Minimum race weight for a Murena?

[Pär Hansson]

Hi all,

New to this forum and I am about to start a race car project based on a Murena 2.2. Two engines are candidates for a transplant into the Murena so far, both PSA engines, XU10J4DZ@155 hp or ES9J4S@190 hp.

The right choice depends on which race weight tha car can be brung down to, so what is your guess on minimum weight ex driver?

The interior will be removed except the dashboard and heater/defroster system and of course the necessary controls. Two race seats @ 15 kg together will replace standard seats and a rollcage @ appr 25 kg will be added.

I have an opportunity of buying an XU before I have had a chance to examine the car, but I doubt that the car can be lightened to about 960 kg ex driver (I read some topic which I can't find right now that there is litte to do about the weight)? This would be required in order for the XU package to be competitive. I have to decide about the engine fast and that's the reason for this question, though I have almost no first hand info.

Possible weight reduction objects:
-Fixed headlights for race purposes.
-Thinner body panels in some areas.
-Smaller and surge-free fuel tank.
-Polycarbonate windows (sides and rear).
-XU lighter than standard 2.2 (N9?). (don't know about the ES, but then the race weight can be higher).

Both facts an guesses welcome!

[Anders Dinsen]

Interesting, Pär!

Given that you initially consider an engine transplant, it is obvious that you are not considering classic racing. Fitting an ES9J4S will be a tight fit, but you will be able to tune it to much more than the 190 bhp. Sodemo offers this engine for racing in versions up to more than 650 bhp (with twin turbo chargers, as raced by Pescarolo in Le Mans series in 2000-2003). But don't forget that the standard 2.2 engine can also be tuned considerably for racing.

If you have the money, carbon fibre panels could be an option.

WHP Racing in the Netherlands removed the boot altogether and fitted a frame to give the stiffness otherwise given by the chassis plates. Unfortunately their web site is off line now, but I remember that they mentioned that it also improved access to the engine.

Politecnic will also be able to help as Lennart points out elsewhere on this forum: They worked with Matra creating race versions of the Murena in the 1980's. See http://www.politecnic.com/murenacourse.htm

How do you measure the weight of the car?

Please tell us more about your race project, including what series you are considering to race in. You want two race seats, so I guess it could be rally?

- Anders

[Lennart Sorth]

Carbon fibre panels was actually something Matra were playing with, according to a guy who worked on the Espace development - when browsing around the factory storage shelves, he found a complete Murena rear wing in carbon fibre :-)
I still believe that carbon-fibre some day should/will enter the hobbyist's universe, - but it still seems to be postponed into the distant future.

Even if the bonnet is quite heavy, and begs to be replaced by something lighter, I would recommend trying to make the car lighter at the rear, especially when fitting a heavier engine.

Stig's idea with carbonfibre "motorcycle-style" exhaust sounds like a very good one.

The rear window could be replaced by perspex - F40-style (aka so floppy, you need to be two people to open it)

Some raceers relocate the fueltank to front, to give space to the engine, and to move weight forwards, - personally I find that poses a rather serious risk though.

and obviously you can remove as much of the interior trim you find reasonable.

if possible (for regulations?) save teh taillights, as they are no longer obtaibnable. Fit something else for racing, and either save the glasscovers, or sell them (thus financing your adventure ! :-)  )

Good luck, and please keep us posted

/Lennart

[Pär Hansson]

Oh, It's circuit racing... the two (possibly three) seats will be there because of the Swedish Sportscar Championship's regulations. Hope to be able to use the car legally on the road as well, but in the worst case it will be a pure race car. Maybe our nordic readers will make use of www.spvm.se and it is Roadsports C with a minimum of 7 kg/hp I'm aiming for.

The car is not an object for an original renovation att all, whatever I do with the car will be for the better. So possible purists can sleep calmly...

At least in the first evolution state it will be raced with a stock engine, that's why the original power figures are important. I know of what www.sodemo.com do with the ES... and it's tempting, but out of my financial league, unfortunately. Another interresting reflection is that the ES pushes out 280 hp+ passing a series production line (without extensive testing and tuning) for the former version of Renault Cup Clio V6.

...But the ES doesn't seem such a viable option at all, except for it's voice (not noise) and it's cubes. In roadsports C I will drag around 1330 kg with all of it's implications as tyre stress, bigger brakes and, hence, bigger wheels with more expensive tyres, et.c. And an ES in the higher class brings me back to a weight requirement of about 950-960 kg (without driver) again....

The weight is measured in parc fermé after the race including driver. That means all fluids and a driveable fuel residue in the tank plus 300 ml for probing. But the lower the bare weight, the more ballast to be put in the right places.

Replacing certain tub components with tubing might happen, as you say, dinsen, the engine compartment isn't very accessible to say the least! 

When it comes to weight distribution, I can accept up to front:rear 40:60 for optimised brake performance, the corner balance will be handled by tyre widths and suspension settings. So I don't worry much about removing mass from the front.

Carbon fibre, I might have some connections that might be interested in making moulds... 

Rear window, I've already counted in the Politecnic style hatch (which I would like to try to make myself) with the small upright rear window. The increased cooling to the engine bay wich this solution can provide doesn'nt hurt either.

Fuel tank, I agree with you, Lennart. I wouldn't like to sit with a bundle o' fuel virtually in my lap at any time.....

Nice tip about the taillights, there's tinted bulbs nowadays, maybe the'yre sufficient covered with clear polycarbonate? Have to check.

Thanks for the response! Hopefully I will be able to pay back with reports of progress. However, I need to get my present race car sold to be able to fiddle with the Murena.

So, what do you think? Can I strip her down to 960 kg without driver?

[Anders Dinsen]

So, what do you think? Can I strip her down to 960 kg without driver?

Empty weight is specified to be 1050 kg for the 2.2 with tank full so you are looking for 90 kg weight reduction. I have no experience, but I think it might be possible. The stanard 2.2 engine is said to be very heavy, 50 kg more than the 1.6 (a 2.2 murena is specified at 635 kg rear weight, a 1.6 at 585 kg, and this probably accounts only for the difference in engine weight).

Lennart: The XU is that the engine you have?

All in all.... I'd say it can be done but lets see if someone with practical experience responds.

If you lighten the engine, you need to lighten the front too, as the stock 2.2 is just on the 40:60 ratio.

- Anders

[Lennart Sorth]

Lennart: The XU is that the engine you have?

nope. Mine is the older Peugeot 205gti 8valve - XU9JA/K

If you lighten the engine, you need to lighten the front too, as the stock 2.2 is just on the 40:60 ratio.

nevertheless, I think any Murena will benefit from moving the weight-balance towards the front. 

At the same time, any car will become faster (and possibly better?) by loosing weight in general terms, but my point is just to make sure you at least never end up with a balance further back than originally - I'd certainly prefer the opposite.

Springs and shock-absorbers could possibly be another area where modern racing-type replacements might be both better and lighter.

and of course some "honestly lightweight" alloy wheels, - I have in fact seen ONE place (but only one) where the weight of the alloys was specified ... something I find quite odd. The weight was the initial REASON for inventing lightweight alloys - but I have the feeling many modern alloy wheels are in fact heavier than the old-style pressed steel wheels.

The rubber trim on the bumper is also not light (has a steel reinforcement) - you might save a pound or two by painting a black stripe in its place :-)

/Lennart

[Anders Dinsen]

Lennart: The XU is that the engine you have?

nope. Mine is the older Peugeot 205gti 8valve - XU9JA/K

Ok, I thought maybe weights could be compared with your car.

[Pär Hansson]

I had it wrong, it is an 1.6, but that doesn't matter (?).

Thanks for the ideas and tips, I guess there's prospects of reducing the weight sufficiently then.

The XU10J4* has a cast iron block and a 4-valve head while XU9J* has alloy block and 2 valve head, both with alloy heads, so that makes XU10J4* heavier than XU9J*, but the cast block itself is said (not confirmed) to be only 5-7 kg heavier than the alloy one.

Considering the weight balance, what I meant is that i do not want the balance more aft than 60:40, but I don't mind if it ends up more forward. When brake performance is taken into account, 60:40 is often regarded to give best overall performance, provided that rear tyres are about 50% wider than the front ones. This is, however a pretty impractical and expensive tyre width distribution, 275:185 or 295:195 are within a practical range and I would like to not having wider tyres than 225 of cost reasons.

If the weight balance does not match the amounts of grip on the respective axles, one must refrain to playing with roll stiffness and reduce grip in the front to obtain balance. I encounter the opposite problem with my current Peugeot 205 GTI, where I have to spill grip in the rear to have a balanced car.

[Anders Dinsen]

No the chassis differences between 1.6 and 2.2 are small AFAIK.

The XU10 is a quite advanced engine and it would'nt surprise me if it was only a bit heavier than the 4 cylinder engine. I know that Espace 24V with the same engine is some 50-70 kg heaver at the front than the same car with 2.0 16V engine. This may seem a lot, but you should know then that the 24V in always equipped with the ZF 4HP20 automatic gearbox which alone weighs 89 kg! I don't know the weight of the 2.0 16V gearbox, but since it's a fairly standard 5 speed manual gearbox the weight of it probably doesn't exceed 50 kg. Will (also frequent poster here) will perhaps know more since he has had his engine out of his 24v Espace.

I don't know about the brake performance figures, but I should say that your "rule of thumb" would depend very much on the suspension type used in the car? 295 sounds as some very fat rear tyres. Although the car was developed for road use, the difference between front and rear is only 5%. Further, you won't get a much bigger contact patch with the wide rear tyres unless you reduce the tyre pressure considerably, so I'm slightly sceptical about your numbers. But you know more about racing setup than I do, obviously!

[Pär Hansson]

Maybe there has been a little confusion here, the XU10 is an in line four as well, the ES9 is the 60° V6.

60:40 optimum... From what I know, then you can utilise almost as powerful brakes in the rear as in the front.

The tyre width distribution for balance I mentioned are calculated from obtaining even contact pressures between front and back. Although it's no exact science it gives a hint of what it should be. In race applications, temperature distribution over the tyre width is monitored and actions taken in order to get an even distribution. Tyre pressure, camber and toe are parameters to play with. With semi trailing arms, the wheel alignment is fixed in the original state, but ther are solutions for that coming from the BMW E30 rear suspension which has a similar layout. I'm not sure that the original layout will stay either.

Here is the object, which I collected yesterday BTW:

[Anders Dinsen]

Maybe there has been a little confusion here, the XU10 is an in line four as well, the ES9 is the 60° V6.

The confusion is my fault... I was referring to the V6. I'm not good at the Peugeot numbers, but feel a little more at home in the Renault's

60:40 optimum... From what I know, then you can utilise almost as powerful brakes in the rear as in the front.

Murena does have a brake pressure limitor for the rear brakes which kicks in when the brake line pressure exceeds something like 17 bar, I think, so for moderate pressure on the pedal the brake line pressure is the same on the rear as on the front, but for increased pedal pressure, the rear brakes gradually gets less power. Here are some calculations on the brake distributions of the Murena, alas again in German: http://www.technikhomepage.de/kfz/fahrwerk/brphysik.html

You might get some useful info too by reading this (if you have not done so already):
http://www.matrasport.dk/Cars/Murena/gp_murena.html

The tyre width distribution for balance I mentioned are calculated from obtaining even contact pressures between front and back. Although it's no exact science it gives a hint of what it should be. In race applications, temperature distribution over the tyre width is monitored and actions taken in order to get an even distribution. Tyre pressure, camber and toe are parameters to play with. With semi trailing arms, the wheel alignment is fixed in the original state, but ther are solutions for that coming from the BMW E30 rear suspension which has a similar layout. I'm not sure that the original layout will stay either.

Are you considering a different rear wheel suspension?

Here is the object, which I collected yesterday BTW:

Hmm, it doesn't look too bad. I found the other pictures at the site you are pointing to - they seem to be from the winter time. Just one note... if you'd like to preserve the original look of the car, let me suggest that you replace the rear window with perspex instead of building the "Ferrari rear". The rear window is really a unique feature of the Murena.

[Pär Hansson]

Not quite up to the quoting wizardry of this forum, I try to answer anyway... hope it's traceable.

In understand your confusion, I guess as and old Peugeot buff I don't reflect over the designations and their level of encryption anymore... However, the 60° V6 is a delightful motor, I have the 207 hp version in my day-to-day 406 and it's tempting to fit one. But it would be the older 190 hp version without variable cam timing in that case, since there's quite a penalty for variable cam timing in this series and the potential peak power does not differ that much.

Regarding 60:40: I guess (havent driven such a car) that with 60:40, the appropriate tyre widths an properly dimensioned brakes, you won't have to apply much reduction to the rear circuit, but with virtually the same tyre width in the rear, the rears might lock up otherwise. Haven't examined the brake system at all so this is just guesses. There are quite a few references to these findings, the only one I can think of right now is one "hobby-chassis-dynamicist": http://hem.passagen.se/hemipanter/

The best setup for brake balance is a balance bar system, but that is not approved by neither the Swedish authorities nor the series.

Rear wheel suspension: Yes, I  would like a double wishbone arrangement rear as well, but at least tuneable trailing arms.

Keeping rear window: Hmmm, I begin to agree. No offence to those who made the conversion. I guess that a polycarbonate window is lighter than the bonnet conversion and I believe there is aerodynamical advantages as well. Btw, I will read your aero-article as soon as I can.

EDIT: The other pictures on my Photobucket account, with the car not on trailer, are the sellers pictures. It's been for sale for a while and i would guess that theyre taken during spring 2005.

[Anders Dinsen]

Not quite up to the quoting wizardry of this forum, I try to answer anyway... hope it's traceable.

sure it is

In understand your confusion, I guess as and old Peugeot buff I don't reflect over the designations and their level of cryptation anymore... However, the 60° V6 is a delightful motor, I have the 207 hp version in my day-to-day 406 and it's tempting to fit one. But it would be the older 190 hp version without variable cam timing in that case, since there's quite a penalty for variable cam timing in this series and the potential peak power does not differ that much.

I (or rather my wife) runs that engine in our Espace (part of it visible in my avatar on the left). You won't need the variable cam in the race car anyway if you can recut the cam to something more sporty.

Regarding 60:40: I guess (havent driven such a car) that with 60:40, the appropriate tyre widths an properly dimensioned brakes, you won't have to apply much reduction to the rear circuit, but with virtually the same tyre width in the rear, the rears might lock up otherwise. Haven't examined the brake system at all so this is just guesses. There are quite a few references to these findings, the only one I can think of right now is one "hobby-chassis-dynamicist": http://hem.passagen.se/hemipanter/

I'm thinking that if you increase the width of the tyre, the contact patch area is not increased at the same rate since the deformation of the tyre will be less for a fatter tyre. So you will get a wider contact patch, but also a shorter one, so the area of it will remain with only less increase.

Anyway, Murena is fitted with a reduction valve for the rear brakes.

On the page I mentioned previously, this table is shown:

Brake line P (bar)	Braking force front	Braking force rear
27	19.5 kN	17.2 kN
35	25.3 kN	19.4 kN
70	50.6 kN	29.6 kN

This shows that during modrate braking, the rear and front brakes are almost in balance, but for harder braking the fronts start taking over. Since you will only be doing hard braking when racing, you don't need the reduction valve to work like the stock one, but you can just fit calipers with smaller pistons on the rear (I assume you will be upgrading the brakes to racing standard). You probably do not have to follow the ratio in the table above since I would assume that Matra designed the brake system safety rather than performance.

The best setup for brake balance is a balance bar system

How would that work?

Keeping rear window: Hmmm, I begin to agree. No offence to those who made the conversion. I guess that a polycarbonate window is lighter than the bonnet conversion and I believe there is aerodynamical advantages as well.

I think its difficult to say what would be the best from an aerodynamic point of view (drag and generating downforce). You will probably fit an adjustable rear wing in which case you should be mostly concerned with ensuring a laminar (smooth) airflow to the wing. I would think the rear window would be better at doing so, but on the other hand: The ferrari-style rear will probably have less lift in iteself than the rear window has. If you are really serious, both will have to be tested for performance. But for the looks, keeping the rear window will be best, I think.

Btw, I will read your aero-article as soon as I can.

I will try to make an update this weekend, so you should wait until that's done.

[Pär Hansson]

Regarding the contact patch area, I think that you should  consider the propotionally higher load on the wider tyre. In a static state, the mean contact load divided with contact area always equals to tyre air pressure.

The problem with wide tyres is more of a camber control problem, and that's a field that semi-trailing arms aren't at their best.

Balance bar: I did not get hold of a particularly descriptive page, but http://www.wilwood.com/Products/005-PedalAssemblies/index.asp and http://www.apracing.com/car/pedalbox/pboxp4.htm should give you an idea. Two main cylinders are operated by the brake pedal via a balance lever. Either the load point situation or the respective lever lengths are adjustable. No "break-away point" as with the adjustable brake pressure regulators.

Flow: Im a has-been when it comes to fluid engineering, but near-laminar flow hitting a rear wing will not happen with the Ferrari conversion. It will also create quite an amount of drag. The stock window arrangement will, on the other hand, create a bit of lift. But drag will be less and the air hitting a wing will be less disrurbed and, hence, the wing will provide more downforce over drag.

[Anders Dinsen]

Balance bar: I did not get hold of a particularly descriptive page, but http://www.wilwood.com/Products/005-PedalAssemblies/index.asp and http://www.apracing.com/car/pedalbox/pboxp4.htm should give you an idea. Two main cylinders are operated by the brake pedal via a balance lever. Either the load point situation or the respective lever lengths are adjustable. No "break-away point" as with the adjustable brake pressure regulators.

Ok, I get it now; it's different from a road car which normally has only one brake cylinder of course. The bar is obviously better for a race car since it allows more adjustment, and the illinear reduction valve is of lilttle use anyway. But since regulations prevent it, I suppose you will have to stick to someting less flexible. Thank you for the links

I was thinking that maybe you would be able to get some quality advice on the forum om Race Car Engineering magazine.  I've been lurking for a month or so and have learnt a bit already
http://www.ten-tenths.com/forum/forumdisplay.php?f=16&styleid=1022
It does not require you to actually subscribe to the magazine to read or post.

I'll send you a mail when I have updated my notes on aerodynamics.