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Seibon Carbon Trunk Install on BMW E92 M3

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  • Seibon Carbon Trunk Install on BMW E92 M3

    As we explained in this forum thread there are two types of carbon fiber: motorsport grade dry carbon and "hybrid" carbon-fiberglass with a glossy gel coat for street or dual purpose use. Virtually all of the parts sold by Seibon are the hybrid style, which can be used without the need for adding a UV protecting paint or wrap on the exterior.

    Their parts have a shiny, sparkly carbon fiber with a beautiful weave that attracts the eye, and features that allow for all of the OEM bits and pieces to be attached. Yet these always seem to drop some pounds over the OEM metal panels.

    For this install we had a customer who bought a semi-stripped, caged BMW E92 M3 that wanted to race it at a club style road course where he would keep the car... but still wanted to be able to drive it on the street.

    Many OEMs are seeing the benefit of using carbon fiber in stock vehicles, like this 2017 Audi R8 above - which has visible carbon accents and a wing in addition to the carbon used in the chassis.

    This E92 M3 had the OEM carbon fiber roof option, which includes a glossy gel coated carbon panel that is left bare, right from BMW. So keeping a glossy carbon trunk "bare" made sense in this case. We looked at the options and reached out to our friends at Seibon for this hybrid carbon/composite trunk.

    The "stock" pictures looked great and the outer finish was what the customer wanted. What did it weigh? Nobody knows, but we soon would. The rear trunk shape was modified on this Seibon E92 unit to mimic the popular E46 M3 "CSL" duck tail spoiler.

    It seemed from the many Seibon "stock images" above that this might be a full carbon part on the inner layer, but they never showed that side of the trunk structure in their pics. We noticed that many openings looked to be pre-cut to fit all of the OEM lights, latches, and hardware.

    We found that the inside structure (not visible from the outside) was fiberglass, but that wasn't really a surprise or disappointment, as they told us this was a hybrid composite part. The flat black inner structures are all fiberglass and the outer shell is glossy carbon fiber.

    The final weight of the Seibon hybrid carbon trunk was 12.7 pounds vs the OEM steel hood at 26.2. That means this hybrid carbon trunk drops 13.5 pounds, which is a 51.5% weight savings. Not too shabby, and it looks great. Let's talk about the installation next.


    Brad at our shop spent a tick over 5 hours trimming, fitting, and assembling the various items from the stock trunk and transferring them onto the new carbon trunk.

    Step one was removing the stock trunk, and several wiring assemblies had to be unplugged first. A lot of pieces and parts had to be removed from the old trunk and were stowed inside the spare tire well at this point.

    While there were holes cut into the backside of the fiberglass structure to mount most items, there was still a good bit of trimming needed on the carbon trunk to fit all of the factory parts - which is normal on most aftermarket composite body panels. There were a variety of tools used, from sanders to files, even a die grinder. All of this creates dust so use proper respiratory protection.

    The factory trunk lock cylinder / remote solenoid took a good bit of time to fit into place. This required trimming the backside square hole larger, the outer lock cylinder hole was fit to the part, and even the OEM solenoid itself had a plastic "shelf" trimmed off to make it fit down into the hole on the back side.

    These three square openings for the license plate lights and release handle also took some time to fit, but it all looks perfect after some filing and sanding of the openings.

    The stock rubber trunk "bumpers" had to be removed from the OEM trunk and riveted to the Seibon unit. The factory uses plastic rivets but we used a pair of regular aluminum pop rivets on each bumper. The latch assembly bolts into threaded inserts in the inner structure - like everything else that unbolted from the stock trunk. That's a nice feature for street use, where you need all of these lights and latches.

    Once all of the pieces were bolted into the new trunk Brad fine tuned the fit of the new trunk to the surrounding body work, getting the body lines symmetrical - it fits really well.

    Seibon recommends against reinstalling the two OEM gas charged lift struts, due to the lower weight of the carbon trunk. We found that it worked fine with one strut installed, as shown above. Feels like an OEM trunk support now with half the lift assist.

    Overall we spent the time we expected to for this installation, and the overall look was outstanding. The body lines fit up like an OEM part, and with a 51.5% weight loss and a glossy finish that doesn't need paint, we call this one a win.

    Last edited by modernbeat; 02-19-2018, 05:29 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev