Scratch build Art Deco Roadster

[CoolHand]

Originally Posted by A Glause

OK I might as well jump in here too. First your frame is not lost. Jacob gave you some good pictures. The rear can be stiffened with tube going under the diff, some where out board of the inner u-joints. I've build several Cobra frames, like the originals using a T Bird 8.8 irs and am doing a Model A. The diff is incased in a 1 1/2 inch tube box, there are no outer frame rails from your kick up to the back of the frame. The Model A has a tubing X running from the back of the engine and ties into the rear end box. We are using 32 Ford frame rails, but our X unit is so strong we would not really need the frame, except to hang the front suspension on. If you go and look at the pictures of the Cobra Daytona that was post on metalmeet, the weak frame was stiffened with tubing over the trans/drive shaft and tied to the cowl hoop. This was a patch job, but it helped the car handle better.

Thanks for listening it's just my two cents
Andy

We call that an "underslung tail" design over in the dirt track world, and it is a very stiff design, usable even with solid tube rear axle housings.

The only thing to watch out for is with low ground clearance cars whose suspension wasn't designed around the underslung tail, the lower tubes can bottom out on the ground at the extreme ranges of suspension travel.

My dirt modifieds had 9" total travel in the rear, and the chassis was set up such that the frame tube would ground out at the same time that the shocks would bottom out. That kept the shocks from getting beaten to death on a rough race track (by nearly beating ME to death instead).

Obviously, on a road car, it's not very desirable to have the chassis grounding out, so you'll have to examine your travels and design accordingly.

One other thing to note is that if you go with an underslung tail section, you will essentially create a hinge point where the rear kickup meets the main frame rails.

Whereas you've got flex all along that member now, if you drastically stiffen the rear section and change nothing about where it attaches to the main section under the passenger cabin, you will shift all the displacement to that one joint.

If it didn't fail before at your normal load, it won't fail now, but the displacement will be much larger and much more localized, which could effect your body work (IE your mounts move so much that the body starts to flex in that area). That's a bad deal, 'cause your alum body work will not tolerate much flex work before it hardens and starts to crack.

Just gotta be aware of the fact that the flex chases the weak spots, so if you don't stiffen uniformly, your flex will become more localized around the remaining weaker areas. You might have to take measures to mitigate this effect on your body work, such as moving mounts away from these areas, or mounting to resilient blocks (like rubber or urethane, etc).

[Kerry Pinkerton]

Thanks for everyone's insight. A new chassis may be in the future but for now, I removed the engine and cut out the motor mounts...sorry Grant.



Rather than remove the front of the X, I came off it where the exhaust goes through and ran a piece of 3x2 up to the suspension crossmember. The new piece is welded to the crossmember AND the front of the frame.



Hopefully this and the rest of the changes will help. I can still use my tubular headers. I next need to move the rear loops in the X member for the mufflers I'm going to use. Then I'll move on to the rear of the car.

[bobadame]

Another thing you might consider if this isn't going to be a corner carver, use soft springs at the corners and light anti-roll bars. This will let the suspension system deflect more which will put lighter loads on the chassis.

[Gleeser]

No problem man. I have cut up far more stuff that I made than you have.

[Kerry Pinkerton]

I'm probably over thinking this whole thing. My car lift is right at the back of the front kickup. This happens to be at the firewall and also the back of the engine. This means the entire weight of the motor is hanging in front of the lift point. I think I'm going to make a lifting pad about 18" further forward which will put it in the center of the motor.

What I see if a considerable change in door gaps when the car is lifted off the wheels. Enough that it will chip paint and I won't be able to set gaps. I realize that all convertibles have some flex when lifted but what I'm trying to address is the amount.

[Kerry Pinkerton]

I firmly believe (NOW) that the most important thing in building a car from scratch is what you don't know.

When I was still working we told our clients that they didn't know what they don't know and that the unknowns were going to bite them.

Consider me bitten...several times.

When the chassis was built, in my blissful ignorance, I did not realize:

- There was no listing of mufflers by size...only by make/model
- Mufflers have inlet and outlet pipes that are offset from each other
- MOST mufflers are 4 1/4 or more tall.

We made the X-member with 4" round tubes welding into the rectangular tubing. The holes were inline. When I first went looking for mufflers I was shocked to discover that NOTHING fit without hanging down below the frame. Further the output did not line up with the holes in the X-member.

I was OK with the sound of the turbo mufflers that I first got but they dragged going into my trailer. I then got a set of glass packs and while they were inline and did not hang below the frame, they were too loud. I'm looking for throaty but quiet. This isn't a Honda with dual fart cans.

Now that my frame is basically 5" tall, I had planned on modifing the holes in X-member to make them larger and offset so the larger mufflers would fit inside the height of the frame. They'd be too close to the floor boards but I felt I could deal with the heat with some shielding and such.

Yesterday I may have found the solution. At Advance Auto Parts (My son Kris manages one), I found a Thrush turbo muffler that is only 11" long, 3" high, 8" wide, and has 2" pipes. It will easily fit INSIDE the frame.

However, I'm afraid it's going to be too loud for my engine and it still has offsets. While studying things, I realized I can simply weld two of them together. The result will still fit within the frame and the pipes will be inline.

Anyway that's the plan of the moment....

On to the next thing I don't know that I don't know.

[Gleeser]

You should look at some late model trans am mufflers. Dual inlet, dual outlet. You'd run it near the back perpendicular to the frame rails probable behind the rear-end. They're quiet but still throaty. I dunno, just a thought.

[gator]

You already have the mufflers. Whats stopping you from cuttiny one down to the size you need. They never built the car you have so why settle for off the shelf mufflers. Cut one or both sides down and weld a flat panel on. This should bring the muffler down to about 3 inches. I cut them up all the time. Gator

[dodgedartgt]

Truly impressive build... WOW! I've just spent hours just skimming.
You don;t need to settle just on two mufflers. Use the mufflers plus a pair of resonators, or maybe the glass packs plus the Camaro/Firebird transverse muffler. Lots of possibilities.
Hit the local junkyard, and grab some samples; try various combos for sound while the body is off the frame and easy to mock up.
Mike Bynum

[Kerry Pinkerton]

Been playing housemom for the past couple weeks. Wife had surgery. Today was the first day in the shop and I got the motor re-installed.

To see how much my changes helped, I pointed this cheap magnetic laser pointer from the rear frame to a piece of tape on the radiator.



This was the car off the ground mark and dot.



Then I picked the car up on the lift and you can see how much the dot moved....about 1/16 inch. I'm happy with that as it should translate to very little movement on the door openings.



I was also able to salvage some of Grant Leesers pretty motor mounts.




I got the gas tank brackets re-positioned also and now I can pull the tanks without having to drop the shock absorbers which was a goal.

Body tub goes on next. It will require modification at the back to clear the 2x2 that was added to the kickup.