Making a strut tower bar: Design opinions/help

[EMWHYR0HEN]

I'm making a STB for the front of my car. I know it may seem that a STB is an easy fab, but I had to think about the design a little bit more in my application and I just need a little help with some issues.

 

Here's what I came up with. I used 4130 chro-mo 1/8 inch plate (colored in blue) for the 2 plates on top of the strut towers, and also on the core support.

 

For the main bars I used 4130 chro-mo 3/4 '' O.D. .058 wall (colored in red), and 4130 chro-mo 1/2'' O.D. .065 wall for main bar support (colored in green)

 

 

 

 

well my first issue is that bar # 3 (the bar the connects the 2 bars on each strut tower) will slighty hit one side the valve cover (next to the oil cap) becasue the engine is angled.

 

So should I bend it? or cut the bar into 2, shape the angle I need and tig it back together?

 

The next thing that i'm unsure of is how bar # 1 and 2 will be welded to the plates. (the white crap displays the welds, above pic)

 

cross section like this: (the green = welds)

 

 

As you can see not alot of area from the tube will be welded to the plate.

 

 

I haven't welded anything together yet, so i'm open to any sugestions, changes, opinions.... any help is appreciated.

[blueovalz]

What is your goal? Is it to reinforce the core support, or to stiffen the suspension mounting points?

 

My take on this design is that it does keep the core support and the strut towers rigid in relationship to each other and should help reduce shifting of the radiator area.

 

If you're goal is to improve the rigidity of the suspension pick-up points, then this may not provide what you need. I feel this is one goal you should strive for in tying the towers together.

 

Even though you've got the area forward of the strut tower line tied together rigidly, there is nothing to prevent this entire area from moving in relationship to the rest of the chassis. So what may happen is that this area (both strut towers and the core support) ends up shifting slightly in relationship to rest of the chassis (rear wheels). Two islands tied together by only the frame rails, when you really want a single island with both front and rear tied together. This is why many folks reverse the tubing so that the towers are tied to the firewall, which is tied to the rest of the chassis. Attaching the firewall to the towers then helps eliminate movement of the front towers with the rest of the chassis.

 

As I see it, your drawing offers little benefit over a simple, single bar connecting the towers (not only because of the issue described above, but also because of the forces placed in the middle of the two green bars. Any compressive and tension force between the towers will try to bend the middle bar fore and aft). I guess this all stems from the mechanicals in the way of placing straight bars in better locations, which is going to make this job tough.

[naviathan]

I think, given the area you have to work with the design looks good, but I'd worry about the welds. It might be better to flatten the ends of the bar where it is to be welded then allowing you to lay a three wall bead and get better penetration into the bar itself. I'm also a bit concerned about the stability of the radiator support you're running to in the front. It's not thick metal and given a hard enough brake or corner it could flex and bend. Maybe you could extend the base plate in the front to better support that area.

[EMWHYR0HEN]

Well initially I was planning on NOT extending the bars from the towers to the core support.

 

I do have plans on putting bars also to the fire wall, this is just the front part that i'm working on now. Are the bars going to the core suport worth keeping?

 

Also, woulD I get the same effctive strength if I heated and pounded the bar to a flatter shape, Or if I slotted the bar down the middle and slide a flat peice down the slot?

 

like this:

 

[naviathan]

I think you would get a stronger hold flattening the end as it would maintain the solid strength of the metal instead of adding another weld that could fail.

[Pop N Wood]

Strength at the welds is the absolute least of your worries. None of your welds should fail. You could weld a U shaped bracket to the strut tower and pin it to the cross rods and you will still be 1000 times stronger than you need to be.

 

All you really need to concern yourself with is the rigidity of the crossbars. In that sense try to make everything out of straight pieces with as few bends as possible.

 

IMO connecting the bar to the radiator core support is just so much added weight. See what you can do to get the bar to go straight up over the engine, curving it if need be. Going back to the firewall is what most guys do with their strut supports.

[JMortensen]

Strength at the welds is the absolute least of your worries. None of your welds should fail. You could weld a U shaped bracket to the strut tower and pin it to the cross rods and you will still be 1000 times stronger than you need to be.

 

All you really need to concern yourself with is the rigidity of the crossbars. In that sense try to make everything out of straight pieces with as few bends as possible.

 

IMO connecting the bar to the radiator core support is just so much added weight. See what you can do to get the bar to go straight up over the engine, curving it if need be. Going back to the firewall is what most guys do with their strut supports.

Agreed. What I did was to build taller mounts that hook to the strut towers so that the bar could be straight. Looks like you might have hood clearance issues, but a straight bar would be preferrable to a curved one.

 

Picture is at a weird angle because the car is on a rotisserie, but you should get the idea:

[naviathan]

Looks like you added some forward support down to the frame rails. Nice welds.

[EMWHYR0HEN]

Thanks for the inut.

 

pop, I cant go over the engine, my intake manifold almost touches the hood!

 

I know a straight bar would be the EASIEST and STONGEST way to go, but as you can see, I'm unable to do that.

 

So I ditched the core support bars and came up with this:

 

I'll use the 3/4 '' bar that i was going to use on the core to support the straight bar. Then, i'll use the 1/2'' bar and TRY to fit it going straight.

its going to ve a VERY tight fit.

 

[naviathan]

I think that would still be a very tight fit if it did at all. Is it at all possible to go back to the firewall? That looks very stable, but it will make it hard to work on without removing the bar.

[EMWHYR0HEN]

I think that would still be a very tight fit if it did at all. Is it at all possible to go back to the firewall? That looks very stable, but it will make it hard to work on without removing the bar.

 

 

I'm just building the front part right now, i'm still going to build towards the fire wall later.

[JMortensen]

Can you lower the engine?

[EMWHYR0HEN]

Can you lower the engine?

 

 

yeah, I could but then i'd need new engine/ tranny mounts and drive shaft. Still, I dont think it would be enough to put a bar straight across.

 

I think i'd have to get a greddy intake manifold or go ITB's. Maybe sometime in the future, but right now for a broke college student, no can do...

 

 

i'll post pix of my finished product

[katman]

"I'm just building the front part right now, i'm still going to build towards the fire wall later."

 

Are you building the front part because you need some worthless dead weight up there, or you're afraid your radiator is going to get spooked and jump up through the hood?

 

This reminds me of the joke:

Cop says, "Why sir, are you on your hands and knees in the gutter?"

Dude says "Because I lost my wallet on 3rd street."

Cop says "Sir, but this is 17th street".

Dude says "I know, but the light is better here."

 

Oops, that was mean. Sorry. But really, don't waste your time going forward. The next post is the hot tip, smartly done.

[johnc]

Unfortunately, going forward with the STB will do little to help the strut towers. You really need to go straight across and, optionally, back to the firewall. This design worked very well on my old 240Z and let me increase the front spring rates by 50 lb. in.

 

[olie05]

Thanks for the inut.

 

pop, I cant go over the engine, my intake manifold almost touches the hood!

 

I know a straight bar would be the EASIEST and STONGEST way to go, but as you can see, I'm unable to do that.

 

So I ditched the core support bars and came up with this:

 

I'll use the 3/4 '' bar that i was going to use on the core to support the straight bar. Then, i'll use the 1/2'' bar and TRY to fit it going straight.

its going to ve a VERY tight fit.

 

 

This last picture you drew will not really stop the towers from flexing either. If you think about it, when the device is in compression, the front most bar will still bend. This design, however, would be very good at stopping any forces going towards the back of the car.

[EMWHYR0HEN]

Unfortunately, going forward with the STB will do little to help the strut towers. You really need to go straight across and, optionally, back to the firewall. This design worked very well on my old 240Z and let me increase the front spring rates by 50 lb. in.

 

 

My first choice would be making a bar that goes straight across, but that would cost me too much right now so I have to improvise. I'm just making something for fun in my welding class for my first TIG welded project.

 

If it does SOMETHING, even very little, i'll be ok with that for now, it only weighs like 6-7 lbs.

 

Also, where would be the strongest place to place bars on the firewall in MY engine configuration? and would I have to reinforce the firewall area with 1/8'' plates front and back?

[DavyZ]

...You really need to go straight across and, optionally, back to the firewall...

 

John, just to dovetail on EMWHYROHEN's question above, did you reinforce the firewall where the heim joints were bracketed to the firewall?

 

Davy

[blueovalz]

When I reinforced the brackets to the firewall, I used 1/8" steel plate welded in place. Then I bolted the bars to these plates through captured nuts on the back of the steel plates. The location of these steel plates should be as close as possible to any corners or reinforcing angles that are stamped into the OEM unibody components. I placed mine up against the angles at the front of the cowl, and at the corners under each fender.

 

 

[johnc]

Based on some finite element analysis done by Bill Savage there is no need to reinforce the firewall for a center STB mount. In side view the cowl section is a triangle with the firewall as the base. If your STB mount plate spans the base of the triangle (the top lip and the row of spot welds part way down the firewall) you have a very strong mount that spreads the load into the cowl section.

 

I have some close-up pictures of the mounts in one of my galleries.

 

http://album.hybridz.org/showgallery.php?cat=702