My Citroen XM 3.0 PR-Vestige

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.
Post Reply
User avatar
Dean
Global Moderator
Posts: 6116
Joined: Wed Apr 15, 2009 7:53 am
Location: Isle of wight

Re: My Citroen XM 3.0 PR-Vestige

Post by Dean » Tue Oct 17, 2017 4:20 pm

White Exec wrote:I'm guessing the the height correctors would cope with controlling any height selected between lowest and highest.
Well thats what i thought chris and the more i thought of it the more i thought why did citroen not do it, have an extra height setting on the height control that when selected lowers the ride height by say 20-30mm and triggers the sports damping, that way you get firmer damping, a lower Cd and lower centre of gravity which in such a large FWD, nose heavy car isn't going to turn it into a race car and wafty cruiser in one but it will be more sports than the existing setup if you choose to, the trouble is it all seems so simple it's almost too simple and so doomed to failure for unexpected reasons :lol:

Have you finished your epic adventure yet Russ?

John thank you for the offer, im not sure i have one kicking about but if i dont i may take you up on that.

D
92 Citroen XM Prestige 3.0i Auto R.P5678
14 Mitsubishi L200 Trojan
89 Talbot Express 2.0 coach built Auto-trail Chinook

Addicted to Crackanory

User avatar
White Exec
Citroen God!
Posts: 6642
Joined: Fri Mar 11, 2011 7:38 pm
Orga / RP numbers: RP7165
1996 2.5TD saloon, Exclusive, Polar White
1992 BX19D Millesime, Sable Phenicien
Location: ex-Ealing, Cheshire, W.Sussex & Surrey. Now living in Sayalonga (Malaga, Spain)

Re: My Citroen XM 3.0 PR-Vestige

Post by White Exec » Tue Oct 17, 2017 6:24 pm

One snag I can think of in operating running height at less than Normal is the possibility of 'bottoming' the suspension when road surface abruptly rises. Hopefully, the stiffness of Sport would cope with that. Important that the two bump (limit of travel) stops inside the rear transverse tube are still intact (they can disintegrate and drop off), otherwise maybe a possibility of damage to the rear rams.
Chris
1996 XM 2.5TD Exclusive RP7165 Polar White
1992 BX19D Millesime RP5800 Sable
1989 BX19RD Delage Red Deceased; 1998 ZX 1.9D Avantage auto Triton Green Company car 1998..2001; 2001 Xantia 1.8i auto Wicked Red Company car 2001..2003

User avatar
Dean
Global Moderator
Posts: 6116
Joined: Wed Apr 15, 2009 7:53 am
Location: Isle of wight

Re: My Citroen XM 3.0 PR-Vestige

Post by Dean » Tue Oct 17, 2017 8:11 pm

Yes i may require a little fine suspension tuning, possibly a stiffer damping rate on the wheel spheres with a higher pressure in the hydractive spheres to give a stiffer ride in sports mode but equal softness in auto mode.
Having said that i would not use the setting on rough undulating roads as the normal ride height with sports engaged would give better road holding, it would be used where a low ride height and aggressive damping rates work best, on perfectly smooth, flat roads, of which we now have many........shortly all our roads down here will be new and smooth!

D
92 Citroen XM Prestige 3.0i Auto R.P5678
14 Mitsubishi L200 Trojan
89 Talbot Express 2.0 coach built Auto-trail Chinook

Addicted to Crackanory

Dieselman
Global Moderator
Posts: 13735
Joined: Thu Jun 18, 2009 6:44 pm

Re: My Citroen XM 3.0 PR-Vestige

Post by Dieselman » Wed Oct 18, 2017 11:57 am

I tried lowering and stiffening the suspension this morning.

I wouldn't bother, the ride was poor in comparison to the normal ride quality, even without traversing any speed bumps or large bumps.
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

User avatar
russ92xmsed
Global Moderator
Posts: 5733
Joined: Mon Jun 11, 2012 5:23 pm
Location: Cheltenham
Contact:

Re: My Citroen XM 3.0 PR-Vestige

Post by russ92xmsed » Wed Oct 18, 2017 12:33 pm

Dean wrote:
White Exec wrote:I'm guessing the the height correctors would cope with controlling any height selected between lowest and highest.
Well thats what i thought chris and the more i thought of it the more i thought why did citroen not do it, have an extra height setting on the height control that when selected lowers the ride height by say 20-30mm and triggers the sports damping, that way you get firmer damping, a lower Cd and lower centre of gravity which in such a large FWD, nose heavy car isn't going to turn it into a race car and wafty cruiser in one but it will be more sports than the existing setup if you choose to, the trouble is it all seems so simple it's almost too simple and so doomed to failure for unexpected reasons :lol:

Have you finished your epic adventure yet Russ?

John thank you for the offer, im not sure i have one kicking about but if i dont i may take you up on that.

D
Getting there......

It does seem like an obvious thing to do, but clearly they didn't for some reason. Accountants probably!
Maybe as Will said, the ride is rubbish so they didn't.... Or it just adds more perceived complexity to the average buyer. To scary to comprehend.

Who knows, but it is an interesting idea. They did end up doing something similar o nthe C5. It lowers itself at speed to make it more stable and improve aerodynamics. More about MPG though rather than handling.
Russ

1992 K reg XM 2.1 Auto SED RP 5712
1992 K reg XM 2.1 Auto SED RP 5705 (D)
Also
2003 C5 2.2 HDI Exclusive

I sell Engine bay, 1990 COTY, Total & Club XM Sticker Decals
http://www.rjwcreativedesign.co.uk

xmexclusive
Global Moderator
Posts: 5925
Joined: Wed Apr 15, 2009 8:11 am

Re: My Citroen XM 3.0 PR-Vestige

Post by xmexclusive » Wed Oct 18, 2017 1:41 pm

Much work went into researching the air flow both around and through the body of the XM.
Ride height was chosen for optimum air flow under the car and included air extraction for cooling the engine bay.
The EPA book claims that the original XM's had different size nose cone inlets to match air volumes needed by the different power engines.
One critical item was maintaining the horizontal level of the XM body relative to the road.
Failure to maintain this level impacts on road holding as well as body drag.

Deans proposal set me thinking about the mechanics of selecting a running ride height outside those the XM was designed for.
So I looked for design similarities in the front and rear hydraulics.
Height selector drive rods move identical amounts and the height correcting valves are also identical.
The main difference is that the front suspension height changes vertically while the rear follows the arc of a circle.
To me that suggests that an XM will go a bit nose down as you lower the suspension.

The one bit of this area that I know a lot about is vehicle ride assessment.
I was involved in measuring ride, vehicle suspension movement, surface roughness, speed and personal perception of the ride for a good number of years.
As computing systems developed it was easy to relate very accurately the first four of those factors to a high degree.
The last one was the major problem unless you used a single persons opinion.
People seem to vary considerably in their tolerance to ride variation.
Everyone seems to have their own personally calibrated gyroscope for ride assessment.
Proneness to sea sickness is perhaps an example of this variation.

John

User avatar
Dean
Global Moderator
Posts: 6116
Joined: Wed Apr 15, 2009 7:53 am
Location: Isle of wight

Re: My Citroen XM 3.0 PR-Vestige

Post by Dean » Wed Oct 18, 2017 7:57 pm

Dieselman wrote:I tried lowering and stiffening the suspension this morning.

I wouldn't bother, the ride was poor in comparison to the normal ride quality, even without traversing any speed bumps or large bumps.
Poor in what way? i have tried it and to be honest it felt fine, obviously it was firm but that was because it was in sport mode, this isn't a setting to be used on the average road, I wouldn't deliberately lower the car and turn sports mode on to drive over some craggy old potholed road splattered with speed bumps, it would be for smooth, fast A / B roads and general hoonery, the trouble I had was that a very small movement of the height control lever would result in rather dramatic shifts in the ride height, moving the lever 25mm back from the normal ride height setting see's the car plummet to the ground, to get a 30mm drop in ride height requires a very precise and small movement of the lever which with rough guestimeasurments i think is about 3-5mm of movement on the lever, there could be problems in manufacturing a locking position for the lever so close to the normal ride height but I cannot recall its design.

John, i take your point about the rear suspension but i believe the ratio of ARB arm rotation to suspension travel is the key here, (degrees rotation of ARB to mm vertical body travel being the key which would be governed by the distance of the mounting point at the hub/trailing arm from the centre of ARB rotation point, this does need to be measured. Having said that i don't see a slight nose down attitude to be a problem, nose up would induce what i think pilots call ground effect which may be undesirable for a car you do not wish to fly.

Citroens decision to set the ride height where it did was obviously not taken lightly and with a layman's guess i would say was more influenced by trying to achieve acceptable ground clearance for a given damping/spring rate and adequate suspension travel given the depth of the wheel wells and arch clearances? looking at the boot floor and rear bumper design I refuse to believe Citroen put THAT much effort into airflow below the vehicle.

In my fiddling over the years I have come to the conclusion the car handles smaller undulations and road imperfection better in the high drive setting but when faced with larger bumps feels very rubbery and oversprung, a lower ride height tends to make small undulations smoother but grounding is an issue with larger ones especially in waft mode and small surface imperfections feel more pronounced but then this comes back to the 'perceived' ride quality you mentioned i think.

What i do need to do is set the ride height correctly, i am fairly certain the front end is riding too high which if memory serves me right came about after fitting new ARB bushings and drop links, it could of course equally be as a result of an overapplication of 'fiddling' many years ago :D i need to measure it and have the car up on a proper lift of some sorts.

D
92 Citroen XM Prestige 3.0i Auto R.P5678
14 Mitsubishi L200 Trojan
89 Talbot Express 2.0 coach built Auto-trail Chinook

Addicted to Crackanory

xmexclusive
Global Moderator
Posts: 5925
Joined: Wed Apr 15, 2009 8:11 am

Re: My Citroen XM 3.0 PR-Vestige

Post by xmexclusive » Wed Oct 18, 2017 9:30 pm

The prototype XM's had full length undertrays.
The front vent matching to the engine size changed in production to different wattage fans.
Citroen spent £50M between 1984 and 1988 building and testing the XM prototypes.

The body kit and lack of smoothed headlights will of course alter the airflow around the front of your XM.

John

User avatar
Dean
Global Moderator
Posts: 6116
Joined: Wed Apr 15, 2009 7:53 am
Location: Isle of wight

Re: My Citroen XM 3.0 PR-Vestige

Post by Dean » Sun Oct 29, 2017 9:32 pm

Yes the headlamps may well affect the Cd as will the wider wheels, i do not have a body kit fitted though.

I looked more in depth at the ride height idea this week while i have had some time off and been using the XM fair bit, i have 137mm clearance between the ground and the bottom of the front subframe, the rear end has 425mm from the ground to the rear boot floor chassis rails, this actually gives the car a nose up attitude if you measure from the bottom of the sills to the ground, these run parallel to the floorplan and as far as handling at high speed and engine cooling is concerned this cannot be a good setup?
I also played with the height controls and moving the height lever 10-15mm back and engaging sports mode will lower the car about 30mm fairly evenly at the front and back ends and does make the car feel stiffer and more stable on smooth roads but on rough surfaces does not feel so good which is what i was expecting.......or hoped, so this idea is a go, i just need a contact switch to be able to automatically engage sport when this height is selected which will be easy* to sort.

I have noticed that sometimes under harsh breaking the car dips diagonally down on the O/S/F wheel and further investigation has revealed some unwanted noises from the rear arm bearings in the location of the o/s/r so a new pair of bearings are on the cards for this winter, a strip down and clean will hopefully reveal all that is needed is to spend £10 with the bearing boys and not £100 with GSF for both full kit's.

I brimmed the tank last weekend and having used half a tank of fuel which is roughly 8 gallons over 182 miles i have come to the conclusion being gentle with the right foot with this engine does reward the pocket, my last attempt at this calculation after much hoonery resulted in a number i do not wish to reveal, having said that the smiles/gallon were off the scale.

The fuel cutoff issue between 1750-2100rpm and extended crank time to start from mildly luke warm is still present and while i have put many armchair hours into solving this problem, very few spanners have been brandished, i did swap to Johns manual ECU a while ago again as outlined above and while the fuel cutoff issue was resolved the engine missed and coughed something awful under even the smallest bouts of accelleration and so was promptly removed, the trouble is after swapping back to the auto ecu this behaviour continued in varying degrees (although not as bad as the manual ecu) for many days to the point where it now pulls like a train again, neither ecu has power to the front knock sensor still but i have a third ecu on it's way to me and if it is not code locked i shall try that.

All in all, i am enjoying the V6 experience, i would still not recommend the conversion as i don't believe the few extra ponies justify the sheer amount of time and money such a project consumes if you do not really love the challenge of the conversion itself. Having said that though and having owned more powerful equipment one thing i will say is the noise, oh the noise :lol: one thing the old 2.0 engine and most mainstream turbo engines do not have is a good induction noise, this thing does, a quick stab of the throttle gives a roar from the intake and at 3-5000rpm a howl from the slightly modified exhaust, at low revs below 1500rpm on a trailing throttle there is also a subdued burble and popping from the exhaust which does not get boring.

The auto box is fine when cruising about normally and a little cumbersome when trying to push on mildly but for full-on luny driving it is best to leave the selector in 2nd gear and let it keep the engine whizzing around the red line, this keeps the shifts very smooth too so there are no unwanted surprises mid corner! and you are free to enjoy the old school soundtrack this engine has, the noise did surprise me too as most PRV engines i have heard in video's sounded fairly flat, rattly and awful if im honest, not sure if it's a sound quality thing or the smaller Volvo and deloren units did just sound flat and rattly?

D
92 Citroen XM Prestige 3.0i Auto R.P5678
14 Mitsubishi L200 Trojan
89 Talbot Express 2.0 coach built Auto-trail Chinook

Addicted to Crackanory

Dieselman
Global Moderator
Posts: 13735
Joined: Thu Jun 18, 2009 6:44 pm

Re: My Citroen XM 3.0 PR-Vestige

Post by Dieselman » Sun Oct 29, 2017 9:40 pm

The warm starting and poor running sound like low fuel pressure or possibly weak spark.
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

Post Reply