+1

I had a stock turbo with a large boost leak on the turbo compressor outlet.
It still made power, but we had to pull out 2-3 deg of timing in the top end to get rid of the detonation.
It wouldn't go over 4psi on the boost leak test >.< So it was a BIG leak

 

So a big enough boost leak overworks the turbo into suboptimal efficiency producing a hot air charge driving detonation in spite of lower boost?

Or is it more a medium sized leak allows the turbo to still make the boost tgt at a much hotter air charge?

 

The principle is very simple, if air isn't going into the engine, then it isn't going out the exhaust. If a like volume isn't going out the exhaust, then there's no additional energy to drive the turbine.

The degree of leak doesn't matter with regards to the turbo. The turbo's shaft speed doesn't change significantly with the leak. You won't overspin the turbo. Most anyone that claims that is making those claims based on conjecture. Someone doing testing on a steady state hot gas test stand can overspin turbos all they want by unloading the compressor since the test stand can keep feeding energy to the turbine. But, I'd like to see someone try that on an actual ICE in a test cell. Now, introduction of NOS, or additional fueling on a CI engine, two-step=external combustion, that's plausible for overspinning turbos. However, simple boost leaks without any other changes, not gonna happen. The negative effect is more a function of thermodynamics in an ICE and to some extent enthalpy, not so much rotordynamics. All I can say is that the engine, not the turbo, is put into conditions of inefficiency that lead to significantly reduced VE and primed for detonation.

 

Sorry dude, it doesn't work that way. Show me data or reference to an academic journal that supports this.


One thought, however, with regards to the compressor wheel contacting the housing. I'm wondering if it is possible that the sudden unloading of the compressor wheel, via charge piping popping off, may produce some instantaneous thrust that compromises the thrust bearing and that's why it contacted the housing. But not because it overspun. Then again, the turbo should have been able to take that since that's what you essentially do every time you let off the throttle.

Food for thought: the turbo system on my test car, has a little button that creates an instantaneous boost leak any time I want it, boost rising, boost falling, peak boost, low RPM boost, high RPM boost, whatever. Any time you activate the leak, the turbo speed will drop to the RPM that corresponds with that given pressure ratio +- 500-1000 RPM.

 

Chad, I feel badly that this thread has become a thorn in your side. It was never meant to be a negative thread. If it's any consolation, I love the turbo. It spools really quick and pulls hard all the way to the top. Just the ticket for the type of events that I'm planning to do.