Road trip in GiSelle

By contrast, here is my list of vehicles that sit at 2,500rpm at 100km in top gear:

Peugeot 406 (3 litre V6) petrol manual
Citroen Xantia Turbo CT 2 litre petrol manual
Peugeot 605 PRV (3 litre V6) petrol auto
Citroen XM ES9J4 (3 litre V6) petrol auto
Landcruiser 1HZ (4.2 straight 6) diesel manual
Nissan Navara ute (3 litre 4 cyl) turbo diesel manual

Note - all made between 1994 & 2001.
 
Pre the modern, must have, 10 speed automatic era, there was usually a direct correlation between engine capacity and overall gearing/rpm at 100 kph
Up to 1.3L around 4K.
1.5 to 1.8L around 3.5K
Big 4 cyl and small 6 cyl around 3K
Big 6 cyl and V8s around 2 to 2.5K.
With automatics usually being slightly taller geared.

Of course there were exceptions, particularly with high performance or commercial models.

My '71 F100 ambulance is completely stock, has a 5.0L 6 cylinder, 3 speed auto and 2.75 to 1 ratio nine inch diff. It has 235/75R16 tyres which are the same diameter as the original 7.50x15s, it's only doing 1900 rpm at 100 kph, and it does it easy as.
 
PSA diesels are of course higher geared - we had a 2006 307 (T6) HDi 2.0 litre which from memory was only doing 1,700rpm @ 100km/h.

Of course the power of that 2.0 litre engine was about the same as the 4.2 litre N/A Toyota 1HZ
 
The Beast of Turin does 210kph at 1000 rpm, but rumour has it it's 28.4L, 4 cyl engine has enough torque to handle it.🤔😉

images (71).jpeg
 
We seem to have gone off on a tangent here, but it's an interesting topic.

I recall reading various analyses of engine and car design. Careful selection of engine parameters and gearing to achieve a cruising speed at the maximum power point would also generally coincide with the optimum piston speed. I vaguely recall a piston speed of 2400 feet per second as being seen as a design goal, but would need to look up a few references.

All of the design criteria would combine to make things work best at a particular engine speed, and gearing changes could be used to glean the best efficiency over a range of road speeds.

Very technical stuff, especially when calculations such as Brake Mean Effective Pressure (BMEP) (which I understand to be a calculation of combustion efficiency, but I could be wrong?) were brought in to consideration. I don't pretend to understand much of the engineering principles.

To me, the end result is that small engines tend to reach their power peak at higher revs than larger ones, hence, the gearing in a car with a small engine is selected to give an ideal cruising speed at the engines power peak or thereabouts.

In real terms, my 1065cc Mini*, with 10 inch tyres and a final drive of 3.44:1 is almost dead on 4000 rpm at 100 kmh.
GiSelle, as mentioned, with 1220cc and 15 inch tyres does 4000 rpm at 100kmh as well.
Gaston the 2CV with 602cc and 15 inch tyres does 100kmh at 5000 rpm.
Moby Dick about 3500 or so at 100kmh.
And Pablo the modern diesel auto ticks over at about 1500 revs in 6th gear at 100kmh!
I'm looking forward to getting my 1275cc Morris 1100S on the road. He has a 3.765:1 final drive and 12 inch wheels so should be a comfy cruiser I believe.

At the end of the day, a cruising speed is set more by the tolerance of one's ears (and the speed limit) than the highest obtainable engine speed.

It's all academic really as to me it's more about the fun of driving these beasts than the figures. (But still interesting nonetheless!)

Cheers, Pottsy

(*998cc bored 100thou)
 
pottsy said:
Moby Dick about 3500 or so at 100kmh.
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I can't remember your exact DS model but my '71 D Special is 2900 rpm at 60 mph. I did look up the European specs a year or two back and it said 3000 rpm @ 100 kph for my specific model.
I'm guessing some of the higher tuned DS versions are geared a little differently to match their individual power/ torque curves?
 
The D series are surprisingly low geared given they were designed for highways. Specials have a lower final drive on the same box and spin away near 4000rpm at 100kph. Supers and DS will be down around 3000rpm which is still quite noisy. 5sp DS come down a bit further to 2500ish rpm. A super5 has a lower final drive and different ratios in the 5sp box so they are different again.

Pre 66 long stroke cars are a whole other thing as well.
 
pottsy said:
At the end of the day, a cruising speed is set more by the tolerance of one's ears (and the speed limit) than the highest obtainable engine speed.
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Driving hard in a 2CV powered by a 1220 GS engine for several days to reach Alice Springs in time for the start of the raid a few years back, I found earmuffs helped.

Conversely, I have driven Dees from various eras at well over 100km/h for sustained periods and never felt the need for earmuffs. They aren't exactly quiet at speed but somehow I have never felt the need for ear protection in a D.Just as I have never felt the need for a radio in a D. They really are unlike anything else.

Roger
 
I plugged in the air/fuel meter yesterday and took her for a drive of half an hour or so at 100kmh. Mixture was fairly steady at 11, so running quite rich, surprisingly. I'll look in to that and do some comparisons.
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how did you manage to measure that, Pottsy? Tap and screw an oxygen sensor into the exhaust line, feeding one of those cheap gauges that translate voltage to stoichiometric ratios?

Or something altogether much more clever?
 
Just a cheap gauge and a narrow band sensor in the tail pipe. I'm a bit suss on calibration but will borrow no3 son's whizz bang expensive unit at some stage.

Cheers, Pottsy
 
faulksy said:
The D series are surprisingly low geared given they were designed for highways. Specials have a lower final drive on the same box and spin away near 4000rpm at 100kph. Supers and DS will be down around 3000rpm which is still quite noisy. 5sp DS come down a bit further to 2500ish rpm. A super5 has a lower final drive and different ratios in the 5sp box so they are different again.

Pre 66 long stroke cars are a whole other thing as well.
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Has anyone got the rpm for a long stroker at 110 km/h (70mph)? I recall this is the quoted most efficient speed in the 1962 owner’s manual.
 
SuppleC said:
Has anyone got the rpm for a long stroker at 110 km/h (70mph)? I recall this is the quoted most efficient speed in the 1962 owner’s manual.
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Car specs list a '62 ID19 as having a 3.817 final drive and a 0.852 top gear. With standard 165x400 front tyres, engine rpm at 110kph = 2800.
 
Greenpeace said:
Car specs list a '62 ID19 as having a 3.817 final drive and a 0.852 top gear. With standard 165x400 front tyres, engine rpm at 110kph = 2800.
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You are good. Now what about my ‘66 where they changed the gearbox shift orientation. Just back in Brisvegas after the run to Cit-In. Cruised over most roads at 110km/h and achieved 8.5L/100km over 4500km.
 
SuppleC said:
You are good. Now what about my ‘66 where they changed the gearbox shift orientation. Just back in Brisvegas after the run to Cit-In. Cruised over most roads at 110km/h and achieved 8.5L/100km over 4500km.
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They list the same final drive and top gear ratio for a 1966 ID19, the only difference is the 180x380 front tyres, however these are only 3mm larger in diameter than the 165x400. You'd still be talking near enough that 2800 rpm figure at 110 kph.
If you are running 185R15 tyres these are identical in diameter to the 165x400.
 
The longstroke cars are generally much higher geared and from memory developed more torque than the shortstroke engines

1679894651204.png


For reference, the DS 5sp gearbox 5th gear overall ratio is only .292 and the standard DS 4sp 4th gear overall ratio is .268.

A 5sp DS gearbox in 5th will give you 36.2 Kph/1000rpm accrding to the workshop manual. The shortstroke engines don't have a lot of torque low down which was improved with fuel injection but even then Citroen didn't adjust the ratios.
 
faulksy said:
The longstroke cars are generally much higher geared and from memory developed more torque than the shortstroke engines

View attachment 218866

For reference, the DS 5sp gearbox 5th gear overall ratio is only .292 and the standard DS 4sp 4th gear overall ratio is .268.

A 5sp DS gearbox in 5th will give you 36.2 Kph/1000rpm accrding to the workshop manual. The shortstroke engines don't have a lot of torque low down which was improved with fuel injection but even then Citroen didn't adjust the ratios.
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I came up with 38.56 kph for the '66 per 1000 revs.
Looks like your chart is 38.4. So 2850rpm @ 110 kph would be pretty right.
 
SuppleC said:
You are good. Now what about my ‘66 where they changed the gearbox shift orientation. Just back in Brisvegas after the run to Cit-In. Cruised over most roads at 110km/h and achieved 8.5L/100km over 4500km.
Click to expand...
Greenpeace said:
They list the same final drive and top gear ratio for a 1966 ID19, the only difference is the 180x380 front tyres, however these are only 3mm larger in diameter than the 165x400. You'd still be talking near enough that 2800 rpm figure at 110 kph.
If you are running 185R15 tyres these are identical in diameter to the 165x400.
Click to expand...
Still have the long stroke engine and 165/400 tyres on my ‘66, assembled in Melbourne. One of the last from the ‘61 to ‘66 assembly in Australia.
 
Just so you all don't feel bad about your engine being busy at speed.😉

My father used to have a '73 Daihatsu Hijet van, the one with the 356cc, two cylinder, 2 stroke engine and 10" wheels. He used to drive it everywhere, it was most comfortable at 80 kph, but it would do 100. Every time he sat on more than 80 for too long it would seize up.🤬
Anyhoo it still had the owner's manual (this was in the late 70s) and the diff ratio was 6.66 to 1, it had a 1 to 1 top gear and 5.00x10 tyres.
80 KPH = 7000 rpm, and the times he sat on 100 it would have been sitting on nearly 9000 rpm.🙉
Surprisingly though it would comfortably return 50 mpg or better, even when driving it like you stole it.🤷‍♂️
 
I had a Honda CB175 (new in 1972) - vertical twin air cooled 4-stroke SOHC, 5 speed.

I remember not being too impressed with it's top gear hill climbing ability, so used to knock it back to 3rd to make it hold 60 mph up the hills - at 10,000 rpm!

Shame we didn't have synthetic oils then - probably would have extended the poor little engine's life.
 
We do seem to have strayed somewhat, but an interesting discussion nonetheless.

I have now enhoisted GiSelle and transfused her gearbox's vital fluids with some fresher stuff. The magnetic plug had no more than the usual amount of very fine powder on it. No lumps, chips or similar magnetic bits at least.

The drained oil was also devoid of anything concerning when I intensely scrutinised the pan as I decanted it.

The box of whirly toothy things is now provided with it's full quota of (pretty blue!) Penrite gear oil and a tube of Nulon G70. A drive around the area seemed to indicate a much quieter gearbox, although some of the "zizzes" are still there, albeit quieter, possibly because of the fresher oil. In any case, time will tell how it fares.

The motor also seems quieter now that I've replaced the dead (and rattling) pre-heater pipe section on the passenger side, and tightened up some of the tinware. Once again, time will tell.

Only task left over from the SA trip now is to address the recalcitrant ignition lock which, at times, refused to accept the rightful key into its orifice. Strangely the spare key from Mrs P's handbag slid in and worked smoothly, but, just in case, I left it in the lock until we got back home. I have a spare unit so will address that at my leisure.

Cheers, and thanks for your contributions to a lively discussion, Pottsy.
 
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