Thread: turbo timer v egt gauge

My turbo timer (Rotronics) has 1 and 3 minute intervals. I'll take more notice of the EGTs and times next time I take it for a spin.

strange. Anything under 270* (an arbitrary figure I just thought up, as 250* took too long to get down to) I just shut down. Often this will be almost straight away, if I've just come off a highway where it has been sitting around 400*, it'll be 30 sec at the most.

The idea of a turbo timer is to allow your turbo to slow down as in spinning

If you shut your motor down after a highway or hard drive your turbo can be spinning at 20,000 + rpm , and if you shut your motor down that turbo is still spinning at that speed with no oil to lubricate the bearings inside it

I understand that a turbo will slow down very quickly soon after the engine is allowed to idle - within a few seconds, as it has virtually no exhaust gases driving the turbine and its trying to compress air on the inlet side. But it needs to cool to prevent cooking the oil and eventually blocking the oilways with carbon.

Originally Posted by Graeme

I understand that a turbo will slow down very quickly soon after the engine is allowed to idle - within a few seconds, as it has virtually no exhaust gases driving the turbine and its trying to compress air on the inlet side. But it needs to cool to prevent cooking the oil and eventually blocking the oilways with carbon.

that's always been my understanding, too.

I think it is a combination of factors - speed and temperature. Actually, if spinning fast the turbine will not slow all that rapidly once the engine stops - with nowhere for the air it is trying to compress to go, the airflow past the compressor blades will stop flowing and be carried round with the blades, with relatively little drag. The critical factor once the engine stops is lack of both lubrication and oil cooling for the bearings.

It seems to be less of a problem than it used to be, probably because of improved bearing design and materials. My impression is that special precautions are only needed if the engine is shut off immediately after operating close to full power, certainly the manufacturer does not seem to think it necessary to provide a turbo timer or oil pressure accumulator (which is the alternative).

John

Been looking for an EGT gauge for a while, where did you get your's?

Originally Posted by rangieman

The idea of a turbo timer is to allow your turbo to slow down as in spinning

If you shut your motor down after a highway or hard drive your turbo can be spinning at 20,000 + rpm , and if you shut your motor down that turbo is still spinning at that speed with no oil to lubricate the bearings inside it

Rangieman is spot on again, still spinning, no oil pressure from engine, ball bearing races run metal to metal and need oil to stop galling, slipper bearings or bushes properly lubricated have no metal to metal contact, they rely on a film of oil supplied under pressure, when the oil pump stops pumping, no lubrication, so let engine idle till turbo slows to idle speed then turn off, turbo will stop very quickly from idle revs, whereas from 20,000+rpm it will spin for much longer without lube, Regards Frank.