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Old 08-03-2020, 12:14 AM   #1
RacinNdrummin

Name: RacinNdrummin
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Turbo Wheel speed, Turbo sizing, and piping volume

So the case at hand is not by any means "extreme", but it does have me a bit stumped considering the circumstances.

I have been working with a customer that has a rather eclectic build, and while being fairly mild, the standard sizing procedures I use, have resulted in two turbo failures, with two different engines. The first being on the original engine, corrected by a turbine housing change. The original turbo/engine had a bark on the top end which resulted in the first failure. I replaced the unit, and recommended the next size turbine housing. It was great after that.

The customer wanted a new engine, which I was chosen to build, and it included an upgraded cam, and a bit more fuel.

Fast forward a couple months....

I have personally visited the customer, helped tune in the vehicle, all the vitals are excellent, boost/drive is as good as it gets. The same turbo setup from the other engine now barks like it did before the turbine housing change on the last one. That indicates more exhaust flow through the system, but ratios are still in check, I witnessed it with my own eyes (1:1-1.1:1, and he sees sub drive ratios at altitude 10-12k ft), everything about the vehicle is great, but it's eating turbos.

His setup has a ton of volume, the turbo probably has 12 feet of 2.5" exhaust pipe feeding it, and 6-8 feet of 3" charge pipe post IC feeding the manifold.

My theory is that the excess volume in the system is causing the turbo to overspeed (especially at 5-12k elevation) and it's a matter of the turbo not being big enough.

This rig runs and performs beautifully, but it's eating turbos at elevation, despite vitals being excellent. My recommendation was to get a bigger unit on it for wheel speed sake, but keep a similar turbine housing A/R.

I appreciate any info guys, thanks.

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Old 08-03-2020, 11:11 AM   #2
Leiffi
 
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Piping volume does not cause overspeed but there is more pressurized air flowing backwards when compressor surges, so it might make more damage.
Change to smaller compressor wheel, problem solved.
 
Old 08-04-2020, 08:06 PM   #3
56cummins

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What discplacement? What are the turbo specs?
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Old 08-04-2020, 08:40 PM   #4
Snedge
 
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Fukk. It's like a math problem with nothing but x's.

So... I have no choice but to assume the answer is 42.
 
Old 08-04-2020, 10:08 PM   #5
J-Pipes
 
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I know nothing about turbocharger systems, but why not through my thought out there! Now I could be wrong on my understanding of the situation but, you said a bark on top end, so when in a high rpm/high boost situation? And you referenced lots of intake/exhaust plumbing. My guess is maybe a blow-off valve is needed to relieve the pressure that's in the extended piping when the throttle is dumped, and its not going through the engine anymore, that its in effect backing up at the turbo? Again, I'm likely horribly wrong, but hey, even a broken clock is right twice a day, always a chance of being lucky!

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Old 08-05-2020, 12:42 PM   #6
Ram12vcummins

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Quote:
Originally Posted by J-Pipes View Post
I know nothing about turbocharger systems, but why not through my thought out there! Now I could be wrong on my understanding of the situation but, you said a bark on top end, so when in a high rpm/high boost situation? And you referenced lots of intake/exhaust plumbing. My guess is maybe a blow-off valve is needed to relieve the pressure that's in the extended piping when the throttle is dumped, and its not going through the engine anymore, that its in effect backing up at the turbo? Again, I'm likely horribly wrong, but hey, even a broken clock is right twice a day, always a chance of being lucky!

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That’ll snap a shaft in half eventually I’d assume. If I’m not careful on my series 60, it’ll give a good bark if I let off fast. Not a good sound.
 
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