Turbocharger RPM

Jul 26, 2006 3 Replies

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matthomas 19 years ago

I have a general question about turbochargers. The application would be for domestic cars. I've read a lot about the peak rpm numbers for turbochargers, but no low end numbers. The overall concensus seems to be 150,000 - 200,000 depending on the application. What I want to know is the rpm profile in relation to load and/or an engines rpm. My guess is that it would be a 3-D map similar to a fuel map; however, I need a low value to even begin to make a calculation.

Below are my assumptions. This isn't a model specific question, so I use these as general.

2.5 litre engine
4 cylindar
4 stroke
8.5:1 compression
28/8 Turbo size. Idle 500 rpm Turbo redline 150,000 Engine redline 6000

Questions:

What is the rpm at idle/no load? What's a safe way to measure this IRL? Anyone know a Garrett et.al. engineer...lol?

Thanks in advance for ANY input!

-- Matt

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Kevin 19 years ago

Turbine speed (therefore boost pressure) is controlled by a waste-gate, not by engine RPM's, although at higher RPM's there is a greater flow of exhaust to drive the turbine faster. There are many factors that govern turbine speed, therefore boost pressure (Too many variables to answer your question as stated).. On modern engines the engine management computer uses various inputs to calculate the boost pressure map for the current engine requirements. You should probably read a lot more about turbos before attempting to formulate the equation you are working on.

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jeffcoslacker 19 years ago

My guess is it would be some kind of -V- squared function of exhaust pressure, and would depend on backpressure, pipe size, exhaust tract length, etc...not things you can really neatly fit into a set of equations for any car/motor...

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dyno 19 years ago

snip

If you can find it, there was an excellent book by Hugh MacInnes titled Turbochargers (ISBN 0-912656-49-2) published by HP books. It covers all the basics on sizing turbos. It is a bit dated by today's new turbos though.

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