Power, torque and chassis strength

[Nifty]

I'm assuming it is torque that is causing chassis damage like Arnie's.

 

So what sort of torque figures are 200bhp Scholar 1.9K engines pushing out and would you consider my 1995 chassis (with removable engine bay cross members) able to handle it without modification 🤔

 

Do R400s have strengthened chassis 🤔

 

Your thoughts please

 

 

Edited to say that I intend to fit a ZF LSD too if that makes a difference to the loading on the diff mounting.

 

 

Keep off the straight and narrow 😬

 

Edited by - Nifty on 4 Mar 2006 07:47:59

[Jason Plato]

The 1900's are pushing out between 160 - 178lb torque .

 

I think its more than just torque thats fracturing the chassis - its also down to clutch, gearbox , flatshifting , year of chassis and tyres .

 

 

[AMMO]

And doughnuts. The amount you eat and the amount you do. 😬

 

I have 175 ft lb of torque on my 1989 big tube De Dion. No breakages yet. I keep checking. Matt Deakin's similar vintage chassis broke with a bike engine in. Although it was prviosly fitted with a RK Crossflow I think.

 

Personally I will play a awiting game and see if anything goes before I do anything about it.

 

AMMO

[Normans_Ghost]

My top bracket (n/s) had broken away and we did a quick mig weld fix 4 days before going to Le Mans last year.

 

It broke away again and I stripped the rear and brazed it back on this time with an angled flat bracket brazed in across the bracket to chassis.

 

I've refitted the diff and not tightened the top bolt so as to allow slight movement on take up.

 

I don't do donuts and treat the car with mechanical respect, which, I suspect, makes a difference.

 

I did notice that the chassis metal was much thinner than the bracket which needs some skill in heating the relavant metals correctly.

 

Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here

You and your seven to The French Blatting Company Limited

[oldbutnotslow]

Ive kept saying that having a Papier-mache chassis is not a good idea Nifty despite the weight saving!! 😬

 

Grant Taylor

OBNS Motorsport

 

😬 183 BHP of Black and 'Stone Chip' excitement. 😬 here

 

[EFA]

Clutches are the primary cause, flatshifting is not a problem, clucthless downshifts are a big problem.

 

Norm, If you brazed you chassis rather than nickel bronze welded it, you may find ti a good idea to read this here

 

I also thought they were brazed until I read this!

 

 

 

K2 RUM - The 7 in front of you is a DIESEL

[Shaun_E]

Nifty - my target power was around 200bhp but it ended up a fair bit higher (227). Peak torque is 167 lbft. I haven't had any chassis alterations so I guess I'll just keep an eye on it. My car also has removable engine bay cross members.

 

Yellow SL #32

[EFA]

Engine power is also not really the issue. Its the torque reaction through the chassis from the rear wheels when there is no drivetrain compliance due to high grip sintered clutches and sequential boxes whihc allow clutchless downshifts, as I mentioned before.

 

Remember the Kumschick cars had 300bhp and over 200ft/lbs, but they never broke chassis except upper diff mounts where the chassis design is just simple bad design.

 

I have this week sourced a new (in the Caterham sense) type of proopshaft which is rubber lined between the drive and load shafts (principally like a metalastic bush) This should address the zero drivetarin complance issue but allow the advantages in terms of inertia reduction provided by small sintered clutches.

 

I have strengthened my chassis further (in fact I have cut out the whole rear end of the tunnel and re-designed it to include 6 diff mounts - but this is to some extent academic and just an insurance against the money I am spending on cosmetic reconditioning of the chassis/body)

 

 

So if you have 227bhp amd 167lb/ft on an organic clutch of factory option dimensions, I think you will be fine. Particularly if you have the 1996 onwards chassis which has a much improved tunnel anyway.

 

Remember, we don't hear of any R500's (and there are lots of them around) with these kinds of problems.

 

 

K2 RUM - The 7 in front of you is a DIESEL

[Big Brother]

Anyone know how this works (torque reaction and chassis stress) on a live axle?

 

Am I right in thinking that the majority of the stresses caused by torque will be seen within the axle as opposed to the chassis?

 

Steve

 

 

SE7EN-UP!

Incorporating the Caterham Links Database

[EFA]

Steve,

 

On an LA axle the stressed attachment points are some distance from the axis of the turning moment, on the edges of the chassis. Therefore the torque loads on these points reduce proportionally with distance (lb(load)/ft(distance)...)

 

The issue is that the Di Dion chassis, particularly pre 1996, is a live axle chassis converted to carry the diff. This is where and when the compromise occurred in terms of triangulation and loading. There is not that much difference between a LA and DD chassis, and much of the design was carried over with a view to supporting the diff rather than considering the loads imposed and the structural changes required to cope with this.

 

A rudimetary effort was made in 1996 to deal with this. Not great, but a big improvement.

 

K2 RUM - The 7 in front of you is a DIESEL

[Big Brother]

Thanks Arnie - read your reply, got to the bit about torque/distance and the penny dropped

 

 

 

 

Steve

 

 

SE7EN-UP!

Incorporating the Caterham Links Database

[Grubbster]

Nifty - the ZF LSD will make a lot of difference in your case, but don't worry I'll take it off you for a donation to NTL

 

Roadsport build photo's here

Le Mans 2004 photo's here

 

 

Edited by - Grubbster on 4 Mar 2006 14:33:32

[Bricol]

Pedant alert!

 

Torque is measured in force x distance - so lbft or lbin or Nm or mNm or mNmm etc

 

Spring rates are measured in force / distance - so lb/in or N/mm etc

 

Alert over.

 

But it does bug me - even get "professionals" supplying me info at work in the wrong units . . .

 

Easiest cure for all these chassis worries (apart from buying one of those other "sevens" ) - narrow, hard, rear tyres

 

Bri

[Peter Carmichael]

Here we go talking about engine torque without thinking about the gearing in between the flywheel and where the damage happens. In Arnie's case, the diff ratio is a contributory factor. In all cases, it is much less of an issue once you are out of 1st gear.

[Nifty]

I realise that the gearbox affects torque at the diff Peter .... however, within reason we are all running similar gear ratios anfd therefore the difference between vehicles is the torque going into the gearbox, which obvioulsy affects the torque coming out of the gearbox once the gearing factor has been accounted for.

 

In a mathematical equation way the gearbox is a constant and can therefore be removed from both sides of the equation .. if you see what I mean

 

Keep off the straight and narrow 😬

[Peter Carmichael]

Ah, Nifty, you're sounding like me.

[elie boone]

The torque loads on a LX are also damped by the shockabsorbers.

 

The problem on a DD chassis is that the only mounting points are close to the diff itself.

 

Myself i am not a fan of the DD, it was designed for Astons and big Merc's witch need big differentials to cope with the torque and bhp and still have a accetable level of comfort witch would be difficult with a LX on 60's roads, this is not the case in a Seven where lightness is the most important factor.

 

It puzzels me that some people only reinforce the chassis arround the diff but i never hear of aditional bracing towards the outer tubes of the chassis witch would spread the load much more.