Strut Tower brace in a V8 car or not?
 

I have spent TONS of hours reading threads on NA strut tower braces and can’t figure out what direction to go. It seems there is about equal number of people that would not leave their driveway without one to people who know beyond a shadow of a doubt they are useless.

I don’t want to recharge the debate but I figure this is an experienced and reasonable crowd that will not come to blows over the issue and can hopefully advise me on what to do.

There seems to be no debate over frog arms, subframe braces or door bars so those parts are pretty much ready to weld in. The car is fully seam welded and has a hard dog style double diagonal roll bar.

As you can see I tacked up a brace but not too sure about it. If I finish it I'll probalby drop the threaded rod and just weld thing in. So what do you think, strut tower brace or no?

Strut tower braces make a difference on cars that have struts. The Miata has coil over shocks and a double wishbone suspension. A car with struts only has a lower control arm which makes the upper mounting portion of the strut essentially the upper ball joint. This is not an issue in a car built like a Miata.

What does make a difference is triangulating the engine bay with some type of three-point brace, such as a Cobalt. The fact that the Cobalt brace bolts to the shock towers is irrelevant. It would be just as effective (or possibly more even) if it bolted to something further toward the front of the car.

Keep in mind that I am but a lowly elementary school English teacher, not an engineer.

-Jason

Well now that is the most rational explanation I have ever heard on the subject. I knew I came to the right place! I’m coming to the table from a muscle car point of view and never thought about the way Miata suspension works before.

So if I understand this right the weight of the car is on the strut tower but because of the upper control arms there is no torsional or side load on the strut towers in cornering. It appears that side load goes to the subframe and frame rails. So that is why so many braces do not go over the top of the engine like I made then. Humm. Still you would think there would be some benefit to supporting it over the top and making a box out of the cradle and frame.

Very interesting, and very back to the drawing board! Thanks Jason!!

I just looked more closely at what you made up there and I think it has potential. What I would do with is change the "emphasis" of the structure from going across the bay with a few extra bars going back to the fire wall to the main structure going from the structures you have on each fender (which look nice) to the firewall with maybe a support across to help out. The majority of the work that bar is going to do involves the diagonals, no the cross bar.
Make sure that the attachments at the firewall actually secure it to the firewall "box" not just the thin cowl metal that separates the engine bay from the wiper area. That piece of metal is such a weak part of the structure that you can't even ground to it.

I envisioned making something that would go from the fenders like you have, through the upper "cowl" without being connected to it, and then bolted down into the horizontal surface behind it with back up plates on top and bottom. The flat "floor" of the wiper area is very strong and would make a great place to triangulate from. Should I ever have another reason to take the dash out at some point the above is what I’ll be doing. I already have some OEM braces pulled from a GM station wagon’s bay to that I’ll use.

-Jason

Here's what I have a set of and plan to use at some point:

https://www.v8miata.net/attachment.p...ine=1365706142

-Jason

Thanks Jason! My initial design had another bar going to the back corner off the top of the A. Like the yellow in the pic.

It is a problem on the wiper side I can't get it all the way back in the corner at the top. I could slip it under the motor or just in front of it and it would probably be OK.

Do you think it would be better to have my diagonals from the fire wall longer so they hit the A rather than the cross bar? With bars to the corners that would be about a perfect triangle from firewall to shock tower to the corner. Boy am I ever glad I asked before welding this up!

Yeah that horizontal bar on the back wall is into tinfoil and I figured I would put a brace in there to the floor of it or drop it down lower than it is. Perhaps I should extend the bar all the way to the corner? Wiper is a problem again though…

On second thought since the cornering forces are down on the frame from the upper control arms that yellow brace should not go to the top of the A. Starting at the upper corner of the fire wall seems like it makes sense but the other end should go as low as I can get it to the frame rail. Now that I have power again I'll see what I can do with it tonight.

This is what I came up with.

https://www.v8miata.net/attachment.p...ine=1365904790

https://www.v8miata.net/attachment.p...ine=1365904790

https://www.v8miata.net/attachment.p...ine=1365904790

https://www.v8miata.net/attachment.p...ine=1365904790

And of course frog arms
https://www.v8miata.net/attachment.p...ine=1365904790

I made a couple of brackets to reinforce and box in the thin sheet metal on the fire wall but didn't take any pix of them. So what do you think weld it up or back to the drawing board?