Deep Singh

Yet another group buy to rid you of your hard earned.Getting fed up of having to wait for two minutes after I stop the car to fill up for petrol etc so thinking of organising a group buy on TTs.
So far I've looked at HKS and Blitz,the Blitz is more expensive but a much nicer,slimmer piece of kit.I'm going to find out about the Apexi one tommorrow.If anybody is interested please let me know and also express a preference if you have one.
Its the HKS zero(try HKSEurope.co.uk or tdi-plc and the blitz is the FATT DC one which also does stopwatch,batt volt,digital rev counter,in car temp.This can be seen at www.performanceexhausts.co.uk.

KenG

The 2 minute cooling down period is not necessary on the new models, so a turbo timer is really a waste of money.

Ken

Scott WT

Ken

What? Why is the cooling down period no longer required, what's changed? As I understand it if you don't allow the heat to be dissapated from the turbo, the oil overheats in the bearings turning to muck and ruining the bearings etc etc.....?

Scott

ChristianR

iTrader: (1)

with all turbo cars you should at least do some type of cooling down after a hard drive.

Scott WT

I was once advised that on a Cosworth engine, after driving 'on boost', it was a good idea to let the car idle until the cooling fan came on once and then went off again; the theory being that this first cooling fan cycle was due to the heat coming out of the turbo and being dissapated to the atmosphere, then you could switch off....this seems to make sense to me.

Whats even worse for turbo cars though is switching off the ignition while the engine's still reving above idle. This results in the turbo still spinning for a while (turbos spin very fast 10's of 000s of RPM I think) with no oil to lubricate the bearings!

Scott

KenG

This is from an FHI tech tip bulletin:

"FHI's position regarding this is that it is not necessary to perform a "cool down/idling" procedure, as was recommended with past turbo models. Our current 2.0L Turbo engine has a far greater cooling capacity and coupled with technological advances, makes this practice no longer necessary. This explains why information about a cool down is not included in the 2002MY Impreza Owners Manual.

The heat contained in the turbo will begin to vaporize the coolant at the turbo after the engine is stopped. The hot vapor will then enter the coolant resevoir tank, which is the highest point of the cooling system. At the same time the vapor exits the turbo, coolant is supplied from the right bank cylinder head flows into the turbo. This action cools the turbo down. This process will continue until the vaporizing action in the turbo has stopped or cooled down."

Of course, this may not apply to pre-2002 models.

Ken

dhorwich

It not got that much to do with the coolant..... it the oil....

If oil is settled on the turbo bearing and the engine is turned off no more fresh oil will be pumped to the bearing and the turbo impeller will keep spinning, the oil will literally cook and turn to thick crap... this will inturn be pumped around the engine to all the other oil galley ways... e.t.c and could block oil passage to the turbo e.t.c..

I would definitly not recomed stopping your engine straight away after say a motorway run.....

KenG

Are most people thinking back to when the oil was used to cool the turbo? Things have moved on quite a lot since the old shape Impreza and the cooling down sticker that must not be ignored.

My original response was to the effect that, with the new models, a turbo timer was a waste of money - which it is, not to mention the effect on your insurance that may end up being invalidated.

Personally, I always let any car 'settle' after hard driving and would nver switch off at anything above idle. But, gone are the days of sitting at the petrol pumps for a couple of minutes.


Ken

Dark Blue Mark

Well im interested in the group buy. How about fitting too? I did one on a previous car and it was a bit tricky to get a nice fit.

Ken, if you switch off staight away there is no means for the oil on the turbo to dissipate heat. The turbo can reach temps of 900 deg c IIRC. If you leave the car to idle the oil pump continues to work and allows the oil to slowly cool as it is moved away from the turbo.

I look after our gas turbines, which run on a similar lube oil system. If the turbine trips, it goes to a 10 minute cool stop, purely for the reasons of oil coking. Ok, slighlty more complex but same theory.

I would re-considder their advice.

MB

johnfelstead

Modern turbos have a water and an oil system. The water jacket is used to cool the rather delicate bearing core. The oil simply feeds the bearing and returns to the sump, it has no cooling effect.

Race turbos dont use the cooling jacket and they require a very long rundown period. Road car turbos when you drive them in normal trafic dont need a cooldown period on in town trafic etc as the heat generated is not that great. This is where i agree with the new handbook.

If you start running the car on boost for any length of time prior to stopping, say spirited driving cross country or a good sustained run on a motorway you really need to let the turbo cool as it will fry the oil in the bearing core. This is easpecially so when using the lower grade 5-40 oil that subaru UK use.

The heat generated in the turbo on boost is prety huge, a good modification to the cooling system is to fit a pre rad to cool the water coming from the turbo core before it enters the main cooling system, this can knock 15 degrees C off the running temperature of the cooling system as a whole.

If its fast on boost driving you have been doing, the laws of chemistry havnt changed, you will cook the oil if you dont allow it to cool properly and dont blip the throttle before switching off as it will spin the turbo up. Most turbos run at around 55,000 rpm, they are incredibly fragile, yet incredibly reliable if treated well.

treat the car as per how you have been driving it, owners books are just a basic guide.

Deep Singh

I take it nobody wants one then! Not sure if I do either now!
I w'ont bother going into the details of the discounts I was offered.
ps d'ont come whinging on here when you've knackered your turbos(LOL)