Welding subframe to unibody?

[Bottledbird68]

Tried searching but couldn't find anything, anything negative about making the front subframe a permanent part of the chassis? I figure with subframe connectors and a through the firewall roll cage the subframe isn't coming out anyhow so why not just eliminate the body mounts and make it a solid structure all around. Is there anything inherently flawed with my thinking? I never see a need to remove it anyhow after the connectors and cage are welded to it. So, any good reasons not to?

[astroracer]

If ANYTHING bad happens down the road.... A trip through a ditch, a minor fender bender, hitting a deer, etc., anything that could tweak the body/frame is going to be next to impossible to fix with everything welded solid. Even on full frame cars the body CAN come off. If you have any plans to drive the car on the street you need to have plans to FIX the car if it gets broken... Just trying to think ahead here.
Mark

[Bottledbird68]

Yeah but if you look at almost every modern car out there, sure they have a removeable k member, but all the front frame rails are part of the structure of the car. I come from a body shop background so pulling a frame after a wreck is nothing new to me

[astroracer]

Every modern car out there is DESIGNED that way. I am a designer for GM and I know what kind of work it takes to get these light weight, thin skinned vehicles to work in frontal impact and torsional load situations. It's not as easy as welding in a subframe, believe me.
That old Camaro isn't designed to carry all of those loads thru the body structure. The subframe is mounted to the body with rubber bushings for a reason. Part of the job of those bushings is to limit the amount of twisting the body sees as it goes around corners or into steep driveways. The bushings allow the body to flex independent from the subframe. They also isolate the body from most of the road harshness. Ask anyone who has installed solid bushings in place of the rubber ones what they did to the ride quality.
The biggest worry here is, if the frame/body weldment gets tweaked or bent, you are going to end up with doors that won't close or seal properly and you will have no way to fix it. You can do what you want, it's your car, but I just want you to think about the work needed to fix it if it ever needs to be fixed.
Mark

[Bottledbird68]

Well that's why I was asking. Looking for cons I didn't think of. Ride quality isn't a concern. If I don't weld it it'll still get solid bushings, subframe connectors, and a full through the firewall at least 14 point cage so the chassis will be as rigid as possible anyhow.

[astroracer]

I did the same thing with my '73 Firebird. I put in a 14 pt. cage and I made my connectors out of 2 x 3 tubing. I tied them directly into the forward leaf spring mounts and made them a slip fit into the ends of the sub-frame "just in case" it needed to come out. The connectors through bolted through the subframe with grade 8 bolts.
Mark

[NOT A TA]

Also keep in mind eliminating the body bushings raises the drive train reducing hood to intake clearance, trans to top of tunnel clearance, as well as changing things like front tire to inner fender clearance, driveshaft angle, etc.

[Bottledbird68]

Yeah none of that matters to me anyhow. I'm putting a whole new floor in the car and need to clearance the fenders for the tires I plan to run anyhow. Making the car sit lower wouldn't bother me in the least.

[Build-It-Break-It]

Seems like you have your mind made up on doing it. Post some pictures when you get it done or on the road.

[TheJDMan]

Seems like you have your mind made up on doing it. Post some pictures when you get it done or on the road.

Ahmad beat me to it. Let us know how it works out.

[Bottledbird68]

My mind isnt totally set yet hence my asking. I don't see any downsides that turn me off yet though either. All the rest of the project is pretty well mapped out. Been parts gathering for a few years now and moving into a bigger shop in the next week or two. Should be diving into it shortly after that. When I start on it I'll post up a build thread.

[dhutton]

It's been done before. There is a thread about it here or on the other forum.

Don

[Bottledbird68]

I searched here and didn't come up with anything. Which other forum?

[dhutton]

Ok I was wrong. It was a thread about running without subframe bushings which is similar.

http://www.lateral-g.net/forums/show...subframe+floor

Don

[tooldude]

I know of several people, me included that made weld in subframe connectors by slicing the floor, opening the front of the rear subframe rail, inserting (from memory) 2"x3" tubing into rail and welding it in place, along the floor and on the inside edge of front subframe. You do have 2 raised channels in rear floorpan under the carpet but no negatives really. They are relatively easy to remove if wanted and it really stiffens the chassis. My car is a 68 convertible with an 800hp blown 468 and it made a huge difference over bolt ins. I have no x-brace, cage or cocktail shakers and my car is very rigid. Not sure if I would weld the full front subframe to the chassis as I think you may get alot more nvh from the front suspension and drivetrain transmitted directly to the front floorpan to your feet.

[aronhk_md]

I will mostly be placing the body right on my subframe and welding it to the cage. Can always cut a few welds if needed later if theres a problem. Will also be lowering the engine as much as possible since I am using a front and mid plate to mount. Then I'll be making a whole back-half in a sense to support the 3 link rear.

[Bottledbird68]

Yeah. I'm grafting in the front subframe from an 02 zo6 vette, keeping all the factory c5 suspension mount points and keeping the factory removable aluminum engine cradle.
On the c5 it's all unibody with the removeable k member so by me making the subframe a permanent part of the cars structure I don't see how it's any different from a c5?