Toecutter

Is it a rule or something that Audi owners don't recognize sarcasm in writing?

JasonR-NYC

At 100,000 rpms, the distinctive whine is masked by the cacophonous explosion of metal parts. YMMV.

need_TQM

At the risk of making this technical -- those opposed can just skip this post -- is this correct?

My understanding was that the expansion in the cylinders is fixed by crankshaft geometry (compression ratio) -- so when at high throttle, "lots" of fuel is being burned in the "large" amount of air pumped into the cylinders vs what occurs at idle. This makes the exhaust pressures "lots" higher then they would be at idle. Idle is just enough air/fuel to keep the engine spinning while minimizing fuel burn.

I thought the energy in the high pressure/high temperature exhaust gas is what is used by the turbo to compress the intake air. The exhaust temperature is only part of the equation -- the pressure and velocity of the exhaust gas are the others.

This fits my understanding of the reason higher compression engines can be more efficient -- they can extract more energy from the exhaust gas by expanding it more before having to dump it out the exhaust valves -- more expansion means less pressure/temperature gets wasted out the tailpipes. The Atkinson cycle engine (used in the Prius) does something similar to gain efficiency at the expense of power -- it effectively allows a longer expansion (power) stroke than the compression stroke. You get more out of the fuel/air charge, but the compression is limited - so you limit the amount of fuel/air charge that can be burned -- thus power is down.

yikes, that was a long post...

Scotty (UK)

You're so polite. I was just going to post "No **** Sherlock!"

bimmers2

no beeping sound on my B8 but some fan running sound at idle

ThePiombino

I totally missed the part where he said "idle." Epic fail for me. =0/

BMWBig6

Can you please provide a link to this rule that you mention above?

Just kidding...

Toecutter

Har!

need_TQM

I'm unsure of the details of the IHI in the A4 2.0TFSI, but 100,000+ RPM turbo shaft speeds are not uncommon.

Quickest example I could find with google -- this one goes to 126,000 RPM...

http://www.turbominivan.com/tech/flow_map.jpg

Enwerks Motorsports

lol.

To OP, I hear the same type of beeping when I inside the my 335i. No one seemed to know what it is on the bimmer forum. Just thought I'd share.