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      04-29-2020, 06:23 PM   #1
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kayha12's Avatar

Drives: M3
Join Date: Mar 2018
Location: Frederick, MD

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DIY "Track" Front Splitter - "Chassis-Mounted"

Hey everyone! Putting together this DIY thread loaded with photos since I figure there is little to no information on this topic without digging deeply into the chat threads or build threads. In this thread you'll see my step by step guide on how I built my splitter


Sorry directly uploading to the page makes some of the photos upside down apparently. And haven't figure how to hotlink it from google photos.

About me and the car:

- I am instructor with NASA (Mid Atlantic region)
- The m3 competes in NASA's Time Trial series TT3 (2019 Mid Atlantic champ, woo woo)
- I've been tracking for about 3.5 years
- This is not the first splitter I've built! haha

- NO the splitter is not FULLY chassis mounted. It is indeed attached to the GT4 lip and bumper
- I decided to keep the OEM undertray as it has nice ducting for the oil cooler
- There is little to no real estate to play with in terms of making brackets to go fully chassis mount, when you have the coolers/radiators and all the various lines
- Dogbone was my motivation as his is not chassis mounted and he has extensive track time

SO FAR - since tracks are closed, I've been able to take the car onto the highway and the thing is rigid, hopefully it is the case while at track speeds as well. I also have a video of myself jumping on the thing and it doesn't move (while yes it flexes but it ain't going no where)

There are a lot of photos, and sorry they are not in any specific order but I think you should be able to follow along

Tools you'll need:

- Basic tools to remove the bumper
- Various socket wrenches
- Dremel
- Angle grinder or jigsaw
- Drill with 3/16" and 5/16" drill bits
- Rivet tool (unless you go with nuts and bolts instead)

Materials I used:

- Cheapest plywood to build a template, I paid $14 for a 4x8 cut
- 1/4" Alumalite (you can go thicker, this is all my local shop had)
- 3/16" rivets
- 5/16" clevis bolts (with the pins)
- 5/16" nuts and bolts sizing from 1.5" to 3.5"
- Respective lock nuts and washers
- 1x1" angle bracket, get a long stick and cut it up
- 1/4" edge trim (to cover up the alumalite edges)

For the splitter rods:
- 1/4" threaded rod (at least 16")
- 1/4" eye bolt
- 1/4" threaded coupler (so you can attach the eye bolt to the threaded rod)

For the splitter end plates:

- 22 gauge sheet metal (cut into 3.5" x 9")

The reason I use the eyebolts is that this gives the splitter the ability to flex upwards if need be, but once pressed upon it is rock solid. I also made my brackets this way 1) gives you room for error 2) helps spread the load

Part 1 - Bumper beam support mounts

1) I started this project off by tackling the mounting points at the bumper bar - 4 specifically. 2 of them will sit towards the outer center of the bumper through the grill, the other 2 will sit in the bumper ducts - which is as far to the edge as possible.

1a) Start by cutting up 2" (or so) pieces on the angle bracket, each piece will have 2 x 3/16" hole for the rivet, and 1 x 5/16" hole for the clevis bolt. You'll need a total of 8 of these

1b) For the center mounts, you will need to cut up the plastic air dam that surrounds the oil cooler so these mounts can clear. In addition to that you'll need to notch a few pieces on the bumper grill to feed the splitter rods through

1c) For the outer mounts, you'll need to cut up the bumper ducts as well as the bumper cover itself to clear

1d) Mock up your mounts, drill, and rivet. I like to leave about a 1.5" or so gap between the brackets. After each mount was secured I just test fit the bumper just to make sure nothing crazy was happening

1e) Congrats, you should be able to lock in your eye bolts now with the clevis pin on the other side of the clevis bolt, this first part is complete

Part 2 - Splitter mock up/build

2) Next step, you are ready to mock up your splitter - here is where you're able to do whatever you please. My GT4 splitter is quite banged up so I figure this would give it some extra rigidity

2a) First you will want to secure the plywood to your bumper. This is a great opportunity to figure out where you want to drill into the splitter/bumper. You don't need to tighten everything down but this step will help hold the plywood to the bumper when you are cutting it. I used 14 nuts and bolts throughout, each bolt went through the lip, and into the bumper

2b) Now you are ready to trace your splitter. The trick here is to find a box to help trace your splitter. I actually used a Hawk brake pad box which was 4" wide. Line up your marker at the center point of the box. Slide the box along the bumper/lip with the marker attached to the box.This should give you a perfect outline. For the sides of the splitter - I measured in 1" and drew a straight line to the leading edge, this gives me a 4" extension in the front and 3" extension on the side to the GT4 lip. Total extension from the bumper at the center point is 8"!

2c) Congrats you are now done with the template. Your template gives you the outline of the actual splitter (shape and size) but it will also give you where to drill the holes to attach the final piece to the bumper

Part 3 - Template to final piece (skip if you didn't go the template route)

3) Trace your template onto the alumalite, or whatever material you are using as the final draft, cut out the final piece and drill out the lip mounting holes

Part 4 - Re-install the bumper

4) With the new splitter attached to the bumper, its a great time to mock it up to the car - you are also now able to button everything up if you wish

4a) Because the bolts I used were so long, I did have to trim part of the belly pan to fit around those bolts. You will know if the bumper isn't sliding on properly!

Part 5 - Splitter mounts, on the actual splitter!

5) VERY similar to the step where we made the splitter mounts for the bumper beam. Here I decided to do 3.5" long brackets, with the idea to help spread the load, 3 x 3/16" rivets on the bottom side 1 x 5/16" hole for the clevis bolt

5a) Be very mindful on the placement here. Truly measure twice and rivet once!

5b) You'll need to measure out the threaded rod but since everyones eye bolt might have more or less on the rod end, I can't give precise length here. To give you an idea, I started with 6" and had to cut down a few times

5c) The splitter will sag a bit, so make sure when you are measuring, you are pulling the splitter up a bit. There should be some tension here but at the same time you don't want your splitter angling up - I did use a leveling device here.. my phone hahah

5d) Once you've finish all 4 of the brackets, your splitter is pretty much done. You can paint the brackets black, you can also put some edge trim tool since exposed alumalite looks horrible. Give it a little nudge, stand on it, jump on it, it should hold!! CONGRATS!

Part 6 - My take on splitter end plates

6) I found some cheap sheet metal at the hardware store for $6, I figure go with something you can bend but that isn't too flimsy. I ended with 22gauge (I think..?)

6a) I cut the pieces into 3.5" x 9" rectangles, and leading into the end plate at 3.5" I gave it a slight bend.

6b) You should be a pro at making angle brackets now, I put a 3" bracket on the long end and 2" bracket on the short end.

6c) Plastidip everything black, and riveted away onto the bumper

That's it!! Once again the purpose of this write up is to give you guys some basis on how to do this, and all in one spot. Good luck!

Bonus photos of me testing fitting some 10.5" wheels up front with 295 slicks
NASA Mid Atlantic - TT3 #97
'12 E92 M3 ZCP
Sponsored by Andrewtech Automotive

Last edited by kayha12; 04-29-2020 at 06:46 PM..
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      04-29-2020, 08:19 PM   #2

Drives: 2011 ZCP M3
Join Date: Jul 2017
Location: Austin, TX

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Welp I know what I'm doing in May. Seriously, thanks for posting this!
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      05-01-2020, 08:13 AM   #3
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SYT_Shadow's Avatar

Drives: E90M/E92M/F80CS/X5 35/MiniCS
Join Date: Sep 2010
Location: Greenwich, CT

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this is pretty cool! thank you for going through all the steps
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      05-03-2020, 06:34 AM   #4
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roastbeef's Avatar

Drives: E92 M3
Join Date: Nov 2010
Location: Orange County, CA

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nice. you have a lot of tire meat showing in the front view. i think you would benefit greatly from spats as well.
Instagram; @roastbeefmike
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