Fastback inner rockers

[aslanefe 333]

7 hours ago, latoracing said:

One interesting thing with 69-70 convertibles, they do not use a one piece seat riser from the factory. I don't quite understand Ford's reasoning on this. When I was upgrading my '70 FB I looked everywhere for a specific one for that year, they didn't make them, so I hacked up an earlier model to fit. 

 

I do not know all the differences between every year and model but they might have used some other component, thicker material on some places etc. Or may be they just didn't care. There are a lot of things they did that doesn't make sense to us now, but it made sense to Ford then. Why did they used galvanized metal on the rockers and let the inside of the cowl bare metal to rust and leak is an other example.

[mustangstofear 608]

Ford did the galvanized  on the outside so you wouldn't  see it rust, they weren't  concerned  with the inner.

[latoracing 256]

If one were to go off the deeper end of chassis reinforcement, I utilized a thread from sn65 (which has been taken down) on areas to focus on. The main point of that information was to have the chassis working as a system, small gains in rigidity and torsional stiffness can be gained, but how does it translate into real word use. The majority of folks who are installing either SFC or inner rockers are pretty much stopping at that point as their cars are not going to a racetrack at any point nor do they want a subjective jungle gym in their car. That being said, my current build (which is ridiculously slow) has incorporated some of the ideals of several builds and innovations from TA racing, B302 and Shelby upgrades. Mind you, I am not building a race car, but an overkill street car that still has a heater, some creature comforts and can be driven to the track (if that ever happens lol).

 The main area of focus, after having installed inner rockers and a once piece seat riser (lower seat pan reinforcements to come) was a multi point cage that ties into the roof above the doors, windshield and A pillars.

The down bars are attached to areas that will be transferring suspension component loads to this area. The rear down bars are located directly over the rear coil over mounts and the front has several bars that transfer loads to the torque boxes and to bars welded inside the upper A pillars

There are a bunch of areas I would have loved to apply more triangulation like the tube running across the firewall to the cage would have been great, but it has a stock heater in the way. I'm sure there could have been more areas that might add a little more here and there, but as far as going beyond the "norm", this might take the cake lol.

[Mach1 Driver 560]

reminds me of the cross bracing in the bow of an icebreaker ;)

[RPM 1,190]

Reminds me of a bad ass car I once saw :)

[fvike 173]

On 1/9/2019 at 10:04 PM, Mach1 Driver said:

Currently the only way to put inner rockers into a fastback or coupe is to use remanufactured sheet metal parts for a convertible. Yes it would be much easier to add sub frame connectors, but the only test available shows that SFCs do zero for torsional stability. When FORD decided how to strengthen the convertible they used inner rockers.

First off; I'm not an engineer, I'm not trained to do the math on this stuff, but I do have eyes.

Having read trough this thread, I've come to the conclusion that the premiss of the discussion is wrong. The premiss that SFCs have zero impact on torsional stiffness. The test that is being laid to ground for this discussion (link) is a '67 coupe that has it's shock towers cut out (removing the export brace, which is alone 25% of the torsional stiffness, according to said test.), and then uses bolt-in SFCs. It is in my opinion the absolutely worst thing one can do to a unibody car. The torsional stiffness is now all in the roof (without the help from the export brace) and floorboard, and a few bolts. The test has absolutely no value for modifying a stock unibody Mustang with shock towers. The only thing he documents is how removing the shock towers kills the torsional stiffness of the unibody.

Edit: The windshield and backlite should also be in the car when testing for torsional stiffness. They are a huge part of the cars construction.

I say this, because in my experience, making a Mustang handle, is all about stiffening the platform (unibody) and reinforcing the shock towers, so that they don't move around. That is why we have the big block shock tower bracing, the boss 302 shock tower bracing, the triangulating of the top of the shock tower with the export brace and the Monte Carlo bar. And for the Boss 429, the shock tower-to-firewall brace. Think about it, all racing modifications on a Mustang is about minimizing flex in the shock towers. So how will that car perform when you remove the shock towers all together?

Over to the SFCs. We all know, if you put a jack next to any given wheel on a stock Mustang, and jack it up, that wheel will come off the ground, and the 3 others will remain on the ground. I have the TCP SFCs with the X-bar installed on my car. When I jack up my car, 3 wheels will come off the ground, and the wheel diagonal to the jack will remain on the ground. There has to be some torsional stiffness there, right? I can see it.

Also, I've said this before in other treads; when I installed my TCP front suspension, I drove the car a few days before I installed the SFCs. It was not until then, I felt that I had a new suspension on the car. It felt the same as stock without the SFCs. Again, that tells me they do something.

So, those are my claims; I better back it up.

My brother has a '70 Plymouth Barracuda, with the XV Motorsport level II suspension. XV didn't do anything half-assed when they developed their stuff. They went to Multimatic, to get the Mopar E and B-body torsion tested on a four post rig, and to then develop the suspension. They found torsional stiffness to be on par with modern sedans, and wanted to get them ut to sports car standards. They did it with a boxed front radiator support (like the Mustangs have), shock tower-to-firewall braces, and SFCs. Their SFCs is laser cut to follow the floorboards, and are fully welded in. You can see this on episodes of Dream Car garage, ep 2, ep 3 and ep 4. It's very cool stuff. My brother's 'cuda is like my Mustang, jacking it up will lift 3 wheels.

Here is another proof for my claims. These pictures show my car hanging on a rotisserie, mounted at the rear bumper mounts and the front bumper arm mounts. It is hanging upside down with mint door gaps. It has all the shock tower braces (big block, Boss 302 and Boss 429 style) and TCP SFCs (minus the X-brace) It does not have the Monte Carlo Bar and Export brace installed. The chassis is of course bare, with no extra weight. I'll dare to claim, that a stock unibody Mustang could not do that. I do not believe that SFCs do zero for torsional stiffness, at the proof is in the XV Motorsports videos, where a world leading company like Multimatic is performing the tests on state of the art equipment. If you don't know who Multimatic is, they helped develop the new Boss 302 and the new Ford GT.

On the discussion itself, I belive the convertible rockers will make a difference, but the car should have rear torque boxes as well. But I believe SFCs will do a better job for less money and work.

 

[aslanefe 333]

3 hours ago, fvike said:

I have the TCP SFCs with the X-bar installed on my car. When I jack up my car, 3 wheels will come off the ground, and the wheel diagonal to the jack will remain on the ground. There has to be some torsional stiffness there, right? I can see it.

Can you jack your car up without the X-brace with just SCFs that connect only right front frame rail to right rear and left front to left rear frame rail and see if you can lift all 3 wheels?

[Rsanter 152]

On 1/9/2019 at 1:04 PM, Mach1 Driver said:

Currently the only way to put inner rockers into a fastback or coupe is to use remanufactured sheet metal parts for a convertible. Yes it would be much easier to add sub frame connectors, but the only test available shows that SFCs do zero for torsional stability. When FORD decided how to strengthen the convertible they used inner rockers. The current method looks like this: see pics There will more posts to show what I propose as an alternative. This is a test to see how visible the drawings are when inserted here.

 

That went well, more pictures to come!!

For a car that you want to put carpet in, this is how I do it along with adding the front torque boxes.

for a race car we just stitch weld in rectangular box steel tubing and you can either use the front torque boxes or you can triangulate the area the torque box would go with steel tubing

 

also stitch weld the unibody seams per the Boss302 chassis mod guide

[Mach1 Driver 560]

7 hours ago, Rsanter said:

For a car that you want to put carpet in, this is how I do it along with adding the front torque boxes.

for a race car we just stitch weld in rectangular box steel tubing and you can either use the front torque boxes or you can triangulate the area the torque box would go with steel tubing

since the 69s come with torque boxes all around, I assume this is for those years that don't have torque boxes?

[Mach1 Driver 560]

Here is a picture of Total Control Products SFCs that fvike mentions above. They are obviously a whole lot less work than inner rockers. If I may intercede here for a moment, what aslanefe is trying to verify is what happens if the cross bracing is removed. What we were shown by the torsion test is that with only the rails installed and no cross bracing, three wheels should stay on the ground and only one wheel will lift (the chassis will twist). That would confirm aslanefe's contention that it is the cross bracing connecting the two sides that will best prevent torquing (twisting) of the chassis. If I've misspoken here please correct me. This would be a very important test, and a big PITA for fvike, but a teaching moment for all of us.

[Rsanter 152]

2 hours ago, Mach1 Driver said:

since the 69s come with torque boxes all around, I assume this is for those years that don't have torque boxes?

Yes I am talking about mustangs in general. However it is important that when adding inner rockers to a car with torque boxes, you need to properly tie them into those rockers and just welding them to the angled face of them on the inside of the car is not enough. 

You will need to cut the torque box open and insert the inner rocker into them so it can be welded to,both the front and rear surfaces

[aslanefe 333]

4 hours ago, Mach1 Driver said:

Here is a picture of Total Control Products SFCs that fvike mentions above. They are obviously a whole lot less work than inner rockers. If I may intercede here for a moment, what aslanefe is trying to verify is what happens if the cross bracing is removed. What we were shown by the torsion test is that with only the rails installed and no cross bracing, three wheels should stay on the ground and only one wheel will lift (the chassis will twist). That would confirm aslanefe's contention that it is the cross bracing connecting the two sides that will best prevent torquing (twisting) of the chassis. If I've misspoken here please correct me. This would be a very important test, and a big PITA for fvike, but a teaching moment for all of us.

 

Yes. Remember what I said in one of my previous posts; "strategically placed tie between right and left rocker decreases twist". Fvike tied the right front rail to right rear rail with welded SFCs, the front rail is already tied to front torque box which is tied to front rocker, same for the rear. Then the X-brace tied the SFCs to each other (right front to left front, right rear to left rear), so in doing that he tied the right rocker to left rocker both at front and rear and did what I said is required.

[Ridge Runner 1,112]

4 hours ago, Mach1 Driver said:

Here is a picture of Total Control Products SFCs that fvike mentions above. They are obviously a whole lot less work than inner rockers. If I may intercede here for a moment, what aslanefe is trying to verify is what happens if the cross bracing is removed. What we were shown by the torsion test is that with only the rails installed and no cross bracing, three wheels should stay on the ground and only one wheel will lift (the chassis will twist). That would confirm aslanefe's contention that it is the cross bracing connecting the two sides that will best prevent torquing (twisting) of the chassis. If I've misspoken here please correct me. This would be a very important test, and a big PITA for fvike, but a teaching moment for all of us.

The only problem i see with this set up is ,the front of the SFC only ties into the floor support ,i have replaced a bunch of these and there is very little strength in the floor support other than supporting the floor ,they bend and twist very easily ,the reason i have replaced so many of them. If they attached to the frame rail its self that would be a different story 

[Ridge Runner 1,112]

This is the reason i dont like the sub frame connectors ,you are only tieing into the floor support in the front ,unless you split them open and insert square tube first you are only tieing into a thin sheet metal 3/4 side box with very little strength .

This is an aftermarket floor support ,a,little heavier gauge than original but still not very strong .

Here is a 67 coupe ,you can see the kink in this one ,maybe from a jack under it or running up on a curb

[Ridge Runner 1,112]

You can see there is a lot of leaverage behind where the torque box would end ,arrow is the front

[fvike 173]

15 hours ago, aslanefe said:

Can you jack your car up without the X-brace with just SCFs that connect only right front frame rail to right rear and left front to left rear frame rail and see if you can lift all 3 wheels?

I have not tried that. The X-brace is the anchoring point of my torque arm, so It's never been off the car (while driveable). I can do it for you if you find it important that I do, but per now, I do not have the windows in the car. So it will have to wait until I do.

My brother's 'cuda can perform the same "3-wheel trick", and it does not have an X-brace. It does have SFCs cut to the underside of the floor, and welded entirely, except for a window to let the parking brake cable pass thru on the driver side. This is the underside of that car.

 

[fvike 173]

3 hours ago, Ridge Runner said:

The only problem i see with this set up is ,the front of the SFC only ties into the floor support ,i have replaced a bunch of these and there is very little strength in the floor support other than supporting the floor ,they bend and twist very easily ,the reason i have replaced so many of them. If they attached to the frame rail its self that would be a different story 

 

3 hours ago, Ridge Runner said:

This is the reason i dont like the sub frame connectors ,you are only tieing into the floor support in the front ,unless you split them open and insert square tube first you are only tieing into a thin sheet metal 3/4 side box with very little strength .

I have to ask; did you replace them due to rust, or due to dis-forming?

I studied the damage to my Mustang after my crash, and I studied the load paths the energy of the impact had taken thru the chassis.

The crash: rotated into an armco section on the left side of the roadcourse with the passenger side front corner of the car hitting first. Eyewitnesses said the rear of the car was 1 meter off the ground and recoiled back out of the armco. So not the hardest lick, a hit to the driver side front corner would have been much harder. Pictures of the crash damage is in my build thread.

The damage: Pass side  framerail bent, radiator support bent, top of cowl on both sides bent (which is why I installed Boss 429-style supports after). The top radiator support was twisted. That means the load path went thru the frame rails and back, and thru the shock tower, thru the export brace and bent both corners of the cowl. Everything in front of the firewall needed to be replaced. The floor support did not.  There was enough "real estate" that direction because of the SFCs to "bleed off" the energy.

I can easily believe that without SFCs, the damage to the car would have been greater, because the load path would have ended at the floor support. The energy shockwave of the crash would have nowhere to go. The SFCs made it so that the energy could be taken up by the whole unibody structure, not just the front half. As we know from racing, crash protection is all about dissipating energy. The more structure you have to dissipate that energy into, the lesser impact the energy will have. The stock Mustang unibody is two structures, front and back frame rails. With welded SFCs you have one structure.

The floor support is tied to both the transmission tunnel support and the rockers thru the torque box. The front frame rails is cradled by the floor support, and the floor itself boxes them off. I found them undamaged by my crash, and I believe they are stronger than given credit for. EDIT: Or are they made "stronger" by SFCs because crash energy can pass thru them, not end in them?

So it is in my opinion wrong to think of the floor support as a weak part - which a U-shaped rail is - but one has to think of it as a whole structure. It is in fact the part that ties the car together. Frame rails, torque boxes and transmission support is tied into it, and SFCs when added.

I like this picture, because the different part are in different colors and shades. It shows the frame rails, torque boxes and transmission support tied together by the floor support.

Pictures of floor supports and installment of new frame rails.

[aslanefe 333]

1 hour ago, fvike said:

I can do it for you if you find it important that I do, 

You do not have to do it for me. I have been an aeronautical engineer designing aircraft structures for a long time (30 years).

But I went to the shop and did something for you. Subject car is a 1969 Grande, all original sheet metal except replacement left door skin. No modifications to body and structure, not even extra welding. It has an export brace but I loosen the shock tower bolts that hold the export brace so the body can move anyway it wants. No rear glass, no seats and door and rear quarter interior panels. No fuel in the tank and no exhaust pipes after the mufflers .

See pictures of right front, right rear and left rear tires;, only left front wheel touching the ground.

[fvike 173]

That is impressive. My car did not do that. But it's been known for a long time that drag racers prefers the coupe over the fastback due their stronger construction. I'd like to see this on a stock fastback.

As an engineer, do you agree with my thinking in the above post? About load paths thru the unibody I mean. It is at least the way I understand what happened to my car in the crash, and my reasoning around it.

[aslanefe 333]

8 minutes ago, fvike said:

That is impressive. My car did not do that. But it's been known for a long time that drag racers prefers the coupe over the fastback due their stronger construction. I'd like to see this on a stock fastback.

As an engineer, do you agree with my thinking in the above post? About load paths thru the unibody I mean. It is at least the way I understand what happened to my car in the crash, and my reasoning around it.

I would prefer to be in an accident with a car without SFCs so the floor, rockers etc will bend and absorb energy instead of my body absorbing that energy. Anything that bends during a crash is absorbing energy that will otherwise be transfered to occupants.

Put a brace like the coupe has behind the rear seat and increase the torsional stiffness of the fastback.

[RPM 1,190]

2 minutes ago, aslanefe said:

Put a brace like the coupe has behind the rear seat and increase the torsional stiffness of the fastback.

For the average Mustang owner without a lot of cash, equipment, skills or knowledge,  I think if the rear seat brace, export brace and Monte Carlo bar were installed they would have a much stiffer chassis at little cost in time and money. 

[Ridge Runner 1,112]

40 minutes ago, fvike said:

 

I have to ask; did you replace them due to rust, or due to dis-forming?

I studied the damage to my Mustang after my crash, and I studied the load paths the energy of the impact had taken thru the chassis.

The crash: rotated into an armco section on the left side of the roadcourse with the passenger side front corner of the car hitting first. Eyewitnesses said the rear of the car was 1 meter off the ground and recoiled back out of the armco. So not the hardest lick, a hit to the driver side front corner would have been much harder. Pictures of the crash damage is in my build thread.

The damage: Pass side  framerail bent, radiator support bent, top of cowl on both sides bent (which is why I installed Boss 429-style supports after). The top radiator support was twisted. That means the load path went thru the frame rails and back, and thru the shock tower, thru the export brace and bent both corners of the cowl. Everything in front of the firewall needed to be replaced. The floor support did not.  There was enough "real estate" that direction because of the SFCs to "bleed off" the energy.

I can easily believe that without SFCs, the damage to the car would have been greater, because the load path would have ended at the floor support. The energy shockwave of the crash would have nowhere to go. The SFCs made it so that the energy could be taken up by the whole unibody structure, not just the front half. As we know from racing, crash protection is all about dissipating energy. The more structure you have to dissipate that energy into, the lesser impact the energy will have. The stock Mustang unibody is two structures, front and back frame rails. With welded SFCs you have one structure.

The floor support is tied to both the transmission tunnel support and the rockers thru the torque box. The front frame rails is cradled by the floor support, and the floor itself boxes them off. I found them undamaged by my crash, and I believe they are stronger than given credit for. EDIT: Or are they made "stronger" by SFCs because crash energy can pass thru them, not end in them?

So it is in my opinion wrong to think of the floor support as a weak part - which a U-shaped rail is - but one has to think of it as a whole structure. It is in fact the part that ties the car together. Frame rails, torque boxes and transmission support is tied into it, and SFCs when added.

I like this picture, because the different part are in different colors and shades. It shows the frame rails, torque boxes and transmission support tied together by the floor support.

Pictures of floor supports and installment of new frame rails.

Rust free cars in Cali. This is damage due to a jack or running on a curb but the end of the floor support doesnt handle much of a load before it will bend

[fvike 173]

6 minutes ago, aslanefe said:

I would prefer to be in an accident with a car without SFCs so the floor, rockers etc will bend and absorb energy instead of my body absorbing that energy. Anything that bends during a crash is absorbing energy that will otherwise be transfered to occupants.

Put a brace like the coupe has behind the rear seat and increase the torsional stiffness of the fastback.

My thinking is opposite. I would prefer the energy to dissipate thru the strongest part - the frame. I would not like the sheetmetal of the roof and floor to handle the impact forces. There is a more direct line thru the car with SFCs, instead of going thru the torque boxes and rockers. But now we're talking head on energy handling, not twisting motion.

[fvike 173]

3 minutes ago, Ridge Runner said:

Rust free cars in Cali. This is damage due to a jack or running on a curb but the end of the floor support doesnt handle much of a load before it will bend

Well, that is a entirely different thing. Force going from the bottom up, not thru it front to back. It's like a empty coke can; it is immensely strong up and down. If you balance right, you can stand on it with one foot. If you do that and tap the other foot on the side of it, it will crumble instantly. It's just the can or part doing the job it was designed to do, then it is strong. Put some other force on it, and it's weak. 

[aslanefe 333]

24 minutes ago, fvike said:

My thinking is opposite. I would prefer the energy to dissipate thru the strongest part - the frame. I would not like the sheetmetal of the roof and floor to handle the impact forces. There is a more direct line thru the car with SFCs, instead of going thru the torque boxes and rockers. But now we're talking head on energy handling, not twisting motion.

If a part is not bending and deforming, it is just tranfering the energy, not absorbing it.