CWP ratios

[smallfry]

Can lower ratio CWPs be got for the Rover axles/diff ? Something like 2.8 to 1 ? Not for a LR though, but a P5 Rover car, which of course has smaller wheels. 

[Chicken Drumstick]

That would make the gearing very tall in a P5. Unless it is rocking 250-300bhp+ I'd have thought with such gearing it would be a slug and lethargic to say the least. Probably best to see what ratios where offered with the automatic Rover cars, they are likely to be tallest factory options. I know on my TR7 (different axle) there was a 2.84:1 for those that like acceleration recorded on a calendar. 😂

[Anderzander]

P5’s were the other way weren’t they ? 3.9 and 4.3 ? 

[FridgeFreezer]

Volvo diffs are VERY similar (but built much more Swedish) and some are lower ratio due to being in front of portal boxes and may bolt in to a Rover axle:

Ratios:

• 9×33 = 3.666666:1 (x 2.06 = 7.553333:1 overall)
• 9×31 = 3.444444:1 (x 2.06 = 7.095555:1 overall)
• 11×32 = 2.90909:1 (x 2.06 = 5.992727:1 overall)
• HOFS did a ~5:1 overall ratio diff

[smallfry]

2 hours ago, Anderzander said:

P5’s were the other way weren’t they ? 3.9 and 4.3 ? 

Yes they were. Might have been higher than that ! Can't remember offhand.

The V8 was 3.54, same as RRC and Defenders.

[smallfry]

4 hours ago, Chicken Drumstick said:

That would make the gearing very tall in a P5. Unless it is rocking 250-300bhp+ I'd have thought with such gearing it would be a slug and lethargic to say the least. Probably best to see what ratios where offered with the automatic Rover cars, they are likely to be tallest factory options. I know on my TR7 (different axle) there was a 2.84:1 for those that like acceleration recorded on a calendar. 😂

Um, it might be doing just that, with a modern(ish) diesel conversion maybe. Its not a sports car anyway, and I am more interested in MPG, so I can use it more.

The SD1 autos had a 2.83, (that might actually be the solution ! ) and they were not that slow. Three speed and no overdrive top remember.

For my sins I actually liked the TR7, a shameful admission according to some, with a view to converting it to V8, but never got round to it. Too many LRs ! 20 odd years ago I was offered one for nothing, green with a tan tartan ? interior and Webasto sunroof. Had nowhere to put it at the time.

[smallfry]

13 minutes ago, FridgeFreezer said:

Volvo diffs are VERY similar (but built much more Swedish) and are much lower ratio due to being in front of portal boxes, they're in the 2.x:1 region and may bolt in.

I did think of a 740 axle with LSD and disc brakes. Used to be able to get them for next to nothing, but rare now, and sadly the ones I have seen are off of banger raced cars, and might well be bent or damaged in some way.

[Snagger]

8 hours ago, smallfry said:

Um, it might be doing just that, with a modern(ish) diesel conversion maybe. Its not a sports car anyway, and I am more interested in MPG, so I can use it more.

The SD1 autos had a 2.83, (that might actually be the solution ! ) and they were not that slow. Three speed and no overdrive top remember.

For my sins I actually liked the TR7, a shameful admission according to some, with a view to converting it to V8, but never got round to it. Too many LRs ! 20 odd years ago I was offered one for nothing, green with a tan tartan ? interior and Webasto sunroof. Had nowhere to put it at the time.

You’ll get worse mpg from overgearing it than being similarly undergeared, but will also be a pig to drive.  I found exactly that on my 109 - it is undergeared with the standard SIII transmission with overdrive, but overgeared with 3.54 diffs - they resulted, in combination with the overdrive, in not only sluggish acceleration by comparison, but also in stripping teeth off third gear.  The mpg with the 4.71 diffs was 27, but 26 with the 3.54s.  You spend too much time labouring the engine to accelerate, too much time in lower gears and too much time below the peak rev band with tall diffs.  Manufacturers spend a lot of time and money working out and testing the best overall drive ratios for a given engine, so sticking close to that will be prudent.