Traveller still a bit thirsty

[gtt1951]

I've now had a long trip to Gaydon and back, running on motorways all the way home at an average sustained speed of 60mph. This morning I took out plugs 1 & 3 to check on the colour[frame][/frame][frame][/frame]Mixture doesn't look rich - there is a bit of oil fouling, and it looks like I'm running at quite a high oil pressure.
Not getting better than 30mpg - what else do I need to check?
George.

[mike.perry]

What engine/box/diff ratio/speedo TPM have you got?

[bmcecosse]

If anything - looks a tiny bit weak. Check the REAL miles covered against fuel consumed...... But running at 60 with a v un-aero shape car, 30 mpg is not unexpected......

[lambrettalad]

At that speed 30 MPG is very good,I get 37 when cruising 50 -55 mph ,but It plummets to the late 20'sif driven very hard.The plugs are not far off perfect,I would be very happy

[aupickup]

i get 40 to 45 at 50 to 55 mph motorway etc

[gtt1951]

What engine/box/diff ratio/speedo TPM have you got?

Engine = 1098
Gearbox = 1098
Diff = 4.25 (approx - counting turns)
Speedo = 1000 TPM.
Odometer error, having checked this with "satnav" and known journey distances, is 39%, and is allowed for in my mpg calculations.

Having referred back to the previous topic of "Thirsty Moggy", I've noticed that IslipMinor suggests that a 4.22 diff will go OK with a 1504 speedo. I've got one of those and will clean it up and fit it to see what happens on the reading accuracy point.

[bmcecosse]

A 4.22 final drive ratio should be paired with a 1408 speedo. The 1504 is for the 4.55 ratio. However neither is accurate, and indeed a 1504 won't be far away with 4.22.

[MarkyB]

What tyres pressure do you use?
Any roof rack or habit of carrying a ton of spares

[bmcecosse]

Spares are good to have ....

[gtt1951]

A 4.22 final drive ratio should be paired with a 1408 speedo. The 1504 is for the 4.55 ratio. However neither is accurate, and indeed a 1504 won't be far away with 4.22.

Just come back from a road test with the cleaned up 1504 (had to take the bezel off to get at the filthy glass interior and a bit of a dirty face).
IT WORKS better than the 1000! Checked against my Geko Garmin Navigator (basic GPS device that uses about 6 satellites for a greater accuracy - down to 16ft when measuring distance). All the main speed indications (30, 40 50 and 60) are good, except for the needle swaying more than it used to. So at a real speed of 40 the speedo needle wobbles either side about 3-4 miles and sometimes locks on "steady".

Looks like a result for me - will have to take it on may journey to work and back and check out the odometer.

Thanks to all the very friendly members that have had an input on the "gear train" topics.

George.

[gtt1951]

What tyres pressure do you use?
Any roof rack or habit of carrying a ton of spares

I'm currently using 28-30 PSI (28 on front and 30 on back).
No roof rack (although the car came with a period 2-piece high-ride rack - will take a photo, sometime, of it fitted).
The spares I took to Gaydon did not weight much (except for the jack) - the human load would have been greater (I currently weigh in at 16st 10lbs)

[gtt1951]

Spares are good to have ....

You are so right - if you've got them with you, then you won't break down. BMC, you were mentioned in Despatches on thread
http://www.mmoc.org.uk/viewtopic.php?f= ... 9&start=15 regarding carrying spares.

[IslipMinor]

I've noticed that IslipMinor suggests that a 4.22 diff will go OK with a 1504 speedo

I did, and it does not!! I have no idea why I mixed up the diff ratios and speedo tpm, but for clarity:

Series II 1000 tpm speedo and 5.375 diff ratio

948 1504 tpm speedo and 4.55 diff ratio

1098 1408 tpm speedo and 4.22 diff ratio

P.S. I have updated the previous thread with the correct figures.

[gtt1951]

But Richard,
the 1098 engine/rib-cased gold-seal box, 4.25 (approx) diff with the 1504 speedo looks to be nearly spot on compared with what I had.
The 1000 speedo, which I have just taken out, seems to be a pristine "as new" unit with no tarnish, whatsoever, on the chrome.[frame][/frame]
(the bulb insert, with the cut off wire is from the 1504 "spare" that I had)
All I have to do, now, is get the needle to settle down - hopefully with a replacement speedo cable.
I'll do a trip to work (50 miles round trip, exactly) and see if the odometer also shows a trip record of 50. If it does, then I'll be keeping the 1504 unit connected, for now.
Maybe I mis-counted the revolutions test and the prop shaft turned 4 1/2 times over 2 wheel revolutions?
When I changed the gearbox out, over to the spare that the car came with, there was no change to the speedo readings.

I'm wondering if this thread should be moved to "General" and out of "Mechanical".

Thanks, George.

[bmcecosse]

Why? It's a mechanical problem. You will be needing to at least lubricate the speedo cable, although a new inner would be wise anyway. The 1408 speedo gives v optimistic readings - even with the old crossply tyres - see the original road tests. So there is every chance a 1504 will be more accurate. I can tell you that a 1248 tpm is DEAD ACCURATE on a 3.7 final drive with 155 tyres on van rims.

[gtt1951]

BMC,
I forgot to say that I'm running the rear axle with 155/80R14 tyres.
George.

[bmcecosse]

You can only do the usual things - raise the engine compression ratio, and the temperature...(88 degree stat). Check the rolling resistance ie no dragging brakes or tight bearings. Weight reduction to an extent will help too. Blow the tyres up hard, and change the final drive ratio to say 3.9 or 3.7. Extreme measure would include removing bumpers/gutters etc to 'streamline' the body - and perhaps an under-tray, although beware overheating the oil.......

[mike.perry]

On the subject of speedo gearing the 948, 1098 and 1275 Midget boxes have the same pinion/drive gear ratio, 5/13 I believe. The 803 box has a different pinio/drive gear ratio, 2/9 I think. This is why the higher the ratio diffs - 948/4.55 - 1098/4.22 the lower the tpm -1504 - 1408. The 803/5.375 does not fit the pattern with a tpm of 1000.
However, as most speedos overread it is quite possible that a 1504 is more accurate on a 4.22 diff and a 1408 is more accurate on a 3.9 diff (from my own experience).

[bmcecosse]

[gtt1951]

...However, as most speedos overread it is quite possible that a 1504 is more accurate on a 4.22 diff and a 1408 is more accurate on a 3.9 diff (from my own experience).

Mike, BMC,
I've got the results of my run to work. I've been doing this particular run since May 1984 in various cars (started off with a 1964 Series 5 2-dr saloon) and the round trip distance is (+ or - 1/2 mile) 50 miles.
The current drive train of 1098cc Engine, Ribbed-case gearbox, 4.22 (approx) diff and 155/80R14 rear tyres, using a 1504 speedo, produced an odometer reading of 47 miles.
This is a trifle lower, but a lot better than the 71 miles the 1000 speedo was showing. I'll stick with this set-up for a while and do a fuel usage recalculation on the next full fill.
Still need to work out how to get the piddly small modern fuel nozzles to "cut-out" on splashback, as I always spill some fuel.
Yesterday's fill at a Sainsburys fuel station (just before joining the A316 to head for the M3) was 129.9p/litre.
The actual displayed speeds (apart for the needle wobble) seem to tally with the my Garmin Geko speed display.
Picture of the 1504 speedo, in situ, below (doesn't have the "IND" light of the 1000, but that wasn't wired up anyway)[frame][/frame]The journey started at 58211.