herders

Hello All,

There is lots of great information about subframe connectors.

I am going to build my own...

- What kind of material is used? I was at the metal shop yesterday and asked the guy the best kind of metal to use? the size and thickness? what is stronger round, square, or rectangular tube

- he suggested that the rectangular tubing - is the strongest laying horizontal to the direction of the force and that the square/rectangular is stronger than the round tube all things being equal - the cold rolled steel is what I was looking at

- he mentioned that most who build roll cages use the cold formed round welded seam tubing 2 or 3 x 1/4 and that this is stronger than the mild steel tubing

- looking at 1.5 x 1.5 x 1/8 square as well as the 2 x 1 x 1/8 is lightweight and seems to strong enough to provide the needed support, with 1/4 plate for support and gussets

- it seems to me that a 2 x 3 x 1/4 would end up being very heavy would provide the best support is this too much

I have a couple of questions:

What would be the best size - thickness - weight for building subframe connectors? No racing currently a 305, I am thinking about upgrading 383 in the future.

One thing that nobody talks about is how the connectors are welded in.
- why not cut out the floor to weld straight in with the contours of the floor, I am thinking in terms of moisture getting in between the floor and the connectors, the same goes to welding to the pinch weld along the rockers.

Any guidance would be appreciated.

Thanks

Paul

QwkTrip

iTrader: (22)

Round tube saves weight but takes more skill to build with, and not necessarily a handy shape when it comes time to weld to the car. The main reason you don't see it used with the aftermarket subframe connectors is higher cost to manufacture. I can't think of a round tube subframe connector other than the [no longer in production] Kenny Brown, which was a top of the line product. The Kenny Brown was a fantastic design that boxed the rear control arm mount, and had a Y that tied into the front trans tunnel.

83 Crossfire TA

iTrader: (2)

1- round is going to be the strongest in all directions if comparing comparable cross sections, but if you're going for stiffness in one direction then you can stack the deck by making it wider in that plane. Of course real world you want stiffness going in the vertical plane and you have more room in the horizontal :-/

2- a few manufacturers have offered them on chrome molly, but most are mild steel (likely 1018). I'm not sure why since rigidity should be the same. GW offered a set with chrome molly tubes and mild steel load plates to make them easier to weld. Still not sure why. DOM (seamless) tubing will be the strongest (and required for roll cages used in faster cars) but most steel suppliers don't have it laying around/can't get it. If I could get anything reasonable I would get 1025 DOM, but that's a special tube used for aircraft structures. Real world, I would use what I have laying around (I've made SBC out of things like computer equipment rack uprights...), or if I'm purchasing it would be mild steel (usually 1018)

3- there is sort of a pocket behind the pinch seam on these cars that is the natural place to tuck a SFC. There is a size tubing that fits best in there (I think 2" or 1.5" square, I haven't measured it). Honestly if there is a size that fits better then that would likely decide what you're doing.

4- the bigger the cross section the more rigid the tube. I've considered making a spreadsheet to compare the rigidity based on cross section vs wall thickness to pick the optimum rigidity vs weight that will fit in the available space, but I wouldn't be surprised if that ended up being something relatively thin walled in like a 2x3 section or something.

5- welding to the rear torque boxes is the optimum for the rear attachment point. The front there really isn't a good one, there isn't a solid pickup point like that that doesn't get in the way of something else, which is why there are loads of different designs. My suggestion is to get under the car, figure out what you want to clear and then find the biggest attachement point that you can hit well in the front. Then if you can tack it every couple of inches to the pinch weld seam/back of the rocker, that will add major strength.

What would be slick would be to hydroform them like GM started doing with truck frames in the late 90's and exhausts about the same time also, then you would end up with something stronger, more rigid and that would fit better than making it out of square or round tubing, but that would be a $$$ deal and would require a lot fussier work to weld them in (the high strength structural steel that they use can't just be booger welded with any success like most subframe connectors end up being)

DynoDave43

iTrader: (11)

These appear to meet a few of those criteria. If the OP is set on making his own, these might be a good guide.

http://www.top-downsolutions.com/cha...d-(aka-f-body)

406TPI

iTrader: (1)

If you are willing to cut the floor, DSE has a really nice set for 3rd gens.

91ls1t56

This may help. Make all of your brackets out of 3/16 wall square tube, connect
them with 1 5/8 .120 wall DOM round tube. 1/8 is all you need for mounting plates/brackets, but 3/16 worked out perfect for the lca pockets so I used it throughout. I used plain basic steel A-36/A-500.
https://www.thirdgen.org/forums/fabr...l-exhaust.html

Nighthawkf-117

iTrader: (1)

Not sure what your metal shop guy is talking about...

DOM (drawn over mandrel) mild tube will provide the most strength in all direction compared to the same weight of square tube. Chrome molly will be lighter for the same strength. This is because the stronger material can be in a thinner wall thickness to produce the same amount of strength compared to mild steel. However chrome molly presents a challenge for welding. I believe most classes of racing that require roll cages require that chrome molly cages be tig welding.

This being said you will find square tube is very easy to build sub-frame connectors with on these cars. I did mine in an afternoon without much fuss.

83 Crossfire TA

iTrader: (2)

I've never been a fan of alstons... the farther away you are from the center of the twisting axis the more rigidity you have, and they mount on either side of the tunnel. A bunch of people have added them in addition to perimeter SFC, but at that point I feel you get a lot of weight for the stiffness, you'd get more by building up (a cage)

I always thought that their stuff was unnecessarily expensive, but after looking at the instructions on their sight... well nice stuff if you're willing to do the cutting... I tend to build everything myself, but if these fit like they do in the pics I would spend the $ in a second on them

I haven't looked at you thread yet, but your description basically sounds like the GW ones, except they use chrome moly 1-5/8" DOM.

83 Crossfire TA

iTrader: (2)

So, are you just parroting what you've heard before or do you have some numbers behind it?

Loads of people think that chrome moly is stronger so you can use thinner wall stuff and have the same strength, but, 1- we're talking about rigidity, not yield strength, and I don't believe there is any significant difference in rigidity, and 2- even wRT yield, normalized 4130 falls in an overlapping range with standard 1018 so it's no stronger. Yes, it would be if you heat treated it, but you're not doing that for large chassis parts.

As far as welding is concerned, MIG and gas welding is a proper technique for 4130 aircraft structures, it can be done correctly, the reason that it's not allowed in NHRA and IHRA roll 4130 roll cages is that it would require the inspectors to actually know what they're looking at. For that matter the NHRA and IHRA roll cage rules don't make any sense WRT to chrome moly since the cages really aren't any stronger with it AND they are more dangerous (other racing classes don't allow any chrome moly anywhere near the driver/passengers).

Saxondale

iTrader: (2)

I installed the Alstons and it helped a lot. But could be stronger in my opinion. Not saying the Alstons not good, but rather considering adding a perimeter style. Overkill? Some of the outer styles are a bit concerning because tack welded next to the rocker, which seems like a place for debris to gather and rust.

herders

Thanks everyone for all the great info.

One last question that I would like a little more feedback on

What about cutting the floor to do the install? is this wasted effort? or would it be beneficial?

I did look at the DSE SFC I am not adverse to cutting and welding the instructions are very indepth and I think they provide extra support but that would just be a guess...I am no expert.

Again thanks for all the great info.

Paul

clubber

iTrader: (1)

I have Alston's and Spohn's. The Alstons fit to perfection and the Spohn's nowhere close. The car feels MUCH tighter. Someone earlier mentioned that this type of combo would be unnecessarily heavy and that may be. However, I don't care as I'll never have a cage and I really like the ride, handling, and rattle improvements. I'd get a different brand outer SFC though. Building your own, you should be able to get a killer result if you take your time.