Starting cage build! EXPERT ADVICE NEEDED!

[M3 GT3]

Hello Everyone!

First of all, I would like to recognize and pay due respect to the wealth of knowledge and experience that this community possesses!

I have recently started stripping the interior or my M3 and preparing it for a 8pt cage that I will be fabricating. I have a few questions regarding attachment and installation.

I will be replacing everything from the firewall forward except for the engine rails with tube. I know this will boot me from a few classes right away, but the car has had some damage to the strut towers and upper rails, so I'd rather save some money and weight and just run in the classes that allow it.

I will be doing something similar in the rear, just not as extensively. Rear shock towers will be staying, but the trunk floor will be cut out and replaced with tube. This should save a few pounds and allow me more flexablity with fuel cell placement.

The main cage will be 8pt with rear subframe bracing. I will be using 1 3/4 x 0.095 1020 DOM tube for all main components, and 1" 0.095 for everything else.

Here are the questions I have so far:

Which method is preferred for attachment? Rocker boxes or foot plates? Each has its advantages and disadvantages, but I am leaning toward rocker boxes for simplicity. Each is comparatively strong, unless the tube passes all the way through the floor pan with another plate welded on the bottom "sandwiching" the floor pan. This seems like overkill to me, but thats why I'm asking for advice.

Second, should I go with FIA spec A pillar brace or not?

Third, concerning the spaceframe up front, am I allowed to tie the "upper rail tubes" into the front tubes or does this pose a safety concern? The other option would be to mount the upper rail tubes to the chassis instead of passing through the firewall.

Fourth, for the main hoop, roof bars, and rear bracing what are the advantages of using two tubes in an X configuration vs a single diagonal tube? Obviously the X configuration will be stronger, but how do you determine which best suits the car/application? I am leaning towards using an X configuration in the rear bracing and main hoop for added stiffness and using a single diagonal for the roof bar. Again, not sure this is all necessary so I would like as much advice as possible.

Fifth, my main hoop is going to sit relatively aft of the B pillar because I'm 6'2. I have seen a few builds that do not have a harness bar in the main hoop and instead use a harness bar tube that is welded between the rear tubes and x brace. This seems easier, looks cleaner, and allows more room for harness hardware. My only concern is that the main hoop would be weaker against side impacts. Would this be legal in as many cases as a horizontal harness bar in the main hoop? Are there any specific rules against this?

Sixth, Door bars. X or Nascar? One thing that confused me is one set of rules I looked at said the door bars must not be bent further than 6" from where they attach to the main hoop/ down tubes. With this example, driver clearance would be challenging because my main hoop is going to sit 8-12 inches behind the B pillar and getting the door bars away from the driver for more room would be hard. Which option will be legal in as many cases as possible while still providing ample driver room? I like the gusseted X bar designs that are bent outward away from the driver and into the door, and it seems like a good all around design that will work for most rule books but I'm not sure.

Seventh, I have seen a few designs with a second set of rear tubes that attach to the main hoop near the door bars and the rear shock tower. I suppose this is to further triangulate the rear shock towers and add stiffness. Good idea or not? Will the addition of these bars kick the car out of a class/series it could otherwise run in?

And FINALLY! When the cage is complete, what steps do I need to take to get it certified? I will definitely be posting pictures and asking questions during the build to get everything as close as possible to passing. Will an FIA or similar certification work for multiple classes/sanctioning bodies? Or will I have to get the cage inspected for each sanction individually?

I am doing my best to use what I have available and build this car to be legal in as many events as possible. I know some of the things I'm planning will exclude me from several, but this will be my first purpose-built racecar. I will likely go back to autocross to work out the bugs when It's done, then some HPDE stuff, then eventually when I can afford all the safety equipment I would like to run in GTS. I'm also planning on keeping it street legal.

I think the car will be GTS legal as described, but would like to be sure so I don't spend two years building a beautiful car that I can't race because some of small detail. I would also like to be able to branch out a little bit and run in some other wheel to wheel racing or possibly time attack.

So, in a nutshell, I'm looking to build a cage that will allow me to be as flexible as possible while being competitive and safe.

All advice and opinions are appriciated! Criticisim-
constructive and otherwise is also welcome.

Thanks!

-Will

[MPWRCPE]

Will,

Shoot me a message, I'm in Prescott Valley. My car is headed down to Phoenix next weekend for a full cage, corner balance and a few other things.

I'd love to check out the car.

-Dave.

[M3 GT3]

Pm'd! Good to know there are some enthusiasts up here.

[boostedinaz]

My expert advice would be.. do not build your own cage, it simply isn't worth it in the end. In general I tell people who want to start fabricating or simply like the DIY route to start on something that is NOT a safety device. On top of that this is also one of the most permanent and hard to replace items on a race car. If it doesn't turn out well then what?

There is a lot of skill, tricks, and specialty tools, that go into building a really nice cage, especially one as extensive as you are talking about.

Here is pretty much the exact cage you described in your first post. I had almost 125 hours into this cage. A little side note. My old boss was a little over 6' and fit in this car with no problem.

[M3 GT3]

My expert advice would be.. do not build your own cage, it simply isn't worth it in the end. In general I tell people who want to start fabricating or simply like the DIY route to start on something that is NOT a safety device. On top of that this is also one of the most permanent and hard to replace items on a race car. If it doesn't turn out well then what?

There is a lot of skill, tricks, and specialty tools, that go into building a really nice cage, especially one as extensive as you are talking about.

Here is pretty much the exact cage you described in your first post. I had almost 125 hours into this cage. A little side note. My old boss was a little over 6' and fit in this car with no problem.

Very good work! Very similar to what I'm planning. I know it's going to be a massive project, but I already bought tube so I'm committed! I'm mostly worried about missing some small detail and failing the first inspection. Once I get started on it I'll start a new thread and post pictures and maybe you guys can call me out if you see some sketchy things happening.

I think I am going to go with an X in the main hoop rather than a single diagonal in case I want to get into time attack.

I was reviewing the NASA rulebook and it sounded like the harness bar is required to be a part of the main hoop. Is it illegal to have a harness bar between the rear tube/x brace for NASA?