There has been a lot of discussion on several of the turbo boards here about turbocharger maintenance, care, and premature failure prevention. I recently rebuilt my engine and have tried several turbocharger combinations with the help from Kevin at Alamo Industries who has been kind enought to work with me in trying and evaluating the perfromance characteristics of several turbos. The most recent turbo is a TO4S-66 that Kevin built with his bearing and thrust washer upgrades. This turbo has approximately 500miles on it and 20 or so dyno pulls and about 2.5 hours of track time.

I am ever consious about letting the car idle 2-3 minutes after tracking the car or running it hard, and 2 minutes after just general driving EVERY TIME. I just sent this turbo to Kevin to inspect and he laughed and said he could tell that I did 1 hot shut down. He is probably right that while on the dyno, I probably only let the car idle down for .5-1 minute of time which is not enough. In any case, the Incanel turbine shaft has an imprint of the bearing on the shaft. He explained to me that the turbo was hot and the oil (Mobil 1) that is between the bearing and shaft just burns up from the heat and the deposits are left on the shaft. After repeated events like this, the deposits start to build up and will very quickly decrease the bearing to shaft clearance.

I've asked Kevin to post the pictures so you can see the damage from a hot shutdown and put this debate to bed once and for all. Kevin should be able to provide a better explanation that I have.

 

With Geoffrey permission I have enclosed a picture of his 8mm shaft. There has been alot of debate about hot shutdowns, the only positions that I can offer is that repeated carbon deposits on the shaft will over time accelerate the wear rate of your bearings/bushings.
<img src="http://boards.rennlist.com/upload/P1010199.JPG" alt=" - " />

 

Which turbo timer would you guys recomend to put in?

 

Kevin ..... do KKK units also suffer the same problems from early shut-offs or are they able to better weather this kind of abuse?

 

The important thing to remember is that "hot shutdowns" refers to shutting down while the turbo is hot - not when the engine. If you're just cruising around, you're not going to be on boost very long, and your turbo is probably going to be at roughly the same temp as if you were idling your car on the driveway. I think idling for two minutes every time you drive might be overkill.

 

Garrick;

The KKK's do seem to oil and cool the turbine wheel a bit better. However, they are not immune to a hot shutdown. I failed to mention that the black small circles on the turbine wheel are imprinted from burnt oil/imprinted from the bearings.

 

Kevin, have you had a chance to inspect turbos from 951's? Does the water cooling and auxillary water pump really have a significant effect on keeping the oil from coking?

 

Steve;

Turbochargers that have watercooled bearing housings do very well to cool the shafts down.