My new project

The place to show off and tell us all about your XMs (or even other cars). Should it be a big project, or just some general pics, start your thread in here.
maxferreira
Knows how to use the parking brake
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Re: My new project

Post by maxferreira » Fri Aug 05, 2022 7:27 am

I’ve even calculated it using maths! Same results

I’m quite unsure how it’s managing it, but I can’t complain, rather impresssed I must admit

Dieselman
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Re: My new project

Post by Dieselman » Sat Aug 06, 2022 8:11 am

On a run the auto can theoretically give greater mpg than a manual due to having full torque converter lockup in 3rd and 4th gears and the final ratio being slightly taller than the manual gearbox.
Manual gearbox gives 27.2mph/1000 revs
Auto gearbox gives 28 mph/1000 revs.

Given the Xm has a low drag coefficient (0.28), then that small increase of final drive is apparent when the gearbox is fully locked up.

During regular driving the auto gearbox suffers greater losses due to pumping the Atf taking energy and the torque converter slipping.
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Dieselman
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Re: My new project

Post by Dieselman » Sat Aug 06, 2022 4:37 pm

Your mpg result has prompted me to look up some official figures.

2.1 td.
Urban
Manual = 35.8
Auto = 29.1
23% difference manual to auto.

Constant 56 mph
Manual = 57.6
Auto = 52.3
10% difference manual to auto.

Constant 75 mph
Manual = 43.5
Auto = 39.8
11% difference manual to auto.

Drag coefficient for the 2.1Td is 0.29Cd and the frontal area is 22.7 Sq-Ft.

The 2.0i has the drag coefficient of 0.28Cd. The only change I can see is the tyre aspect ratio is slightly lower profile.

The longer final drive ratio never fully compensates for the additional energy losses of the auto gearbox.
92 2.1SED M.RP5740 ECZ Sable Phenicien
92 3.0 V6-24.Rp 5713 EXY Black
92 2.1SD M.RP 5685 ENT Blue Sideral
Prev
90 2.1SD M.RP 5049 EJV Mandarin
92 2.1SD A.RP 5698 EJV Mandarin
94 2.1SD A.RP 6218 ERT Triton Green
91 2.0SI M.RP 5187 EWT White

maxferreira
Knows how to use the parking brake
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Joined: Tue Apr 05, 2022 6:59 pm

Re: My new project

Post by maxferreira » Sat Aug 06, 2022 7:16 pm

interesting.....

it's got me rather interested in how mine is being so staggeringly good on fuel

i wasn't hanging around either, but yet it's been calculate with filling at half a tank and working out fuel consumed and miles covered

i'm not going to complain, i seem to get around 500 miles to half a tank, plus the guage is quite accurate

xantia_v6
XM Guru
Posts: 1633
Joined: Sun Mar 31, 2013 5:09 pm
Location: Christchurch, New Zealand or Beaune, France

Re: My new project

Post by xantia_v6 » Sat Aug 06, 2022 8:51 pm

Is it accurately measuring distance traveled?
1999 XM Exclusive V6 24V ES9 Manual (LHD) 105,000 km
1997 Xantia Exclusive V6 (RHD) 45,000 miles

Dieselman
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Re: My new project

Post by Dieselman » Sun Aug 07, 2022 8:30 am

xantia_v6 wrote:
Sat Aug 06, 2022 8:51 pm
Is it accurately measuring distance traveled?
The only way I can see the mileometer over-reading is if the drive gear at the gearbox has been swapped for a different one.
iirc, the 2.1td uses a green drive gear.
92 2.1SED M.RP5740 ECZ Sable Phenicien
92 3.0 V6-24.Rp 5713 EXY Black
92 2.1SD M.RP 5685 ENT Blue Sideral
Prev
90 2.1SD M.RP 5049 EJV Mandarin
92 2.1SD A.RP 5698 EJV Mandarin
94 2.1SD A.RP 6218 ERT Triton Green
91 2.0SI M.RP 5187 EWT White

Julianw
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Orga / RP numbers: 4937

Re: My new project

Post by Julianw » Sun Aug 07, 2022 1:40 pm

maxferreira wrote:
Sat Aug 06, 2022 7:16 pm

... i seem to get around 500 miles to half a tank...
:o

maxferreira
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Joined: Tue Apr 05, 2022 6:59 pm

Re: My new project

Post by maxferreira » Sun Aug 07, 2022 8:18 pm

Surely it has to be?

But admittedly it does seem to last a very suspicious amount of time, certainly I’ve apparently done 200 or so miles and it’s just above 3/4 tank…..I’d say I’ve done around that too

Dieselman
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Re: My new project

Post by Dieselman » Mon Aug 08, 2022 7:00 am

The first quarter of a tank takes longer to register due to the filler pipe adding to the volume.

Just keep logging your brim to brim mileage and fuel quantity and any inaccuracy will balance out.
92 2.1SED M.RP5740 ECZ Sable Phenicien
92 3.0 V6-24.Rp 5713 EXY Black
92 2.1SD M.RP 5685 ENT Blue Sideral
Prev
90 2.1SD M.RP 5049 EJV Mandarin
92 2.1SD A.RP 5698 EJV Mandarin
94 2.1SD A.RP 6218 ERT Triton Green
91 2.0SI M.RP 5187 EWT White

Julianw
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Posts: 224
Joined: Tue Dec 30, 2014 3:45 pm
Orga / RP numbers: 4937

Re: My new project

Post by Julianw » Mon Aug 08, 2022 10:38 pm

maxferreira wrote:
Sun Aug 07, 2022 8:18 pm
Surely it has to be?

But admittedly it does seem to last a very suspicious amount of time, certainly I’ve apparently done 200 or so miles and it’s just above 3/4 tank…..I’d say I’ve done around that too
I may have used the wrong emoji. I was trying to convey shock, but not disbelief. My relatively short period of XM use led me to believe there were lots of 'free' miles to be eaked out of a tank, and i can't find it now, but iirc an owner (dollywobbler?) on another forum got near to 1000 miles from a tank on a 2.1td XM... Whatever, i hope it can be true, but I'll accept it may be unfounded

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