Re-Design

With the arrival of a supercharged 4.0liter Jaguar AJ-V8, the chassis is obviously going to need attention.

Also on the attention list, is the gearbox and possibly the differentials.

According to Ford Germany, the standard MT75 gearbox is rated at 300Nm / 221lbs/ft torque.

I can’t find any figures for the front and rear differentials, but according to various ‘so called experts’, seem to be 350Nm rear / 300Nm front.

The standard Locost chassis was designed for around 130Nm. I have added quite a bit of triangulation to the rear but I have neglected everything forward of the seat.

The Jaguar V8 puts out 525Nm / 387lbs/ft. Forget the extra weight for now, that’s 4 times what the original car was rated at.

I need to chase my FEA (Finite Element Analysis) mate again to see if he can analyze the stresses through the chassis.

Has anyone else done FEA on a Locost or Haynes Roadster?

In the mean time I have been modelling the AJ-V8 and turning the chassis into a reinforced monocoque. Un-like a traditional Locost, this build is going to have full bodywork. I want to use a lot of aluminium sheet to generate a monocoque frame around the steel tube chassis. With added triangulation and a solid roof I’m not worried about the rear half of the car. The last time I saw the FEA the area that needed attention was around the windscreen / bulkhead area. Stresses from the suspension, engine torque, cornering etc, all seemed to use this point as a ‘hinge’.

On the subject of weight; in conversation with ‘my FEA guru’; he pointed out that perfectly matched corner weights are undoubtedly a good start, but as cars accelerate, brake and corner the weight on one wheel can increase by at least 10 times. A poorly set-up suspension will totally void all those hours weighing components and setting up corner weights. Weight shift has as much to do with road conditions as it has driver action and weight distribution. Perfect weight distribution may give better predictability but according to ‘my guru’, once you are in the ball park, don’t get too hung up about it, as there is a massive list of other factors to contend with. Height of centre of gravity, brake balance, spring rates, damper settings, tyres, chassis flex, play in rubber bushes, cornering force, acceleration, braking, poor driving etc etc………

Perfect weight distribution is only the ideal under cornering, for optimum acceleration or braking this would not be the case.

Chassis

Note the width of chassis at the front compared with the surrounding bodywork.

I’m not building a stripped out, ultra light racer. This ‘Haynes Roadster rebody’ is an exercise in Locost CAD engineering, the driving experience is not on my mind yet.

The other major change is the gearbox. I have found several sources that suggest the RB26DETT gearbox from the R33 Nissan Skyline is good for at least 540Nm in standard form and the Getrag 6 speed model closer to 650Nm.

RB26DETT gearbox

This gearbox is wider, longer and heavier than the MT75. It may even compromise the pedal position. I need to get hold of a box first and offer it up into place. There is a strong possibility the Locost chassis underneath will be completely scrapped and a new wider and much more rigid semi-monocoque chassis take it’s place.

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