Okay, I didn't see this in the threads, but maybe I missed it. I know that BMW claims that they have eliminated the turbo lag, but the other thing I have heard about turbo is letting it wind down before shutting off the car. Does anyone know if this will be true of the 2007 turbo for the MINI?

 

Yes. I was just talking to a friend about this. He drives an '06 Lancer Evo and bought a device called a "turbo timer"... or somthing like that.

The idea is that the engine should run for a couple minutes after the turbo has been in use in order to allow it to cool down properly. The Turbo Timer allows the engine to run for a set period of time (1-2 minutes) after you've turned the key off and taken it out of the ignition.

I brought up the obvious security concerns of getting out of your car... leaving it running... locking the doors and walking away. He assured me that any attempt to take the car out of park kills the engine immediately. I'm still skeptical.

 

I dont' know how it's cooled. IF it's water or oil, it's nice to let it get cool a bit before shut off. But with all the electic stuff on the car, it's possible the ECU runs the cooling a bit after shut off.

This was a big issue in earlier turbos, and less so now. Those wishing the ultimate in longevity will cool down the car, and not just stop after an intense session. Kind of like a cool down lap at the track...

Matt

ps, it's not called wind down. That's a lowering of RPM. Its cool down.

 

Thanks... I have never owned a turbo, so the lingo is unfamiliar to me. So it sounds like it is not an issue that the driver will need to manage but most likely will just shut down the car as usual, or maybe something built in to allow the turbo to cool down on its own.

 

I read the document from Peugout on the engine. The MINI turboed engine has a secondary battery operated water pump that starts when the car is switched off. It runs for a while to cool of the system. (It was not clear whether it was timed or temprature controlled.)

The system that is in the MINI is a oil bathed water cooled turbo. It has pressure fed oil into the bearings that then drops out back into the crankcase. This keeps the oil supply very high when the turbo is in operation and then when you shut it off the oil drains away from the turbo so it can not "coke" up and cause trouble later. Also current synthetic oils do a much better job of not breaking down in the heat from turbo systems. 20 years ago you were using refined dinosaurs and the oil had problems. There is also a sealed water system that keeps water flowing thru the center of the turbo to cool this high temp area during operation. The auxilary water pump will solve problems with cooking the oil after operation.

The only steps that usually need to be taken on a modern well designed turbo car is to not hammer the car at WOT and then shut it off. This is really hard as all parts are at maximum temprature and then you shut off oil and water cooling supply. With my Subaru it recommends 1 minute of run time after WOT to cool it off before shutting of the engine. If you do a hard run at night and quickly stop and look under the hood you can see the turbine side glowing red.

Subaru also properly designed their cooling system with the turbo in mind. There is an auxilary water tank above the turbo. With the heat generated the water rises up to this tank and colder water flows into it. This is via thermodynamics. No water pump is needed to keep this flow going. I am not sure on the Mitsubishi how it is built.

 

The issue of letting the car idle is not to let the turbo cool. How cool do you think it's going to get in a couple of minutes of idling (which still generates heat)?

The reason is to let the turbo impellor slow down from the many thousands of rpm's it's spinning to a much slower speed at idle, while the bearings are still being bathed in oil.

Cutting the car off with the impellor spinning at high speed makes for an extended dry spin down. Wears out the impellor bearings that much faster.

 

I agree with letting the turbo spin down. But that does not take to long with the throttle closed. 5 seconds at most at closed throttle will be fine.

However the turbo needs to cool. Idling temps are in the 300-400 EGT vs. 1700-1900 EGT at WOT.

 

So... it is winding or spinning down?

 

Matt

 

I agree with wrx_xb9r 100% on this topic. The turbo does not need long to lower it's impeller speed, even from maximum boost levels to idle will only take a few seconds. It has been common practice for a long time to cool off turbo charged cars by driving at lower RPM for a couple of minutes after a hard run, or to let the car idle for a minute or more so that it cools off. Obviously new technology has helped some with this, but people that own turbo cars need to understand that the intense heat they generate needs to be slowly cooled to protect the turbo and the engine. Oil cooled, water cooler, whatever the turbo uses will only be able to help so much. Proper care of turbos will help them last for years and years.

Drew

 

I have owned several turbo cars over the years. Just drive the car easy before you park it. When you park, roll up the windows, undo the seatbelt and turn off your engine just before you exit... Thats all it needs to let the turbines slow down. Synthetic oil and water cooled bearing also make turbos live much longer...

 

If you were running laps at the local track, then yes let it idle a bit so the turbo spins down. Otherwise I really don't believe there'd be much of a need. The motor has all sorts of high tech stuff, like an on demand oil pump. I'd bet a days wages that they have the turbo cooling issues worked out for the turbo after shut down. To me it's a non issue.

 

This was the rationale given in the owner's manual of my '89 Saab 900 Turbo. The turbocharger on this car lacked bearings between the impellor and the body. A thin film of engine oil at pressure provided seperation between the moving parts. In addition to the spin down time (20 seconds) it wass recomended that boost be avoided before the oil reached running temperature. I followed these instructions religiously and the turbocharger was trouble-free for 200K+ miles. I'm not sure if this design was unique to old Saabs.

 

I agree with what Saab told you. That was good practice back in '89. Turbo tech has evolved quite a bit in the 17 years since they told you that. Letting the turbo spin down & cool down in the '007 just isn't as necessary as it once was. I'd bet that in the owners manual from a new Saab that cool down isn't even mentioned. It's not in my Forester XT (turbo) manual.

 

The cooling after shutdown was looked at and solved. There is a secondary electronic water pump that turns on after the engine has been shut off.

Older turbos were single bushing center sections. This was true for the older Saab Turbos. A presurised stream of oil was sent into this area and the shaft did litterly float on oil. Also a water cooled center was very rare and only used on high end race cars. At the same time the blades and housings had to have a fair sized gap to keep them from contact because the shaft could float around.

Current turbo design for most commerical cars is a bearing on each side of the turbo with a water cooling jacket inbetween. This allows less heat transfer and tighter tolerances. Some really high end stuff has zero tollerance on manufacture. The blades are coated with an abrasive that clearances the housing on operation for a really tight fit for maximum efficiency.

The twin scroll turbo on the new engine is also realitively new technology. It was developed for consumer operation where turbo lag was a selling downfall. Having boost as early as 1800 rpm in this engine will be very nice. For comparison my STi comes on boost at 4,000 rpm stock. With the exhaust change and ECU tweaks to ignition and cam timing it is now down to 3,000. This is a world of difference for driveability but still nowhere near as instantaneous as my wifes MCSc.

Subaru's ej20 and ej25 series engines are designed with a cooling system that will flow with thermodynamics from the turbo. This is why there is no mention in the manual.

 

Thanks for the reply. I learned a lot.

 

We'll have to agree to disagree. Absent any 'braking', there is no way the impellor, spinning at thousands of RPM, and presumably with bearings and some type of even vestigal lubrication, will spin to a halt in 5 seconds after the throttle is closed. Probably not even 60 seconds, depending on the specific design.

 

Actually there is quite a bit of residual force when it is spining at thousands of rpms. The compressor side is trying to build pressure on the intake charge. This uses up a lot of energy. Without a constant supply on the turbine side to keep the shaft spining it slows down in a hurry.

For example on my current STi. When I got StreetTuner (ECU self tuning software) I was dropping down to the 5-6psi of boost range on my slow .35-.40 second upshifts. I worked on my shifting down to .25-.30 seconds and raised my pressures to 8-10psi. The really quick guys shift in .15-.2 seconds and have pressures in the 11-13 psi range. Now this is coming from 17-20 psi depending upon tuning and running condition variables. If I loose 2/3 -3/4 of my pressure in a 1/4 second imagine what happens in 5 seconds.

Now it will not come to a halt while the engine is running because there is some exhaust gas pressure turning the shaft. It may even take 30-60 seconds to reach zero rpm. But in 5 seconds the shaft is turning in the low thousands and not going to lock up.

Also when you lift the compression side is no longer building pressure = heat. The cool intake air is lowering the compression blade temps. The same is true on the turbine side. EGT drop into the 3-400 range and are removing temp from the turbine blade. The center section is removing heat with oil and water flow.

Now all of this is determined by the earlier statements of "just motoring". If you are running at WOT for a long pull you need extra time for cooling (coming of the racetrack).

 

Good info. Thanks.

The point of the spin down re wear on the impellor is that you want it to spin for a minimal amount of time without getting lubrication. If you just shut your car off without letting it spin from the many thousands down to a much lower speed at idle first, you will have it spinning down absent any lubrication, which equals bearing wear.

Some modern systems still provide some level of lubrication after shutoff for a brief period of time, again not to cool anything but to provide lubrication while the impellor spins from WAY fast to a halt.

 

Modern or not, I don't think that you can be too careful with a part as expensive as a turbocharger, and, if I owned one, I would observe the same care and feeding instructions which helped my last turbocharger last 200K+ miles. This would include staying out of boost until the oil reaches operating temperature in addition to allowing for spin down time.

EDIT: Just read elsewhere on NAM that the new engine will feature an on demand oil pump among other things. If it is used in part to maintain oil pressure for a short period following engine shut-down, then I suppose even a conservative person such as myself would consider spin down time to be unnecessary. I still think that allowing for warm up time would be a real good idea.

 

should always let a motor warm up before doing any reall hard driving.

 

Just a note, but turbo lag has not been eliminated. It's been trimmed down some, but BMW hasn't changed the laws of physics yet.

 

They are trying really hard though.

 

How are you defining "lag"? Not sure there are any industry standards of measurement. Sure there will always be a lag but that may be below the useful operating RPM of the engine (somewhere under 1400RPM in this case) or just not noticable. If it reacts as fast as the current MCS and has more torque at all RPMS over 1400 then I say they eliminated it.

 

Off topic but has anyone, when racing from a roll, lets say 30mph at 3k rpm brake with their left foot but keep on the gas so the turbo is starting to spool and your building some boost then 3 beep or whatever and dump the brake so when the car starts to drive under its own load theres already boost being built.