Well, the problem with using oil-cooled turbos on factory cars is that most people do not realize that they need to cool the bearings before shutdown. And many who know about hot shutdowns still buy turbo timers for their water-cooled turbos. It's not going to hurt it, but it's not necessary either.

I never said a Mitsu turbo is not capable of power. But I was really only comparing bearing sizes. Even the difference in sleeve bearing sizes is substantial. While this should be little issue to most users, a set-up that yield less blow-off on throttle closures will experience surge and I would opt for bearings that can take more thrust loading. Not to mention the GT series turbos are really pulling some nice numbers.

I wouldn't say it's stupid, but being that it's so simple on a car that comes with a factory turbo to watercool an aftermarket one, it would make things much easier to maintain. I hate waiting for my timer. Albiet, it's only 30 seconds, I'd much rather just be able to get out, arm the alarm and walk away.

TIP: What most people seem to forget... you don't have to spend 1 minute at idle before shut-down on an oil cooled turbo. It's just as effective to ease up on the throttle for the last minute of driving. So, if you can manage 2200rpm shifts while pulling into your street/area, you'll be just fine. :ylsuper

Dammit thanks to you guys Im gonna be giong to bed later than I wanted to. Damn informative posts!

This is some good **** right here. Its one of the best/mature posts Ive seen on NICO in a while. Keep up the good work.

jdmfreak03 wrote:This is some good **** right here. Its one of the best/mature posts Ive seen on NICO in a while. Keep up the good work.

I just want to second that. This is a great thread. I've learned a ton by reading through this.

These are the kinds of threads that separate us from other forums on the internet. No flaming or name calling, just a good friendly and healthy informative discussion/deabte. I'm really impressed by the knowledge that you guys have and the compossure and maturity that you are showing.

Thanks and keep up the good work.

If you want to get involved or read some great turbo discussions, a lot tend to take place in the KA-T forum.

Thanks, I rarely venture in there since I have VQ35 and don't plan on getting a KA-T. I guess it would be worth the read though.

rydwhite wrote:Welcome to NICO MapleLeaf.

ditto from me. we're glad to have to aboard!

i rarely stray away from any of the 240sx related forums, but after reading through this thread i can see that i'm missing out. thanks MapleLeaf and C-Kwik for such a healthy mature discussion.

-demetrius

if you don't need to cool down water cooled turbos.. why does my stock DSM manual tell me to do so? it's water cooled. and coasting down does help but per the manual you should idle before shutdown and the time varies based upon how hard or long it was working before beginning to idle. if you live 1/2 block off the freeway and you just ran a 140+mph little practice run against a supra, and the npark... water cooled or not, you need to idle for 1:30+ if you live 2 mile soff the freeway after the same practic erun.. and drive really nicely all the way home, ok.. maybe 30 seconds or so...

C-Kwik wrote:Well, the problem with using oil-cooled turbos on factory cars is that most people do not realize that they need to cool the bearings before shutdown. And many who know about hot shutdowns still buy turbo timers for their water-cooled turbos. It's not going to hurt it, but it's not necessary either.

I never said a Mitsu turbo is not capable of power. But I was really only comparing bearing sizes. Even the difference in sleeve bearing sizes is substantial. While this should be little issue to most users, a set-up that yield less blow-off on throttle closures will experience surge and I would opt for bearings that can take more thrust loading. Not to mention the GT series turbos are really pulling some nice numbers.

I wouldn't say it's stupid, but being that it's so simple on a car that comes with a factory turbo to watercool an aftermarket one, it would make things much easier to maintain. I hate waiting for my timer. Albiet, it's only 30 seconds, I'd much rather just be able to get out, arm the alarm and walk away.

30 seconds is as much as you need to run a car for an oil-cooled turbo in most situations. The reason a manufacturer will say to do more in a water-cooled turbo is to be on the safe-side. Trying to educate a consumer as to when it is necessary and when it is not can get complicated and may be misleading. Also, it is much cheaper to print that text into the manually and be extra safe than to have to replace turbos under warranty and get a poor reputation for having a problematic motor. If you hit 140 mph, chances are by the time you come to a stop, the bearings will be quite a bit cooler than it was when you were boosting full. Consider that the oil in a watercooled bearing is still cooling the bearings. And water is also a much better heat transfer medium than oil. Not to mention more water is flowing through the housing than oil. You only need to cool the overall components of the turbo to a point where the hottest part of the turbo will not transfer enough heat into the bearing after shutdown to cause the oil to coke onto the bearings.

C-Kwik wrote:30 seconds is as much as you need to run a car for an oil-cooled turbo in most situations.(....GSXTASEE edited out some stuff.....) If you hit 140 mph, chances are by the time you come to a stop, the bearings will be quite a bit cooler than it was when you were boosting full. Consider that the oil in a watercooled bearing is still cooling the bearings. And water is also a much better heat transfer medium than oil. Not to mention more water is flowing through the housing than oil. You only need to cool the overall components of the turbo to a point where the hottest part of the turbo will not transfer enough heat into the bearing after shutdown to cause the oil to coke onto the bearings.

o.k... now your bearing is cool after slowing from 140mph at full boost.. but the housing the bearing is mounted to is glowing orange hot (ever looked at your manifold at night after a hard run?). so you turn off the motor and the water and oil in the bearing starts to soak up the heat from the still orange hot exhaust housing... and you still coke the bearing. if you time it down for 1-2 minutes, the housing has time to cool down some as well.

and I think you meant "30 seconds is as much as you need to cool a _water cooled_ turbo" ??

Boy, you guys really drive your cars hard. And you do that OFF track? I've had one too many friends lose their lives due to street racing with cars/motorcycles. I understand the need to flex some muscle on the street but please.... for everyone's sake (including innocent people around you) .....KEEP IT SAFE. :icesangel

Getting back to the water/oil cooling issue, I'm not sure everybody reading this post is understanding what some of us are discussing, so in everyone's interest I'd like to point out that "Water Cooled" Turbos are Turbos that are Water AND Oil cooled. The "water"/coolant circulates thru the turbo much better at lower RPM's than the oil does (since the waterpump is belt driven). The oil inlet pipe, in contrast, supplies the turbo with a tiny stream of oil and even less than that at idle. This is due to less oil pressure created by the pump at lower RPM's. This is why an Oil ONLY turbocharger takes a longer time to cool than a Water cooled turbo.

If you are coming off of a hard 140mph run off the freeway, I'm sure you can use your better judgement and give the turbo a couple of extra minutes to cool off. This is common sense.

agreed about being smart on the street. this was a hypothetical situation and I should have probably said "after a couple hotlaps on the road course, or a nice 1/4 mile pass"

Well, I don't consider running at a track or 140 mph to be most situations. My turbo has probably seen that less than 1% of the miles on it. And if you are coming off a road course with no cool down lap, you are asking for warped rotors as well. A bit off topic, but I use a full cool down lap to get everything down to reasonable temperatures anyways. And at a drag race, you typically get a long drive back down the pit lane at like 5 mph.

And no, I in fact meant that oil cooled bearings only typically need about 30 seconds.

I am quite aware of the different parts of the turbo transferring heat into bearing after shutdown. That is exactly why I stated, "You only need to cool the overall components of the turbo to a point where the hottest part of the turbo will not transfer enough heat into the bearing after shutdown to cause the oil to coke onto the bearings." But also keep in mind that additional heat goes also soaks into the manifold and the downpipe.

As far as oil and water flow, consider that oil pressure is never really all that high in a turbo. Or at least it should not be. Typically, you should somewhere between 5-25 psi. Too much pressure and oil will leak past the shaft seals. That means there is not a whole lot of oil to take away the heat. The water connections are larger and can handle more pressure as the water jacket is isolated from the bearing. In any case with so much more flow and the fact that the water is a better medium, the bearing section will stay significantly cooler. In fact it stays cool enough that the oil temps don't really reach temperatures where oil breakdown occurs. Of course oil still breaks down faster than in an NA motor, but an oil cooled turbo can actually operate at temps where the oil can breakdown.

And just from my own experience, I've used an oil cooled turbo for 2 years. I have my turbo timer set at 30 seconds. I had to replace my turbo recently. But there were no signs of coking. The bearing was just starved of oil for a small amount of time. In any case, if 30 seconds was not sufficient, then I'm sure I would have seen some problems.

my apologies on my assumption... I guess this comes down to who likes to turbo time or not.. but from my own experiences and info on FI cars, it's wrth the 30seconds -2 minutes of waiting (or a TT) to make certain my car and turbo remain in good working order.... until I am good and ready to break it :-)