Turbo Overspeed

[Rabbit TD]

I thought I'd start a new thread on this from the answers I got from some of you about the dangers of turbo overspeed and the damage it would cause.  I was asking about boost levels and blocking wastegates and such when the overspeed word came up and I think a lot of us need to understand this better.  So from what I gather and totaly agree with it's not so much too much boost but the actual speed the turbo gets to that causes the damage to the turbo itself from a wheel exploding.  In other words then it is a matter of turbo rpm is that correct?  I guess the next question then is then does excessive or dangerous turbo rpm come from excess boost and what would be considered excess boost on a 1.6 T/D Garrett T3.  Some of you said that you've had them fly apart, I would be curious to know at what boost levels they came apart at and I didn't even mention excessive EGT's that could maby weaken the turbine.  My point is though and I am new to the turbo game here, but with the boost levels some of you guys are running on t3's should a person need to worry about 10-12 psi with EGT's around 1100 with a blocked wastegate.  I haven't seen more than 10 yet but isn't that considered pretty safe and I think that is about where the wastegate is supposed to be set on these if I am right, my actuator is shot, that's why it's just got the valve in there by itself.  Is there more to this than meets the eye, I'm sure there is but I'd like to know more and what some of you put these turbos through that survived and the exploded ones too, not to mention the engine itself.

[hamradio]

I don't think I'd be worried about the turbo...my vnt15 makes 12 psi while I'm cruising down the freeway at 70.

[Rabbit TD]

I don't think I'd be worried about the turbo...my vnt15 makes 12 psi while I'm cruising down the freeway at 70.

12 while cruising, what does it go to when you wind it up, what is considered normal for a turbo like that.

[Vincent Waldon]

My K14 has seen nearly 30 psi... albeit briefly... and it's still in one piece.

[1slowvw]

I have snapped the shaft in a K-24 at 20psi. have piled up several at the same boost level on a 1.9.

[Rabbit TD]

My K14 has seen nearly 30 psi... albeit briefly... and it's still in one piece.

Why does the factory set the boost levels so low if these turbos can go much higher safely and make more power, is it an emission thing or something like that?

[anto]

My K14 has seen nearly 30 psi... albeit briefly... and it's still in one piece.

How often would you see 30psi vince?
I have a k14 with the wastegate fully wound in so it boosts to 26psi max.
I was led to believe that it was a ticking time bomb at that level....however i wouldnt be hitting 26psi every gear change or even every drive in the car.
What are your views?

[arb]

When I worked in a Melt Lab with super alloys (some air craft turbos, all jet engine hot section parts, EcoBoost turbo) I learned it was not just what the exact chemistry of the alloy was, but how it was melted, what order the ingredients are added at what temperature, how long it is molten, what if anything is used to top the casting for cool down, type of casting, how it is handled post casting, treatments (gas, quenching, etc) and so on that dictated how strong the allow was. HUGE variances is then the alloy would fail based upon these variables.

So, the point is, each turbo is different even within the same type. The only way to know with some certainty is a turbo speed sensor. Some aircraft have these. Then, the number is only important if you have the design limits from the OEM...

Pushing it hard and often, I'd call a time bomb. :-D

[Vincent Waldon]

Yup I'd agree... 25+ psi is asking a lot of a tiny little K14.

My view would be:  it was designed to run at 10-12 psi for years... 20 psi is probably well within its design limits for daily commuting, and the occasional flirtation with 30 psi for those emergency "gotta get ahead of this truck on the on-ramp" might even be ok.

My problem that if the poor little gaffer is pushing 30 psi I'm also burning enough fuel to push the EGTs into the critical zone as well... so again, something for brief sorties only.  ;-)

[Smokey Eddy]

My old t3 with a blocked waste gate will see 28 or so for less than a minute at a time doing a hill climb. It's still okay but i do get a lot of oil into the intake.

[Rabbit TD]

My old t3 with a blocked waste gate will see 28 or so for less than a minute at a time doing a hill climb. It's still okay but i do get a lot of oil into the intake.

I don't know if it's the way it's designed or not but on both my t3's there is a line that goes from the canister directly to the bottom of  the turbo inlet opening that has a fitting with a metered orifice in it and if I take the rubber boot off mine the little oil trail goes right over that opening and looks to me like it might be designed to let some oil in the wastegate actuator to lubricate the valve guide because it damn sure gets in there, at least it did on my rebuilt one and it's funny that hole is directly on the bottom of the inlet like that if it wasn't designed for that purpose also.  While I'm on this subject does anybody out there with a lot of turbo experience know if it's normal for a little oil to be visable in the inlet when you take the boot off, just a little black trail on the bottom.  I have 2 of them and they both do about the same thing, one has 400,000 on it and the other has 4,000 and both are about the same as far as the oil trail.  I don't know if the 400,000 one is the original turbo though but it's the one I'm using now but the engine uses very little oil and doesn't smoke at all with either of them, the new one is just too big.

[vanbcguy]

The oil more than likely comes from the breather, not the turbo...  Yup, pretty normal.

I actually saw somewhere in a VW paper (I THINK it was the 1.5 SAE paper but I can't remember for sure) that part of the idea behind routing blowby into the intake is giving the intake valves a bit of lubrication... Probably doesn't hurt the turbo either...

[Smokey Eddy]

The oil more than likely comes from the breather, not the turbo...  Yup, pretty normal.

I actually saw somewhere in a VW paper (I THINK it was the 1.5 SAE paper but I can't remember for sure) that part of the idea behind routing blowby into the intake is giving the intake valves a bit of lubrication... Probably doesn't hurt the turbo either...

Ah Ha! and the boost pushes it everywhere.

[anto]

Yup I'd agree... 25+ psi is asking a lot of a tiny little K14.

My view would be:  it was designed to run at 10-12 psi for years... 20 psi is probably well within its design limits for daily commuting, and the occasional flirtation with 30 psi for those emergency "gotta get ahead of this truck on the on-ramp" might even be ok.

My problem that if the poor little gaffer is pushing 30 psi I'm also burning enough fuel to push the EGTs into the critical zone as well... so again, something for brief sorties only.  ;-)

Thats sort of what i was expecting you to say (and hoping).
The car sees mostly gentle driving but every now and again itl see max boost when the foots to the floor, needing to pass etc
but that isnt every day so it should be fine for a little while longer.

The oil more than likely comes from the breather, not the turbo...  Yup, pretty normal.

I actually saw somewhere in a VW paper (I THINK it was the 1.5 SAE paper but I can't remember for sure) that part of the idea behind routing blowby into the intake is giving the intake valves a bit of lubrication... Probably doesn't hurt the turbo either...

Combined with the egr on my peugeot and it isnt such a good idea, lots of gunk on the valves....

[gldgti]

i've had my little k14 on my aaz running just over 20psi daily for a good while now... about 4 months, 700km/week.

before that i was at about 18psi for a year.... 50,000km. i drive it hard too.

i think the worst i've given it has been having an intake pipe blow off and making the turbo go mental. just for a second it must really sing.

i think you can do a lot with preventative maintenence - keep good oil in it and change it regularly, and let it cool down before shutdown.