I've said previously that I enjoy the learning curve that comes with these projects and this week highlighted yet again how little I really know!.....
....the plan has always been to be as faithful and accurate as possible to a genuine in-period RS/RSR. Visually....naturally but also with the integrity of the components used and mechanically most definitely so that the car drives as close to the real thing as possible........in an ideal world that would mean using all genuine original parts although practicality and realism dictates there was always going to be compromises along the way....
....one of those variances is the engine cases. For many reasons this Carrera 3.0 is a great base for this project and the 930/02 engine with it's aluminium block and 6-bolt crankshaft the perfect core for a 3.0RSR spec build, however visually it differs underneath and this is a point I have to accept...........the matching numbers gearbox on the other hand looked exactly like any magnesium box of that era, it obviously needed modification but seemed perfect and therefore I gave it little thought.....
....having secured an original 10K tacho recently my thoughts turned to my other gauges. Due to their scarcity I thought it unlikely I'd find an original 180MPH speedometer and therefore planned to send my current speedo to North Hollywood to be converted however on inspection I noted the trip button sticking out the front of the gauge.....
.....worse was to come when I flipped it over
.....
.....the bloody thing is electronic rather than mechanical!......this obviously meant my gearbox was also missing a mechanical drive and something I'd overlooked when I dropped the end case to Ben Coles for machining last year!!!
.....
....onto 'Plans B/C/D'.......one option was to modify my gauge anyway and keep the electronic drive which would have meant losing the trip functionality, a pants idea!.....or find another speedo to modify and look at gearbox options later.......a quick call to Gary Cook for advice and I couldn't have been happier.....
'don't worry about adapting a speedo' he said,
'as I've been saving an almost new original 180MPH gauge for you!' ....
....just how cool is that!
Mr Cook is absolute legend
........ultimately it has to be a mechanical speedo, electronic just wouldn't have been right....
....with thoughts now turned to gearbox spec I started looking at exactly what my 915/61 gave me......in addition to now needing an end case with a mechanical speedo drive, other issues were adapting the clutch mechanism to the earlier type and lose the omega helper, simple......although fundamentally different to RS spec is the 8:31 crown wheel pinion......those who know will tell you that whilst the later 8:31 is a stronger and more reliable option, it doesn't have the liveliness of the earlier 7:31 CWP and the car would lose some of it's low down zip
......
....I was expecting to change gears to build an RS spec box although things were now building up and whilst I liked romance of keeping the car 'matching numbers' (nonsense I know considering the modifications) a better option was to possibly switch to the very good 73 915 gearbox I'm fortunate to have....
....thankfully Mr Bainbridge had other ideas and feels the current gearbox with its later stronger input shaft is better equipped to deal with 320HP going through it......to retain the feel of the RS box he recommended a Tandler 8:35 crown wheel pinion which has no noticeable difference to a 7:31 but is again a stronger upgrade.....
.....with ZF diff already sourced through Mike
.......
....specification of the gearbox is now:
Number 7174852 - 915/61
8:35 crown wheel pinion
RS Gear Ratios:
1st - 3.18 (11/35)
2nd - 1.83 (18/33)
3rd - 1.26 (23/29)
4th - 0.93 (27/25)
5th - 0.72 (29/21)
Plate Type ZF Limited Slip Differential
RSR Oil Pump with Trombone Cooler
A slight deviation from stock but a worthwhile upgrade and still pure RS in spirit plus the car remains matching numbers!
I wonder what else I've missed!!!
Cheers,
