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Thread: Frame suggestions

  1. #1

    Frame suggestions

    I know this is a bit off topic as far as Fiero's go, but as some of you may know, I am planning a ground up custom build of an F40.

    I am in the process of designing the frame, and have pretty much decided on using square tube for the entire undertray and most of the vertical supports with round tube for the roof supports.

    Any suggestions on what size tubing to use?

    I was thinking 2" square for the base/undertray with 1.5" square for the verticals and 1" round for the roof.

    Would this be adequate, do you think? Or should it be a bit more?

    Thanks in advance.

  2. #2

    Re: Frame suggestions

    From what I've seen of the custom lambo chassis that looks about right. I read a post where a welder recommended wall thicknesses of .065 -.125.

    Do you have a good chassis book? Chassis Engineering by Herb Adams is good stuff.

  3. #3

    Re: Frame suggestions

    I am researching doing something a bit similar, not as extensive though... I have an F-40 kit I want stretch to get the rear deminsions a bit more accurate and shorten the nose. If the measurements work out here is what I want to be able to do:

    Stretch the rear, and remove the trunk, the F-40 rear grill vents the engine bay and has a clear line of sight to the back of the transaxel and Cat and exhaust. Modify the frame to accept C5 Suspension arms and the Transverse springs and brakes. Rather than stretch the rear frame rail, I want to stretch the chasis beind the doors... this will give the cabin more room like the Ferrari and allow for real side rear windows. Modify the rear to accept either ferrari curved glass or the MR2 rear glass... MR2 is cheaper. The Automoblila book on the F-40 shows good diagrams of frame components and the tubing layout for the engine bay. Good reference for your project. I think that doing an entire frame is probably unnecessary, since the Fiero cockpit is a good starting point. IMO.

    Are you modifying a current kit for the Fiberglass, or are you doing it from scratch?

    2 inch box tubing has been used for many a frame build up. By sticking with modifing the Fiero and an existing kit you can drastically reduce the time of fabrication, and cost. Just a thought.

    Of course I am open to any ideas you might have since this has been a project I have toyed with for years, I never completed the kit because I always wanted to modify it. At this point I may be forced to abandon the idea for a while... depends on what happens next (Family health problems).

    Anyway, Once I figure out the deminsions, I hope I will have room for a longitudinal engine install. Shouldnt be a problem since I have seen a Fiero GT with a longitudinal chevy v8 and toronado trans shoe-horned into it. But if it will work, the the engine idea is the LS6 with a porsche transaxel. The LS6 revs close to 7000 stock, is a very good torque engine, 405HP 400Ft lbs, and winds up like a dream. With slight modifications it can easily get 420-440HP. LS1 edit can use a laptop to program for changes in the stock PCM. This with reliability, good fuel economy. (my 02 vette gets 32 MPG interstate at 70-80 MPH, and it has only airbox mods and a K&N) Couple these pluses with the fact that exhaust Fab for this setup would be too easy, and I think you have a winner combination. (and close to real Ferrari HP) And of course, with the extra room generated you could always do something insane like twin turbo's for even greater output.

  4. #4

    Re: Frame suggestions

    Oh, and one more note: Nascar chasis use something in the neighbor hood of 2" Round tubing, all over the vehicle. For something that extensive you would want ot invest in a madrel bender, or at least suck up to someone who has access to one. If you get one I will suck up to you! LOL And a tubing notcher. Just for a good reasource you can easily get your hands on to see how they build the cages, get a copy, or rent one, of Days of Thunder. You can learn alot just by watching the build process and examining how the chasis cage is layed out. (The barn sequence when they build his car) I have watched a few programs that covered nascar build ups and all of them basically fabricate what you are talking about, except for the Round tubing. The F-40 uses a combination of round and rectangular in the engine bay.


  5. #5

    Re: Frame suggestions

    I'm planning on doing the body from scratch. I purchased a really good 3D model of the F40 that needs a bit of tweaking to get it right. I plan on making molds from it too so that if the "unexpected" happens, I can replace a panel. May look at doing turnkeys too eventually (in about 10 years at the current pace ) as it would be virtually useless just selling the body panels as they wouldn't fit on any stock chassis (except maybe a real F40 chassis).

    I have a good majority of the frame plans done up (rough draft), but still need to edit it for some discrepancies in the 3D model.

    If you could scan some of those frame pics in your F40 book for me it would a big help. If not, don't worry about it though.

    The main reason I am looking at doing the frame myself (at least the design. will probably have to get someone to physically build it to my specs) is that I just don't want the hassle of so many mods to the fiero frame. Basically, the rear would have to be lengthened, front shortened, tub moved forward, roof lowered......just too much to worry about

    I'm also looking at using the Audi 3.6 V8 with a lower compression ratio (10.5:1 stock - I want about 8:1 stock) and adding the twin turbos that the real car has. Mate that to a Porsche 915 or G50 trans. I want it to be as close to the real car as possible.

    Anyways, thanks for the info.

  6. #6

    Re: Frame suggestions

    OK, your request is fulfilled! I have the larger files saved also in case you need them emailed. (Planning ahead)

    The two frame shots show you the simplicity of the frame and how the body panels attach.

    This is a cutaway which I find very usefull for locating gas tanks, of which there are two, one on either side, and the like. Doors are comosite and very lite, the whole body is Kevlar and carbon fiber. And note, the doors have no structural steel, and no interior door panels. The windows are lexan and the section that opens slide back in a side track built into the main lexan piece in the door frame.

    Engine bay, which shows the use of mixed tubing. Note the koni coil overs.

    And the suspension, which will show you how your attachment points will be.

    Now, if pure accuracy is needed then by all means make a whole cage. But again, I will offer this opinion, even cutting up the Fiero chasis and welding on a simple front and rear, and even if you chop the roof and weld in roll bars like pictured above, you would still save a whole lot of time. By the time you Fab doors and mounting points and electrical grounds and brake lines, etc etc, you are really gonna be into some time and money. Use what you can, a lot of the work is done for you already. If you add the rear frame and top and front frame, it really should be quite simple. But hey, if you want to go for it, well, then go for it. If we could find a real body to splash, I might try to tackle this frame idea too. Note that the F-40 is low on creature comforts. The interior is sparse, it is a race car made legal for the street.

    C4/C5 suspension would be perfect, and relatively cheap to get. Compomotive makes the perfect wheel and they will do it for any bolt pattern. I suggest the c5 brakes, they stop the c5 faster than most of the real Ferrari's (60-0 118 ft). And cheaper than Brembo. Even if you use the Baer Eradispeed rotors. has an Aurora Manual for racing modifications. I don't know that much about the Audi's, but the aurora was used in Indy and it really sounded Ferrari-ish... they can really tach up and put out 700HP or more naturally aspirated. Indy cars were doing 235Mph with restrictors (and very short straight-aways). If you have not heard an Indy car in person, then trust me, it is a more than viable alternative. Even Turbocharged. (the sound of those engines as they went by gave my girlfriend THO's - titty hard ons!! no lie!


  7. #7

    Re: Frame suggestions

    Hey, here's another idea!

    Check out my post to F40 fans... and my suspicions as to how that kit evolved, you might like this idea, since it would be a whole lot faster, cheaper, and technically you'd own a Ferrari.

    Then check out this link:

    For 12,500 and some fiberglass work, you'd have your f-40.

  8. #8

    Re: Frame suggestions

    Ok, last item, I need to go to bed, it 5:30 AM!

    I think you can download a trial software to view this.

  9. #9
    Senior Member
    Join Date
    Jan 2002

    Re: Frame suggestions

    Don't mix round and square, stick with square. 2" is very heavy and is well beyond the requirements.
    Round is much harder to work with and to weld. In a true space frame you try to direct forces along the axis of the material that is why you do not need large dimensional steel. on parts where forces are against the axis like the A pillar you would use a stronger material.

  10. #10

    Re: Frame suggestions

    I already have a couple of those pics, but if you don't mind emailing me the set it would be greatly appreciated.

    I am well aware of some of the things you had mentioned - no support in the door, it's actually just inside the door in the coc kpit (<---stupid filter changes that to "thingypit" if it's together), no "comforts" etc. *But hey, that's half the fun.Who needs a stereo (wouldn't be able to hear it ayways ).

    I've been a fan of this car since the day I first saw one, and just can't afford the 1/2 million to buy one.

    I would love to be able to splash the real panels, but when just the front clip lists for about $30K US, I don't think many F40 owners would be willing to let someone do that

    Anyways, you can email the pics to

    Thanks a million.

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