Jupiter diff. ratio change.

[Kevin Lord]

Jupiter going well with new radial tyres. And lots of minor tinkering. Currently running Javelin differential. 4.875/1. Have available 4.27/1 or would original 4.55 be more suitable if one is available. Any thoughts on loss of power on hills, against higher cruising speed, and loss of pepiness. Anybody done this or similar change. Comments appreciated. Kev.

[Keith Clements]

A Javelin diff makes the engine scream at Motorway speed. The Jav diff is narrower than the Jup and the Panhard rod needs to be changed (shorter I think from memory).
Ideally you need an even lower ratio than standard for modern roads. (If you have any down there!
Overdrive is advised. Only possible use of Jav diff would be for hill climbs or towing a caravan, since engine has broad torque band.
I would go for the 4.27 and if you have another one I will purchase! I will figure a way of getting it back; perhaps with a New Zealand rugby player that is about to join our club.

[Keith Andrews]

Kevin , give Neil Moore a ring in Auckland...hes does a lot of classic car racing racing and every yr travels great distances in his Jupiter...plus a heap of jupiter stuff overseas.
Hes seen it all and a very knowledgable and practical man

[Keith Clements]

I have Raced and Rallied the Jup for years, some with a Jav diff and some with a Jup with Overdrive and without. I had a quick change overdrive that allowed me to take it out between practice and race to suit the circuit. See pics on http://jowett.org/jowettnet/dt/tech/mod ... rdrive.htm

I have also competed in Javelin with and without overdrive.