Boost Pressure VS turbo life
03-17-2017, 06:56 PM
#1
Instructor
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Boost Pressure VS turbo life
Looking for some input regarding turbo longevity in relationship to boost pressure. I would imagine at higher boost pressure
The turbo is spinning faster for longer periods of time. Does this affect reliability? Are certain turbos better than others for boost over 18 psi?
The turbo is spinning faster for longer periods of time. Does this affect reliability? Are certain turbos better than others for boost over 18 psi?
03-18-2017, 08:25 PM
#2
Burning Brakes
I think it depends on the size of the turbo. A small/ stock turbo will be pushed to the limit at high boost, while a large turbo will have excess capacity.
A few things I have found to reduce a turbo's life is;
A tight BOV, one that surges and bucks when rolling off the throttle. This sends a shockwave back to the compressor wheel and tends to stress the thrust bearing over time.
Hot shut-down. Turbo's run hot, give them time to cool off before stopping the engine.
Anything that harms the #2 rod bearing can also stress the turbo, they both need a good supply of pressurized oil to survive.
In case the oil supply is compromised, a ball bearing turbo can handle brief periods of low oil pressure without damage, while a journal bearing turbo needs a constant and larger supply of oil at all times.
A few things I have found to reduce a turbo's life is;
A tight BOV, one that surges and bucks when rolling off the throttle. This sends a shockwave back to the compressor wheel and tends to stress the thrust bearing over time.
Hot shut-down. Turbo's run hot, give them time to cool off before stopping the engine.
Anything that harms the #2 rod bearing can also stress the turbo, they both need a good supply of pressurized oil to survive.
In case the oil supply is compromised, a ball bearing turbo can handle brief periods of low oil pressure without damage, while a journal bearing turbo needs a constant and larger supply of oil at all times.
03-18-2017, 09:44 PM
#3
Rennlist Member
There is a lot of science in the size of the turbo and boost levels. Your motor will probably give out before the turbo.
Garret has a tech section on turbos to help neophytes learn about them.
https://www.turbobygarrett.com/turbo...rbo_tech_basic
Garret has a tech section on turbos to help neophytes learn about them.
https://www.turbobygarrett.com/turbo...rbo_tech_basic
03-19-2017, 01:50 AM
#4
Three Wheelin'
You're not gonna blow a turbo at 18psi due to too much RPMs. If you blow a turbo at 18psi, it's because something else is very wrong. Some of the main reasons they go is due to lack of cooling, oiling, surging, and mechanical debris getting sucked in the compressor/turbine.
In addition to what rlm328 mentioned, every turbo has its own efficiency range, including its 'sweet spot'. There are modern turbos that are just coming to life at 18+psi. So in your case, you need to find what turbo will best suit your application at the boost level you want to run. It's not so much the 'over-revving' you need to be concerned about. The key is to find a turbo that will be in its 'sweet spot' at your desired boost level, which will give you the most power under the curve.
In addition to what rlm328 mentioned, every turbo has its own efficiency range, including its 'sweet spot'. There are modern turbos that are just coming to life at 18+psi. So in your case, you need to find what turbo will best suit your application at the boost level you want to run. It's not so much the 'over-revving' you need to be concerned about. The key is to find a turbo that will be in its 'sweet spot' at your desired boost level, which will give you the most power under the curve.
03-25-2017, 10:14 AM
#5
Nordschleife Master
A couple more things
A number of sensible things mentioned. I don't want to pretend to be an expert, but I'd add the following:
The compressor has a mass flow limit at which point the tips go sonic and no more air mass will flow thru the compressor even if the shaft speed is increased. I've read somewhere that this sonic choke is hard on the compressor wheel. Minimizing the compressor inlet restriction and thus maximizing the pressure at the compressor inlet is one way to move that sonic wall out a little bit.
High (cycle average) exhaust manifold back pressure is another thing that can be hard on a turbo. For example, we hooked up a blowby meter to the the turbo oil drain sump. The turbo blowby is (close enough for government work) proportional to the square root of the maximum of the intake and exhaust manifold pressures. So higher exhaust manifold pressure usually means more turbo blowby. The best way to reduce the required exhaust manifold pressure is to reduce the pressure at the turbine outlet with a free-flowing turbo-back exhaust.
The compressor has a mass flow limit at which point the tips go sonic and no more air mass will flow thru the compressor even if the shaft speed is increased. I've read somewhere that this sonic choke is hard on the compressor wheel. Minimizing the compressor inlet restriction and thus maximizing the pressure at the compressor inlet is one way to move that sonic wall out a little bit.
High (cycle average) exhaust manifold back pressure is another thing that can be hard on a turbo. For example, we hooked up a blowby meter to the the turbo oil drain sump. The turbo blowby is (close enough for government work) proportional to the square root of the maximum of the intake and exhaust manifold pressures. So higher exhaust manifold pressure usually means more turbo blowby. The best way to reduce the required exhaust manifold pressure is to reduce the pressure at the turbine outlet with a free-flowing turbo-back exhaust.