engine and drivetrain Couple of quick cage type questions - front end mostly......

[winstontj]

I see the rear end as being very fastener oriented and load driven, meaning the subframe and diff bolt to the chasis and the load paths are straight forward. As for the front end however I have a few questions. Is this where the boys are seperated from the men in terms of cage design/build???

There are three areas I'd like to discuss. First is the subframe/frame rails. Engine bolts to subframe >>>> Subframe bolts to frame rails. What is the popular opinion on where the loads generaly distribute from the frame rails to the chasis and when you build a cage how is this addressed? Next, the forward inner fenders. The heavy gauge steel that forms the engine compartment and seats the strut tower bearings. Where I would assume that the frame rails have more of a clockwise/counter clockwise rotational force, applied by the engine. I see the inner fenders having strictly vertical force from changes in road terrain relayed through the suspension as well as a marginal amount of compression and tension (strut bar) in cornering and braking. Final item is in followup to my post of "how the **$%*& do I install the rocker panels I just got from BLUNT?!". After holding the outer rockers in my hands it was aparent that they were more structural than I had imagined. Being a unibody chasis, how important are the rocker panels (heating ducts in a VW) to chasis stiffness and/or chasis flex?

To tie these three together, how is energy / load / force / etc, transferred from the engine and suspension into the front chasis? Or how is the torque of the motor and the force of suspension travel transferred through the chasis into the wheels? As I design the front of my cage I would like to know that the motor and suspension are tied into the chasis in the same way that the drivetrain is.

Only it doesn't seem that easy..... Is there a standard layout or is it all top secret?

Thanks,

TJW

Both of these areas mate to the firewall area

[bmw1602.com]

check out the cage pics on my web site and on skidmark racing website...

http://bmw1602.lostbrazilian.com/v1/viewer.php?album=albums/Gallery/Roll%20Cage&pn=1

and

http://www.skidmarkracing.net/photos/index.php

these are probably the photo's you are looking for tho...

the first the (yellow) are from one of the skidmark cars.... pretty good triangulation and support of the stru ttower. The last one is a Ireland Eng. customer car.......it's stong and less intrusive of the engine compartment but probably a bit less effective than the skidmark design

[winstontj]

I've been to both sites and I appreciate you posting all of those photos. The FAQ and it's members really are the best tool one can have in the toolbox.

It looks like the standard is to run those two forward tubes from the dash bar (????) out next to the strut tower mounts and then down to the frame rails. What I don't see is anything like the E30 designs running a section from the forward base (by the door hinge/dead pedal) up to the strut tower. Is that what I'm looking at in the Ireland car? I like that the Ireland cage seems more triangulated however that's only one awkward view. It seems that a good cage will tie in the rear suspension to the chassis and remain solid all the way up to the firewall/dash but forward of the dash there's only one section per side with small triangles going back through where the heater would be. I can understand how this would help (as well as a strut tower brace) with compression and tension but my main concern/question was how are the vertical loads handled forward of the firewall and how is that tied into the cage?

Should I just assume that what you see is what you get and that it's been working fine for years or is there a better way to do things now that we have 30 additional years of cage design under our belts? I see many differences between standard issue 2002 cages and more modern E30 - E46 designs.

Thoughts and input always appreciated....

TJW

[TJW]

You could go from the knee bar to the shock tower like this.

http://autodynamicsltd.photosite.com/~photos/tn/24_1024.ts1077868390000.jpg

[TobyB]

Well, here's the deal in front-

I crash- tested mine this weekend, and it seems to hold true.

The car has little strength in front of the shock towes- intentionally, to crumple.

But after the shock tower, there's a heavy triangulation that transfers loads to the firewall/a- pillar area. It's stiff in 3 dimensions, as it has the inner fender as its inside 'wall'. It drops to the lower frame 'rail' that carries the subframe. So that structure in front becomes quite strong- when a street car hits a wall at 20mph, the a- pillar area deforms (and your doors don't close anymore)

In an 8- point cage, if you catch the top of the firewall, right under the dash, you take the loads from that (very strong) sheetmetal structure and load them into the cage. Your lower front point can (should) catch the inner rocker right where it meets the floor, so now you have the lower corner of that structure, and if you're clever, your 100 square inch plate can collect the frame rails too. All of a sudden, you have a structure that's triangulated and very strong. If you then triangulate the cage back from those points, the booger becomes VERY stiff. If I have more than 1/32" irregularity between my jackstands, the car will rock on 3 points.

I'd argue that it's a lot stiffer than a 6 point with a bar that runs forward, and that the front frame rails and inner fenders become the sacrificial elements- it becomes a sheet metal repair.

Assuming, of course, that your front fenders are in good shape!

Also, look at your rules- a GT cage is virtually free, but any extra body attachments will kick you out of ITB. An 8- point cage can be very strong, if done well...

my '02,

t