Coilover front suspension

[krede]

I got a set of these with my "gaz" kit when I bought it... but Mr.Dinsen and Lennart convinced me that if I fitted it, the chassis my car would surely crumble, and send me flying off the road and into an ENTIRE class of school children killing them all (on their birthdays)  .!

Now... I after comparing the murena chassis with some of the Kit-car chassis Ive seen recently, I have begun to doubt how bad this flex might actually be, and whether the torsion bar suspension isn't really more about the desire to use off the shelf parts, and the wish for a low "nose" rather than the necessity of moving torsional forces "inboard" 

I was going to fit the coilovers next time I get to work on the car, as i find it highly unlikely that it will do anything but IMPROVE the handling.

But if anybody has any hard facts about this "issue" please speak up!

Michal I believe your car has a very UNoriginal sparx kit fitted ... and If I recall correctly you drive your car pretty hard on the track... any thoughts?   

[Oskar]

ive seen many porsche 944 that convert from torsion the same way as this.  and they have the bars from the shelf from earlier 911 as in this case for the murena. 

But it should be very easy to reinforce the upper mount with some L-mounts welded and a stroutbracket cross the bay.

I say go for it! 

[JL]

In thoery there is no problem with the conversion to coil over shock front suspension as long as you brace horizontally and diagonally between the two front chassis rails and preferably back to the front bulkhead. The difficult part is sorting out the front spring rate.  Having raced many rear engines cars in the past I can confirm that spring rates are not an exact science and will involve plenty of trial and error; nevertheless seems to be an interesting project, plenty of photographs and info please.

Regards
John

[krede]

I had GAZ make up the kit, and all they needed to know what that the car in question was a Murena.
And just to clarify.. the coils in question are not of the same type as the rally car pictured elsewhere but looks like this :

[JL]

Looks good to me, do you know what rate the front springs are?

John

[michaltalbot]

Michal I believe your car has a very UNoriginal sparx kit fitted ... and If I recall correctly you drive your car pretty hard on the track... any thoughts?   

   yes there were Spax absorbers when I've bought it and I must to say, that it's much better than original suspension on my old silver 2,2 but I'm affraid that I won't help You, because on my car, on the front, there are only absorbers without springs, it means that torsion bars stayed at their place, but I think that it works perfectly.
 I also agree with Anders and Lennarth that fitting the springs as it is on the picture is not a good idea. It can be fine, but this point is not constructed to resist off big pressures, so it will be working inside of the material and one day it blows out.

[Anders Dinsen]

I think the trouble is as much the lower end of the damper, as the top. If you look at uprights and wishbones designed for coil springs, you'll notice that they are very heavy in the place where the spring is connected. The Simca uprights have only a small stud potroding out on the front of the lower wishbone. It's clearly not designed to take heavy loads.

It may work out without breaking off on the Murena since the car is so light fronted, but you probably need some good quality bushes in the lower end to make them last. I've heard about bush wear being a common problem with front coil over setups. This could include the bushes in the swiveling points of the wishbones, as the wishbone will be loaded unevenly.
It has to go on the outside of the A-arms to allow for drive shafts to pass through on the front engined Simca's, and with the shock fitted "outside" the box formed by the legs of the A (the front side of the wishbone is straight), the loading will not be even.

/Anders

[krede]

Well... as Carsten pointed out to me... the Spax kit is Tüv approved. And they usually dont lend their name to something that is going to fall apart

[krede]

JL: The springs that shipped with the GAZ kit are 2.25x9"- 275lbs

[Anders Dinsen]

Well... as Carsten pointed out to me... the Spax kit is Tüv approved. And they usually dont lend their name to something that is going to fall apart

I agree!

/Anders

[krede]

Right.. Tüv is good enough for me... they are going on the car when I evenually get to it again. 

[JL]

Thanks for the info. They are are almost the same as one of my old Imp race cars.

Regards
John

[Lennart Sorth]

Well... as Carsten pointed out to me... the Spax kit is Tüv approved. And they usually dont lend their name to something that is going to fall apart

?

- are you saying TüV has approved that kit for fitting onto a Murena in the described way  ? -  without any mention of extra chassis support ? or just the kit itself ?

I am not sure I understand your objective - If all you want is a lower nose, then why don't you just adjust it down ? - thats the beauty of the torsionbar arrangement.

With regard to the strength of the chassis, even with L-brackets and diagonal support, the chassis was never constructed to take much load there - and remember handling has a lot to do with chassis stiffness (well, on a gocart you actually use the flexing of the frame as suspension, but thats another story).  The torsion bars cleverly move all the weight-force into the centre pan of the chassis, where it is strongest, and only the shock-absorber affects the chassis directly.

Admittedly an absorber gives a fair load - and I believe a Murena would handle better with a strut-brace fitted, - but it is in my view counter-productive to also move the full force of the weight onto that same (over)loaded spot.

Play around with absorber settings, or even antirollbar if you want to explore the possibilities with the front suspension, but I would leave the springs alone where they are.

So you see, - I didn't mention the risk of you killing ENTIRE class of school children on their birthday (nice one though, Krede)  :-)

/Lennart

[krede]

- are you saying TüV has approved that kit for fitting onto a Murena in the described way  ? -  without any mention of extra chassis support ? or just the kit itself ?

This is what is says at Simons site:

"Spax-Sport-Kit     
This complete kit is a devolpment from „Fleischmann-Tuning“ only made for the Matra Murena. The front torsion springs will change for a coil spring with an adjustable shock absorber. The hight is adjustable stepless and the hardness in 14 steps. A complete kit contains the following parts:
          
-    4 Spax shock-absorbers (adjustable)    
Zur Vergößerung bitte auf das Bild klicken.Order-Nr. 24031
-    4 Eibach Springs
-    spring plates
-    TÜV-certificate and fitting instruction"

I'm not 100% certain that you don't have to do further modifications... but i find that HIGHLY unlikely as this is not normally how tüv approval works.