Holset turbo warning... Please discuss

[gearheadstik]

I pulled the turbo apart last night to find that it is the same as last time... The exhaust bearing is the one with most wear, looks nearly double of the compressor sides bearing... I'm thinking of sending the shaft off to be balanced again, maybe that will make a difference. If I had the machining capabilities, I would attempt to convert to a ball bearing, but not sure what work would be involved.

[dr_hunt]

Diesel temps, on the other hand, are usually around 900 degrees and can exceed 1000 degrees under heavy load.

 

No, 900 is the limit if it is measured on the cold side. If that is the hot side then it can be that or alittle more.

 

From wikipedia;

 

The average temperature of a piston crown in a gasoline engine during normal operation is typically about 300C (600 degrees Fahrenheit)

 

When auto enthusiasts want to increase the power of the engine they may add some type of forced induction. By compressing more air and fuel into each intake cycle, the power of the engine can be dramatically increased. This also increases the heat and pressure in the cylinder.

 

The normal temperature of gasoline engine exhaust is approximately 650C (1200F). This is also approximately the melting point of most aluminium alloys and it is only the constant influx of ambient air that prevents the piston from deforming and failing. Forced induction increases the operating temperatures while “under boost” and if the excess heat is added faster than engine can shed it, the elevated cylinder temperatures will cause the air and fuel mix to auto-ignite on the compression stroke before the spark event. This is one type of engine knocking that causes a sudden shockwave and pressure spike, which can result in an immediate and catastrophic failure of the piston and connecting rod.

 

The “4032” performance piston alloy has a silicon content of approximately 11%. This means that it expands less than a piston with no silicon, but since the silicon is fully alloyed on a molecular level (eutectic), the alloy is less brittle and more flexible than a stock hypereutectic “smog” piston. These pistons can survive mild detonation with less damage than stock pistons.

 

The “2618” performance piston alloy has less than 2% silicon and could be described as hypo (under) eutectic. This alloy is capable of experiencing the most detonation and abuse while suffering the least amount of damage. Pistons made of this alloy are also typically made thicker and heavier because of their most common applications in commercial diesel engines. Both because of the higher than normal temperatures that these pistons experience in their usual application and the low-silicon content causing the extra heat-expansion, these pistons have their cylinders bored to a very loose cold-fit. This leads to a condition known as “piston slap” which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures. These engines should not be revved when cold, or excessive scuffing can occur.

Edited March 5, 2009 by dr_hunt

[NissanEgg]

Nice info gearheadstik. You just got all the guys over at Z31Performance freaking out. The newest craze for the Z31 guys is the Holsets. Luckily I saved up and got a big Garrett.

 

Hey Aaron, you gonna have that orange heap ready again for DNI? You still have any Z31 parts left at your place? I might be heading to Dothan in a few weeks.

[ktm]

dr hunt, I do not know where they temps were measured on the diesel application. I was looking for this information and ran across a Cummin's diesel website (pickups) that discussed EGTs. Some members were reporting tempertures around 900, peaking over 1000 under heavy loads. Where they were measuring it was not reported.

 

 

Here is a great link regarding Holsets:

 

http://www.dsmtuners.com/forums/turbo-system-tech/145691-holset-turbos.html

[Netrix]

I was always under the impression that diesels ran "hot" per design. Some of those high horsepower diesels are running like 50-80psi of boost. Albeit not on a stock turbo, but they can do 30-45psi on stock turbos. Seems like the high compression of diesel engines, plus high boost would make for high temps. However there is the element of the BTU of the two different fuels being burned. I wish I had the time to research this more, now I'm anxious to see where this thread goes.

[DRZ man]

For the turbo leaking oil, I was talking to a friend that deals with Holset and Garrett turbos mainly for diesels, he said that when Holsets are installed on a gas motor, they leak oil if the crankcase pressure builds up to high, because the turbo oil drain is by gravity and if the motor is building to much pressure on the oil panthe oil wont drain therefore is going to get out somewhere(mostly seen on the turbo intake pipes).

 

Also the turbo creates presure itself, Im currently running a Holset turbo in my Z and had no problems so far, the turbo had a lil over 100k before I installed and didnt have any shaft play, Im only running 14psi.

 

I work on diesel shops for the last 5 years and I have seen turbos leak to the intake pipes on the Fords more than anything and thats a Garrett turbo.

[GrayZee]

For the turbo leaking oil, I was talking to a friend that deals with Holset and Garrett turbos mainly for diesels, he said that when Holsets are installed on a gas motor, they leak oil if the crankcase pressure builds up to high, because the turbo oil drain is by gravity and if the motor is building to much pressure on the oil panthe oil wont drain therefore is going to get out somewhere(mostly seen on the turbo intake pipes).

 

 

Now that makes sense.. maybe all we will end up needing is crazy catch cans for our Z's I know the Honda guys often weld extra nipples to their valve covers and run extra hoses for their catch cans.

[Guest Turboedmav]

VNT or VGT turbos haven't been widely used on gas engines as OEM (apart from some Dodges in the early 90's -Shelby CSX, Daytonas- and on Porsches a couple years ago) precisely because of the high EGTs for the VNT mechanism.

 

I'm almost sure the turbine and other internal parts are fine with gasoline exhausts temps but the VNT mechanism (wether it's a movable vane design or a movable exhaust housing) is not sitting very comfortably with the kind of temps seen in even the best tuned engines, let alone engines running lean mixtures!

 

Keeping exhaust gases as hot as posible before they reach the turbine is best pactice in regular, water/oil coooled gasoline turbos, but the same cannot be said about a turbo originally engineered to run on a diesel engine. If I ever tried using one of these turbos on a gasoline engine, I'd try letting the exhaust gases cool off a bit before they got to the turbo by placing it farther away from the head, keeping the manifold unwrapped, uncoated and using anything for the manifold but stainless steel, which is a known bad heat conducor, meaning it would dissipate less heat between the head and turbo. A/F mixture MUST be right on target, go lean and EGTs will go up, go rich and some fuel will still be burning on it's way out, hurting the turbo either way.

 

That was my five cents...