What is the minimum amount of bar that would need to be added from the back towers to the transmission cross member? Understanding that I am running a bar from the back hoop of the cage to the shock tower.

Could I just run a bar from a plate on the rear side of the shock, midway to the top of the transmission cross member? Just a simple triangle. Would that help?

Picture below.

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OK added a picture for clarification.

I like the job that Anklebiter did back there.....as far as he went.
If I ever do somthing like this I would eliminate the shock towers entirely and make shock mounts that will accept the "eye" type upper mount. A great selection of hi-zoot shocks are then available to you.

Eliminate everything from the firewall back except for some simple bracing to hold the bumper and trunk up. Run one tube from the firewall back to the shock towers. Copy Sheridan's car I don't have a pic on this computer.

Yes, that would help.

However,
the higher the attachment point on the shock tower, the better. See the pic JP posted for reference.

You don't need the X as in the pic above, a V would be enough on your car.
Andy

I think Randal is putting in the down tubes from the cage to the towers.

Brett, if what you are advocating is what you actually wrote...... it's drivel.

Horseshit. Its a race car cut out everything not needed. That means rear shock towers, tranny crossmember, rear inner fenderwells, etc. Look at the rear structure on this car. Notice how it all ties into the main cross bar at the shock towers. Bring your down bars down from the main hoop to the top of the shock tower cross bar. The bring a bar from the shock towers forward to the firewall inline with the door bars. Create a nice triangle. Then weld on some small tubes to attache the rest of the bodywork with. Trunk lid should be glass as should rear bumper and fenders, so the remaining sheetmetal won't weigh anything.

The advantages of removing the stock rear shock towers are numerous, including the fact that you can use double eye shocks and get some nice cheap shock options.

thread I did on the bird board a few years back with Sheridan's car shown - I drove the 3hrs north of LA to take the pix and BS with him (it had been awhile since I bought his body kit and he was first building the car).

http://forums.pelicanparts.com/showthread.php?t=253609

This is good, but that's not what you wrote the first time then is it.

Something like this is what Brett is talking about I think.

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Thanks for the responses.

I'm going to run bars from my new cage front hoop the front shock towers and also from the rear hoop to the rear shock towers.

I don't want to be adding a lot of weight, but I'm thinking at the minimum, based upon the comments received, that this might be effective, i.e., the picture below.

The question is whether this modification is worth the weight it adds.

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I like the tubes in Blake's car - except I can't see how the 901 mounts to that configuration...Thanks for sharing! Can't wait to see the whole thing, engine and all
If 222 is AX only, maybe the twisting won't interfere with shifting and grip (lsd?), so low weight is the goal? Are bolt in braces lighter?

Something very similar to what Blake has. Yes, JP, that is exactly what I said in my first post. I just didn't draw a verbal picture.

Here's what i think you should do ...


The green is how i would add the braces for the tranny mounts. Start them as high as you can on the shock towers.
They don't have to meet each other in the middle, that cross section is plenty strong so getting the braces to the inside of each tranny mount should give you some nice stiffening there.

IMHO, the blue bracing is only needed if you decide to cut out the rear firewall. Right now, with the firewall still in place, i don't think you'd need that bracing.

Andy

Andy's mad paint skills are better than mine. His design is much better than the grey line original. Make the whole thing out of 1.75 .065 or.058 wall tubing to keep the stiffness up and the weight down. I would reinforce the mounting points with .065 sheet.

But cutting out the rear shock towers and firewall willl give you better shock options.

I understand what you are saying, but I wonder what the double triangle buys you when one would work, i.e., with two tubes coming from the towers meeting in the middle of the rear transmission mount cross member.

Although I guess he is adding about 5 feet of tubing, so 5lbs isn't that much and his set up would be stronger.

My "uneducated" guess is that Anklebiter's setup would be perfect if I was getting rid of the shock towers, but do I need this if I keep mine?

What Andy has drawn up will work gud if you keep the rear engine room bulkhead.

I'll probably never go to the point of eliminating the shock towers or even cutting out the trunk floor. There is a small weight loss to be had and the shock selection would be nice but the latter involves a bunch of money.
If I had those extra funds I'd spend them on fitting R25 Hoosiers radials to the car.

My winter mods are cheep this year. Lowering the car and doing something unconventional to the trans.
Sticker tires will be forthcoming, but that is conventional.

This is what I would do Randal:
Get rid of the top of the sheet metal behind the engine compartment and install a tube going all the way across, just ahead of the shock towers. You can terminate the main hoop braces onto the cross tube or land them on reinforcing pads at the ends like in my pic. My design improves engine compartment access, and you can add small triangulations between the rear braces and the crossbar if you want.
Then attach the tranny crossmember braces to the shock tower crossbar next to the shock towers. Don't put the rear attachments together to form a triangle. It is better to keep them apart and land them just above the tranny mounts.

Do you a slightly bigger picture that shows both ends of the cross pipe Chris?

Thanks.

I can't draw a picture with the tube in front of the shock towers, but you get what I mean.

Like this?

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I'd still like to see a picture of what the cross pipe looks like at the ends.

Thanks again Chris.

I don't have a larger view, but I do have a different detail:

Here's a pic from another car:

Thanks for all the help.

I'll be posting pictures as soon as we get started taking the cage out of my car and putting it into Mike's car.

We'll also be documenting the building of my new cage.

Randal, have you noticed any issues with the trans mount bar flexing? I had a 200 lb guy stand on it and then jump on it and didn't see any flex. I would think that some pretty lightweight bars would be all that would be needed for a little 'added insurance'. The area is pretty strong as you have it, IMHO.

Assuming a magically rigid chassis from the rear shock towers forward, I can't see how the rear frame (shock towers to trans mount) would flex. If your shock towers flex, they'll take the trans mount bar along for the ride. But once your cage locks those rear towers into place, the transmission is going to have a hard time going anywhere.

Again, I would think some really small bars would be all you would need, or nothing at all.

What size Mark?

I usually use 1 1/4" x .083. 1" x .065 is the lightest I would consider using. Reinfocement will definitely make a difference once the floor has been cut out around it.

Mark, IMO your test method leaves a lot of room for error. The weight of an engine/trans assembly is at least 200 lb on that crossbar and the forces applied in operation are certainly greater than someone jumping up and down on it.

Chris, I realize my 'test' isn't very accurate. I only reference it to indicate that the cross bar is quite stable in it original form.

I think the cross bar is absolutely stable in a left-right motion. The bar is only 12" from the shock towers and that's a very short run with a boxed frame to support it. I think in the left-right direction there is very little force.

Forward-back is definitely not an issue.

Twisting along the length of the bar is tied directly to the shock towers. If the shock towers were magically solid and untwistable/unmovable, then the trans bar would never twist. Therefore, the trans bar twist is directly linked to shock tower movement.

The final force I can imagine would be for the center of the bar to move up and down due to the transmission/engine weight bouncing up and down. Since we already know the bar can handle 200lbs + gravity/acceleration of a jump, then it seems to me that the bar would not need much more support. While the stresses of racing will create forces in excess of this 200+ lbs, those forces will not be purely vertical (and if they are, then you are not in a corner, so who cares). So 200lbs at a 90 degree angle (i.e. vertical) does have some similarity to 500lbs being pulled at a 45 degree angle up and left/right.

I still maintain that shock tower movement in turn moves the trans bar, and that a solid, unmovable shock towers would mean that the trans bar is solid as well (in every respect that's important).

Thanks for the good pics, Chris. Is it OK if I abscond with a couple of your good ideas for the back of my car too?

They say, imitation is the sincerest form of flattery!
Of course it is ok!

Chris:
The first pic of that bracing had me going " uhhh....I dunno bout that"
The second pic made much more sense. The sumbitch certianly looks strong enuff.
The cross tube is perfect for adding a clevis to mount ring eye shocks, but I still think dead ending the down tubes on the longs rather than the fender is the way I'd go.

Here are some others:

http://www.pwr-tech.com/project_links_trial20.htm
http://www.pwr-tech.com/project_links_trial3.htm

I would agree 100%, except that the benefits I get from this configuration are too significant to pass up.
The inner fender in that area is quite stiff, and my plates tie in to the shock tower box. So I don't feel that the compromise has a negative effect.

There she is naked.

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There's nothing like starting with a clean sheet of paper.
Are you doing the cage DIY or hiring it out?
Making it SCCA legal would be wise either way....overkill for an AXer....but wise nohow.

This job is way beyond my current metal working skills and it has to be safe - so hiring it out JP. Aaron at Pacific Custom Fabrications.

It will be SCCA legal, so no issue with hill climbs.

BTW the (door) cross bars and front suspension tie downs will end up looking a lot like The Beast. Only difference is that we will be going straight forward to the shock tower instead of off to the side... pretty much like you did.

The front (dash) hoop will be above the steering wheel and
the top cross bar coming from (6 inches below) the rear hoop forward will end up opposite the bar going forward to the front shock tower (through the hole).

What I don't like is the final height of the rear hoop, which will be sticking way up there; but those are the rules.

BTW Mr. K. (914 Magazine) is going to do a write up on the new cage for "222" as well as the installation of my old cage in his car.

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3-4 inches above the targa bar won't be pretty, but it will be legal.
My bunny ears were intstalled to "kinda" get there, but they are "kinda" half assed. Your's will be much better.

We are putting the front hoop above the dash to decrease the angle and make the rule, i.e., a straight edge from the back hoop to the front not hitting the drivers helmet.

I'm thinking body color, like you did, on the cage. That and using the body angles (on the hoop) might help to pretty her up?

Yeah, I like cages body color. Makes it look as if it belongs there. PITA to paint.......most of the paint goes elsewhere.

A word of advise. Get multiple reinforcements on those door bars. They will fail if hit hard enough.

OK, so I guess you mean gussets in the interior X on the door bars? Or on the outside of the door bars?

Both the intersection of the X and the joints at the main hoop and a-pillar. After you reinforce the X you move the weak point to the outer edges.

What you have there is plenty stiff from a chassis flex perspective Randal. The concern is being T-boned and having the door bars break in the middle. Last year at Lime Rock someone got hit by a Miata and the Miata's front bumper got all the way to the center console of the other car because the X bars tore where there is only a single tube thickness.
Use taco gussets (plate bent into a U shape so both inside and out are reinforced) on the top and bottom of the X. Reinforcing the front and back triangles of the X won't do a thing for side impact protection. Gusseting the ends of the X bars is much less important.

Do you have a picture of a taco gusset?

I wouldn't be worried about the reinforcement just running autox's, but hill-climbing is a different game.

OK, found some. Got any of those pieces (second picture) lying around Chris?

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Real good how to at: http://bmw1602.blogspot.com/

Looking good so far. Let me know when Aaron is going to start his magic. I'd like to come get some photos and get a couple of quotes for the article. ETA?

I am referring strictly to a side impact protection aspect. This is a Koni challenge RX8 I did last year. The two door bars are two uncut tubes. bent together and welded and then I reinforced the joint with some tube sheet gussets.

Both of the pictured cars are done the way I specifically stated is NOT correct for the cage in your "beast" Randal.
Because of the crossing arrangement of the X bars what you want is to double up in the center where it is weakest.
The pictured cars have two independent bars that come close at the center, and are bent outward as well. That is a much better arrangement and the pictured gussets will work ok for that system.

I'm not sure which "pictured cars" are good Chris. Which example or examples are correct? Thanks.

From what I gather is Chris is saying the X is bad as it really bring two bars to a single bar strength at the intersection. The RX8 looks to actually be two bars that do not cross though. Chris?

The RX8 is two individual bars that do not bisect each other, but do touch each other at the apex. Then are reinforced over a 20in span on both sides. In addition to two 1.75in tubes capping the end of the gussets.

The problem with the simple X bar is the lack of weld surface area. Basically you have the small weld area at the point of contact on either side of the tube. That is the point of failure. By adding the gussets you increase the surface area of the weld ten fold.