Roll cage question, Aluminum cage and monocoque?

[jan bot]

Dear all,

We are currently preparing a car to get back on track after 30 years in hibernation..
It has been designed for the 1979 season of the Group 5 category, but was raced in the 1980 IMSA GTX class and the 1982-3 IMSA GTP class and to make things more complicated... altogether it did 6 races (4x IMSA GTX, 2x IMSA GTP) with 3 different engines, but was designed for an engine that never materialised..
It has an aluminum roll-cage that has been riveted to an aluminum monocoque, basically trying to get through a loophole in the 1976 Group 5 regulations which read:
" No modification may be made to the series coachwork and/or the
original chassis and bodywork, except as regards the lightening of the structure by removal of material and the adjunction of chassis reinforcements."
Comes from here
Yes.. they removed all of the original chassis for "lightening" purposes and added an aluminum monocoque as "chassis reinforcements"..only an English firm can get away with that


I've read in the App K that an aluminum roll-cage is strictly forbidden for every GT car in group 5, and for example some porsche 935 owners have replaced their alu cage by steel ones accordingly. But I've also heard rumours that this does not apply to aluminum monocoque cars, which shouldn't exist in group 5 because of the rules above and therefore it would be unnecessary to mention the exception in the appendix K for group 5..
The cage tubes are 1.5 inch in diameter and .128 inch thick, if size matters.
Replacing the cage by a steel one will be a lot of work and may damage the chassis, so we hope to get away with this original one.
So.. does anybody know about aluminum roll-cages in cars with an aluminum monocoque that are presently competing in historic racing and seem to have a "legal" status ?

Looking forward to your input,
Jan

[terence]

Perhaps a 917 owner could tell you.

[gt917]

All 917 cages were alluminium, and even the replica that David Piper built up has one. 917s of any type were never monocoques. They were alloy space frames. (three were magnesium tubing !!)

When i built my own up (not FIA/HTP able) i took no chances and made it in steel so as not to fall foul of the scrutineers, but i powdercoated it to look like alloy. Never been queried at any meeting including SPA but mine is not of 1969 to 1972 vintage.

A very grey area !!!
GT

[gt917]

Mind you though, there is not much to a 917 rollcage, so may not be a good comparison.

[jan bot]

Yes I'm aware of the 917 story, I understood that it wasn't necessary to replace the alu because the frame is the rollcage.
So the rollcage is a structural part of the car in the case of the 917 and therefore impossible to replace..
That's the story, but i wonder if another reason is that the whole structure is alu and so it would be silly to have a steel rollcage?
Another example i found is the Porsche 935 Moby Dick, it has an aluminum tube frame and is build for the same class. From this video I suspect that it still retains the aluminum frame.. http://www.youtube.com/watch?v=RZ7qDwUZv1Q
And yes, it's allowed to race in competition: http://www.youtube.com/watch?v=VF5pHpTf0hU

So there is still a possibility to get a HTP with an alu cage?

[Mike Bell]

I take it the car is your March? Maybe it has to be looked at from the point of view that it was an integral part of the structure when built, so while not impossible, very difficult to alter. Also by changing the material, the originality of the car would be affected?

Then there is the question of whether, even if HTP granted in that form, individual countries Motor Sports Accociations rules would allow it to race? Not sure which would have priority if questioned!

[gt917]

[QUOTE=jan bot;3191491]Yes I'm aware of the 917 story, I understood that it wasn't necessary to replace the alu because the frame is the rollcage.
So the rollcage is a structural part of the car in the case of the 917 and therefore impossible to replace..

Jan, no.

The roll cage on a 917 was, and is NOT a structural part of the chassis. In 1969 it was not neccesary to have a roll cage fitted. Then from 70 onwards it was, so brackets were welded on to the chassis and a roll cage was bolted onto the upper chassis. There were subtle variations in the cage and its bolt fixing as many were made up by the various teams and not Porsche themselves.

Besides, you would not be able to take the engine out or work on various things if it were welded in.

[JimW]

Originally Posted by jan bot

. . . Yes.. they removed all of the original chassis for "lightening" purposes and added an aluminum monocoque as "chassis reinforcements"..only an English firm can get away with that.. . .

I didn't know that TWR did work on those cars?

Jim

[Alex E]

I seem to recall reading that when alloy cages were banned there were exceptions for certain historic cars. I think they used a Porsche 908 as an example. But I suppose that has a spaceframe as well.

Personally I doubt you will be allowed to race the car like that.

[gt917]

At the end of the day there is only one way to go.

Get it looked at by "historic qualified scrutineers" who, if all is OK can give you written approval. The 935 does give you a precedence, as the earlier 917 programme continues to do.

[JimW]

But perhaps also you might consider whether the existing cage will offer you sufficient protection in the event of being needed.

Regards

Jim