the fan to try and stop it from spinning ? and u can hear the difference as 1 sounds nice and the other is ment to b a real horrible fluttery snezzie type noise dont no if this is true but it made sense to me so yea






cheers Josh

Ahhhhhh nope!