Strut tower failures are a known issue on the 991 generations GT3s and the same-era GT4s. They typically occur from a sharp impact such as curbing at the track. I’m sure every 911 and Cayman/Boxster of the same era has the same vulnerability, it’s just that the GT3 and GT4 owners push their cars harder than the typical Porsche owner.
E-Motion Engineering decided to do something about it and designed a reinforcement brace system that’s superior to the factory Porsche Motorsport strut tower caps. I say ‘system’ because the setup is significantly stronger than the Motorsport caps and typical simple bar that connects the tops of the strut towers. Aside from the reinforcement brace system helping to prevent strut tower failure, the brace system significantly increases the rigidity of the frontend of the chassis.
I appreciate good packaging. Everything was well-protected in the cardboard box that the components were shipped in.
The E-Motion install video covers all the major steps. My car, having stock SPASM dampers, has some variation compared to the GT car with KW dampers in the video. Step 1 is to remove the main center cover. You’ll need to remove the two side covers also.
I pulled up this plastic housing that holds the air compressor; most new cars come with a compressor and goop instead of a spare tire. It’s annoying, but I get the desire to reduce weight (emissions/fuel economy, acceleration) and costs. The air compressor would live under the brace making it very inconvenient to get to in an emergency situation. So, I’ll just put the compressor into the frunk and ditch this housing for some weight reduction.
The air filter housing has a few clips on the backside of the lid that are a little tricky to get to.
E-Motion made a tool to mark where to cut the lid. I took some measurements instead of fabricating a tool.
10 comments
Shame they didn’t double bolt the bar. The bar can only handle tension and compression and no bending moment as designed.
Spoke too soon. My bad. Nice tie in to the subframe. Didn’t see it initially.
Yup, it’s a super beefy support bar for the heavy factory battery. Quick search shows the factory battery is about 45 lbs.
Strut/shock tower loads are basically vertical-a horizontal bar does little but add weight.
Remember this is a strut setup, so lateral loads are transmitted into to strut towers. Notice Porsche has black bars going from the strut towers to the rear bulkhead to add strength. Uneven vertical loading, from bumps or cornering, will try to twist the chassis and a rigid horizontal bar can add some resistance against that twisting. This particular design from E-Motion ties the horizontal bar to the strong battery brace that runs the span of of the chassis, boxing it in. Additionally, by tying down the horizontal bar to the battery brace bar, it’s clamping down on the top of the strut towers to help resist the vertical loads which have lead to strut tower failure on this chassis.
Lateral loads at the top of the strut are quite light as most lateral loading goes through the lower arm to the chassis.
I’ll calculate some approximate numbers. My car is about 3000lbs with 45%/55% weight distribution and I’ve pulled 1.4G lateral. At max lateral G, we can assume the inside front tire is not loaded to simplify the napkin calculation. I assumed the control arm is 6″ above ground and the strut tower is 24″ above ground. Crunching the numbers, it’s about 1890lbs at the tire contact patch, 2520 lbs at the control arm joint, and 630lbs at the strut tower. Those are all the lateral loads. Remember, there’s still the vertical load on the strut tower that’s about 1350lbs. And that vertical load is trying to cause displacement of the strut tower relative to the other strut tower; i.e. twisting the chassis. And the E-motion brace setup resists that vertical displacement and lateral loads. If you didn’t already look up GT4 strut tower failures, go ahead and look.
Photos of the strut tower failure imply a vertical component caused the failure, not a lateral load. Vertical loads are considerable when the suspension is fully compressed. That bar you are hawking does nothing for vertical loads.
Of course it’s a vertical load that causes the failure of the strut tower. And I mentioned that in the article when I mentioned sharp impacts. I would note, I never asked E-Motion for any type of discount and they didn’t even know I was writing an article on the reinforcement brace; so, I’m not ‘hawking’ anything. Same goes for their suspension components; I paid full price including the installation costs.
And of course the brace system counteracts vertical loads. Even if it were just the bar alone, it would have some resistance to vertical loads because the bar attaches to the strut tower cap piece as a rigid joint which resists bending, as opposed to many bars that have a heim joint that would rotate. But what really helps this brace system resist the vertical loads are the two vertical posts that tie the bar to the battery sub brace. Those two posts are fastened with M8 size fasteners; you could lift the front of the vehicle from the E-motion brace because of how the braces uses the vertical posts to tie to the chassis.
Go ahead, draw out the free body diagram and analyze the loads and interactions.
You’re the one selling something. You draw a diagram and be sure to include the CG, roll center, and wheel diameter this time. You left out those items in your last calculation.