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Thread: Interior Prep: I have questions.

  1. #1
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    Interior Prep: I have questions.

    Hi all. Some friends and I are starting a build of a Z3 coupe (3.0) for WRL GP2 class. None of us has done an entire racecar build before, and I had a couple of general questions for the board.
    We have a bender on the way for our cage, and have a couple of weeks before we start that install. I am currently working on the wire harness, eliminating all the extra wires, etc.
    As soon as that is finished, we will need to get started on the interior.
    So the plan is to remove all the extra brackets and stuff that is throughout the interior. They are all spot welded on. What is the best way to get rid of these? Is drilling the spotwelds best, or simply cutting the brackets off as close to the body as possible?
    Secondly, (bear in mind, I know nothing about paint) we plan on painting the interior, after the cage install. Does the interior need to be sanded down to metal, or is there a paint product that I don't know about that we can just paint over the original paint? (car has no rust, and is very clean inside.) Is there a product that is preferred? (i.e POR 15, or something like) that does not take a lot of experience to get a decent result?

  2. #2
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    On my track rat I cut the unnecessary brackets off as close as I could and ground the remaining metal down to the body. I'm not a painter so I can only say what I've seen on other car builds, but many of them who painted the interior and cage to match scuffed the paint like you would an exterior paint job, then primed and painted. From what I've been told it's more difficult on the interior due to more angles/curves/hard to reach places. Not that the painting may be more difficult, but the prep is more time consuming.

    As far as the cage goes, the advice I was given early on when I started building was that unless you are a very experienced welder (with a working knowledge of how load bearing structures function) you should pay to have someone who is experienced build your cage. I couldn't weld a clean junction if my life depended on it so it was a no-brainer for me, but just something to think about.

  3. #3
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    So when you cut the brackets off, were there like sharp edges/things for hoses,wiring, etc to get snagged on?
    On the cage, it is a team effort. We have a pipe fitter, and a guy that builds metal staircases and railings for a living. We should have the basics covered.

  4. #4
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    Quote Originally Posted by bionicbelly View Post
    So when you cut the brackets off, were there like sharp edges/things for hoses,wiring, etc to get snagged on?
    On the cage, it is a team effort. We have a pipe fitter, and a guy that builds metal staircases and railings for a living. We should have the basics covered.
    Buy a spot weld cutter, and get after it

    Doing this on my car now, tore it back down to bare chassis-ish and removing what I didn't on the initial build (like the secondary firewall). Combination of spot weld cutter and angle grinder. Pretty simple, whatever is left just grind it flush.

  5. #5
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    Quote Originally Posted by Matt330LS View Post
    but many of them who painted the interior match scuffed the paint like you would an exterior paint job, then primed and painted
    ScotchBrite pads (https://www.3m.com/3M/en_US/company-...8711730&rt=rud) from the automotive supply store (auto painting supplies) work awesome for scuffing the surface to prep for painting. I've used the reds for the job many times in the past. Then as a final prep step (after vacuuming up all the dust/dirt/debris) is a good wipe down with automotive wax and grease remover.

  6. #6
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    Awesome. This info is much appreciated.

  7. #7
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    Quote Originally Posted by bionicbelly View Post
    So when you cut the brackets off, were there like sharp edges/things for hoses,wiring, etc to get snagged on?
    Initially when I cut them off there were but I ground down anything sharp.

  8. #8
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    On the cage, it is a team effort. We have a pipe fitter, and a guy that builds metal staircases and railings for a living.
    This is a bad idea. Of all the safety equipment you need to invest in when you build a race car, the cage is probably THE most important place where genuine engineering *and* proper construction really, really matter. Besides, the technical scrutineer may fail your cage when you go to have the car inspected for your logbook. If he/she deems it not to be safe, you're back to square one anyway.

    Find someone who has done road race car cage builds before (not drag racing), hopefully in the same kind of car you're building, and either have them do it for you or listen very carefully to their advice.
    Last edited by emoore924; 11-26-2018 at 08:24 PM.

  9. #9
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    So, I got some cheap spot weld drill bits from harbor freight. https://www.harborfreight.com/38-in-...ter-63657.html They work pretty well, as long as you go through and hit each spot weld with a little pilot hole. Don't have to drill all the way through, just a little divot to keep the spring loaded center pin from walking.
    There will be a bit of grinding after everything is off, but I think this will leave a good enough finish.

    Thanks to all for the helpful advice.

  10. #10
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    If I shouldn't do my own cage work because my life depends on it, I guess I should quit doing my own brakes, hubs, fuel system, fire suppression, seat installation . . . .
    Last edited by JBasham; 12-07-2018 at 01:40 PM.
    If God meant for man to motor-swap LS engines into track cars, He wouldn't have created Corvettes.

  11. #11
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    Quote Originally Posted by JBasham View Post
    If I shouldn't do my own cage work because my life depends on it, I guess I should quit doing my own brakes, hubs, fuel system, fire suppression, seat installation . . . .
    Come on, really? That's a poor argument and you know it. None of those items are anything close to designing and welding such a significant structural item.

  12. #12
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    I race an E36 M3 and it is a forgiving car on track and there has been multiple off track events.
    The Z3 ould not be my choice to race. It is a much more difficult car to control at the limit.
    If you guys have 10 years experience racing you can ignore my comment.
    Good luck with the build.

  13. #13
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    Quote Originally Posted by Franky goes View Post
    I race an E36 M3 and it is a forgiving car on track and there has been multiple off track events.
    The Z3 ould not be my choice to race. It is a much more difficult car to control at the limit.
    If you guys have 10 years experience racing you can ignore my comment.
    Good luck with the build.
    I know it is far from the ideal chassis. I have had it for eight years now, and bought it to autocross and race. The year that I wrecked it, I won several time trials in it, and set a few track records. It absolutely is more difficult to control at the limit, but I have sorted it to be fairly predictable, and honestly, it fits my style.

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