Full-Frame Chassis for Unibody Cars

[Silver69Camaro]

Prodigy,
I think there must be some miscommunication.

The ONLY way to install this chassis is to channel the body over the frame. The outriggers of the floor support are made to be the same width as the vehicle's pinchweld-to-pinchweld width. The floor of the vehicle is removed, right up to the pinchwelds, and the body is dropped on and new floor pans are made. So, like you said, the body is dropped 4" without any changes to the front and rear rail height. The body is NOT simply sitting on top of the frame.

As far as ride height is concerned, each frame is custom made to the customer's desires. If he wants a 10" rocker-to-ground clearance, fine. If he wants 2", no problem. He can have 2" in the front, and 5" in the rear if he wants. However, suspension is always left unchanged to maintain correct geometry.

[race-rodz]

what does the "average" chassis tip the scales at? complete with all the suspension........ add the weight of the body shell and new int tin, how does it compare to a traditional unibody car?

obviously sacrificing "some" weight for the rigid, updated suspension.... is acceptable.... im just curious about how much.

[ProdigyCustoms]

The problem I see is the interior flooring and seating has to be on top of the frame rails. If you channel the body on a Camaro, you will need to be 5'6" or less to sit in the car in the front seats, and worse in the rear seat.

[Silver69Camaro]

Race-Rodz,
The average chassis weighs about 425 lbs complete less brakes and axle shafts. Bare chassis weigh somewhere between 160-200lbs.

This WILL weigh more in a traditional unibody...thankfully you are adding weight to the center and down below. The weight difference isn't a whole lot, and is certainly offset by the increased performance.

Prodigy,
I understand your point. Keep in mind the floorpan in which the seat bolts to is already raised high above the rest of the floor, and there are a multitude of seat brackets (and you can make/modify your own) to make things work. Not all seats have the same padding height, either. We have a builder who built a car using our chassis for a guy that was about 6'2" (and about 230lbs, big guy), and he fits in there very comfortably. I believe that car was sectioned 3-1/4". This is a common concern for people, but is often not a problem.

[TravisB]

Originally Posted by Silver69Camaro

Prodigy,
I understand your point. Keep in mind the floorpan in which the seat bolts to is already raised high above the rest of the floor,

The factory floor pan in my A-body....the seat mount area is even with the top of the rocker!!!!!! So you would be loosing nothing.

[Mean 69]

Unibodys are extremely flexible, and that is generally frowned upon. Even with subframe connectors, the chassis is still overly flexible for high-end performance. The springs should be doing the work, not the chassis. A properly designed full-frame will greatly increase strength and solve that issue.

I'll agree 100% that a rigid chassis is paramount for high performance, but I'd really caution against making a statement that a full frame dropped into a uni-body car is stronger than a unit body car with a good set of sfc's. It is really going to depend on how each is executed. The main nasty that shows up in a performance aspect is torsional rigidity, and in and of themselves, neither a ladder type frame, or a unit body car are very good.

However, the unit body cars can become really darned good with the application of a proper set of SFC's, such as the DSE through floor units. The reason is that while a full frame is bolted to the car with eight or so locations, and rubber bushes, the unit body car is welded to all of the frame elements. As such, all of the bent up sheetmetal, i.e. the floor pan, back seat brace, roof, pillars, everything becomes part of the structure, in three dimensions. Still not adequate for ripping up the road course with the C6R Corvettes, but not crap by any means either. All of the those little bends, divets, wrinkles, risers, etc in the factory sheet metal integrate and form a pretty darned stout structure. Compare a tin can with a smooth barrel, to one with the ridges in it, big difference!

Now, in the case you describe, the frame "would" be integrated into the body, much like a unit body car is, but depending on the floor that goes in, still might not be as torsionally rigid. Torsional rigidity is more dependent upon the design of a structure, than it is on the wall thickness of tubes used, take a look at a Maserati birdcage for an extreme example of frame-triangulation. The only way to know for certain if it is indeed more torsionally rigid is to measure it directly, it is super hard to model in FEA, for instance. I'd really be interested in seeing the difference.

Take a look at a contemporary World Challenge race car, those cars really heavily on a rigid chassis, and it is all done through the roll cage. Every tube on there is there for a reason, and it's all about triangles. Most of those cars are unit body cars.

I take nothing at all away from the frames Art makes, they are really nice works of art, really nice quality, and they clearly work pretty well.

Mark

[ProdigyCustoms]

Originally Posted by Silver69Camaro

Race-Rodz,
Prodigy,
I understand your point. Keep in mind the floorpan in which the seat bolts to is already raised high above the rest of the floor, and there are a multitude of seat brackets (and you can make/modify your own) to make things work. Not all seats have the same padding height, either. We have a builder who built a car using our chassis for a guy that was about 6'2" (and about 230lbs, big guy), and he fits in there very comfortably. I believe that car was sectioned 3-1/4". This is a common concern for people, but is often not a problem.

The car built for the 6'2" guy, was that a Camaro? A Camaro seat pan is about 2" below the rocker top at the front edge, and about 3 1/2" below the rocker top at the rear of the pan, making the seat go lower as it goes back. The stock floor actually dips lower then the bottom rocker on a Camaro at the seat pan on the bottom of the car.

If the seat is at the top of the 4" rocker, which it would be in a full channeled application, with the thinnest of seat bottoms, a full grown man cannot ride in it. Also, floor pans that are the same height, or almost the same height as the seat tend to cause circulation problems in the legs on long trips, making it uncomfortable to drive, so building the seat into a recess bucket of sorts is not an option either. I only speak from first hand experiance trying to chassis these cars. We have done it, but there are always sacrifices unless you can get the exhaust out the side with fenderwell outlets, or through the tunnel. Then the floor can be at the bottom of the frame, belly style, curing all the issues. As I said, we just finished one of these. If your frame was modified slightly, changing the exhaust routing, this could be done and would be a popular swap. It would only require changes to the center rails, or removal of the center rails if you think it would be strong enough without those rails.

[Silver69Camaro]

Prodigy,
I won't name names, but it was a Challenger. The car sat EXTREMELY low and still mainainted 4" of ground clearance, the roof may have been chopped also. But anyway, The seats were angled back a bit to get the man to fit (I asked Craig, he's 6'3").

All in all, this chassis is nothing new. Many builders have been using it, and seat height just hasn't been an issue; there are many ways around it.

Mark,
I agree with your statement wholly. Like you said, the chassis should be welded to the body (and is how we recommend it). I also agree that you really cannot start to dramatically increase torsional rigidity until you triangulate the chassis in some manner (or other means). Simple engineering statics, no big deal. However, we aren't dealing with the type of customer who is willing to turn his Chevelle into a Cup car.

I also agree that unibody cars can be quite good with SFC. Take my car, for example, as I installed DSE SFCs a while back (with solid bushings). Is the car still flimsy? Yeah, it is. Don't get me wrong, it's a world of difference, but it's still not very rigid (and I agree, it's not crap). But, if you were you jack up the car by the rocker (just rear of the front wheel), the front tire will be completely off the ground before rear really starts to rise. This is a rust-free original car w/ no prior accidents.

Now, try this with a new unibody car (RWD, though). The wheels will lift pretty close to the same time. I mention this because I have nothing against unibody cars, and like you said, they can be made quite well (and are often light weight!). Newer technology has greatly enhanced the stiffness of unibody chassis, something that may be lacking with older cars.

The only thing that we can produce is a conventional-type frame that has increased stiffness, both bending and torsion. I apologize if I sounded as if it was the stiffest thing available, but it IS better (through hand and COSMOS evaluations) than factory-stock frames. In my eyes, comparing the torsional strength of this chassis of this chassis to a high-end monocoque or caged chassis would be unfair, it's a whole differrent ballgame.

Well, this post has taken a turn that wasn't intended. My orginal thoughts were to gather some market data on how to ease the predetermined notions of pain about installing these frames. But hey, I enjoy addressing concerns or new ideas.

[ProdigyCustoms]

Originally Posted by Silver69Camaro

Prodigy,

Well, this post has taken a turn that wasn't intended. My orginal thoughts were to gather some market data on how to ease the predetermined notions of pain about installing these frames. But hey, I enjoy addressing concerns or new ideas.

I hope I did not turn the post, this was not my intent as I am a big advocate for full chassis, in fact we just finished using one of your chassis in a 55 Chevy project and we loved it. There was a thread on this subject on another forum, installing it in Camaro's, and the solution proposed by someone then was to eliminate the center rails, as some builders have done. I believe it was Craig that ultimatly came in and said the center rails would be needed, at least in convertibles if I remeber correctly. I really think it is a fantastic chassis, and I love the full frame idea. We have two projects, one in house and another for a client, that both need full frames. Maybe next week we can get some measurements and share some ideas, off the forum, for fitting into a Camaro and curing my concerns.

[Mean 69]

Please don't take my comments as offensive, and I appreciate the response. The point I was trying to get across is that "if" a person does want a really rigid chassis, it can be done without a full frame install. If a person is really concerned about ultimate cornering, etc, then that person should also be very concerned about safety, which would merit a cage. A cage is an easier install than a full frame as I understand the complexity of the full frame install, it is pretty invasive, and as you pointed out, it adds quite a bit of weight to boot.

You will never be able to eliminate torsional rigidity issues, but for the vast majority of folks, the DSE type sfc's are adequate. Hell, my late model 911 has chassis flex, I can feel it easily, but the car still handles extremely well, and flat hauls ass. I feel less chassis flex in my 69 Camaro than I do with that car, by the way.

M