Notices
928 Forum
Sponsored by:
Sponsored by: 928 Specialists

DIY Strut brace

 
Old 07-07-2019, 04:35 PM
  #1  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default DIY Strut brace

Since I’m going full tilt on my exhaust and airbox, of course I’m working on my strut brace as well. The ITB’s and any airbox for them will interfere with the factory strut brace. Several months ago I stumbled accords a pic of mark Anderson’s old race car which is now in the custody of Rob Edwards. He was kind enough to loan it to me so I could use it as a starting point idea wise. I like the shape and materials, so I initially planed to make a jig and just copy it, however it was made for the race car and doesn’t quite match up with the factory mounting points.

Here is a pic of the cross brace sitting in place:



This is it next to the factory support.




The material is a Chromoly streamline tubing so I ordered the tubing and some 16 guage steel for the mounting plates. With some carfull measuring I found that the steel is angled @ 13 degrees where it enters the tubing, so I had a friend bend my two 6x6 16 guage steel 13 degrees down the middle and I will made all the cuts and holes drilled based on the bend.

The outboards on this one go to the chassis of the race car and I will add similar ones that go to one of the bolts on the strut tower of each side similar to Louie Ott’s.

Here is the 1st iteration of the brackets. Just rough cuts.




Here they are cleaned up a bit and drilled.



The holes are a little off but they need to be slightly larger and slotted so I was able to even them out with the round hand file.

Here they are mounted on the car.




Here is where the controversy is. The factory braces and any aftermarket ones have slotted holes for fitment. The rear holes are further apart than the front holes. Since these mounting points do indeed move a bit (for example when the car is jacked up) i decided to make the holes slotted as well. It makes for ease of use and it also makes it easier to make.

Steramline tubing comes in tomorrow, so I will start cutting and shaping as soon as it arrives.

Here is an assortment of tools used so far. I had to go old school on the bolt holes and used a round file to elongate them.



I have a basic jig for the assembly once I get to that point.




My plan is to tack weld it together, and then have someone locally weld it all up, and have it powder coated.

Last edited by 928sg; 07-07-2019 at 06:21 PM.
928sg is offline  
Old 07-07-2019, 07:14 PM
  #2  
dr bob
Chronic Tool Dropper
Lifetime Rennlist
Member
 
dr bob's Avatar
 
Join Date: Oct 2001
Location: Bend, Oregon
Posts: 18,026
Received 13 Likes on 12 Posts
Default

Looking good!

The factory tabs/mounting points look like they depend a lot on the rigidity of the bar itself to keep from folding vertically. There's a slight stiffening rib formed into them but it's not a lot. the ideal grab points are probably the shock and spring towers since they are right where force is applied to squeeze or stretch the cowl. The braces on the Mark/Rob crossbar move the functional mounting further towards the towers, but more importantly move any horizontal bending away from those original mounting points.

Are you going to run a lower frame crossbrace? That would reduce the distortion in the front box and likely reduce the load on the top brace.
dr bob is offline  
Old 07-07-2019, 07:21 PM
  #3  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

The secondary bars will go to the bolts circled in red.

928sg is offline  
Old 07-08-2019, 09:46 AM
  #4  
Petza914
Addict
Rennlist Member
 
Petza914's Avatar
 
Join Date: Oct 2007
Location: Clemson, SC
Posts: 11,165
Received 63 Likes on 50 Posts
Default

That's a bunch of cool tech you have on that engine, from Carl's crankshaft dampener to the intake and throttle setup.

Nice work on the brace too.
Petza914 is offline  
Old 07-08-2019, 10:29 AM
  #5  
V2Rocket
Rainman
Rennlist Member
 
V2Rocket's Avatar
 
Join Date: Jan 2007
Location: Nashville, TN
Posts: 42,814
Likes: 0
Received 11 Likes on 11 Posts
Default

thank you for the tip on the streamline tubing - been planning on a strut bar myself but wanted something with a smoother profile but couldnt find it.

cool project!
V2Rocket is offline  
Old 07-08-2019, 12:32 PM
  #6  
Chris Lockhart
Addict
Rennlist Member
 
Chris Lockhart's Avatar
 
Join Date: May 2001
Location: Taylors, S.C.
Posts: 2,099
Received 2 Likes on 2 Posts
Default

Looks great so far Sterling!!
Chris Lockhart is offline  
Old 07-08-2019, 01:26 PM
  #7  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

Originally Posted by Petza914 View Post
That's a bunch of cool tech you have on that engine, from Carl's crankshaft dampener to the intake and throttle setup.

Nice work on the brace too.
The damper is actually one of ATIĎs hubs and it didnít fit so Iím gonna end up going with the Greg Brown damper
928sg is offline  
Old 07-09-2019, 10:43 PM
  #8  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

Even though the flat steel was bent pretty close between the 2 pieces I had to tweak a bit on each one to get them at the same exact angle.




I went with 9 degrees angle instead of the 12-14 degrees ( one of each so I originally split the angle at 13 degrees) on the model bar because I want the bar farther than 1/4th of an inch away from the hood.

Streamline tubing came in and I got them cut. It is going to be a painstaking process to get the angles cut and precise. My geometry sucks, and I hate math so this is one of my least favorite parts of my build.



I bought enough tubing to do it twice, so I should be able to nail it, and only have wasted material.
928sg is offline  
Old 07-10-2019, 12:47 AM
  #9  
soontobered84
Addict
Rennlist Member
 
soontobered84's Avatar
 
Join Date: Mar 2002
Location: Texas
Posts: 5,032
Received 4 Likes on 4 Posts
Default

A chop saw would cut your tubing and have the correct angles easily.
soontobered84 is offline  
Old 07-10-2019, 07:33 AM
  #10  
beran earms
Addict
Rennlist Member
 
beran earms's Avatar
 
Join Date: Dec 2014
Location: THE GRANITE STATE
Posts: 535
Likes: 0
Received 0 Likes on 0 Posts
Default

Just a suggestion you could use a cheap piece of pine the same dimensions as your streamline and cut and fit and adjust. Then stick it with some hot melt glue as a mock up. Once you are comfortable with the compound angles a little isopropyl alcohol will easily separate the bond and you can set the saw to the mock up piece.
beran earms is offline  
Old 07-10-2019, 08:38 AM
  #11  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

I have a chop saw but it is a fixed blade. Looks like I may be shopping for or renting a compound miter saw. That will be much easier for me to do the angles with. and yes I will be testing and experimenting with wood 1st.

Last edited by 928sg; 07-10-2019 at 01:26 PM.
928sg is offline  
Old 07-10-2019, 01:42 PM
  #12  
dr bob
Chronic Tool Dropper
Lifetime Rennlist
Member
 
dr bob's Avatar
 
Join Date: Oct 2001
Location: Bend, Oregon
Posts: 18,026
Received 13 Likes on 12 Posts
Default

Originally Posted by beran earms View Post
Just a suggestion you could use a cheap piece of pine the same dimensions as your streamline and cut and fit and adjust. Then stick it with some hot melt glue as a mock up. Once you are comfortable with the compound angles a little isopropyl alcohol will easily separate the bond and you can set the saw to the mock up piece.
^^This^^

Buy some wood doweling/round, maybe like a closet bar but smaller. Add longitudinal lines to indicate the streamline tubing axis when you are done. Record the cut angles.



---

I often model things like this in 3D CAD, then go measure the results rather than try to calculate all the cut angles and rotation up front. Saves a TON of work and frustration. Start off by duplicating the factory bar in CAD, including mounting angles. Then mock the mounts as fixed reference, and show the interference points like intake and oil filler as boxes.


Knowing what I do and don't about the 928 chassis stiffness, I'd be looking hard at a pair of plates that attach at the top shock mounting points. Plates would extend forward and up along the fender lip. The actual crossbar could be round, maybe even the original or a CF replacement that would bolt to the plates. The goal is to limit cowl collapse under suspension and lifting loads, so the bar would be under compression only, and place only shear load on the shock mounting studs. It would unload the fenderwall and ultimately make a more torsionally stable front box.
dr bob is offline  
Old 07-10-2019, 03:41 PM
  #13  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

Originally Posted by dr bob View Post
^^This^^

Buy some wood doweling/round, maybe like a closet bar but smaller. Add longitudinal lines to indicate the streamline tubing axis when you are done. Record the cut angles.



---

I often model things like this in 3D CAD, then go measure the results rather than try to calculate all the cut angles and rotation up front. Saves a TON of work and frustration. Start off by duplicating the factory bar in CAD, including mounting angles. Then mock the mounts as fixed reference, and show the interference points like intake and oil filler as boxes.


Knowing what I do and don't about the 928 chassis stiffness, I'd be looking hard at a pair of plates that attach at the top shock mounting points. Plates would extend forward and up along the fender lip. The actual crossbar could be round, maybe even the original or a CF replacement that would bolt to the plates. The goal is to limit cowl collapse under suspension and lifting loads, so the bar would be under compression only, and place only shear load on the shock mounting studs. It would unload the fenderwall and ultimately make a more torsionally stable front box.
If I had the CAD skills I'd do it that way, but I don't so I can't. I will be working on a bracket to bolt on the top of the struts and act as an outrigger to the main bar. I'm not trying to build the space shuttle, although I feel like it sometimes. Just trying to build a bar that equals what the stock bar and just gives me room for the air box. Picked up a compound miter saw at harbor freight today on sale, will get some blades and get to it. will buy some wood to start with.
928sg is offline  
Old 07-11-2019, 10:49 AM
  #14  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

Originally Posted by V2Rocket View Post
thank you for the tip on the streamline tubing - been planning on a strut bar myself but wanted something with a smoother profile but couldnt find it.

cool project!
The streamline tubing Iím using is STREAMLINE 2.360 X .960 X .049 from aircraft spruce. 3 feet is enough.
928sg is offline  
Old 07-11-2019, 01:32 PM
  #15  
928sg
Resident 928 Modiholic
Rennlist Member
Thread Starter
 
928sg's Avatar
 
Join Date: Mar 2013
Location: Texas
Posts: 2,111
Received 9 Likes on 9 Posts
Default

Originally Posted by dr bob View Post
^^This^^

Buy some wood doweling/round, maybe like a closet bar but smaller. Add longitudinal lines to indicate the streamline tubing axis when you are done. Record the cuts

Home made streamline tubing



928sg is offline  

Thread Tools
Search this Thread

Contact Us - About Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: