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Author Topic: Bagheera Roll Cage wanted  (Read 67269 times)
andyowl
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« Reply #150 on: September 03, 2010, 10:54:37 am »

A few more Etretat pictures...
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andyowl
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« Reply #151 on: October 05, 2010, 10:41:13 am »

Extract from a post in the Murena section of the Forum about the "MECUK Competition Team" at the Debden Sprint on Sunday with the 2.2 Murena of Graham Pryme...

From me...
Thank you for posting the link to the results of the Debden Sprint. Makes interesting reading!

My Bagheera is clearly "outclassed" in my class (Class 9: Modified Limited/Specialist Production Cars over 2000cc) and I think I need to re-open the debate with the regional championship organiser as to which class we should be in.

Even if we were to be in the class I consider appropriate (Class 3: Road-going Series/Specialist Production Cars over 2000cc) along with your 2.2 Murena I would have been 10th out of 12 entries. No competition there then!

Your Murena has the smallest engine in that class anyway with the majority being over 3 litres! My "Baggy Joe" at 1592cc x the 1.4 factor because of the supercharger would be rated at 2223cc. You would still have the smallest engine!

An alternative is to fit an early Bagheera 1293cc engine (1293 x 1.4= 1803cc) and be in the 1401-2000 class and be beaten by a Renault Spider (1998cc) and a Peugeot 405 LeMans 5 door saloon (also 1998cc). At least they are both French!

Good fun!

Andy

"Good fun" it is but it would be nice to be sometimes better than last!

My two practice times (P1 and P2) are better than my 1st timed run because I got over-confident and braked too late for the roundabout and decided to go straight on and make a 270 degree  turn before going around the circle! It had also started to rain (wipers were on "slow") and I had not allowed for the slippery surface. That cost me 9 seconds! The 2nd timed run was in heavy rain (wipers on "fast") and everyone was slower than the first run.

My fellow Class competitors were AWESOME! The MGB with the V8 3.5litre engine was last year's championship winner while the Mazda RX7 had just been fitted with a nearly new Chevrolet Viper/Corvette 5.7Litre V8. Wow! No shame in coming last there then!

You see why I want to be put in a more modest class then?

I tried one of my alternative silencers at the meeting - see the other thread for a test report on 5 silencers (to follow shortly).

Andy
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andyowl
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« Reply #152 on: October 14, 2010, 11:29:24 am »

More Debden pictures and an interesting comparison with the Murena!

Stiffer anti-roll bars would seem to be a good idea?

Comments welcome!

Andy
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Anders Dinsen
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« Reply #153 on: October 14, 2010, 01:58:56 pm »

Stiffer anti-roll bars would seem to be a good idea?

NO!

Anti-roll bars are load transfer devices (am I repeating myself?) - they help transfer load diagonally across the car. e.g. from the outer rear wheel to the front inner. If you start playing with them, you'll be getting oversteer/understeer. Or improve it/make it worse if you have that problem already.

The correct solution is stiffer springs.

Or improve your driving Smiley

A couple of weeks ago, I watched a beautiful Porsche 904 race a few other cars on a race track in southern Sweden. It battled with a Lotus Cortina and had a hard time keeping up with it. Which makes no sense: We're talking about a Le Mans prototype against a tin top car of roughly same age. The 904 is 600 kg, the Cortina is probably much more! A mid engined car against a front engined. He should have had no problem keeping up with the winning Lotus Elan.

Why?

He did all the corners wrong. He turned in early, breaking all the way through the corner. Here's a photo proving my point:

http://gallery.dinsen.net/v/biler/motorsport/hmsknutstorp2010/DSC_7970b.JPG.html

I can't tell you how to learn racing as I don't do it myself, but I know it takes a lot of practice. Training with a pro might be fun and a good experience too?

You are already having fun! Thanks for sharing your thoughts, experiences and photos, Andy!

/Anders
« Last Edit: October 14, 2010, 07:04:37 pm by Anders Dinsen » Logged

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andyowl
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« Reply #154 on: October 16, 2010, 10:59:21 am »

Roy wrote to Andy (permission was given to include the text here)...

Dear Andy,
I noted your comment on the forum about the amount of roll the Bagheera
is getting into corners.  Actually it is mainly rolling at the front -
the rear does not look too bad.  This is a fault of springs being too
soft for hard cornering in competition mainly.

Before you go fitting thicker front roll bars, do you have a brace
between the tops of the front suspension?  The Bagheera and Murena use
a very similar chassis at the front, and whilst the lower chassis is
quite complete, the top wishbone mountings are on sections that can
flex, probably more on these cars now as they will not be as rigid as
when first built.  It might be good to fit a brace across between the
top mountings, similar to the one in Graham's Murena, if you haven't
already done so.

Regarding the anti-roll bar - depending on what diameter your bar is, a
Murena 2.2 one may be thicker and should fit I think, so may be an easy
upgrade if it is thicker.  The 2.2 certainly has a thicker bar than the
1.6 model.

Since you have lowered the car by adjusting the torsion bars, the front
will be softer as the bar will not have as much wind-up in the static
position.  To retain the strength whilst lowering the suspension it
really needs different rate front torsion bars, but why not add some
small coil-over-shock springs to assist?  The chassis may need some
strengthening though.  Stiffer front shocks may help but they may make
the front more fidgety and any loss of tyre contact over bumps loses
grip so that may not be best.  Adjustable shocks will help find the
best compromise.

Regards,

Roy
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andyowl
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« Reply #155 on: October 16, 2010, 07:48:10 pm »

Roy wrote..do you have a brace between the tops of the front suspension?

The picture shows what I believe is the top suspension brace. The tube that the spare wheel leans against. It also has webs below to brace the sides of the front chassis extensions. Looks fairly solid to me assuming the basic metal is solid too!

I don't think lowering the car, reducing the ground clearence, changes the spring rate. You only do that by changing the diameter. The idea of adding "Coil over shocks" I will examine. If the right size can be found they could replace the existing shockers.

I did not understand that the Murena anti-roll bar was larger than the Bagheera. My Bagheera book only shows one size. I need to measure those fitted on the car. I did find a man who made special anti-roll bars and he may be worth contacting again.

I'm still digesting Ander's message. Driver training sounds a good idea although I don't understand why an anti-roll bar should transfer load to the diagonal corner rather then the other wheel on the same axle.

The suggestion that the front of the car is rolling more than the back puzzles me too! Surely that implies that the chassis is twisting? I don't see that in the pictures either.

Andy


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Anders Dinsen
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« Reply #156 on: October 16, 2010, 08:44:48 pm »

I agree, it's not quite obvious. Smiley

Let me try to explain.

The anti roll bar does not trafer *load* from the outer wheel (under load) to the inner. In fact it does the opposite - it will try to lift the inner wheel off the ground, fighting against the spring and shock on that side. Of course, the spring is much stronger, so it will still manage to keep the wheel against the ground, but the force is actually reduced.

This reduces the chassis' tendency to roll at that end, but with properly designed suspension, roll is not a problem in itself. It's the shifting of the centre of gravity caused by roll which can cause problems.

However, the chassis will transfer the load to the inner rear wheel to the outer rear wheel, and THIS is why the front anti roll bar is a load transfer device from front to rear, and the rear anti roll bar is from the rear to the front.

As for driving, keeping the car in balance is what drivers say is important. Think of it this way: You are essentially driving a shopping cart. Try turning it around a corner and it will initially resist your turning force. But once it is in motion, it will try to keep on rotating.

A car is the same: After you get off the brakes and start turning, initially the car will fight against your steering. But once you get it rotating, it will try to keep the rate of rotation. Hopefully, by the time you are over the apex, you are going slow enough to have enough grip to get the car pointing forwards again, and by the way, you'll be shifting the COG backwards as soon as you get back on the throttle. With the rear weight bias of the mid engined car, the COG will be closer to the heaviest point of the car, so the rotatinbg inertia of the car will be reduced, making it easier for you to get out of the corner. If you have enough power, that is. But you have Wink

I hope this explains a bit of the dynamics going on in your car while you're taking it through the corners, but as a race car engineering book I once enjoyed reading said at the beginning of each chapter: It's just not that simple! Cheesy

/Anders
« Last Edit: October 16, 2010, 08:49:02 pm by Anders Dinsen » Logged

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Anders Dinsen
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« Reply #157 on: October 16, 2010, 08:52:13 pm »

The suggestion that the front of the car is rolling more than the back puzzles me too! Surely that implies that the chassis is twisting? I don't see that in the pictures either.

Nonono, it doesn't have to twist. Go to your car and push down one corner and you'll see.
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Spyros
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« Reply #158 on: October 16, 2010, 09:41:42 pm »

Page 116 of my manuel.

Diameter of the torsion bars :
Bagheera 17.2
1100, Rancho : 18
1100 improved suspension : 20.3
Horizon automatic gearbox : 17.6  (the manual gearbox is only 17)
Horizon improved suspension : 19.6
1307/1308 : 19
1307/1308 improved suspension : 20.9
1309 automatic gearbox : 19.5

About the top suspension brace, the comment was directed to the Murena who is lacking the very heavy brace of the Bagheera.

Now, don't forget : 1307... Solara torsion bars are longer than the Bagheera ones and requieres some modification to your car.

The number I gave are the Bagheera serie II
The first ones had 17.5 mm diameter torsion bars

It's the reverse that what they did for the rear torsion bars (ticker on the serie 2 than the serie 1)

There is also a difference in the antiroll bar but it seems that you are pointed to the torsion bar

I hope this can help
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andyowl
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« Reply #159 on: October 17, 2010, 01:19:07 pm »

Anders wrote... It's just not that simple!

Yes, I see what you mean.

Maybe I should find that "Suspension for racing cars" book I bought when we started on this project. "Doing it" was so much more interesting than "reading about it"!

My suspension knowledge, such as it is, was learned from the articles in "CAR" magazine by L.J.K. Setright. Sadly he is no longer around to ask!

Andy
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andyowl
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« Reply #160 on: October 17, 2010, 01:28:45 pm »

Spyros wrote... Diameter of the torsion bars :

These are the torsion bars, not the anti-roll bars?

Using a thicker torsion bar will make the suspension stiffer i.e. less wheel deflection for a particular load. That would seem to be a good idea since, having lowered the car, it must have less deflection available. We fitted "tell-tales" on the rear shock absorbers for the Mallory Park track day and could see that we were using all the suspension travel, i.e. it was "bottoming" at the rear. We didn't check the front but that may be bottoming too. So fitting the Simca 1100 or Improved Horizon front torsion bars is worth a try?

What can we do about the rear torsion bars? This is a Series II so we must already have the thicker torsion bars.

Andy
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Spyros
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« Reply #161 on: October 17, 2010, 02:27:00 pm »

On the rear, you won't find any ticker torsion bars than the one you have.
New ones will probably be stiffer but not a lot.

So the only option at the rear would be to fit coil over dampers.
But I would first try Rancho front torsion bars.

This is an idea I have in mind since a long time.

Or you can have custom torsion bars or anti roll bar made but who can do that ?
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andyowl
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« Reply #162 on: October 17, 2010, 07:12:29 pm »

Spyros wrote... Or you can have custom torsion bars or anti-roll bars made but who can do that ?

Last year I did find a company in the UK Midlands who were able to make custom torsion and anti-roll bars. I have it written down in the files somewhere. All he needed was an example of the old one to copy.

Andy
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andyowl
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« Reply #163 on: November 05, 2010, 09:40:37 pm »

MSA UK Sprint Championship, Southern Region, 2010

I have just seen the results for the Championship for 2010.
There were six entries in the "Modified Production Car" Class, over 2litres*. They were:-

Name                Car                           cc            Points
Steve Cox   TVR V8S 500   4997   40.0
Alastair Flack   Triumph TR7 V8   3500   10.0
Kevin Salisbury   Ford Sierra Cosworth 1993   12.0
Geoffrey Martin   Ford Escort   2300   -
Andy Owler   Matra Bagheera S   1592   20.0
Jason Easton   Ford Sierra 4x4   2933   -

That seems to make a Matra Bagheera 2nd in Class!

* We are in this class because
a) the Supercharger attracts a penalty of 40% extra capacity giving us a notional capacity of 2229cc and
b) Matra did not produce a supercharged Bagheera and therefore this is a "modified" car  rather than just "tuned".

If I had done two more events** this year and marshalled at least once I would have had 45 points and therefore first in Class! Somethng to aim at for next year!

** I had entered two more events (Sprint Royale and Lydden) but had to withdraw from both as "Charlie" (my wife) was in hospital. She is now back home again and making good progress. We hope for better things in 2011!

Thanks for all your support and interest.

Andy and Charmian Owler
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suffolkpete
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« Reply #164 on: November 06, 2010, 10:29:48 am »

Congratulations Andy!  That's quite impressive, considering the competition.  I'm sure your huge band of followers on this forum will wish you well next season.
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