Legend 2.7 4AT mph/1000rpm

[Laird_Scooby]

Out of curiosity does anyone (Stu!) know the mph/1000rpm of the 2.7 Legend auto please? Got a strange anomaly that i'd like to get to the bottom of and that seems a logical place to start..........

Thanks!

[AhsyV6]

I know I'm asking a dumb question but what does that exactly mean? 

[Laird_Scooby]

It's not a dumb question at all - the terminology is confusing but the answer is in fact fairly simple.

 

Usually it's quoted for top gear (unless "otherwise stated") and is simply how many mph you achieve for each 1000rpm of the engine. For example, a car that is quoted as 20mph/1000rpm will produce 20mph for each 1000rpm of the engine in top gear so 2000rpm will give 40mph, 3000rpm will give 60mph, 4000rpm - 80mph and so on.

In more "real world" terms, if your rev counter is showing 3000rpm at 70mph (assuming both are accurate) then mph/1000rpm is 70/3 (the 3 comes from 3000/1000) which is 23.333mph/1000rpm.

 

It is also sometimes quoted slightly differently to give speeds through the gears. This would usually be a little table such as :

1st  6mph/1000rpm

2nd 10mph

3rd 15mph

4th 19mph

5th  23mph

If the car in question has a 7000rpm redline then the theoretical max speeds in each gear would be 42, 70, 105, 133 and 161mph.

Hope that explains it.

[CharlesM]

Very clear and very precise Dave. 

I'll let you explain the role of diff ratios too!

 

[AhsyV6]

That is a seriously technical answer!!!!

Clearly too technical for me.

I did have a workshop manual and I'm sure the answer would've been in it but I gave it away when I sold mine. 

Sorry I can't be of help. 

[hughezee]

Not having the service manual handy, I would say 20 mph/1000rpm as you already suggested Dave

[Laird_Scooby]

25 minutes ago, hughezee said:

Not having the service manual handy, I would say 20 mph/1000rpm as you already suggested Dave

Close but no cigar Stu! This is what the Rover WSM says and what my coupé does - 21.3mph/1000rpm in top with torque converter lock-up. You might be forgiven now for thinking it was a trick question on my part but it's not and here's why.

In the past i've checked the Sterling speedo against a dedicated sat-nav and also against a speedo app that uses the GPS on my phone and it's pretty accurate. That in itself is a surprise. I've also checked the rev counter against a digital automotive multimeter that was calibrated at at least two points in its life. Again, it's pretty accurate.

Now for the anomaly - at 70mph it's showing just under 3000rpm which works out to about 23.9mph/1000rpm. According to the Rover WSM, the final drive is 4.2166:1 and so i was wondering if the Legend had a different final drive or if there was an alternative ratio  - perhaps for other markets and a second hand box had been fitted with a different final drive. The Sterling has always felt more relaxed at motorway speeds than the coupé despite being (allegedly) mechanically identical and also more relaxed than other 827s i've driven/owned.

Perhaps i've been over-thinking this (don't agree - ANYONE!!! ) but it has been niggling me for a long time now. It did cross my mind a diff from a manual gearbox may have been fitted for the purpose of giving it slightly longer gearing although i think the manual is 4.2:1 instead of 4.2166:1 so only slightly longer legs. A quick bit of calculator bashing shows that would only give about 21.4mph/1000rpm so rearranging the figures to work out what it's likely to be from the speed/engine rpm against what it should be gives a final drive of 3.76:1 from (21.3/23.9) x 4.2166 or ( theoretical speed / measured speed ) x theoretical diff ratio.

Are there any other final drives with that ratio or similar that are likely to/would fit inside the box i have?

 

2 hours ago, CharlesM said:

Very clear and very precise Dave. 

I'll let you explain the role of diff ratios too!

 

Thanks Charles - as for diff ratios that's a whole different thread although it could quite easily come into this at some point!

[hughezee]

1.3mph difference could be the legend had a mechanical wire instead of a electronic speed sensor, you never know not forgetting the legend had 15inch rims and rover had 16inch as standard?

Also if the sterling is happier at cruising speeds maybe it could be an different control unit as I am not aware of any significant mechanical differences in the transmissions, so could be a tuned differently buddy?  

[Laird_Scooby]

Hmm, see where you're going with the 15 and 16 inch rims but the tyres are 205/55 on the 16s and 195/65 on the 15s so give the same rolling radius. Perhaps it was another of Rovers infamous prototypes that somehow sneaked into production - i know of an M reg Vitesse Sport (200bhp 2.0 T-series turbo with a KV6 gearbox!) coupe that shouldn't exist that somehow escaped from the factory.

Also i'm not aware of any difference in the ECUs, i'll double check to see if they have the same part number but i think maybe a bit of side by side testing is called for. Seeing as my old 827 SLi is owned by a friend, i should be able to get him to follow me and tell me what speed his is showing and what revs when i'm doing a set speed. Then again that one had a few unusual extras from the factory as well.

 

Got a feeling this is going to involve a lot of investigation and either a really exciting conclusion or no real conclusion at all.

[hughezee]

The rolling radius will always vary when switching to larger rims and smaller walled tyres, my coupe ended up being 1mph ish faster according to the wheel calculator going from 16"s to 17"s despite reducing the tyre size  

In regards to different driving experience between the coupe and sterling, have they both been decatted, just a shot in the dark there anyway given your experience on cars I doubt its something simple as that. Also Knowing Rovers inconsistency when building cars it could well be something technically experimental Honda dropped in the mix or just a favourable production mistake.

Either way sounds interesting so keep us posted on your findings buddy

[Laird_Scooby]

This is the tyre size calculator i use with the results shown for changing from 195/65/15 to 205/55/16 which shows negligible difference, certainly not enough to make the difference i've got.

http://www.etyres.co.uk/how-to-change-your-tyre-size/

Current tyre size

Tyre width: 195

Tyre profile: 65

Wheel size: 15

Overall diameter: 634mm

New tyre size

Tyre width: 205

Tyre profile: 55

Wheel size: 16

Overall diameter: 632mm

Difference in diameter: -0.32%Actual diameter change: -2mm

 

As for the decats, the coupé currently has a Rover decat box fitted and somehow since May last year i've not got round to fitting the home made decat pipe to the Sterling yet.so it's still running the cat!

I think you're right, it's going to work out as something experimental or as you suggest, a favourable production mistake. Either way i'm unlikely to find it for sure so i think for now i'll concentrate on the "more important" stuff and just enjoy the more relaxed cruising abilities of the Sterling. If and when i find a reason for it then i'll update this but don't hold your breath!

[Laird_Scooby]

Just an extra thought on this - was there any form of Limited Slip Differential such as a Tor-Sen, Trac-Loc or similar ever fitted to any FWD auto Hondas?