What exactly are subframe connectors?

[qwikrex]

Okay, I've done a whole lot of searching today and I can't seem to get a straight answer to this that makes sense.

 

It looks like bad dog makes replacement/strengthened frame rails, and even an extension which connects the front frame to the rear. But this is not a "subframe connector" is it?

 

As far as I can tell, a subframe connector is basically boxing the framerail that's beneath the floor with some material on top of the floor. As far as I can tell there isn't anyone who "sells" this, it looks more like you just get some appropriately sized U steel channel and weld it in inside the car on top of the floor. Kinda like the below image from this thread.

 

 

Am I right? Does anyone "sell" subframe connectors, or is it more of a one off deal?

 

Sorry if this is discussed somewhere, I simply could not find it.

[rsicard]

qwikrex: The photo you provided appears to be a rectangular tube with a cut in the floor wherein the floor is welded to the new tube. The bad dog reinforcement channel goes on the outside of the original subframe to beef up same. I am going to use 2x3" rectangular tube which will join the front and rear structures. My 240Z passengers floor is buckled up along withe original subframe. Will require cutting out part of the original subframe and joining in the new 2x3" rect tube. Maybe I will take the same tack as the one in the photo on your post wherein the floor is cut and welded to the 2x3 tube. On second thought this maybe very good as I can weld a roll cage directly to the 2x3 tube.

[johnc]

A subframe connector "connects" the front a rear subframes. They are a number of different ways to accomplish that and the Bad Dog parts are indeed subframe connectors.

[qwikrex]

Heya,

 

Thanks for the explanation. I kinda thought the Bad Dog piece was a "sub frame connector" but it was always described as a "frame rail". Just a problem with lexicon I suppose. Thanks again for clearing it up. I'll try to ask more interesting questions

[JMortensen]

Heya,

 

Thanks for the explanation. I kinda thought the Bad Dog piece was a "sub frame connector" but it was always described as a "frame rail". Just a problem with lexicon I suppose. Thanks again for clearing it up. I'll try to ask more interesting questions

Bad Dog makes replacement frame rails for the Z, which replaces the original rail and DOES NOT connect the subframes, it stops under the seat area, and they also make subframe connectors. That's probably where the confusion comes from.

[rsicard]

Heya,

 

Thanks for the explanation. I kinda thought the Bad Dog piece was a "sub frame connector" but it was always described as a "frame rail". Just a problem with lexicon I suppose. Thanks again for clearing it up. I'll try to ask more interesting questions

qwikrex: I saw a post here on Hybridz concerning the application of Bad Dog subframe reinforcements. With all due respect to the folks here and Bad Dog, after reviewing the posts the Bad Dog parts appeared to be a BANDAID to the original subframe. This reinforced the thinking of cutting out the bent portion of the subframe rail and putting it 2x3" rectangular tubing and welding same to front and rear structures. This should be MUCH stronger than patching with Bad Dog pieces from what I have seen of the pictures on that Web site.

[Roostmonkey]

True, adding a box tube to tie in the front and rear subframes will be stronger and building a cage that ties into the box tube will be even stronger. But for the average Joe that just wants to stiffen a failing stock rail, the Bad Dog rails are more than adaquate. And adding the BD subframe connector to a new rail makes things alot stiffer than stock ever was.I designed and fabricate the BD rails and subframe connectors and they are purposley made for the average joe.They were designed to fit over the stock rails to minimize installation.That said, they are not for everyone, I am doing an RB swap and have gone the box tube route for the added strength.I'm using 1.5" X 3" with a .120" wall for the main rail. Its mounted half in and half out of the floor pan. It is tied into the rear of the rockers and when I build the 4 point cage, the main hoop will weld directly onto the new frame. This will be plenty strong to handle the added HP.It comes down to needs and abilities...if you dont have the need or the ability to install a full frame, then the BD parts are for you.

[rsicard]

Roostmonkey: Thanks for your comments. If the original subframe channels are not rusted nor bent, then adding the BadDog channels is a good strengthening move. People should uncover the original channels to make certain they have good integrity. If they are rusted through then adding the BadDog channels may add only some integrity i. e. a chain is only as strong as its weakest link.

[johnc]

Welding the BD rails to the floor pan makes a box with the pan as the top.

[JMortensen]

Z's shouldn't rely on a ladder frame for stiffness, since ladder frames are inherently not stiff and they don't take advantage of the unibody construction of the chassis. Subframe connectors should be just one part of a bigger plan if torsional rigidity is the goal, and in that context I'm glad I put Bad Dog subframe connectors on my car.

[dsommer]

Here is a pic of Bad Dog frame rails and the Bad Dog sup frame connectors installed on my project. As you can see the sub frame connectors attach where the frame rails end and then attach to the rear sub assembly of the car behind the floor tub. Do they strengthen the car? I would imagine so.

 

I will also be running a SCCA bolt in roll bar and strut tower braces. Ultimatly a cage would be the best for rigidity but this is not a race car.

[rsicard]

My intent to use 2x3" rectangular tube is to be able to ALSO weld a Roll Cage to these tubes to ADD torsional STRENGTH, safety and protection. It was only will recently that I learned through pictures how the Bad Dog subframe reinforcements worked. Additionally, my passengers floor and original subframe is bent upwards requiring cutting and removing same and then straightening the bent subframe and welding it back to the floor. Rather than that process, just remove portions of both subframes and fab in 2x3" tubing and weld it in to join the front and rear sturdier structures. Then add a Roll Cage and other ladder frame structural stiffeners. Again, a chain is only as strong as its weakest link.

[JMortensen]

My intent to use 2x3" rectangular tube is to be able to ALSO weld a Roll Cage to these tubes to ADD torsional STRENGTH, safety and protection. It was only will recently that I learned through pictures how the Bad Dog subframe reinforcements worked. Additionally, my passengers floor and original subframe is bent upwards requiring cutting and removing same and then straightening the bent subframe and welding it back to the floor. Rather than that process, just remove portions of both subframes and fab in 2x3" tubing and weld it in to join the front and rear sturdier structures. Then add a Roll Cage and other ladder frame structural stiffeners. Again, a chain is only as strong as its weakest link.

You must be planning a tall ride height.

[Roostmonkey]

rsicard- are you planning on welding the 2x3 tube to the bottom of the floorpan? If so, as Jon pointed out, you will lose 1.5" of ground clearance. ( stock rails are approx 1/2" tall ).

[rsicard]

Gentlemen: The stock 240Z subframe rails are approximately 1.5" tall already. So maybe if I put the 2x3" rect tube BELOW the floor then I will lose 0.5" ground clearance. If the floor is cut to 3.0" across and the 2x3" tube is extended above the floor by 0.5" then there will be nearly no loss of ground clearance. I want to keep the nose of the 240Z as low as possible and put an air dam with splitter to reduce any lift generated underneath the front of the vehicle. I am leaning toward extending the tube above the floor as it makes for a good place to weld the Roll Cage to the rect tubing to torsionally stiffen the whole thing. The strut towers and Roll Cage will also have triangulated stiffening added yielding a more rigid structure. Will try to get lighter weight tubing (.085 4130 steel) above the floor to keep the CG as low as possible.

[johnc]

Roland,

 

I have no idea where in your car the 2 x 3 subframes are going but the main hoop and door hoops of your roll cage should be tied into the rocker panels, not any subframe that's running nearer the centerline of the car.

 

NHRA still gives a weight break for 4130 and you can save weight with 1.625" x .083" tubing. If you plan on running your car with most any road race/track sanctioning body here in the US, .083" 4130 tubing is only allowed if the tubing is 1.625" OD. And, BTW, DOM tubing of the same dimensions is allowed so the extra cost of 4130 doesn't get you any weight savings.

 

EDIT: The above road race tubing dimensions are for a car weighing 1,700 to 2,699 lbs. without driver. If your car weighs in at 2,700 lbs or more then you'll need 1.75" x .095" or 1.625" x .120" wall tubing.

Edited May 6, 2009 by johnc

[rsicard]

Roland,

 

I have no idea where in your car the 2 x 3 subframes are going but the main hoop and door hoops of your roll cage should be tied into the rocker panels, not any subframe that's running nearer the centerline of the car.

 

NHRA still gives a weight break for 4130 and you can save weight with 1.625" x .083" tubing. If you plan on running your car with most any road race/track sanctioning body here in the US, .083" 4130 tubing is only allowed if the tubing is 1.625" OD. And, BTW, DOM tubing of the same dimensions is allowed so the extra cost of 4130 doesn't get you any weight savings.

 

EDIT: The above road race tubing dimensions are for a car weighing 1,700 to 2,699 lbs. without driver. If your car weighs in at 2,700 lbs or more then you'll need 1.75" x .095" or 1.625" x .120" wall tubing.

John: The 2x3 rect tubes replace the original subframe rails. I reviewed photos and I stand corrected they only extend downward 1/2 to 3/4". These are only the start of the project to eliminate the bent upward passengers floor and subframe below it. I want to extend outriggers from the 2x3" tubes to accomodate added round tubes that I would like to run behind or tied into the rocker panels. Outriggers will be added both front and rear. If I can, it would be good to go from outside to outside on the rear to cross the longitudinal 2x3" rect tubes and cut sandwich and weld the 2x3 long and cross tubes behind the seats. The round tubes would join outriggers at the front and lateral cross member 2x3 tube at the rear. I want to get a tube bender and standardize on 1.75" tube whether it be 4130 0.083" or 0.120 wall DOM. I will purchase a TIG welder or get someone to use same on the Roll Cage and joining 2x3 rect tubes. Safety is PARAMOUNT and thanks to you have already picked out certified racing seats and belts.

[JMortensen]

Gentlemen: The stock 240Z subframe rails are approximately 1.5" tall already. So maybe if I put the 2x3" rect tube BELOW the floor then I will lose 0.5" ground clearance. If the floor is cut to 3.0" across and the 2x3" tube is extended above the floor by 0.5" then there will be nearly no loss of ground clearance.

Go look again. The frame rails under the floor are about 1/2" deep because of the reduced ground clearance there. The 280Z frame rails are a little deeper, but they run higher. You can put a 3x2 tube in, but if you have 1.5" sticking up through the floor I think it gets a little clumsy for your feet, and if you stick more out of the floor you'll run into ground clearance issues.

 

I want to keep the nose of the 240Z as low as possible and put an air dam with splitter to reduce any lift generated underneath the front of the vehicle. I am leaning toward extending the tube above the floor as it makes for a good place to weld the Roll Cage to the rect tubing to torsionally stiffen the whole thing. The strut towers and Roll Cage will also have triangulated stiffening added yielding a more rigid structure. Will try to get lighter weight tubing (.085 4130 steel) above the floor to keep the CG as low as possible.

Try using your 2x3 tube to reinforce the rockers and welding your cage to that. It's been discussed a couple times previously. If you search for "chassis stiffening" I'm sure you'll find one of those discussions.

 

EDIT--I typed this up then had a customer call, so it sat and then I posted without re-reading the thread.

[Roostmonkey]

I'll take some pics of my frame tonight after work.It will show how I tieing the rails to the rockers and to the hoop. This car will never see an SCCA event, I'm just stiffening the car for the extra hp I'll get with the RB.

[johnc]

This car will never see an SCCA event, I'm just stiffening the car for the extra hp I'll get with the RB.

 

One thing that's nice about building to SCCA roll cage rules is that they've been developed over decades of real world, multi-car crash experience at speeds above what you normally encounter on the street.