Turbo R - MPH per 1000 RPM?

Robert Chamberlain · Posted: Fri Aug 03, 2018 12:47 pm Post subject: Turbo R - MPH per 1000 RPM?

I'm not 100% convinced that my transmission is properly locking up so would be grateful if someone can tell me roughly what MPH I should be seeing per 1000RPM engine speed.

Many thanks!

John Murch · Posted: Fri Aug 03, 2018 7:05 pm Post subject:

I’m sure you have had a trawl on line to find the information, out of curiosity I did, with a resounding lack of success. Do you know the rear axle ratio, with that and tyre size it should be straight forward to calculate 😄

Robert Chamberlain · Posted: Fri Aug 03, 2018 7:48 pm Post subject:

Yes John - I couldn't really find anything either. I was hoping I'd just be able to compare with fellow owners but as you say, if all else fails I'll have to dust off the abacus!

Roger Mathew · Posted: Sat Aug 04, 2018 10:32 am Post subject:

My Continental R registers 1750rpm at 70mph. I should imagine that the Turbo R is the same, ie 40mph/1000rpm.

With a very gentle foot, the torque converter lockup can be detected by seat-of-pants as things settle down after a burst of acceleration sufficient to unlock it (if that makes sense).

Robert Chamberlain · Posted: Sat Aug 04, 2018 4:14 pm Post subject:

Thanks Roger. What year is your car? Mine is 1992 and has the column shift three speed box so I wonder if it revs higher than the four speed for a given speed? The handbook mentions 40MPH per 1000RPM but I'm not sure if that is referring to the final drive ratio or something. I just thought with all the torque available that 2,500 RPM at 70MPH might be a little on the high side...?

John Murch · Posted: Sat Aug 04, 2018 8:59 pm Post subject:

That represents 28mph / 1000rpm. Sounds not right to me!
If your handbook talks of 40mph/1000 are you sure you are getting into top?!

Robert Chamberlain · Posted: Sun Aug 05, 2018 8:54 am Post subject:

Well that's why I was a little concerned/confused. It's a three speed column change box, so I'm pretty sure that will rev a bit higher than the four speed but with all the torque that's available I would have thought it would be a bit lower than it is. Having said that, I believe the engine produces maximum torque at 2,500 rpm so ....

John Murch · Posted: Sun Aug 05, 2018 11:41 am Post subject:

The GM400 3 speed box (I assume that is what is fitted) would appear to have ratios of 1; 1.48; 2.48.

So if in direct top you have 40mph/ 1000. Then second would be 27mph/1000 and first 16mph/1000.

It should be easy to see if you are getting two gear changes.........

P.S. don’t trust my mathematics! I just find it all most interesting.

Robert Chamberlain · Posted: Sun Aug 05, 2018 4:46 pm Post subject:

Thanks John - that's saved me a lot of brain ache! Very Happy

. I shall pay particular attention to the gear changes and see if I can detect them. It will soon be going in to Duane Starman (absolutely brilliant RR and Bentley independent next door to Flying Spares on Market Bosworth) to have the throttle body gasket changed (lumpy idle - I've already rebuilt my twin distributor and changed the plugs etc) so I shall ask him to have a good look at it.

John Murch · Posted: Sun Aug 05, 2018 5:32 pm Post subject:

Have you found the RR Owners Club of Australia, a great source of useful info.
eg. http://rrtechnical.info/sz/cs/tsd4440.pdf
http://rrtechnical.info
It seems to confirm 40mph/1000rpm

Robert Chamberlain · Posted: Mon Aug 06, 2018 8:13 am Post subject:

Yes thanks John. As you say there's loads of information there, but everything I've found so far talks about the four speed box - which is indeed 40mph per 1000 rpm. Three speed box information mentions an 'intermediate' selector position and a low. My car has (starting from the left) P,R,N,D,3 and 2. I'd really like to get to the bottom of it all - it's rather bugging me now!

Robert Chamberlain · Posted: Mon Aug 06, 2018 2:57 pm Post subject:

Well, as Alice said "curiouser and curiouser". I've just found a short film of a 1991 Turbo R, and the gear indicator panel on that one shows (from the left) P, R, N,D I and L. So that matches up with the diagram I found for a three speed box car. I'm beginning to wonder if mine does have a four speed, but with a column change? But if it is a four speed, then 2,500rpm at 70mph is too much. All very odd......

John Murch · Posted: Mon Aug 06, 2018 3:09 pm Post subject:

The gear selector positions sound more like that of a 4 speed box! Why is there a ‘3’ and ‘D’? A visit to your specialist and a look underneath to confirm which gearbox you have sounds like a worthwhile investment!
What happens if you change from D to 3 while doing a reasonable speed, say 60?

Robert Chamberlain · Posted: Mon Aug 06, 2018 3:16 pm Post subject:

I've not tried that yet John - but I thought it was a bit strange that I have the D, 3 and 2 positions. As you say a trip down under with a torch is required methinks! My instruments exactly match the handbook, but according to everything I've been able to find so far, the four speed box has the central gear change lever and not the column change.

Paul Spencer · Posted: Mon Aug 06, 2018 8:56 pm Post subject:

http://www.automobile-catalog.com/auta_details1.php, shows 29.8 mph per 1000 rpm for a 3 speed box. So yours could be within measurement errors. But I agree that having a "3" setting is strange. The same site shows a 1998 4-speed as much higher geared - even third gear is higher at 31 mph per 1000 rpm, while 4th is 41.4.

Robert Chamberlain · Posted: Tue Aug 07, 2018 7:59 am Post subject:

Well I've been searching the internet for 1992 cars for sale - and they have the same instrument panel as mine, with a column change. 1991 cars have the 'I' and 'L' rather than 3 and 2 as mine.

Roger Mathew · Posted: Fri Aug 10, 2018 10:14 pm Post subject:

John Murch · Posted: Sat Aug 25, 2018 5:27 am Post subject:

Robert, have you had any luck in identifying your gearbox?

Robert Chamberlain · Posted: Sat Aug 25, 2018 1:18 pm Post subject:

Not yet - my daughters wedding took over! Car performed for it admirably though...