Chassis Reinforcement

[Duk]

Something that always interests me is chassis design and worthwhile reinforcements. Over the years there have been high performance cars built on relatively modest chassis that have utilised additional bracing to help improve the chassis behavior. 3 cars that spring to mind are the BMW E36 M3's and the Nissan R33 and R34 ( and probably the R32, as well) Skyline GTR's.
Now with my 75 I've added bracing inside the front guards to triangulate the upper box section (the box section just under the bonnet) and am in the throws of making a brace that ties the box sections that come from the A pillars and that have the top control arms and damper top mounts attached to them. Please enjoy my awesome artistic skills   Where red lines equal my additions or intended additions.
Now, the reason for starting this thread came about when I saw a picture of a 75 without its hood lining. What struck me as strange is that there is no diagonal or central horizontal bracing inside the hood lining. So it has me thinking that there could be potential ride and handling improvements (even in 'just' a road car) by directing the forces fed into the A pillar into the diagonally opposite C pillar. Again, please enjoy my fantastic art work

Thoughts?

*** The picture of the car without its windscreen is not my car but a pic I pinched from AlfaBB ***

[Sheldon McIntosh]

These pics may interest you.  I noticed these cracks have surfaced in my engine bay since I put my large TBs in, so there's obviously a fair bit of force, and flex, going on.  Pics taken from inside the wheelarch.

[Duk]

Sheldon, that is disturbing  .

I think this emphasizes what Mats Stransberg (on GTV6.com) says, that the forces of the front suspension aren't just resisted at the torsion bar chassis mounts, but mainly by the lower control arm chassis mounts. If the torsion bar can't (or hardly) twist because it's so thick, then that bump force is transferred directly into the chassis via the lower control arm chassis bolts, into the chassis, mainly through the box sections in the engine bay that transfers that load into the A pillar, but obviously there is plenty of load going through the engine bay sheet metal, too.

Apparently the Nismo built R34 Skyline GTR used a layer of carbonfibre inside the engine bay to help add torsional strength to the chassis. That has me thinking about a carbonfibre insert that is molded with box sections, that is then bonded and/or bolted to the A and C pillars. Could even extend the design to include a lateral mound between the B pillars. Would only make the box sections in CF, the skin between could be a layer of fibreglass. Glue a layer of fabric over it and it could double as the hood lining.

[Sheldon McIntosh]

Sheldon, that is disturbing  .

Tell me about it, I discovered them the day before the 6 hour, that put my mind at ease for the next 90 mins of track time.....

This is a bit of an extreme case though, 32mm TBs, and running on slicks.  I'll be ripping the engine out next year, so I'll seam weld the engine bay while I'm at it, and put a cage in.  Should do the trick.

Apparently the Nismo built R34 Skyline GTR used a layer of carbonfibre inside the engine bay to help add torsional strength to the chassis. That has me thinking about a carbonfibre insert that is molded with box sections, that is then bonded and/or bolted to the A and C pillars. Could even extend the design to include a lateral mound between the B pillars. Would only make the box sections in CF, the skin between could be a layer of fibreglass. Glue a layer of fabric over it and it could double as the hood lining.

Imagine the squeaks!!

[Duk]

Imagine the squeaks!!

Wrong bondage if it squeaks, you want to use the adhesive bondage, not the other one. 

[Colin Byrne]

Very interesting topic, and totally agree that there are massive gains to be made in chassis strengthening, particularly when you start make suspension changes, as the stiffer the chassis the more apparent changes will become to the driver, the result being that smaller changes will be noticeable, this is something I've spent a lot of time on in my car. 
   On your first sketch you show a nice triangulated joint with a bar running down from the top of the triangle to the middle of a straight bar, this is generally something you try and avoid with space frame design as it puts the straight bar in pure bending, rather than tension or compression.  So rather than adding weight (and time) for no real benefit you might want to re think it's position, or get rid of it all together, Just a suggestion

Nice work

[Duk]

Cheers for your input, Colin. It's a subject that I find very interesting, even more than the majority of engine modifications these days.
Is this the piece you were referring to?

[Colin Byrne]

yep that's the one, sorry a bit late on the comment

to make the most of it if you could find another point on the chassis to feed into this point you would then create a proper node?

just having another look at that photo, how do go with wheel clearance in full bump?

[Duk]

Yeah, I did wonder about the value of that piece. I figured it didn't weigh much so shouldn't be an issue. Do you think that it could reduce the effectiveness of the actual triangulation? I actually did that years ago, but the car has been off the road for nearly 3 years   and I don't even know how effective it is.
Wheel clearance looks pretty good, I bounced the Be-Jebus out of the front with the TB set pretty damn low and never got incontact with it befor the bump stops. Maybe with some mad steering lock, but that combination is very unlikely. Jacking the suspension without the TB and the guard on had the top of the wheel high inside the guard before it contacted. Intended spring rates will be fairly high. The red spring in that photo is a lower rate than wanted 'cause I stuffed up my motion ratio calculations (225lb/in when I wanted more like 350lb/in to get me close to the same wheel rate as a 28mm TB), but thankfully LaStreganera put straight with the number crunching.

[Colin Byrne]

It won't reduce the effectiveness of the triangulation much so don't stress about it.

As far as wheel contact goes, I wouldn't rely on spring rate limiting travel, if there is a possibility of contact before the bump stops there is a good chance it will happen on the track.  I run have run some pretty serious wheel  rates in my car  in the past and I still hit the bump stops and therefore spend a lot of time getting them in the correct spot to eliminate the possibility of contact.

[Duk]

Cheers mate.
With you dropping the 'track' word, I just want to make clear that this is a road car. Hence my comments about the Nissan GTR's, the M3 and hiding bracing inside a hood lining (if such a concept would even be worth while) rather than talking about some massive 50 point cage.