Mazda RX7 Racing Experience

[yelwoci]

Does anyone on the Forum have experience of setting up or racing RX7s.

Your input would be appreciated.

For those of you have engineering experience but not necessarily with the car, here is the background.

Racing RX7s in Group-1 spec are 930kgs (2050lb)(55:45), 200hp@rear wheels racecars, running on road tyres (Dunlop D84J radials)
The car has Macpherson struts at the front with caster bars and a stabiliser/roll bar.
The rear is a live axle with lower (46cm?) and upper (15cm?) trailing arms. The upper links are mounted on the outer ends of the axle, rather than the more sensible location around the diff casing.
The Watts linkage is a very clever, but possibly suspect design, using asymmmetric link lengths and located forward of the axle, with the pivot point about 20cm from the axle centre line.
The rear suspension suffers bind after about 3.5deg of roll.

There are two approaches to the setup: High or Low.

I run the car in the rarer low configuration. (4.25" measured at the chassis rail under the drivers feet) The roll centre at the front is above ground and is estimated at around 6". The front track control arms are just higher inboard at rest. But the roll stiffness is very high with 300lb front springs and Racing Beat 1 1/8" stabiliser/roll bar with approx 12" 'legs'.

The rear runs 4.5" at the forward mount of the trailing link. The geometry put the roll centre in the road. There is no stabiliser/roll bar and the springs are about 200lb.

The car, according to your view, looks after the tyres or doesn't use them hard enough. It corners very flat and requires an early turn in. The car slides on all 4 tyres together.

Raising the ride hight would increase the roll and weight transfer and may be improve the turn-in and braking grip, but it it will also increase the effects caused by the poor rear-end geometry.

Any thoughts?


IanC
PS Caroll Smith may email me personally!