Drive from this output sprocket on the gearbox is by a sequential two chain set-up driving initially to an interim cushion hub, with the second chain driving from the hub to the sprocket on the axle differential shaft. Typical of the man, mechanical sympathy is in his blood and whilst conversions of this nature have been done with direct drive from the output sprocket to the diff shaft, Dave’s design minimises shift and drive shocks to the transmission and clutch.
Next we get to the subject of gearing and the choice of drive sprocket sizes. This particular engine is the 137Bhp version (that’s 117 Bhp more than a stock ‘500’) and given the size of the car, that power would result in a top speed of over 200Km/h, something Dave is not interested in doing, so the gearing had been adjusted to a max speed of 171 Kmh at 9000Rpm or 190Kmh at the red line of 10 000Rpm. This Final set up being more of a balance between first gear gradeability and top gear noise levels than the desire to wring out absolute maximum speed. Besides….once on full song, just imagine the sound of those close cogs rapidy playing with those engine strings.
Gear Km/h per 1000 RPM Km/h –
1000 9 000 10 000
1 7.25 65 73
2 10.59 95 106
3 13.83 124 138
4 16.61 150 166
5 18.97 171 190
That max speed in second gear bodes well for a 0-100 dash being completed in just two gears.
Initial shake-down tests have shown the gearing choice to be good. Whilst carefully trying the machine out recently, the superbike sounds of the engine and close ratio gears emanating from this machine make for spine tingling stuff according to Dave. The sequential gearbox is a gem, requiring a forward push for upshifts and rearward pull for downshifts.
Reverse gear: There is no reverse….but then again the car weighs in at around 550Kg and is physically tiny….so the lack of reverse is unlikely to be an issue.
Just for the record….. power to weight ratio of this 500 in ‘old speak’ is 8.9 lbs per Bhp, that is in the same ballpark as a Chevy Can Am and a little better than a BMW M2. So… if you let it all hang out, 0-100 is projected to be in around 4.9secs with a ¼ mile in the mid 13’s. That’s the theory.
At this point you are probably saying to yourself “that is all very well but how does one keep this screamer on the road and more important, slow the machine down..”……easy…..you have Dave.
As a development engineer specialising in suspensions, wheels, tyres and braking, my first recollection of the man doing his thing in his chosen field had to do with a severe wheel shake harmonic we were experiencing in the development 38/4100 Chevs of the early 70’s. This was the Opel Rekord/Commodore body shell fitted with the local Chevy straight six. The front end of the car was sensitive to a 15Hz frequency which, when provoked, set the front end jiving, resulting in a serious steering shake. Careful wheel balancing helped but the first harmonic of the wheel/tyre caused a vibration in sympathy with the front fender assemblies…. easily also induced by road input. With the vehicle launch drawing nearer drastic action was required. The original ”final solution ” had been to attach a lateral ‘mini’ damper to the cylinder head and locate that on the inner wheel well in order to damp the lateral engine shake….this was expensive, looked terrible and induced a certain amount of noise into the cabin…..it was also something of a committee design at the time.
In one of the many Development stories I will be posting on the history of work conducted in engineering in the old days, this one took three to tango. Dave is also something of a Noise and Vibration expert and in conjunction with the body engineers, worked out that the shake was caused by the front end moving forward of the bulkhead. Two corner stiffening box sections were introduced into inner wheel wells and “straddle” engine mounts designed to move the mounts off the engine X- member and onto the fender longitudinals.. These two mods stiffened up the front end and importantly changed the natural frequency …..80% of the problem solved…. for the rest it was up to the suspension group to suss out why perfectly balanced wheel assemblies still showed signs of imbalance.
Along came the first car in SA to introduce radial force variation (RFV) matching on wheels and tyres ……the 38/4100 series, courtesy of Dave. What he and the team had found was that due to the large 14” rubber used on what was a relatively light body structure, the inherent sidewall stiffness variation in the rotating tyre assembly had sufficient energy to induce a phenomenon akin to steering wheel shake. To cure this we had a real case of two wrongs making a right. Steel wheels have a natural characteristic in having a measurable high point on radial run out…it’s part of the process inherent in any steel wheel manufacture. Similarly, tyres have a characteristic as a result of the lap joint, which changes the sidewall stiffness ever so slightly as the tyre rotates. By fitting the tyre on the rim at specific ‘high’ and RFV points, the two cancelled out the energy transfer. No more vibes.
So we have a thinker and a problem solver here and as we go through the 500 Testarossa’s design pedigree you will see just how talented is this engineer.
Dave’s Italian leanings facilitated the next piece of magic….the decision on what type of rear suspension to use……. an Alfetta gave up an ‘A’ frame De Dion rear end complete with inboard discs and differential. The unit was cut, re-jigged and welded to cater for the narrower track width…. giving this baby a pretty sophisticated rear axle arrangement.