Are Cowls Structural?

[Jboogsthethug]

So I'm looking into wiring my Z and watched this video of Shawn Basset's 240z's wiring: 

I realized Shawn has completely cut out his cowl! He made the cowl cover in a way that doesn't allow water through, of course. I was thinking of doing the same thing to give me more room for accessibility, etc. Is that structural at all? Will I need to add some bracing?

 

[Jboogsthethug]

Any other experiences with doing this for your car?

[jhm]

Looks like a full tube chassis car (couldn't tell for sure what rear suspension setup he's running); so it's an apples-to-oranges comparison....unless you happen to be building a tube chassis car as well.

 

Can you cut specific parts/pieces of the cowl area out without significantly affecting structural integrity of the shell?  Possibly.  As long as the rest of the forward portion of the shell is sound, and as long as you're not cutting into any load-bearing portions of the cowl/firewall and surrounding areas. 

 

1 hour ago, Jboogsthethug said:

Will I need to add some bracing?

 

Most 50-year old S30 shells are already flimsy enough that they benefit from additional bracing even without cutting any parts out, let alone 50-year old shells that have had pieces cut from them.  Depending on how much cutting you want to do, it's very likely that some kind of additional reinforcement might be required.  (It also depends on how you intend to use the car.  A car intended for heavy track use obviously has very different build requirements than a weekend car for pleasure-driving.) 

 

What specific areas do you want additional accessibility to that cutting the cowl area would help with?  That might help to understand how much cutting you're envisioning, and just how much of a structural impact it could have.  Rewiring work is really quite easy and very accessible once the dash is removed, so maybe you can accomplish your goals without having to cut any sheetmetal.

 

[Jboogsthethug]

So my build is a pure track build for sure at this point. I actually already had my roll cage builder cut out part of the cowl to have some bars triangulated from the dash bar to the center of the firewall. It doesn't look great as it sits so i figured either fix it or cut it all out.

Another point to him is his chassis is completely rebuilt, his panels are all carbon fiber, and he's (I'm sure) running a lexan windshield. The weight in the center of the cowl has got to be pretty much nothing for him.

I do currently have a full cage throughout my chassis, but I haven't yet upgraded my frame rails, which I'd like to do. I'd want to tie the cage into them and that would complete my structural upgrades, but I'm mostly worried about the windshield being too heavy and causing some sort of sag or wiggling around.

As far as wiring, I mostly just want space for different electrical buses/accessories/etc without it creeping into either side's leg room. I figure this would make that even simpler.

[Jboogsthethug]

you can see at 2:23 how he's got it all tucked right into the cowl, it just seems like prime real estate for my electrical ha.

[NewZed]

Here's the basic steel box that everything else is bolted on to.  Might give you some ideas.

 

[jhm]

Ah, sorry -- did not realize you were building a caged dedicated track car.  My bad.  That's definitely an important part of the discussion, as well as the type and design of the cage. 

 

If the weight of the glass windshield is the main concern here, couldn't that be resolved via one of the forward cross braces?  If structural integrity is the main concern, then that would be addressed via the manner in which the cage is tied into the rest of the shell (and any additional chassis bracing you have planned), true? 

 

Sorry if I'm not understanding the full scope of your query.

[Jboogsthethug]

1 hour ago, NewZed said:

Here's the basic steel box that everything else is bolted on to.  Might give you some ideas.

 

Thanks for sharing NewZed. I'm a little confused at what the cutouts are on this diagram. Are those indicating structural reifnorcements?

 

 

1 hour ago, jhm said:

Ah, sorry -- did not realize you were building a caged dedicated track car.  My bad.  That's definitely an important part of the discussion, as well as the type and design of the cage. 

 

If the weight of the glass windshield is the main concern here, couldn't that be resolved via one of the forward cross braces?  If structural integrity is the main concern, then that would be addressed via the manner in which the cage is tied into the rest of the shell (and any additional chassis bracing you have planned), true? 

 

Sorry if I'm not understanding the full scope of your query.

 

Yeah my bad for not giving more background when asking the question, you're all good! I think mostly it is addresses, the triangulated bars will certainly stop the firewall from bowing out under pressure, but I'm thinking I may need to add a leg directly in the center of where the windshield mounts to stop it from bowing downwards without the inner cowl in place. I specifically want to remove just the inside where rain water is directed to the sides of the car. but leaving the top of the cowl area in place.

Perhaps I'll post a picture of my cowl currently to give a better idea and make sure I'm on the same page as you. one moment

[Jboogsthethug]

So you can see how my bars triangulate through the cowl area and I've got a pretty good sized hole here. Currenlty not worried about structure but I figured if I could cut a little bit more weight and have more room for electronics then rock on. 

I did realize in looking at this that I'd need to keep the driver's side mostly intact or fabricate up a mounting solution for the steering wheel/pedals, so If I did cut it it would be everything else until I felt like coming up with all those needs ha.

 

Edited July 29, 2020 by Jboogsthethug

[NewZed]

21 minutes ago, Jboogsthethug said:

Thanks for sharing NewZed. I'm a little confused at what the cutouts are on this diagram. Are those indicating structural reifnorcements?

 

I think that they're showing "boxed" body components.  Integral reinforcement as you said. 

 

Like the rocker panels are one of the most important structural elements of the unibody.  People often overlook that area when dealing with rust.  The "frame rails" are just added stiffeners.  They'll replace the stiffeners and leave the rusted out rocker panels.

 

So, when looking at the cowl, or any body area, look for those reinforced areas.  But, I'm not a structural or automotive engineer, so don't put too much weight in to my words.  

 

Somebody had a thread on the site where they really went deep in to how to reinforce the body.  I think that they even built a framework to load the frame and measure deflection.  It might be in an FAQ area, or might be found by a search.

 

[JMortensen]

I have a very similar setup from the strut towers to the center of the dash bar. The center of the dash is not the optimal place to terminate those bars. There isn't any structure there, it's the middle of a span, no node. I made it a node and sent the load to the diag in the main hoop and then down to the rear strut towers in this sort of arrangement >---< and that works better. It also is pretty similar to a wood model Herb Adams shows in the book Chassis Engineering. Dr Sideways (can't remember his real name) has a similar dash bar and he did it better, with an X between the main hoop and the door bars and a V to the rear struts. Precludes passengers though. 

[Jboogsthethug]

21 hours ago, NewZed said:

 

I think that they're showing "boxed" body components.  Integral reinforcement as you said. 

 

Like the rocker panels are one of the most important structural elements of the unibody.  People often overlook that area when dealing with rust.  The "frame rails" are just added stiffeners.  They'll replace the stiffeners and leave the rusted out rocker panels.

 

So, when looking at the cowl, or any body area, look for those reinforced areas.  But, I'm not a structural or automotive engineer, so don't put too much weight in to my words.  

 

Somebody had a thread on the site where they really went deep in to how to reinforce the body.  I think that they even built a framework to load the frame and measure deflection.  It might be in an FAQ area, or might be found by a search.

Interesting info about the rocker panels being so important, didn't realize that! I'll look into this thread and post a link if I find what I think you're referencing.

 

 

20 hours ago, JMortensen said:

I have a very similar setup from the strut towers to the center of the dash bar. The center of the dash is not the optimal place to terminate those bars. There isn't any structure there, it's the middle of a span, no node. I made it a node and sent the load to the diag in the main hoop and then down to the rear strut towers in this sort of arrangement >---< and that works better. It also is pretty similar to a wood model Herb Adams shows in the book Chassis Engineering. Dr Sideways (can't remember his real name) has a similar dash bar and he did it better, with an X between the main hoop and the door bars and a V to the rear struts. Precludes passengers though. 

I'll look into the book! Thanks for sharing some insights and photos. I'd like to keep the passenger side available so who knows. Thanks for everyone's thoughts!

[NewZed]

I found it.  I was more talkative back then.  Some good comments from other members though.

 

Having problems posting, this is a test.  The site would only take the lin, as a link, not embedded.  Weird.

 

https://forums.hybridz.org/topic/116305-torsional-rigidity-testing-280z/

 

 

Edited July 30, 2020 by NewZed

[jhm]

If you're still looking for inspiration on chassis-stiffening, there's a few good ideas here:  https://imgur.com/a/R27sh.

[Jboogsthethug]

16 hours ago, NewZed said:

I found it.  I was more talkative back then.  Some good comments from other members though.

 

Having problems posting, this is a test.  The site would only take the lin, as a link, not embedded.  Weird.

 

https://forums.hybridz.org/topic/116305-torsional-rigidity-testing-280z/

 

 

 

Thank you, I was coming up short! This is great info!


 

9 minutes ago, jhm said:

If you're still looking for inspiration on chassis-stiffening, there's a few good ideas here:  https://imgur.com/a/R27sh.

What a compilation of pictures! This was especially helpful to visualize how people tie in the front strut towers to the rocker panels inside the front fender panels! I think most everything else I've done with my cage, it's pretty extensive.

This has all been helpful to help me visualize it all, thanks again to you both!