Strength & Front of Engine access

[John Sims]

....I used to have an aluminium for show strut brace which I knew would do nothing for Racing so a Steel brace was made....

A strut brace works in tension so you probably added weight unnecessarily.

 

[924Srr27l]

A strut brace works in tension so you probably added weight unnecessarily.

It does work in tension John, when cornering forces are applied it's rigity (just like the Steel Rollcage) both come into play. ,

All a necessity to be competitive, the added weight can't be helped but without all these structural devices the car would lap slower !

It originally lost 250kg for road use, then for the Racing many things had to be and were added for circuit racing regs and to be on the pace,
(Rollcage, Fire extinguisher, Marine Ply & Aluminium front splitter, Rear Carbon Fibre wing and more) but many other things were disgarded or changed that were not required (The original heater, lots of wiring, passenger seat, carpet / underlay / Rubber sound deadening etc...)

So overall it's still super light and so much stiffer @ 1025kg

R

 

[944 man]

As usual, Rodger has confused his own XXXXXX opinion with fact. Rodger posting nonsense has become the PCGB 944 forum's thing, it would seem.

It would take the mixture of a little research and a bit of humility (ie, not thinking that you know it all Roger, if that helps you?), to establish that the 924 was developed using the lessons learned from Porsche's safety project from the early seventies, and that as a result of this, the car is extremely strong/durable/safe.

 

[924Srr27l]

As usual, Rodger has confused his own half-arsed opinion with fact. Rodger posting nonsense has become the PCGB 944 forum's thing, it would seem.

It would take the mixture of a little research and a bit of humility (ie, not thinking that you know it all Roger, if that helps you?), to establish that the 924 was developed using the lessons learned from Porsche's safety project from the early seventies, and that as a result of this, the car is extremely strong/durable/safe.

As usual the 944mun has contributed virtually nothing to this post (as many forums thing, it would seem) posting nothing other than personal insults and some sweeping statement than this classic car must be extremely strong because of some project done nearly 50 years ago! Would it be too difficult to request you can / could enlighten and educate the forum / club so that we and I can learn more about these car's we all love ?

What's classed and measured / tested as being strong 5 decades ago to a current day production car from Porsche is without a shadow of doubt far higher...

R

 

[924Srr27l]

The NHTSA in the states and the Euro NCAP have both come a long way saving many lives on vehicle safety..

https://youtu.be/Yv8qNPvU3NQ

 

[944 man]

There is no point relying Rodger, because people are tired of listening to your drivel, and I have had you blocked since you first appeared and ruined the forum.

 

[924Srr27l]

968, what's left of it !

R

 

[John Sims]

So overall it's ... so much stiffer

R

Not as a result of that cage it isn't. 4 or 6 point mounting for Club racing is specified in the regs in order to reduce any additional torsional rigidity that the cage might introduce. This is to avoid any such additional advantage of a multi point welded in cage. The Blue Book specifies cage design to protect the occupant without contributing to dynamic rigidity.

It goes back to the days when people were pretty much creating internal space frames out of the cages and regs were revised to avoid this offset in advantage for Club series.

I would also be concerned over your seat belt mounting. A friend of mine almost died in a crash a Snetterton when the belts crushed the seat back allowing him to become loose in the car.

 

[924Srr27l]

So overall it's ... so much stiffer
R

Not as a result of that cage it isn't. 4 or 6 point mounting for Club racing is specified in the regs in order to reduce any additional torsional rigidity that the cage might introduce. This is to avoid any such additional advantage of a multi point welded in cage. The Blue Book specifies cage design to protect the occupant without contributing to dynamic rigidity.
It goes back to the days when people were pretty much creating internal space frames out of the cages and regs were revised to avoid this offset in advantage for Club series.
I would also be concerned over your seat belt mounting. A friend of mine almost died in a crash a Snetterton when the belts crushed the seat back allowing him to become loose in the car.

John, your either being far too grumpy, just plain awkward, or your goading for a response!

If you think a rollcage / strut tower brace etc..does not add torsional rigidity to a car then you're very disillusioned !
Put your reading glasses on and have a look at this:

https://dsportmag.com/the-tech/chassis-tuning-torsional-rigidity/

The seat, belts and their mounting positons etc...are all totally to FIA / MSa specs as passed by FIA Scrutineers @ Silverstone, Donington and Oulton Park
Anything else you want to pick at?

R

 

[John Sims]

The seat, belts and their mounting positons etc...are all totally to FIA / MSa specs as passed by FIA Scrutineers

And so was his, and had passed scrutineering at a great many more than three events. It still broke the seat back and he still almost died.

I agree a strut brace will add rigidity, I wasn't querying that.

My point was a six point cage of that type is deliberately designed not to. RFM.

The additional low rear horizontal bar adds triangulation, and would be illegal in some series, but as it is only relative to the tops of the rear dampers this would have little impact on a 924. It is pretty much just adding weight in this instance.

 

[924Srr27l]

The seat, belts and their mounting positons etc...are all totally to FIA / MSa specs as passed by FIA Scrutineers

And so was his, and had passed scrutineering at a great many more than three events. It still broke the seat back and he still almost died.
I agree a strut brace will add rigidity, I wasn't querying that.
My point was a six point cage of that type is deliberately designed not to. RFM.
The additional low rear horizontal bar adds triangulation, and would be illegal in some series, but as it is only relative to the tops of the rear dampers this would have little impact on a 924. It is pretty much just adding weight in this instance.

Oh....

When belted up with Hans device etc...the angle of the shoulder belts is well within the accepted angle range, it's only when they are fixed
past 45 degrees from horizontal that a collision will put force on the seat back. There's no other method of having it that would be any safer.

I can only think this seat that broke was weak or something ?

My seat is Kevlar and very rigid and strong for it's weight (8kg)

The Rollcage has to be fitted to strengthen the car in the event of an accident! Sure a 16+ Multipoint weld in cage protruding through the front bulkhead and to the turrets etc...would be even more structurally strong but this 6 point Cage or any other does not just sit there for fun and NOT contribute to the structural
rigidity, it's just not possible for this to be so unless it was made from paper mache !

3 positions each side have welded on (Rigid load spreading reinforced platforms & Plates), the Sill, and the side upper and lower rear quarters.
There's no doubt whatsoever that it's made the chassis more rigid, (without finding things on the internet to show you) it wasn't a mild change when it was fitted but a substantial one.

The car also has a lateral bar connecting the 2 C pillar seat captive nuts, and this pushes against the body when tightened up with male rods ends (one left , one right hand thread)

The Rollcage, the additions and everything else on the car is fully legit and legal with all the Racing series in the Uk, and hopefully Europe next year (Spa & Zanvoort)

Motorsport Safety and technical training has been my day job ! Not just on cages and extinguishers but also racewear and helmets etc.. I started Racing John 24 years ago and have worked in and with all the major Motorsport teams in the world including F1, WRC, BTCC and LMP etc...Not to mention the Military!

R

 

[John Sims]

Motorsport Safety and technical training has been my day job ! Not just on cages and extinguishers but also racewear and helmets etc..

Well that is a surprisingly wide spectrum of specialisms. In what capacity were you consulted on these diverse fields of expertise?

 

[924Srr27l]

Motorsport Safety and technical training has been my day job ! Not just on cages and extinguishers but also racewear and helmets etc..

Well that is a surprisingly wide spectrum of specialisms. In what capacity were you consulted on these diverse fields of expertise?

Technical sales (Road and Racing car components) for 5 years

Then 4 years with an American Kevlar Racing Fuel cell manufacturer (2 years Amateur race and rally training, then years 3 & 4 with 6 Formula one accounts (Jordan, BAR, Jaguar, McLaren, Renault,& Minardi ), 1 World rally Team (Skoda), several Le mans GTP / LMP Teams and also Military (Vickers defence), Aviation (Including work with Concorde fuel tanks) and also Marine applications.....

R

 

[vitesse]

Surely anti-roll bars are meant to stiffen the reaction of the 2 connected wheels to roll-no bar=each wheel does its own thing-a bar produces reaction from one wheel to the other via the wishbones /trailing arms.
As far as I can deduce,adding a great stiff beam across the cars front end just moves the deformation possibilities further along the chassis rails-deformable front ends are meant to protect not only occupants but minimise chassis rail expensive repairs .

 

[John Sims]

.....
As far as I can deduce,adding a great stiff beam across the cars front end just moves the deformation possibilities further along the chassis rails-deformable front ends are meant to protect not only occupants but minimise chassis rail expensive repairs .

While I have a strut brace I agree with you. If, in the event of a hard impact, the wings are designed to crumple and splay, a strut brace will change this and the remaining energy will have to go somewhere else.

There again on a 20+ year old car the metal will have flexed, fatigued and changed over that of a new shell so may well behave differently to the fresh new cars used in the testing any way.

 

[graham.webb]

That was my point, really, John. A complex welded structure might not be as stiff after 27 years of flexing. Below the engine, the cross member is a casting and probably retains its stiffness, but at the top of the struts the lateral forces must have some effect. Just comparing it to my work on racking and wind loads in structural steelwork!! I agree that the brace will be most effective in tension, but there would also be an linking effect in compression, depending on how it's constructed...some are just a metal tube, others look like carbon fibre (much better you'd think). A lot of variation there?

On the other hand, I seem to recall that on the le Mans cars, as well as a strut brace there were diagonal braces back to to bulkhead centre? Maybe without that it's a waste of time?!!

 

[924Srr27l]

Surely anti-roll bars are meant to stiffen the reaction of the 2 connected wheels to roll-no bar=each wheel does its own thing-a bar produces reaction from one wheel to the other via the wishbones /trailing arms.
As far as I can deduce,adding a great stiff beam across the cars front end just moves the deformation possibilities further along the chassis rails-deformable front ends are meant to protect not only occupants but minimise chassis rail expensive repairs .

I'm not sure "Stiffen the reaction" would be the best way to describe how an anti-roll bar functions.
A Roll bar is the cars 4th Spring (And the chassis frame / structure the 5th)

This Spring (In the form of a horizontal bar that twists) that is connected to the left and right side of the car produces a resistance when one side does something different to the other.
If both wheels encounter a road undulation nothing happens, but when one side either rises or falls the sprung steel resists this force and the sideways tilting (roll) of the car.

The "reaction" time is denoted by the thickness of the Sprung Steel, a smaller diameter bar will react slower (And allow more compliance) than a thicker one.


"Adding a great stiff beam just moves the deformation possibilities further along the chassis rails"

This application is for Circuit Racing, where additional structural steel fitted protects the driver in the event of the car crashing / overturning etc...
Fitting a strong bar across the ladder frame rails is no different to fitting door bars, which offer additional resistance from a side impact.

In a Racing environment the driver is strapped into the seat permanently with no movement as an production inertia belt works, the driver also has a Head and neck restraint (HANS)
which significantly reducing whiplash and hence the production deformable structures that are further enhanced with additional chassis structural bracing (Rollcage / Strut tower braces etc..)
all offer additional strength to the chassis to protect the driver.

The front rails will deform quicker and easier if I just left them as they are with no frontal connection! but I'd rather they had more resistance than this...

R

 

[924Srr27l]

On the other hand, I seem to recall that on the le Mans cars, as well as a strut brace there were diagonal braces back to to bulkhead centre? Maybe without that it's a waste of time?!!

Yes, the more rigid a car is made the stronger it is, the better it handles and the better the ride quality etc...
Any and all additional tubing / bracing and complex materials (carbon Fibre) used and fitted the stiffer the structure will be.

A Steel Space framed structure with 944 body panels would be significantly stiffer than the production car, as would even more a Carbon monocoque and 944 panels !

R

 

[924Srr27l]

As far as I can deduce,adding a great stiff beam across the cars front end just moves the deformation possibilities further along the chassis rails-deformable front ends are meant to protect not only occupants but minimise chassis rail expensive repairs .

Car manufacturer's use many Different types and grades of Steel Strengths to assist with impact dissipation, Volvo's S40
has a similar (to the 924) ladder design front chassis rails which they use a stronger material for the front X member (Extra High Strength) compared to high strength for the ladder rails.



R

 

[944Turbo]

968, what's left of it !

R

Is it? rear looks like a 911 (964) wing and the engine seems to be missing at the front? (admittedly when I crashed my TR7 the engine removed itself, but it left a hole)