Improving Torsional Stiffness

[DanR]

Here is how I made a couple of braces to improve the stiffness of the rear. I've now done about 1000klms. Some of those roads have been quite rough and the improved tightness and quietness is very noticeable.

These spread the load between the rear bobbin and the next mounting point on the ply baukhead. I had the engine out but I think it could be done with it left in as long as there is plenty of working room above and below the car. Also make sure to mock up and include the side panels because those rawlplugs will have to go.

I'm pleased with the result and won't be taking them off.

With the right hand brace I added that plate with the rolled edges to tidy up the four water hoses. They are stacked on top of each other and are held on with cable ties.

[Vulcan Grey]

If you really want to get industrious you could add the Sport 300 shifter plate like this.

http://www.exit109.com/~mfennell/lotus/chassis/

[Jonathan]

Make sure you make 2...ummm actually 3 though eh just incase the 1st one doesn't fit and then the other 2 you might wanna perhaps.....sell, or....pass on to someone....

Not naming any names

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On a serious note I can't quit make it out - if you've got time any pics would be really much appreciated, might be something to do in the GT2 before the roll cage goes in.

[abrussich]

If you really want to get industrious you could add the Sport 300 shifter plate like this.

http://www.exit109.com/~mfennell/lotus/chassis/

I just had to replace the shift on the 89 after the nylon bushing sheared off. I notice in the photo that the shifter has a tab cast into the side. I wonder, is that a later model shifter assembly and would it work on the 89?

Would you know anything about that?

Al

[Vulcan Grey]

I just had to replace the shift on the 89 after the nylon bushing sheared off. I notice in the photo that the shifter has a tab cast into the side. I wonder, is that a later model shifter assembly and would it work on the 89?

Would you know anything about that?

Al

Yes that is true, the later cars had that stop block for the reverse lockout inhibitor plate molded in a robust one piece design. I don't know when it started but it is on the '91 X180-R.

Don't konw if you can add it for sure, but I would guess so.

[Paul93Lotus]

Yes that is true, the later cars had that stop block for the reverse lockout inhibitor plate molded in a robust one piece design. I don't know when it started but it is on the '91 X180-R.

Don't konw if you can add it for sure, but I would guess so.

My US version '93 had that same style shifter...its build date was 12/92.

[DanR]

Wow Trevor I like that. Did you have to cut the glass tunnel for access and did you make that part or is it readily available?

Jon, the our chassis are like a "Y" at the rear so anything to help limit the spine being twisted by the "v" will be helpful. Especially since the suspension loadings are transmitted through the bobbins on the end to what are quite flexible f/glass flanges off the wheel wells.

Those side panels I referred to:

are the ones that are removed before taking out the tanks. If you look closely they sit on an inverted "u" section which, from their looks and that of the box around the tanks, strike me as very strong. The square tube fits in that "u" and the flat plate is on the other side of the f/glass. Whenever the car is jacked up under the sill the weight of the drivetrain and chassis is held up by the rear bobbins and bulkhead bolts. With my brace that flat plate also takes the hanging load. When the car's on the ground the length of the square tube and flat plate distribute the load almost over the length of those "u"sections. I checked the strength of the braces by jacking up one and then both sides of the car with the two rear bobbin bolts removed.

While it's nothing like the brace 300's have it has made the car stiffer. Also the 300's have lighter glasswork unlike our cars which are more structural, similar to a boat and perhaps better for imparting additional stiffness to the chassis.

I'm not sure if these could be made as a kit but probably need to be individualised for each car.

Hope this is helpful.

cheers

[DBredS4]

this is an interesting thread, I wonder if Lotus made any attempts to uprate the stiffness or develop an OEM option kit such as the S300 engine brace and gear stick reinforcement. I would be interested if they did.

I would also be interested if they could fit a roll cage, nothing too obtrusive as the ones I've seen tend to make the interior look like a building site and restrict access!

I suppose they are concentrating their efforts where they need to, ie on the new Esprit. Oh if I had the money...

[Artie]

I've contemplated increasing the torsional stiffness since owning my Esprit. There are a few ideas I've had. Make a thin box beam X of aluminum and attach it from the bulkhead mounts behind the firewall (would be a smaller spaced leg set on this mounting point) then run the larger/wider top legs outward to the mountings under the rear hatch shocks. Other location for structural support would be under the cabin where the 4 body mountings are, run 2 parallel aluminum box beams(thin like 1" max) attach with the body fixing bolts and run forward into a triangulated brace that attaches to the anti roll bar mounts. This would give a great amount of both body restriction and directly strengthen/support the thinnest/weakest point of the box beam in the frame(under the shifter mechanism where it's prone to cracking). I've also considered running a "strut tower bar" across the boot from the big 19mm body fixing bolts to each other(they'd need to be spaced upward about 1/2" but this would tie the two fixing points together with a common point versus the 4 bolts thru the thin walled chassis tie. And finally considered running a thin I beam aluminum brace across the hatch mounting bolt plates(under the leather surround on the rear window frame)

Artie

[rydning]

I belive this atemd will improve.But not a lot.

I think we need to make of the twisting forces at the rear to be acting more direct on the firewall.

The firewall is made of tick plywood and is bondet to the rest of the car,so this is the best place to beginn at.

In the front of the engine bay where all the tubes in to the box.

If we are able to bolt this better to the firewall it vill help more.

I did think to make a roll bar in the front of the engine bay that are bolted/glued to the firewall.

Make stuts and X struts from the damper to the rollbar will improve a lot (but also a lot of work and removale of some fiberglass).So its fully triangulated

[Artie]

Yeah, it'd have to be triangulated. Any additional stiffness would be a great addition imho! These cars FLEX alot!!!! This isn't a monocoque design so it's limited by the heavy body twisting the main box attached at two ends by a stable frame. If you could minimize this movement it would help, even in the smallest of increments it would be benefitial in both feel and suspension response to twisting.

Artie

[ragingfool35]

load paths are tricky things

no matter what the path is designed to be, it will always be thru the stiffest part.

so stiffen some section with a small plate and it will likely take the loads and fatigue quickly

stiffen both ends of the car and the box beam tunnel will take all the loads and fatigue at any stress concentrations

(any holes like the shifter hole)

bond the chasis to the rigid body structure better and the loads will be trasfered thru the body until it cracks

a roll cage that would link the front and rear wheels (away from the central axis of the tunnel) would do wonders

to stiffen the car, but then the suspension would be all wrong!

the standard thing to do is to model the structures and run them thru an FEA cycling program

go thru iterations of design and FEA testing, then confirm with actual testing

then the biggie for the automotive industry: crash testing and certification!

very unlikely Lotus would think about such an undertaking