Front Underbody Brace
Jul 2, 2016, 11:08 AM
#1
Front Underbody Brace
This is a home made underbody brace that fits just aft of the control arms/subframe.
Cut the piece of steel u-channel to 29" long. It looks "small" but so is the stock evo9 brace in that area. Decided that just aft of the control arms, where the chassis tunnel begins, would be an effective placement. Drilled a 1/2" hole about there on each side (clearance hole for a threaded insert).
Hmm, looking inside the hole I see this is not a single layer of sheetmetal I drilled into, but there is another layer inside, slightly separated.
Now why this was concerning me is that I drilled those holes to accept a 3/8-16 threaded insert (nutsert). These inserts are made to slip into a hole in the sheet metal, then get squished and compressed so they don't rotate or anything, and so provide a threaded hole for your fastener. I installed the nutsert anyway to see what happens. Here is the order of the installation tooling: nutsert, bar with 3/8" hole drilled in end, flat washer, 3/8-16 hex nut, and a long bolt threaded thru everything and into the nutsert. There are youtube videos about this. (note: for this size nutsert a 0.531" hole is required, so you have to dremel or file the 1/2" hole a bit bigger).
Just push the nutsert into the hole and, holding the bolt still, turn the hex nut a couple turns until the nutsert has fully compressed - you feel severe resistance when that happens. (note: the nutserts I bought are for 0.030" to .150 " thick sheet metal)
Badda bing! Now do the other side too. Then you can mark the exact hole locations onto the brace bar and drill 25/64" as clearance holes for the 3/8" screws.
Decided to shim under the brace with 1/8" thick steel. This separated the brace from the cat con heat shield a little bit.
Used 3/8-16 one inch long socket head cap screw with lock washer underneath. Note: a hex head screw would require a socket or wrench to tighten, and neither of those fit in between the edges of the steel channel.
The bar is very close close to the heat shield. I just glued a layer of header wrap to the bar with silicone. Tighten everything up and it just barely pushes the heat shield up. Perfect.
Went for a test ride, no banging noises or anything, screws are tight. Will report again later.
Notes:
The bar is not lower than anything else so have not introduced a ground clearance issue.
Nutserts are cheap to buy, easy to install, and you don't need special tools. I would rather use them to place reinforcements where I want, rather than use existing chassis bolts.
You could use different shape bars, different fasteners, or use the existing nearby OEM bolt to secure your bar. Just wanted to show you where I thought was most effective to place a basic bar.
Cut the piece of steel u-channel to 29" long. It looks "small" but so is the stock evo9 brace in that area. Decided that just aft of the control arms, where the chassis tunnel begins, would be an effective placement. Drilled a 1/2" hole about there on each side (clearance hole for a threaded insert).
Hmm, looking inside the hole I see this is not a single layer of sheetmetal I drilled into, but there is another layer inside, slightly separated.
Now why this was concerning me is that I drilled those holes to accept a 3/8-16 threaded insert (nutsert). These inserts are made to slip into a hole in the sheet metal, then get squished and compressed so they don't rotate or anything, and so provide a threaded hole for your fastener. I installed the nutsert anyway to see what happens. Here is the order of the installation tooling: nutsert, bar with 3/8" hole drilled in end, flat washer, 3/8-16 hex nut, and a long bolt threaded thru everything and into the nutsert. There are youtube videos about this. (note: for this size nutsert a 0.531" hole is required, so you have to dremel or file the 1/2" hole a bit bigger).
Just push the nutsert into the hole and, holding the bolt still, turn the hex nut a couple turns until the nutsert has fully compressed - you feel severe resistance when that happens. (note: the nutserts I bought are for 0.030" to .150 " thick sheet metal)
Badda bing! Now do the other side too. Then you can mark the exact hole locations onto the brace bar and drill 25/64" as clearance holes for the 3/8" screws.
Decided to shim under the brace with 1/8" thick steel. This separated the brace from the cat con heat shield a little bit.
Used 3/8-16 one inch long socket head cap screw with lock washer underneath. Note: a hex head screw would require a socket or wrench to tighten, and neither of those fit in between the edges of the steel channel.
The bar is very close close to the heat shield. I just glued a layer of header wrap to the bar with silicone. Tighten everything up and it just barely pushes the heat shield up. Perfect.
Went for a test ride, no banging noises or anything, screws are tight. Will report again later.
Notes:
The bar is not lower than anything else so have not introduced a ground clearance issue.
Nutserts are cheap to buy, easy to install, and you don't need special tools. I would rather use them to place reinforcements where I want, rather than use existing chassis bolts.
You could use different shape bars, different fasteners, or use the existing nearby OEM bolt to secure your bar. Just wanted to show you where I thought was most effective to place a basic bar.
Last edited by RalliartN; Jul 2, 2016 at 11:17 AM.
Jul 5, 2016, 06:36 AM
#2
Well done! Is there a reason you shouldnt use existing bolts such as the ones just forward of the holes you drilled? Im asking because I know the H-brace for the evo that several people put on their RA attaches at that bolt and then to the bolt that holds the front of the control arms. I know my 9 also has two bar braces under there, one in a near identical location to the one you made here.
Jul 5, 2016, 02:58 PM
#3
Hey Bakuro, thanks for the kind comments.
No, there's no reason not to use the existing bolts.
One reason I did not is I wanted to try working with nutserts. Another reason is I didn't want to compromise ground clearance, so the location chosen has snugged the brace right up against the frame just aft of the existing bracket.
We know that aftermarket brace makers try to use existing bolts so their customers don't have to drill, rivet, glue, or weld anything. If I was them I'd do that too. But that usually compromises ideal location or ground clearance.
Went to the track last night. All I can say is no noises, and no additional oversteer in any circumstance. The car was it's usual super-fun self, so controllable and slidey. More of a good thing with the braces? I think so and would recommend the mods.
No, there's no reason not to use the existing bolts.
One reason I did not is I wanted to try working with nutserts. Another reason is I didn't want to compromise ground clearance, so the location chosen has snugged the brace right up against the frame just aft of the existing bracket.
We know that aftermarket brace makers try to use existing bolts so their customers don't have to drill, rivet, glue, or weld anything. If I was them I'd do that too. But that usually compromises ideal location or ground clearance.
Went to the track last night. All I can say is no noises, and no additional oversteer in any circumstance. The car was it's usual super-fun self, so controllable and slidey. More of a good thing with the braces? I think so and would recommend the mods.
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