Retro overdrive on FHC

[Sheds]

Like many owners I'd like to fit an overdrive unit or 5 speed gearbox to my S1 FHC (not a 2+2) to allow me to cruise at 130 kmph on the continent at lower engine revs, ideally around 2200 rpm.

Looking at 5 speed gearboxes, either they are just too expensive or they require works to the tunnel and crossmember which I'm not keen on.

One other option is the retro-overdrive unit from Overdrive Repairs in Sheffield, which is intended to fit between the diff and the gearbox with a shortened prop shaft. Has anyone tried this approach? The unit is 36cm long and 23cm in diameter, so it might not physically fit due to its girth...

Interested in case someone has already tried this.

Thanks
Piers

[christopher storey]

In my opinion there is absolutely no chance of that fitting without major ( and disfiguring) surgery to the bodyshell and the tunnel, and frankly I think it would be downright impossible on a short chassis car because of the position of the seating . Those units ( which are very good ) are largely intended for separate chassis cars where they can be fitted without too much disruption

[bitsobrits]

The Overdrive Repairs option is not an option without major surgery. There is simply no room for it.

So you are left with the 5 speed options (expensive, but really nice in practice) or a drastic change in rear end ratio.

It would take something like an overall ratio of 2.1/1 to achieve your target 2200RPM at 130km/h which is very low indeed.

What is your current diff ratio?

With my U.S. spec 3.54 diff, 205/70 XWX tires and .73 (5th) 5 speed, I'm about 2700 at 80mph (130kph) which seems fairly relaxed to me.

[Sheds]

Thanks both. I'll take a look next time it's on a ramp and get more familiar with the underside!

In which case my best bet is a 5 speed box, either the Elite Racing or the Crosthwaite and Gardiner one (that is sold by Jaguar Heritage as their box), both of which are Tremec boxes and neither requires any hacking of the tunnel or crossmember. Both have a 0.63 5th gear, so with my standard 3.07 final diff it should give 80 mph at about 2000 revs.

Does anyone on here have an Elite Racing box fitted to their car?

[mgcjag]

There is a huge amount of info on the forum......try a search for Elite ......Steve

[Sheds]

Thanks Steve, yes, I've read all the Elite related posts already. Ideally I'd like to find someone with an Elite box on a 6 cylinder car, but I'll keep looking.

cheers

[mgcjag]

viewtopic.php?f=9&t=7226&p=111227&hilit ... ox#p111227 post 272 onwards

[Simonpfhc]

Hi Piers,

I have a FHC with an Elite Tremec 5-speed. Covered more than 10k miles with zero issues.

PM me if you need any other info.

[Sheds]

Thanks Simon, I've sent you a PM!