Tube Rear end, major chassis modification questions. Scion FR-UTE!
 

Hi All,
2 months ago I bought my 2013 FR-S with full intention to build it to STX Autocross spec. I had some success in the 2 AutoXs I took it to. Then decided to take it to my first ever track day.

I was putting down some really good times and was very pleased with myself, until my little oopsies.

This leaves me with a car that has a messed up rear end. I bought a used rear subframe and checked the mounting locations. The only one that has shifted is the passenger rear. It is pushed into the center of the car about 1/2"

I plan on tubing out the rear end of the car and rebuilding it into a Ute. It is too far gone to go back to OEM, and I have always wanted to turn a car into a little truck!

Question is, Obviously I will have to add some roll bars and chassis stiffening bars. Has anyone else tubed out the rear end and have some guidance on where best to add the stiffening bars?


Here is the cars current condition:https://i.imgur.com/p9jGMbF.jpg

I hope to start fabrication next week!

I'm not too sure where to add bars, but have you looked at doing a full roll cage and just running the rear bars towards the old trunk end?
Between that and welding in a bar straight across at the B pillars almost like a harness bar would be where I would start.

I don't want to do a full roll cage quite yet, but we will be adding a roll bar and harness bar w/ supports to the trunk area. My crash bent my stock seat all out of shape and luckily I have a 5 point harness and Sparco Sprint in my garage to replace it with. So harness bar and a support between the B pillars will for sure happen.

What are your goals for the car? Is it going to be a track only car? Are you planning on changing suspension mounting points?

- Andrew

Originally the goal was a nationally competitive STX car and daily. Unfortunately the STX dreams are out the window. At this point the goal is to get the car back to daily driver status, but I will be taking it to the track again.

Would changing the rear strut mounting points be beneficial in anyway? We can certainly do that. I was planning on using the OE rear subframe mount locations.

I am definitely open to suggestions. I haven't looked at suspension geometry too much yet.

If you have the capability of returning the car to daily driver status, then I'm confused as to why STX is out the window? Unless you mean that returning to DD would be accomplished with the frankencage thing you're talking about...

Most of the time when someone's building something like that with serious metal work, they make some changes to the suspension as well. But for your uses, if it all packages together with the OE subframe, you don't necessarily have to.

Or make it a baja truck. :)

- Andrew

Ok, its going to come across like I am trying to be a d%&$, but I assure you I am not, I am speaking from years of fabrication experience building custom ground up "cars."

Unless you are a suspension expert, keep the geometry absolutely stock, Toybaru did a great job at it.

What is your fabrication skill level?
Have you really thought about your goals for this car? Planning saves a lot of headaches.

You crashed first track day? Get a $2,000 Miata in the meantime and flog that, while you build this, keeps the ambition up and skills improving.

The term stiffening bars makes me cringe a bit, with the rear looking like it is and being unibody...those rear "frame rails" are probably splayed out quite a large amount. I would bring those back in spec, tack a bar or two (angle iron works and its cheap), then once you start grinding, welding, cutting those areas, they will move significantly less.

To Start...

-Starting fabrication next week? Need a solid plan, I often use masking tape to "rough" out a plan of attack.

-I would get a boat load of dimensions from a known good car. Starting a project from an inconsistent base results in poor fitment.

-Is the rear subframe verified straight?

-A good first goal is getting a rear window to fit.

Thank you for all the information. Girlfriend has an FRS and my buddy is actually doing all the fab work (and teaching me in the process). He has multiple years of experience building roll cages and tube frames for proper race cars. He also has a stock FRS.

I have other cars to drive, so no need for another little sports car!

We haven't yet measured against a known good vehicle, but we have checked all the rear subframe points and only the one is out of location. Obviously we will double check with a known good FRS.

I have a 2nd gen MR2 that I have overhauled every suspension component on and mapped out suspension geometry using SusProg 3D. That being said I didn't plan on changing the mounting locations. I love the way this car handles. I will look into suspension geometries in the future, but don't plan on changing them.

Right now we are trying to get the rear end built up enough that we can at least drive it if absolutely necessary. Rear window and bed would be next.

I do appreciate the insight.

+1 to all of this.

- Andrew

I am torn. Do I lift it and make a Scion Baja, or lower it and have a race "truck"


Decisions, Decisions...

For now we are just going to get it rolling again.

That is exactly it.
The car is too far gone to try and repair back to OE, and this gives me an excuse to do something weird. I would still be able to daily it with the tube rear end and half cage.

Obviously that kind of work kicks it out of Street Touring.

Awesome :thumbup: I have seen too many projects get scrapped because people run out of steam or get in over their heads.

Looking forward to the progress :thumbsup:

Not trying to rain on your parade, but what you're talking about sounds like a lot more work than returning it to stock...