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what size tube do i need for my cage?

Old 08-15-05, 04:18 PM
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what size tube do i need for my cage?

I have to put a cage in my car, and im looking to put the minimum leagal requirement in. The car is going to be for autoX only, and im thinking of going ERW insted of using DOM since its cheaper and im on a budget. I called S&W http://www.swracecars.com/ and they have a cage for about 300 bucks out the door. I have helped put some of these cages in my friends mustangs and supras and they arnt bad cages, but it seems that you have to do some fabbing getting these in.
Are there any other options for cages in this price range?

Anyway, i dont know what diameter tube i need because i dont know the weight of my car. I have a 90' FC and my car totaly stripped out. What do these cars weigh in at? Is it below 2500lbs?


I run mostly with the Mid-western Council and some SCCA.
Again, i dont think car will ever do a wheel to wheel race since this car has a non-rotary engine swap. Weight of the new engine is about the same as the N/A rotary.

Thanks
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Old 08-15-05, 04:22 PM
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A roll cage is not required for SCCA Solo-II autocross. Those bolt-in drag race cages will not help the performance of your car; the extra weight will only slow you down. The drag race cages are not legal for any higher level SCCA events that require cages (like time trials or road racing.)

Again, if all you are going to do is autocross, then you do not have to have a cage.

Last edited by speedturn; 08-15-05 at 04:25 PM.
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Old 08-15-05, 04:33 PM
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i need the cage because there is a non-rotary engine in the car and the cars integrity has been compromised. The cage is needed to tie the chassis back together. We all know the benefits of chassis stiffening when you add a cage. All I really need to know is the weight of a Ďrace prepedí FC so I can figure out what diameter and thickness tube I should run.
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Old 08-15-05, 04:40 PM
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Someone correct me if I'm wrong, but tube thickness should be the same specs as what SCCA is requiring. Tube placement for a car whose "integrity has been compromised" as you say is a different story. I don't think a generic bolt in will help you there. Car to elaborate on what that means?
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Old 08-15-05, 05:45 PM
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First, If no cage is required by the rules then you can put in whatever you want.
Second, if you plan on following some sort of SCCA guidelines its either all or nothing on legality. A bolt in cage will do little to stiffen the car. So, for auto x I would use 1 3/4" .095 wall if you go with ERW, and weld it in.
Something to think about, a lot of people start out autoxing and migrate to road racing after a while. Since there is little market for autox cars, and you aren't required to have a cage, why not start out with a roll bar out of DOM (same specs as above) and then you can add on to it as you can afford it? Just a thought. I've done cage jobs twice for the same car a couple times when people decided to put a car they have thousands of dollars in on the track after it started out "just an auto x car...".

I've also watched two different cars roll at auto x's, even though your just stomping on cones, s**t happens. Take your safety seriously.
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Old 08-15-05, 08:42 PM
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Are you looking for a full cage or a 6 point rollbar?

1st... if ERW hasn't been nixed by all of the above mentioned sanctioning bodies, it will be shortly. ERW is not allowed in any new cage construction for the SCCA.

2nd... NHRA requires a min. tube thickness of .118... which means the bent bars have to be .134 wall to meet the requirements in the bend (they sonic test).
3rd... SCCA Auto-x bumps you into a whole new class if you weld anything in. Although, I've heard that the work around is not using a 5 point harness (which is a little scary w/a full cage)

If S&W has a full cage from 1.75x.134 wall DOM for $300 and that includes shipping... Jump on it. At todays steel prices, they'll be out of business before too long The cage I just finished was ~$275 for the tubing/pad materials.
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Old 08-15-05, 11:18 PM
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I'm looking for a 6 point and wondering if someone could check the rule book for what size and thickness for road racing, lapping and Time trials.
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Old 08-16-05, 12:19 AM
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2nd... NHRA requires a min. tube thickness of .118... which means the bent bars have to be .134 wall to meet the requirements in the bend (they sonic test).
Actually Scott, NHRA does not sonic test the bends, only the straight tubes. That is what I have been told by Division Techs and is what I have observed during testing at the tracks and at my shop. The reason for the .134" erw is the mill spec. dimesions are so inconsistant, you need to use heavy tube. One side of tube could be .134" and the other could be .125". If you use .125" ERW, you will most likely be thin.

Now SoloIIdrift,

I presume you have a small block in your car. I would full cage your car from front to rear to help with chassis rigitity. Get a 10-12pt kit, should work good enough to help out. Remember, full NHRA cages help with stiffening chassis up in straight line, not hard cornering. Won't be cheap, but if you skimp now, you will pay for it later!
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Old 08-16-05, 12:54 AM
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Also - keep in mind that there is a VERY limited market for race/track cars of any kind. Unless you are absolutely SURE that you will never want to either sell the car, or upgrade to further motorsports, it is always good to put a cage in that meets the reg's of as many organizations as you can! Once it has an ERW cage in it, it will be unsellable to ANYONE in the general public becasue they definitely don't want cages in their cars. It will also make it unsellable to 90 percent of those involved in motorsports because it won't meet anyones minimum requirements. That leaves you something like .... um .... let's see .. carry the two .... statistically ZERO potential buyers if you ever want out of it. Racing of any kind is a great way to spend a lot of money on a car that will be worth PENNIES on the dollar if you have to sell. Even that is far better than paying someone to haul it to the scrapyard because it is unsellable.

( PS - I know what I am talking about! I finished up a rough restoration on a 1974 BMW 2002 tii that had a full cage in it. It was horrifying to drive on the road because it only had lap belts, and I knew that even a minor fender bender would have killed me when my unprotected head smashed into the unyeilding DOM steel of the front hoop! My knees always got bruised from banging against the door bars and it made it a serious PITA to get in and out of. Unless you intend to ALWAYS wear a 5 point racing harness AND a helmet when you run down to the supermarket for ice cream, you should NEVER put a cage in a road car. I had to completely remove the well installed cage in order to sell the car. Good luck with your project!)

Last edited by Boswoj; 08-16-05 at 12:57 AM.
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Old 08-16-05, 10:36 AM
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With the motor swap you are already put into the Solo II Modified classes, so bolt-in vs. weld-in is not a class legality issue. Like everyone is trying to tell you, a bolt in cage will not give you the chassis stiffness you need. If you are going to put in a cage, then you need to put in a full SCCA legal cage. A cage is like a foundation for a house - if you screw up the cage, then everything that follows later will be messed up too. Do it right the first time. Get a cage builder who knows the SCCA rule book forwards and backwards, and because of your motor swap you will have to build it per SCCA GT car specifications (to be legal for Super Production class running.)
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Old 08-16-05, 12:45 PM
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Originally Posted by OC_
i need the cage because there is a non-rotary engine in the car and the cars integrity has been compromised. The cage is needed to tie the chassis back together. We all know the benefits of chassis stiffening when you add a cage. All I really need to know is the weight of a Ďrace prepedí FC so I can figure out what diameter and thickness tube I should run.
I'm curious how big of an engine it takes to compromise the structural integrity of an 2nd gen RX7? Most of the small block V8 installs are bolt in jobs, that I know of.

About the weight, It should be under 2500# if the entire interior is stripped along with with the doors hulled out and the impact bars and mounting brackets for the front and rear bumpers.
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Old 08-16-05, 02:01 PM
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Ill post pics of the engine swap after itís done. The engine is rather long so I had to cut the firewall open and the box where the wipers are. But that box is a huge structural member, I need the front cross bar on the cage it take its place. Donít worry, my friends and I have figured all the technical aspects out.

But it sounds like I should really go DOM, so I guess Iíll have to bite the bullet and get that.
Now im confused about the thickness.
I have heard 2 things now. 1.75x.120 or 1.5x.095 I was looking though a scca rule book yesterday and I though it said something to the extent of 'all cars over 2000lbs = 1.75x.120'
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Old 08-17-05, 08:22 AM
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Nah I just want a 6 point, what size tubes would be legal for lapping and time trials if I decide to add onto the cage later?
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Old 08-18-05, 01:53 PM
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Cars with V-8 engine swaps like yours will end up in the SCCA Super Production road racing classes. Super Production classes must meet the safety requirements of SCCA GT cars. The GT and Production cars roll cage rules are spelled out in the SCCA rule book under Section 18 Roll cages, and especially 18.4 GT automobiles:

For GT and Prod cars that weigh over 2500 pounds the minimum tubing size is
1.50 OD x 0.120 wall
1.75 OD x 0.095 wall

With your V-8 and american transmission, and with the added weight of the cage, you better count on weighing over 2500 pounds even with a stripped out car

Don't cheat on wall thickness. The SCCA tech inspector can make you drill inspection holes in the cage anywhere he wants to (I had one demand that I drill 4 inspection holes!)

There is a whole lot more to it than tubing size. There are many other very specific SCCA rules about the mounting plates, diagonal braces, etc that you must meet exactly or else they will kick you out. Build it right the first time, you will only have to pay once, and it will be smooth sailing thru tech inspection and further down the road when you go to sell the car.
If you ignore the rule book, you will have to pay again to have it built like the rule book says you should have done to begin with.
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