Increase the torsenstiffnes in the Esprit

[rydning]

Is it any on this forum that have done anything to the torsenstiffnes of the Esprit?

Fred Basset wrote this:

We had John Miles at one of our Club Lotus meetings last year and he told us that the torsional stiffness of the Esprit was many times less than an average family saloon and it really was at the limit of it's design with the V8 power. Apparently they built a prototype with bracing between the bulkhead and the rear suspension top mount in the flying buttress and it made the world of difference to the car.

I have been thinking of making the torsenstiffnes better for several years now.

Does any have info about this?

Is it possible to ask John Miles for pictures?

Edited August 22, 2006 by rydning

[Jonathan]

Considering the chassis was debuted with the 160hp 2l lump and went on to support the 350hp V8 it's actually an excellent design. However I think I'm right in saying it's not as stiff as the Elise !

The s300 brace is 1 option, imo thats the weakest part of the chassis as the space frame goes around the engine....all race cars had it or a diagonal brace along with the roll cage which will increase the stiffness significantly....iirc the X180-Rs that were raced in the states had about 200% stifness on the production Esprit at the time !!

[esprithk]

hmmm...if someone can get his hand on a X180-R

it may be able to study its chasis design

[ragingfool35]

travis is a big x-180r buff

and has discussed this subject before with illustrations

contact him

[Vulcan Grey]

travis is a big x-180r buff

and has discussed this subject before with illustrations

contact him

Here is the X180-R roll cage, made by Saftey Devices in the UK.

Or you can make a slightly different rollcage like my friend Johan did.

http://www.extremeesprit.com/Safety_Mods_/...e/rollcage.html

and here is the Sport 300 bracing.

I've driven the X180-R and of course it is much much stiffer than a normal SE.

Here are some more details of the X180-R cage.

Edited August 23, 2006 by Vulcan Grey

[DanR]

Where do the bolts at each end of members #25 connect? I've studied my chassis and there doesn't seem to be any provision for their connection.

Edited August 23, 2006 by DanR1201

[Jonathan]

Back where the body bolts to the chassis and just infront of the bulkhead - can't be seen on that drawing, try and chase one up tonight.

Quickest way to increase stiffness is the cross brace, imo this is the weakest part of the chassis.

Post some pics later.

[Vulcan Grey]

Where do the bolts at each end of members #25 connect? I've studied my chassis and there doesn't seem to be any provision for their connection.

The Sport 300 bracing will not bolt into a stock SE-S4s. You would need to weld flanges into the car.

[Guest rflowers]

The Sport 300 bracing will not bolt into a stock SE-S4s. You would need to weld flanges into the car.

Travis,

Wasn't there something to strengthen the shifter box area in the frame (interior area) too?

Thought there were picture links a while back on the TurboEsprit list.

Also, anyone ever seen parts #20 & #25?

[karmavore]

Now I KNOW I could have a S300 style set up made with out too much time or cost. How hard could it be??

Lucas.

[Vulcan Grey]

Travis,

Wasn't there something to strengthen the shifter box area in the frame (interior area) too?

Thought there were picture links a while back on the TurboEsprit list.

Also, anyone ever seen parts #20 & #25?

Part #15 above is the plate to strengthen the hole around the shifter.

[rydning]

Thanks for this info.

Is that front brace #15 helping much?

I think to adapt my sandwich roof and glue it with fiberglass/CF to the body. Rollbrace in front of the engine compartment with crossbraces from the shocks.The rollbrace have to be glued and joinet to the roofsection. And braces from shocks straight forward to frontbrace where the crossbace from the other shocks is conected.And some more braces to link this whit the chassi.To get a complete rigid rearend.

To keep the interior nice and free from parts.

Is it any with some more ideas?specialy in the front?

[Vulcan Grey]

Thanks for this info.

Is that front brace #15 helping much?

I think to adapt my sandwich roof and glue it with fiberglass/CF to the body. Rollbrace in front of the engine compartment with crossbraces from the shocks.The rollbrace have to be glued and joinet to the roofsection. And braces from shocks straight forward to frontbrace where the crossbace from the other shocks is conected.And some more braces to link this whit the chassi.To get a complete rigid rearend.

To keep the interior nice and free from parts.

Is it any with some more ideas?specialy in the front?

Yes, the hole around the shifter is a large problem for chassis stiffness. One of the best things you can do to the car would be to add #15.

[Jonathan]

S4S had that iirc

From looking in the engine bay there is definatly places where the brace can be fitted.

[Htown]

got stiffy?

http://www.autofoam.com.my/index.htm

[Vulcan Grey]

I have not fit the plate, but Michael Fennell has

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

he actually bought the sport 300 plate, but his mechanic thought it was too wimpy, so he made his own.

You can see his comments here

http://lotus.roadfly.com/turboesprit/searc...l&o=default

[Jonathan]

Very interesting - might have a go at that sometime.

[Guest rflowers]

I have not fit the plate, but Michael Fennell has

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

he actually bought the sport 300 plate, but his mechanic thought it was too wimpy, so he made his own.

You can see his comments here

http://lotus.roadfly.com/turboesprit/searc...l&o=default

Travis,

If there is additional bracing in a S300 engine bay over a stock SE/S4/S4s bay can you post pictures?

[Vulcan Grey]

Now I KNOW I could have a S300 style set up made with out too much time or cost. How hard could it be??

Lucas.

Well you might have to remove the engine to weld in the required mounting points...

Other than that, not too hard.

Johan's roll cage guy was very good, and even did some of the welding with the interior in place (only one small burn). But he had to remove the dash, engine, rear window, front windshield (broke into a million pieces upon removal by glass technician). And it took months!

[Vulcan Grey]

Travis,

If there is additional bracing in a S300 engine bay over a stock SE/S4/S4s bay can you post pictures?

The only items that I know of that aren't shown here are extra points where a full roll cage could be mounted, and those are probably similar to the X180-R.

The front roll cage mounting flange to front shock tower looks like this.

And in the rear it (the cage) makes replacing the suspension very difficult.

[karmavore]

Sure, I'll bet a roll cage would be a huge PITA.

Kirt makes roll cages all the time. Every one custom and on every type of car. To do that engine bracing couldn't be more than a day or two's worth of effort ..besides, as you say, the engine removal. I'm surprised more people haven't done it.

Are there any reviews on the S300 rigidity vs. the SE?

[Jonathan]

Yes it's much improved, if you have a model of the chassis (like me ) you can hold the 2 front hubs with one hand and the rear hubs with the other and twist - the flex is in the rear space frame where the 2 upper beams running from the chassis to the rear suspension upper fixings move side to side like a parallelagram.

The cross brace stops this action, the front cross member imo is pretty darn strong.

Yes I know it's only a model but it's not going to be far off.

The brace is shown in red and sits over the engine (not drawn very well but nemind)

It stops the paralellogram action.

Other racers used this kind of option to do the same thing - it's MUCH less intrusive into the engine bay.

Why does no one fit the S300 brace ? Dunno, mebbe because it's do bloody hard then to work on the engine - reading the Esprit book here the engineers on the line HATED the S300 brace becuase it was so hard to assemble and do work on the cars.

I have a photo of the S300 brace but it's at work

If in doubt buy the latest Esprit story book - SOooooooooooo interesting if you're into all that, LEW has a discount on it too if you're a member, it's easily worth every single penny and shows stuff like this.

[DanR]

I doubt there's flex is in the rear frame section. With my engine out I set up a wire pointer from the rear inverted U channel to a point between the lower control arms. Jacked up one side at a time under hub/disc. There was absolutely no deflection of the pointer. The twist is in the spine, thus the cracks around the gearshift opening.

I think there is a lot of torsional rigidity added by the rear bulkhead. There is only that bulkhead and the two rear mounting bobbins, which have a history of cracking, to add extra stiffness from the body itself. I read somewhere the body doubles the stiffness of the chassis. Probably does as long as those points don't become loose (bulkhead) and/or break (rear bobbins).

I'm considering fabricating another bracket from the engine mount brackets that spread the load to the longish channels which support the shields alongside the tanks.

[Jonathan]

There's a fair bit of flex which is why the brace was there, according to the book that is, I dont have it here so I can't quote it. I was always told triangles offer the best rigidity, where is there not a triangle ? in the top box shape of the rear chassis - every single race car I have seen uses a chassis brace here.

Originally the rear cross member brace, between the 2 rear suspension turrets, wasn't there under Colin's insistance it wasn't needed....one day they used pre production S1 Esprit to pick him up from heathrow on an F1 journey and the rear hub carrier broke (know the feeling) becuase this brace was not there....which is why it exists today.

If you jack the car from the centre hoop under the gearbox without the rear cross member the tops of the 2 dampers move apart slightly as the weight is taken off the chassis at those points - on both the cars I've had to put some weight on the wheels in order to put the cross member back due to flex, doesn't move a huge amount but enough. Without the engine you're not loading the wheels enough so I don't doubt there is any flex.

Not sure about the body affecting the stiffness - jack it up on one of the 4 body jacking points and watch it twist, open the door and see - body don't seem that strong to me

[DanR]

Know what you mean about the chassis splaying when jacked without that U channel. The brace would be nice to fit. Still I think that spline/backbone section, though stiff lengthways, isn't in the twisting plane. This is a normal feature of backbone chassis design and evident in production cars too eg those with T tops like Pontiac Firebirds, 280ZX and MR2.

This article http://www.lotusespritturbo.com/Lotus_Espr...7_Road_Test.htm

mentions the added stiffness from the Esprit body.

When I did the jack and pointer test, even without the engine , I had expected the slightest deflection (a degree would have been about 2-3mm so nothing suggests it's stiff in that plane). Ideally if the front could be locked down and a long beam be fitted to the rear crossmember, greater leverage could be applied and some ballpark figure of the bending force per degree worked out.