Will this work or stress the body too much?

[MCMLXIX]

I have a 67 Chevelle that the frame has been boxed and braced. While this makes it much more rigid then stock, it’s still only one dimensional. I do not want a cage, so please don’t tell me to go that route… The car will never see the drag strip. It may see the occasional autoX but that’s it. It will be a daily driver that will need unobstructed access to the rear seats….

https://static1.pt-content.com/images/pt/2009/03/DSC04723-1.jpg

Ok… now for my idea.
Most of the weight is where the engine and transmission are located and the frame kicks up and out. What if I was to have some front down tubes made to connect the front of the frame at the core support up the firewall where the fenders meet it. Now I already plan to have the firewall smoothed. I would have some heavier plate welded under the dash to support the mounting point. The bar would have another plate and sandwich the firewall and bolt together. I found these nice connectors for the front…. See the pics below.

https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif

The general idea….


https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/pt/2009/09/nova8-1.jpg

Now I will be using poly body mounts to further reduce body flex but this would be a 100% rigid mount.
Will this cause too much stress and cause the body to crack or tear at the firewall?

[64Chevelle]

I have the same plan for my Chevelle, I'm eager to see where u'r going with this. You might get a piece of poly and cust cut that to match between the firewall and the brace mount. It will cushion the firewall a little while also providing some sound and vibration dampening. Not as rigid though, but a good compromise for a daily driver

[41565 chevelle]

I like your idea as well. I am on a similar course too. I am thinking of welding a plate inside of the firewall, drilling one hole for a bolt. Inside of the tubing I would weld in a thick steel puck, drill and tap it and the bolt will tighteing it down to the smoothed fire wall???? You like? think it might work.

I dig your extra bracing on the frame. I would run something like that but mine is already powder coated.

[Chicken Coupe]

I'm far from being any kind of an expert on this kind of thing, but I'd say you have 2 issues off the top of my head.

The Nova in the pic is much more of a uni-body design with a lot more structural integrity in the body. There are no bushings to compress when the sub frame wants to flex the body and the body was designed to take that load. Nova's have been "tested" with those supports and I believe that the bodies react well to the added triangularity.

The Chevelle is a chassis design with the body held on by flexible bushings. The body was never designed to take those loads. Yes it adds rigidity to the whole assembly (body + chassis), but I'd bet money that there's no way the firewall (and maybe even the body) could take the pounding of a flexing chassis w/o inflicting major carnage.

My gut also says that reinforcing the firewall only means that it will transfer the stress to the next weakest point in the body (might be the bushings/body bolts, might be the pillars, but somethings going to react)

Aftermarket chassis' either have an arch that connects the main rails with the front kick-up or are made from a different strength and gauge material with internal trusses for that reason.

I would think that if your idea was the right one, it would be incorporated into aftermarket chassis' and/or be available as a bolt-in (like the bars that go from the upper rear crossmember to the lower control arm bolts)

So my un-expert opinion is don't do it.

Sure would like to hear from some chassis guys. Where's Craig Morrison (son of Art Morrison and a member here)? I'd ask him to go dig into their R&D guys for answers.

[John McIntire]

Good topic. I wonder if that would help much? I know how much my frame flex's when i have it up on jackstands with the weight of the big block.
I don't think that the firewall itself is strong enough to handle the weight and flex. On most cars that have the down tubes in the engine compartment, they go straight through the firewall and tie into a cage with a crossbar under the dash.
I can just see the down tubes on my car pulling out or buckling the firewall when I have it jacked up and supported with a jack stand on the frame right where the door meets the fender.

[rixtrix1]

How about adding a curved bar from your tube, to the frame in front of the firewall? My thinking is that the firewall would just become a stabilizer and locator for the back of the bar. The type of material used on your body mounts can also affect the strain on the firewall. When I caged my '66 Malibu, I did solid body mounts at every available mounting point, to help stiffen the car even more( It's backhalved with 2x3-.083 wall square tubing, NHRA Super Stock legal). I even utilized the unused mounting point just ahead of the rear wheels, which looks in your pic like it wasn'tused either. I used solid aluminum, shimmed to fit the bodyperfectly; poly bushings will stiffen the car at the expense of some comfort while still allowing a little flex. A lot of offroad racers mount their cages to the frame using poly bushings. Maybe you could incorporate something like that at the frame. Nice job on the frame; are you going to brace tha new x-member to the frame, too?

Ric

[The WidowMaker]

i was thinking the same thing, then i thought about getting impaled on it during a front end crash. unless youre tying it into a full cage, i would think its a no go. i just dont think you could EVER reinforce the firewall enough to make it safe.

on a side note, i have since thought of making some bracing from side to side in front of and behind the motor that would tie the frame rails together. maybe even one that ties the suspension mounting pts together. this "hoop" would add the third dimension that a cage does, it doesnt require a full cage, and its not going to kill you.

btw, the bracing you have done helps a ton. i'll shoot some pics of mine once i get the body off, but it was about a 200% improvement in rotational flex when on the rotisserie. that was with the frame boxed, and i didnt test just the boxing before the bracing.

also, why not delrin or aluminum body mounts?

Tim

[MCMLXIX]

While I want the car to handle, I need to balance performance and comfort. When my current lease is up, this will be my primary vehicle. I chose poly body mounts as a step above stock but solid would be too much for a daily driver.

I thought about using a crossbar under the dash tied into the A-pillar. Much stronger then the firewall. Then tie the down tubes into that and just pass through the firewall... Also I could isolate the down tube under the dash with a poly mount... It would have the same flexability as the body to frame mount..... I would also like and engine crossbar from side to side if there's room...

https://static1.pt-content.com/images/noimg.gif

[DRJDVM's '69]

I agree with the others....having the body on poly mounts but then having a rigid connection from firewall to frame is a bad mix. If nothing else use solid mounts on the body to frame mount.....then you wont have nearly as much flex.

[The WidowMaker]

i like the idea of the under dash bar (could also work as your wilwood pedal mounts), but i still dont see how you could tie it in enough. all that sheet metal would be no match for a front end collision. unless you braced it backwards, i dont think it would be enough. but if you do, youre now into full cage territory.

i think you will be suprised at the difference that will be made with the bracing you have. if its your dd, i dont think you want too much.

Tim

[camaro2nv]

What if you go through the firewall a couple inches and 90 with some down tubes through the floor and connect to the frame? I might have miss read the post so take it for what its worth.

[Mathius]

I've never built or engineered my own frame, so my knowledge is by comparison pathetic to some of the guys on this forum, but just from my basic knowledge of steel which I work with every day, looking at that first picture, the transmission cross member which appears to be a piece of angle is pathetically undersized. It appears it was even bent in two places where mounted to the frame rails. I would have gone with a piece of tubing, or baring that, a piece of c-channel before ever using a piece of angle that thin.

Mathius

[MCMLXIX]

I've never built or engineered my own frame, so my knowledge is by comparison pathetic to some of the guys on this forum, but just from my basic knowledge of steel which I work with every day, looking at that first picture, the transmission cross member which appears to be a piece of angle is pathetically undersized. It appears it was even bent in two places where mounted to the frame rails. I would have gone with a piece of tubing, or baring that, a piece of c-channel before ever using a piece of angle that thin.

Mathius

The C Channel was just a temporary piece to hold the trans in place. I am waiting to put the body back on for final engine placement. I want it back as fas as possible.

[bexupnorth]

I have no technical knowledge to call on, but I plan to modify my Zephyr (which is a unibody construction) so that it has a central spine that forces can be transferred to. I borrowed the idea from Summit's Project SR61.

http://www.summitracing.com/expertadvice/storydetail.aspx?id=91b447ee-05a7-4bf2-9d9e-fe8e92a136fc

I don't know if this will help you, but I hope so :)

Ade.

[mikey]

I know you said no cage but you may want to look into the tiger cage from ridetech. I was also against a cage for rear seat access issues. I spent some time talking to them and looking at one at the Kansas goodguys show. The rear crossbar is adjustable in height and the door bars are along the bottom of the seat. The cage I looked at was in their chevelle.
http://www.ridetech.com/catalog/TigerCage-2490-1.html