Frame and X Member Design for Model A Coupe

Hey guys,

I've tried my hand at searching the subject and haven't quite found all the info Im looking for. On that subject, if you do know of a previous thread, I would love to see it.

I've been tinkering around with designing my frame for my '29 Model A coupe project with a 500 Caddy/Turbo 400 drivetrain and a good ol' 9 inch rear. The front of the frame will be 2x6 rectangle tubing back to the cowl and down to 2x4 from the cowl back.

This is my first build so Im looking for the great knowledge and experience from you fella's on the HAMB. Considering the torque that this engine will put out, I want to build the frame right the first time. Im most concerned with chassis twist and flex.

If anyone can help me in the right direction for the best/strongest X member design it would be great. I also read on another thread, that building up (roll cage) helps substantially with twist. So any and all input will be greatly appreciated.

Littleman did a great job on his A. I was thinking something similar with the addition of a round tube brace around the cowl and behind the seat and to the rear for additional twist resistance. So my question is really how to design it properly to avoid twist. I dont want to just build something that doesnt function and takes up space.

Thanks

 

Chassis engineering or Daigles? have the best designs. Avoid the tubular things. They are worthless and just take up room.You want a full X member with a central torque box to carry the load from one rail to the other. I would run the 2x6 full length.

 

Are you planning on racing your coupe? The reason I ask is that sounds like a stout frame for a street car.

Anyways here's my frame which sounds similar to what you want to do.
My front rails are 2" x 5" tapered done to 2-5/8". The rest of the frame is 2" x 4" with a x-member made out of the same. If you do the solid x-member remember to make access holes for fuel, trans lines etc. I did mine afterwards and it was kind of a pain in the ass.

FWIW the guy that did my cage said I overbuilt my frame. He's built quite a few drag chassis and told me I could of got away with 2" x 3" because of my cage.

 

Duece rails with that heavy powertrain.

Look at some of the X-member designs Randy does here. Great engineering and he can sell you anything from a full roller to just the bent parts of the x-member.

http://www.lrschassis.com/

 

Matt, I was hoping you might chime in on this. I have been drooling over your truck ever since I found the build. I actually printed off a picture of it and hung it in my garage. Thank you for the input. I just want it to be right... The first time! I plan on mostly street with the occasional run down the strip just for grins. Not for competition. Does your chassis twist much under wide open throttle and and cause any issues with the cab/windows/etc? That's what I worry about on mine. I dont want to stress the body or anything else.

Andy, tell me more about the "central torque box" if you dont mind.

Thanks guys

 

Scottybaccus, awesome link! Thank you.

 

Thanks for the compliment.

My chassis is very stout, I can't feel any movement what so ever. I also don't have good tires on it yet, so the tires just spin.

You can hurt anything building too stout of a frame. So if you have any doubts build it heavy. I'm sure your 500 caddy will move your coupe just fine.

You should PM Littleman, his truck is on a boxed A frame. I want to say he was in the 10's before he had issues with flexing. Now he's running 9.70's with the same setup!

Feel free to shoot me a PM if you have any questions. Just remember like you I was making educated guesses.