Airflow and Intercooler thoughts
Turbo Mini Forums

Another thread I just posted on got me thinking.....

My mini has a side rad, no mechanical fan, electric fan only.
I can sit all day at 60mph on an clear road and my water temp is a rock steady 78 degrees.
Now on the same road if a lorry is in front of me (not tailgating either), within a minute my water will hit 95 degrees and the fan will come on.
So clearly due to quirky aerodynamics and the wake from a truck there is hardly sod all air entering the engine bay.

Getting to the point of all this..... If this phenonomen is preventing my radiator from doing its job then what problems will this cause to intercoolers and intake temps? Maybe just a small loss of power. For a high boost engine maybe some damage.....????
Any thoughts on this

(A magazine article about mini aerodynamics I read recently stated that most of the airflow coming through the grill exits via the side radiator and out of the near side wheel arch so the location of my rad is irrelevent.)

Its not supprising, after all tailing a lorry get the old fuel consumption down as your not fighting against the air etc, I don't think it's much of a problem tho because if your tailing a lorry your not going to be boosting along at high revs, you'll just be poddling along off boost as such so the intake temps arnt going to be excessive anyway.

Cruising fine, but if you then boot it to overtake????

Well you'll boost and out into the other lane, not long enough for the temps to build up and do any damage. The temperature won't just go bang straight into danger itl rise and by that time youre well past your lorry and back in the air where your intercooler will be doing it business.

Edited by Rick.SPI on 4th Feb, 2011.

You certainly need to keep your ears open for det, my 205 turbo will occasionally knock if it has been sat in very heavy traffic and then you suddenly boot it off up the road. This is with an ECU compensating for intake temp as well, so with a Mini equipped with a good old SU you need to be careful.

What was the article on aero in? The testing at MIRA showed that most air exits under the car.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Can't remember where I read it, I think it was a Vizard article. The gist of it was that load of air goes through the side radiator and gets stuck inside the wing causing lift

IF you're doing 60MPH, you'll soon find yourself under the back of the lorry

I think that this is wrong, the spinning wheel will totally mess up any stactic tests that have been done. From what i have read, spinning wheels create a low pressure around them. IMO you need a fan on a side rad constantly to ensure good air flow. In fact I think that you have sort of proved this!

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Edited by Brett on 4th Feb, 2011.

Yes i moved to the darkside

Instagram @jdm_brett

Ok putting aerodynamic reasons to one side for a minute, my findings on the road have verified there is a lack of airflow through the front grille when travelling behing other vehicles.
Certainly bad enough to allow water to overheat in the radiator. The saving grace is the fan so no problem....
But what about the intercooler, which must be also struggling to do its job in these conditions. Most intercoolers don't have fans. Why not?
Whilst looking for the articles on mini aerodynamics I came across this one about intercooler fans instead.

http://autospeed.com/cms/title_Triggering-...78/article.html

Edited by dazibee on 6th Feb, 2011.

Why are you all driving so close to the vehicles in front ?

Either leave a safe distance, or pass !!

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Sure it's not lack of air not going through the side mounted rad apposed to not enough air going through the front. If u stick your hand out the window there's still air there and theres still a big space at the front, as someone said above most the air leaves out of the bottom according to tests. You can't really compare a front mounted intercooler to a side mounted rad, surely.

but the intercooler being at the front no matter what will be getting more airflow. just because its getting some airflow in a side rad in open conditions dosnt mean it is in these conditions, not a be all and end all but theres always air hitting the front of the mini you dont drive into a vacuum, but maybe there is enough drop for it to not get airflow into a side mounted rad, however there will always be air hitting the front end, there isnt going to be a situation where the airflow at the front can avoid the whole grille area and only hit other places. im not explaining myself well but im sure you can see what im getting at.

Break out the wool 'n cellotape.

I don't think a wheel will have a lot of effect, it's round 'n it doesn't move relative to the body. You could always test the theory next time you're stood next to the rollers of a dyno. I'd expect a dirty great bow wave off the relatively flat front, depends how much turbulence it creates for it to fill in the low pressure behind it.

I would think the intercooler itself will be the main heat sink if you boot it from an off boost bimble. You can't dump heat unless there's a temperature differential - heated intercoooler in cold air.

Actualy the wheels are a huge part of aerodynamics, it's why when testing aero they do so on a rolling road, it's
not just a simple thing either.
It will always differ with what cars/ lorrys your following too, but I'm guessing people are looking at a worstcase senario?

David.

My point was not wheels or aerodynamics really, but the reduction in flow through the grill when stuck behind vehicles. I mentioned my radiator and water temps just to demonstrate that this does indeed happen.
So is the reduction in air coming in the grille enough to allow the intake charge to rise too high. Anyone done any testing or data logging of intake air temps?

How come your mini is the only one ive heard of that has huge problems.
they get a little warmed if your tailgating but if thats tipping your cooling system over the edge maybe its only just upto the task in the first place

Yes i moved to the darkside

Instagram @jdm_brett

Forgive my potential ignorance but your saying that your temp rises by 20 degrees when your driving behind a lorry? So a restriction of air flow? The only reason I can see for this would be tailgating.

Following another vehicle at a safe distance shouldn't affect air flow so as such shouldn't affect your running temperature. So your either far too close thus restricting airflow through your grille or if you are leaving a sufficient space in front and the air flow isn't being restricted then you need to take a look at your cooling system.

I think you should maybe educate yourself on aerodynamics before commenting. I am not by anystreach of the imagination knowledagable on the subject. but I have actually read quite a bit on the subject, especially about wheels.

On a rolling road there is only static air.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Im going have a guess and say its because your that close to the back of the lorry that your only getting low pressure air in thats travelled under the lorry which has already gone through the lorry rad to cool it and also around the engine aswell so prob a bit warmer than usual. As all the cooler air thats gone around and over the lorry also goes over the top of a mini with it beeing so close and small. Prob wrong but thats my theory :-S

one day boost will be mine!

I think that we have established that he is not that close to the lorry. The turbulence behind a lorry is pretty bad though.

dazibee, I think you need to answer this yourself. Get some temp measuring gear and start logging...

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