Aerodynamics

[Anders Dinsen]

I would like to draw readers attention to a book title that seems interesting on the subject of aerodynamics: Race Car Aerodynamics by Joseph Katz.

On the publisher's web site there is even an interesting full chapter excerpt from the book available complete with pictures.

The full link to the excerpt (and book description is available from there) is http://www.bentleypublishers.com/gallery.htm?code=GAER&galleryId=768

I think reading this will give a much better perspective on understanding the good aerodynamic properties of the Murena.

Personally, I'm still waiting to receive the book through Amazon.

[Anders Dinsen]

After reading Katz' book my thoughts have been running... Lennart, when I showed the book to him, anticipated we'd be seeing diffusers, spoilers, diveplates and other stuff appearing on my Espace now!

Maybe we will....... but since I expect to expand my car collection with a Murena 2.2, and I've been reading anything I could find about the car lately, my thoughts about aerodynamics started turning around this little sports car

I'm actually very impressed with the Murena's aerodynamics after reading Katz' book. It's not a race car, but a road going vehicle, and it's not a 2006-creation, but a design from 1980. But it looks like the engineers and the designer have worked extremely well together to create a sound aerodynamic body with good stability. Which is also what Murena-enthusiasts tell me!

So I wrote down my ideas, and have put them on my home page. This is all theory!! After all I don't have a car to try it on. I don't even have a car to look at! But I think the ideas are good anyway - and it would be fun to try out some of them, though they are probably more difficult to implement than I have anticipated.

Anyway, here's the link and I'd be happy to hear any kind of comments to my thoughts:

http://dinsen.net/murena/aerodynamics/

Cheers,
Anders

[Matra_Hans]

Hi Anders,
You did not get much reaction to your ”article” regarding improvement of the aerodynamics on the Murena. However here are a few facts and comments:

Hot air flow though the wheel wells: The hot air from the radiator is in fact on the original Murena directed to the wheel wells (or at least part of the hot air) through a hole in either side of the chassis. The size and shape of holes in the chassis can of cause not be changed, but the shape of the surrounding fibre glass panels are not optimal for the airflow so some improvements can be made in this area.

Hot air directed up through the bonnet/ heated air into the cabin: The fan and the air intake for the cabin heater is on the Murena not placed in the middle of the car but the fan is placed in the right side of the car more or less where you will find the glove compartment on most cars, but of cause the fan is placed in the space in the front of the car just behind the right front wheel. One will have to remove a small panel behind the front wheel just below the windscreen in order to get access to the fan. Even though I have repaired and finally changed my fan a couple of times I have forgotten where the air intake is (and I do not want to dismantle the thing to check it out) but is most likely in the inner wing just behind the front wheel between the glass fibre inner wing and the passenger cabin. Consequently if the hot air from the radiator is flowing over the top of the car this will hot heat up the air going into the passenger cabin.

Understearing: When I have been pushing my Murena at the limit I have normally not experienced under steering but the back of the car has been loosing the grip. However power from my engine is up a little from standard as I have a Politecnic 152 cv camshaft and a 4-in-1 exhaust.

Rear diffuser: I think that a rear diffuser can be integrated in the middle of the rear bumper with out changing the looks of the car too much. Personally I will prefer a rear diffuser compared to a big spoiler as the shape of the car will be unchanged.

In my opinion the Murena is not designed for high speed cruising but for maximum speeds at small twisted roads.

Regards Hans

[Anders Dinsen]

Hi Hans

Thank you for your comments and clarifications! It feels good getting feedback

In my opinion the Murena is not designed for high speed cruising but for maximum speeds at small twisted roads.

... which is exactly why you want downforce!

About the air flow... I didn't know that there were openings to the wheels! But the radiator box is also open in the bottom, or is it not? If it isn't, then there obviously isn't that much to gain.

According to the repair manual, the cabin air intake is in the whole width of the car and is between the two chassis plates sitting over each other in front of the wind screen. It is ingenious, but makes it difficult to change.

A rear diffuser has to be coupled with a smooth underbody with air channels and a very sharp turning point where the diffuser starts. The lowest pressure will be at the turning point.

Seeing pictures of peoples Murena's, one problem will be to get the undertray/diffuser fitted under the exhaust silencer which apparantly sits quite low on some Murenas.

But I have been thinking lately that the main problem will be to get past the engine. We can't block the engines sump that needs the airflow, so a channel will have to be made on either side. These channels turn into the diffuser. But I'm afraid there's no space for it? Of course, the serious will convert the engine to dry sump lubrication with all the necessary accessories to accomplish that....

I just did this sketch. The blue rectangle is where the diffuser can sit - and the problem is really: How do we get a free flow of air to it?

- Anders
(still thinking )

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[Matra_Hans]

Air flow: The radiator box is open at the bottom.
Diffuser: Attached is a picture of a Murena with a turbo engine.
The silencer is a short and light carbon fibre unit and is placed longitudinally under the middle of the boot. With this layout a rear diffuser will be a possibility.

Hans


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[Anders Dinsen]

A carbon fibre silencer is a bit too extreme (aka expensive?) for my taste, but it can't be argued that this guy's car looks severe.

I have been looking at the Lotus Elise, and think the underbody of it should serve as inspiration. It is reported to work well. The two cars are similar in some ways with both with transversal mounted engine, though the Elise is somewhat smaller than the Murena. Further the Elise has a dedicated oil cooler and side air intakes (similar to the Murena 4S), so it can be completely closed in the bottom. But the ride heights of the two are about the same, so ground effects are similar.

On the Murena, we need an underbody opening to the engine room for air intake and oil pan cooling, and also for engine room cooling. This will interrupt some of the flow, so it will not be possible to make a diffuser with the same effect as on the Elise.

It seems I need a car to take measurements from.

- Anders

[Matra_Hans]

I refer to the discussion on the mail forum, but as the webpage (whpracing.nl) with the pictures has been closed, and I do not have my own webpage where I can up-load the pictures I am uploading the pictures here.
The pictures shove a Murena bonnet with louvers in the cars colour, and a bigger radiator from a Tagora.

Regards Hans


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[Anders Dinsen]

These pictures are really interesting and makes me wonder if it is after all possible to make an air outlet in the bonnet and the car will still be recongnisable as a true Murena - i.e. something that won't be considered blasfemical to the original design? I know Murenas take many forms, maybe people didn't think the original design was worth preserving - but I do!! 

Where has WHP Racing gone, are they not racing any more?

Best wishes,
Anders

[Matra_Hans]

Hi
I saw the WHP-Racing's car for sale some time ago on the Dutch page "MatreTeKoop.nl" so I guess that they have given up racing.
Attached are two pictures of a French racing Murena with a different design of air louvers in the bonnet.

Regards Hans


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[Anders Dinsen]

More interesting pictures, Hans!! Thanks for posting.

This is more aggressive looking, but probably not necessarily more effective than the louvered (louvres are grills, just for the record) bonnet in creating airflow through the radiator. The steep edge behind the radiator will probably add downforce though since it will be a higher pressure area when the air is deflected upwards.

It is an enormous rear wing they have. It suggests that they were running a very twisted track or has upgraded their engine severely.

Have you noticed the underlip?

Hans, do you know who engineerd this race car and when it was raced?

Sorry to hear about WHP Racing, I hope they had fun with the car and that it's now in the possession of someone who will take care of it.