well i have been thinking for a way to do a few things to my 1983 z28. first i want true duals, and im not looking to run them down one side, or run a y pipe. also i want to bump up the structure of the car, with out caging it.
now before everyone calls me a retard and such, i want everyone to know that my car is far from perfect, and rust has been a problem for awhile. my shell is great but the rear "frame" and rear floor have seen better days. damn t-tops, nova scotia weather, and other owners driving it in the salt. Also the front floor pans that have been repaired, by myself when i was 16 years old with a 110 mig welder and no prior experience, hell i didnt even have the right wire (gas, flux core wire with no gas)lol the only thing that keeps my car together are the sub frame connectors. so you may be able to tell why i want to change them now, especially after getting into the welding trade as a certified welder.
so heres what im thinking, i want to make a complete sub frame, that runs right into the front frame and goes clear to the back bumper. while fixing my rust issues and making room to tuck up a true dual exhaust and bigger tires, and a lot of others. so call me crazy, but its a project and this is what their for, to experiment with and learn.
so tell me what you think, its not something thats set in stone, it hasnt been started and wont be for a while yet, its all just a idea in my head right now so input is welcome. just want to do some research and go into the project with some knowledge.
thanks

here is a pic of some alston rails i found in another post on here, to give an idea of what direction i kinda want to go.

 

If you are going to remake the entire subframe my only word of advice would be to tie it in the opposite site in the front and back to stiffen the entire structure.

 

ya i did plan to tie the whole thing together with a few cross members, i was also thinking on a new torque arm that dosent mount to the trans, which would require a cross member if im not mistaken. there are lots of options here, and i know i will run into problems with it but its not impossible

 

no other input???

 

You're better off finding another car than trying to replace the frame on a unibody.

 

If he has the knowledge, why not completely cut apart the unibody frame and create an entirely new subframe to tie in the rear suspension with the front k-member? It won't get any stronger then that!

 

thank you, as i said before, its a project, something to play with, besides why would i want to get another car when my shell is in good shape, its just the rear floor thats not the best. i also dont want to replace the frame i want to make a frame , theres no fun in just getting another shell. besides it has sentimental value to it. this car is my very first car, i have pretty much built it to the way it is on my own, ive built the motor myself along with so many other things on the car. ive kept it this long, and i have no intentions of getting rid of it, im sure theres lots of gear heads who wish they could still have their firsts cars, well in some cases lol.

 

I have never done this before but what logically makes sense to me is if you are going to rebuild the frame, you might as well overbuild it.

I'd cut the uni body frame out all the way up front and back, run new tubing from the k-member back to the rear suspension. Under the front seats have it run towards the outsides of the doors perpendicular in an "I" design. Build a new crossmember and have it tie directly into your new frame rails. This would make your new frame stiff from front to rear and side to side. Keeping the weight down will be the biggest problem.

Beware though, this is a serious project and I think you are in for a large amount of work if you do this.

 

oh no doubt its gonna be a ton of work, but heres what i was thinking, cutting the old front rails from behind the green line in the pic, (disregard the red lines, from another thread) and slide rails right inside the stock front frame to stiffen that as well, then build the rest off of that, hopefully making the room i want for the exhaust as i go. im going to keep looking at more pics and i may start drawing some sketches up in the next few days.
thanks zraffs these are the posts i was hoping for, to bounce ideas off others and come up with a plan before i go into this project

 

Sliding it into a part of the old rails up front and in the back is probably the best bet. You can get a good weld around most of it and bolt it in with gusset plates for extra insurance. Maybe you should have it bang a 45 degree or so bend right off the front rails (such as running it directly behind the Z28 side skirts).
Then again I've only ever modified a frame on one thing (a street bike powered quad) and my design worked awesome.

I'm sure if this is done properly it can yield some impressive results in overall structure and handling.

 

Not necessarily , but what a helluva project.

GO FOR IT.

As a fabricator of much smaller scale stuff, my :
Plan on building 2 of every system/component -- you always get
better ideas, and construction techniques after the first one.

Good luck, & keep us posted.

 

There are several things I don't like about the 3rd gen unibody/frame set up.
1. the torque arm mount on the transmission.
2. the way that the front frame tails turn in toward the middle of the car under the floorboards make it very hard to run long tube headers and pipes straight back.
3. the spare tire well kicks the rear frame horn behind the axle over to one side making the run of the frame rail crooked and unbalanced from side to side.
4. the strut front spring mount/spindle assembly

And don't get me started on 305's!

Anyway, I've always had a notion to remove all of the 3rd gen crossmember and etc. and put a 2nd generation front subframe under the car and tie it to the rear frame area with rectangular tubing along the inside edge of the door sill plate. And eliminate the spare tire well and straighten out the rear frame horn.

If you don't want a roll cage, an elevated driveshaft tunnel with bridgework sides tying into the aforementioned rectangular tubing would really strengthen the chassis.

 

you think like me lol, but whats wrong with the 305's, the stock engine that was in this car took one hell of a beating from myself when i was 16, lol, but massively under powered, hence the 410 sbc thats there now, but i have to agree why gm used these gutless motors is a big question.
also i defiantly not interested in a roll cage, this is a car that will be mostly a street car with the occasional strip run.

 

when i drove my car from toronto area to calgary on a uhaul dolly (gave my trailer away cause i was an hour late) and since it was originally a v6 and i put a v8 and the exhaust wasnt hooked up so i took a piece of alum and 2 hose clams to hold er on till i got home but sadly didnt.... heres the damage and what i did to replace it, i dont have a finished pic yet but might help ya

i added in subframe connectors before i started this, and cut out all the **** metal, first project this big hopefully it work, but my 2 cents is, if you dont fix it, how will you learn? replacing the car is the easy way out, cant but the built nor bought sticker on those

 

You should see how little room I have with 2-1/4" primary tubes and 4" collectors trying to squeeze past those frame rails. If those frame rails didn't taper inwards, I'd move my engine back at least another 6".

 

haha EXACTLY! i just finnished up a set of 2" primaries with 3.5" collectors and I HAVE NO ROOM! the headers came out ok and I just finished wrapping them with DEI titanium wrap... that SHlT IS SOOO SEXY!

Anyway I clearanced the firewall and had my BBF sitting back about 4" from the stock location, but due to how the frame rails taper inwards i had no choice but to move the engine back to "about" where the stock location was, its prob still sittin 1/2" farther back lol. IF those frame rails werent there.... man i would have had some fun. I woulda just grabbed the shifter linkage on the trans and shifted it that way!

 

now for the original poster...

Im currently running true duals, 3" header extensions into 3" xpipe that goes into 3" thrush mufflers and has turndowns. IN order to acheive this i knotched the stock subframe so i could tuck the header extensions against the floor. I boxed them when i knotched them. Now I would never do this on a stock car, but I had already installed thru floor subframes that i designed and I also installed some perimeter style subframes that i designed. Otherwise the stock subframe would have been weakened too much with the knotches (maybe). Now i have an 8pt roll bar and the car is stiffer than she ever was.

Point is that the stock subframes are very weak, stamped 18-16 gauge steel (most of it is 22gauge floor steel) and its only a C channel that is spot welded to the floor boards. Replacing this would be a massive undertaking as you will run into some issues at the front of the car mostly where the subframes attach around the firewall and strut towers. The front subframes is actually part of the strut tower. Replaceing sections of the stock subframe would be possible and i would def reinforce the stock subframes with subframe connectors. Otherwise you could build a frame around the stock stuff and then weld it in. Then cut out the stock subframe completely and that way the cars body doesnt shift on you.

If you build a frame i would def get the tq arm off the trans. Im using the jegster tunnel mount tq arm (bolts to the trans tunnel and is very strong) and then i built an adjustable tq arm for it. The tunnel mount is also bolted to the floor plate on the inside trans tunnel bars on the 8pt roll bar.