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Thread: Modern-day Miura

  1. #61
    Awesome build Joel!

  2. #62
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    You've changed the appearance of the Corvette door glass's shape along the trailing edge by covering it with the up-swooping rear door post. That works to fool the eye but without door glass that's actually rounded at the back, I think you're going to have problems when you try to lower the window. The bottom corner of the very square and vertical trailing edge of the Corvette glass will not likely go very far down before interfering with the inside of the very rounded trailing edge of the door. You may have to alter the path of the tracks to swing the rear edge of the glass downward rather than have it travel in a more typical movement. Though that will also limit the amount you can lower it.

  3. #63
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by jm14 View Post
    Awesome build Joel!
    JM: thanks for following the build.
    Joel Heinke
    Be original; don't be afraid of being bold!

  4. #64
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    Quote Originally Posted by Bloozberry View Post
    You've changed the appearance of the Corvette door glass's shape along the trailing edge by covering it with the up-swooping rear door post. That works to fool the eye but without door glass that's actually rounded at the back, I think you're going to have problems when you try to lower the window. The bottom corner of the very square and vertical trailing edge of the Corvette glass will not likely go very far down before interfering with the inside of the very rounded trailing edge of the door. You may have to alter the path of the tracks to swing the rear edge of the glass downward rather than have it travel in a more typical movement. Though that will also limit the amount you can lower it.
    Bloozberry: You're right, making sure the Corvette side window can open and shut correctly in the Miura body context is a key issue to work out. The root cause of the issue isn't from the trailing edge shape though as the rear bottom corner on Corvette glass is actually rounded more than original Miura side glass. I think the issue is because the Corvette window is a completely frameless design and Muira has a frame rail up the rear edge to locate and support it. With the window completely raised on Corvette, there's still 6 inches of glass below the exterior seal inside the door. This extra unseen glass is used to lever the window edges against the door opening seal. On the original Miura, the rear frame rail holds the glass against the seal. Bottom line, Corvette side window glass is taller than Miura glass and I'll need to figure out a way around that to resolve the issue.

    I found these pictures of Miura door insides in my archives:





    Yes, that's a very complicated set of cables and pulleys used to raise/lower the side glass. I'm glad I don't need to replicate that mechanism in my car

    The one thing I've noticed from these pictures is that the window doesn't retract all the way down into the door when opened. This isn't really surprising to me as the Miura isn't a "hang your elbow out the window" kind of car. I'll most certainly end up with exposed side window glass using the Corvette windows.

    I do have a question for anyone familiar with electric window regulators/lifts. It appears that the motor raises and lowers the window glass until it reaches a physical stop. In other words, the electric motor is stalled by a stop and not turned off by some sort of locating switch. I've looked and can't find any switches like that so my deduction is that the electric motor is of a design that doesn't get damaged if/when stalled. If this is true, I might just be able to raise the entire lift mechanism higher but leave the top stop where it currently is. This will keep the bottom of the window up higher when retracted but will also stop the window vertically at its current raised level.
    Joel Heinke
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  5. #65
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    Quote Originally Posted by C5GTO View Post
    I do have a question for anyone familiar with electric window regulators/lifts. It appears that the motor raises and lowers the window glass until it reaches a physical stop. In other words, the electric motor is stalled by a stop and not turned off by some sort of locating switch.
    The window is probably controlled by a current sensing circuit similar to 2nd gen Fiero headlights, in case you're familiar with those. Once the window reaches the physical stop, the electrical current spikes, which is sensed by a solid state circuit that then turns off the power. It'll either be in a separate window control module (as in the 87-88 Fiero), or integrated with the BCM (Body Control Module).

  6. #66
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by Bloozberry View Post
    The window is probably controlled by a current sensing circuit similar to 2nd gen Fiero headlights, in case you're familiar with those. Once the window reaches the physical stop, the electrical current spikes, which is sensed by a solid state circuit that then turns off the power. It'll either be in a separate window control module (as in the 87-88 Fiero), or integrated with the BCM (Body Control Module).
    Bloozberry: thanks for this information. There's 6 heavy gauge wires connected to the window switches and only 2 of those go to each of the motors. I can also see a small circuit board on the backside of the main/driver side switch. So I'm guessing GM built the window control module into the main switch on the C4 Corvette.
    Joel Heinke
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  7. #67
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    Post Top chop - well a virtual chop anyway

    The previous feedback was that the roof line was sitting too high and this resulted in a bloated look. So I lowered the windshield/cowl/door unit such that the top of the windshield frame is now 43 inches from the ground, so a 1.5 inch chop. Iím guessing this will give a roof height of about 44 inches. The car bottom is set at 5.5 inches from ground, so where I want it to be.

    I repeated the routine of pushing the car out of the garage, taking photographs, and adding on the bodywork with Photoshop. The top car is an unaltered Miura SV, the middle is the stretched rendition Superleggera/Mark did, and the bottom is my chassis with bodywork copied from top car (and tweaked to fit).



    I think the top chop has made a world of difference in the look. It gives me confidence that the Corvette windshield and side glass will work out. I think thereís still room for more body shape refinement but Iím happy with the vertical windshield placement now. Iím also going to start experimenting with shortening the electric side window lifts. It looks like I need to take about 4 inches out of the 20 inch tall lifts while retaining the current fore/aft closed window placement. I think itís doable but will take so work to figure out how.
    Joel Heinke
    Be original; don't be afraid of being bold!

  8. #68
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    Post Attaching windshield/doorpost assembly

    The previous mockups gave me confidence that the proper horizontal and vertical placement for the windshield has been determined. It was now time to attach the windshield and door post assembly to the chassis. The first step is to ensure the chassis and windshield are leveled up. I use a digital level for this to ensure precision down to a 10th of a degree.



    I had used small wooden blocks to set the windshield height during mockup and hereís what I had to start with.



    I decided the drilled out spot weld holes across the doorpost bottom would make for good bolting points. A small block of ĺĒ thick aluminum was used for bottom mount such that I could tie the floor and the small chassis side upright together with the door post. A second ĺĒ aluminum block was used above that with bolts running from chassis upright through to the door post.



    This gives two very strong mounting points for the door post. Next some triangulation was added. The Corvette door posts have a hood latch mount at the front top and these had triangulation bars running down to the frame. As luck would have it, these bars could be re-used along with the hood latches. I cut the frame end off the bar at an angle such that I could weld an attachment plate on it and then bolt it into the chassis right next to the front bulkhead.



    With these mounting points, the windshield is now firmly and securely mounted to the chassis. I will add some sheet aluminum mounts on the rear and backside of the door posts even though theyíll probably only add marginal additional strength.

    The way the windshield and door post mounts worked out, it really looks like the chassis was designed for the C4 Corvette assembly as a donor. Thereís even provision for a speaker mount in the chassis foot box and the door post wraps right around where the speaker is positioned. Itís like these two assemblies were meant to go together but the truth is that Charlie included what he thought Iíd need in the chassis with no idea that Iíd be using these parts in the car. So far, luck has really been on my side for the Miura project!
    Joel Heinke
    Be original; don't be afraid of being bold!

  9. #69
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    Post Mocking up the doors

    With the door posts now in final position, itís time to figure out what can be done to convert the Corvette doors into Miura doors. I want to keep the Corvette door glass and needed to figure out what modification is needed to the electric window regulator to shorten the door height. Hereís the door I have with the window in the down position as a starting point.



    Ideally, the door should be shortened by 5 inches with that coming off the bottom side. I came to this number from using the height of the Miura rocker panel that is positioned under the door. From close inspection of the window lift mechanism, I found that 4 inches could be taken off the top mount without disrupting the rivets attaching the guide channels to the frame.

    So I removed the window glass and lift mechanism from the door and cut the 4 inches off. Using wood blocks, the lift mechanism was temporarily re-installed and secured enough raise and lower the glass to ensure the door window could be properly aligned to the windshield. Given the vertical guide sits at a slight angle, the lift mechanism needed to be moved rearward about ĺ inch to make up for the 4 inch higher vertical positioning. With this, the side window now closes tightly when raised to the seal on the windshield post.



    Next I wanted to see how much of the side window would stay exposed when it was completely lowered. I also wanted to see how much could be taken from the door bottom. I lowered the door glass down till it approached the wood blocks. It turns out the window bottom and lower door hinge bolts are at about the same height. I decided to add some masking tape to give me a sense for the Miura door outline.



    All in all, a successful mock-up exercise. It looks like I can easily cut 4 inches from the door bottom. While 5 inches is ideal, my next step will be to get a visual confirmation if 4 inches will be enough. To get the extra inch, the lower door hinge would need to be re-positioned upward and more extensive door window lift modifications would be required. In other words, a bunch of work just to get that next inch. So I think it might just be worthwhile to push the chassis outside for more pictures and Photoshopping to see if an inch shorter rocker panel will work.
    Joel Heinke
    Be original; don't be afraid of being bold!

  10. #70
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    Post Validating rocker height

    My primary objective with this round of Photoshop work was to validate the visual look of the rocker panel height with cutting 4 inches off the bottom of the Corvette door frames. I had marked the door frames with blue masking tape for the photo session so I could use this as a marker for rocker panel placement.

    Hereís the resulting mockup. Actual Miura SV on top, my Miura with body work added via Photoshop on the bottom.



    Well for one thing, my Photoshop skills are getting better with practice. I went the extra step this time and added wheelbase markers, a neutral background and included the planned Campo wheels in the intended tire height. I also took the photo of my chassis from further back to reduce the fisheye effect and thus give a more accurate placement for wheels and the masking tape door markers.

    My conclusion is that the rocker panels at this height look fine. In other words, thereís no need for extra work to give another inch of rocker panel height. I did determine that I hadnít angled the back edge of the doors enough. The bottom rear corner needs to move forward by 2 inches. Iíll make this adjustment to the marker masking tape and verify the door frame will still clear the window glass when fully lowered.

    The other thing I added while Photoshopping was a windshield post in the body color with polished trim. This did make a noticeable difference in the visual look. My conclusion from this is that Iíll need to find a way to add a paintable windshield pillar down the Corvette windshield post. The standard Corvette windshield trim is a very narrow strip of blacked out aluminum. Iíll need to figure out a way to replace this with a 1.5 inch wide strip of bodywork with some shiny trim on both sides.

    I think Iím starting to capture the Miura look better with this picture but itís still not quite there. I didnít fiddle with it too much to refine the overall look as my real objective was to check the rocker panel height.
    Joel Heinke
    Be original; don't be afraid of being bold!

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