GTI Turbo 'squatting under power

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Bilkob
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GTI Turbo 'squatting under power

Post by Bilkob » 22 Nov 2019, 23:46

So, after deciding to keep my GTI turbo I seem to have finally got the old crate running ok. After lots of work and head scratching the final upgrade was a handmade stainless exhaust after the old system disintegrated. This has made a huge difference to the car, it's faster and far smoother running
This extra oooomph seems to have thrown up a new issue. Having had 'new' spheres fitted all round the car is now prone to squatting quite alarmingly under hard acceleration in the first 3 gears. Now, I'm not sure if the spheres are turbo or standard spec but could this really make a difference? The squatting is quite alarming and feels almost like it is pumping itself down at the back and w ont settle until I let off the power...
One more thing is I've always thought it sit slightly high at the front but only by say 10mm
Any thoughts??

Peter.N.
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Re: GTI Turbo 'squatting under power

Post by Peter.N. » 24 Nov 2019, 11:36

Sounds as though the rear spheres are to soft - or it might be all that power, never had that with my 2.5 diesels. :wink:

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Mandrake
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Re: GTI Turbo 'squatting under power

Post by Mandrake » 24 Nov 2019, 12:41

In my experience all older Citroens which have a reasonable amount of power squat at the rear under hard acceleration in low gears. It's just because the suspension is very soft and has lots of travel, and a CX does have a lot of suspension travel even by Citroen standards.

It's the reason why a Hydractive Xantia puts the suspension into firm mode for 3 seconds when you accelerate from a standstill and also if you push the throttle enthusiastically while driving - if you disable the throttle sensor for the Hydractive system by unplugging it the Hydractive Xantia also bottoms the rear suspension "alarmingly" ever time you accelerate. :) I once had a CX2400 (not turbo) and it also squatted a lot at the rear under heavy acceleration.

I would check to make sure you do have the correct rear spheres fitted - there is a considerable difference in sphere tuning between a standard CX sphere and the Turbo sphere's - the gas pressure is the same (I think) but the damping is much firmer on the Turbo spheres and this reduces the apparent squat under acceleration by slowing down the response time, however there will always be a noticable amount of squat compared to a "normal" car as even CX Turbo spheres give a soft ride compared to conventionally sprung cars.

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GiveMeABreak
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Re: GTI Turbo 'squatting under power

Post by GiveMeABreak » 24 Nov 2019, 12:44

We had a CX GTI in the family years ago - and the same happened with that - I rather liked it - squatted when tearing off under power and rose up when hitting the brakes hard, then settled - was quite a sight for onlookers when I was tearing about. Standard spheres - no mods and previously owned / maintained by a Citroen technician.

Bilkob
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Re: GTI Turbo 'squatting under power

Post by Bilkob » 24 Nov 2019, 15:35

Thanks for replies, I think I'll have to try and get hold of some genuine GTI turbo rear spheres, I appreciate that these cars are soft, it's one of the appeals but this is quite extreme and alarming, almost like it's pumping itself down! It is quite grunty now though!

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white exec
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Re: GTI Turbo 'squatting under power

Post by white exec » 24 Nov 2019, 16:47

Make sure spheres are correct volume, gas pressure, and damping figures.

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Mandrake
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Re: GTI Turbo 'squatting under power

Post by Mandrake » 25 Nov 2019, 11:25

One other thought - is it a Mk1 or Mk2 CX ?

I remember that Mk 1 and Mk 2 used different diameter hydraulic rams for the front suspension, thus required differently tuned spheres to achieve the same ride/handling tuning, or in other words the same sphere would give a different result when fitted to a Mk1 or Mk2.

The Mk1 had a smaller diameter piston therefore if you fitted a Mk2 sphere to a Mk1 it would be overly soft and without sufficient damping.

I don't recall off hand if the rear suspension piston diameters differed as well, but I have a vague memory that the Mk1 might have used 35mm and the Mk2 used 38mm. Can anyone look this up somewhere ?

I remember back when I had my CX (1998 to 2003 ish) that there were only one set of spheres available to buy for non-Turbo CX's which did not differ for Mk1 and Mk2 and were apparently tuned for the Mk2, because when you fitted them to a Mk1 they were too soft and wallowy! We had to modify the damping slightly (reducing the centre hole diameter from 1.65mm to 1.4mm on the front spheres) to firm up the damping a bit to give an acceptable result otherwise it was like a boat.

Bilkob
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Re: GTI Turbo 'squatting under power

Post by Bilkob » 26 Nov 2019, 18:37

It's a Series 2 turbo 1, ie- early S2, but non intercooler. Just out of interest I put the car in high setting and listened to the (new) main accumulator sphere, as I added more LHM it clicked increasingly less and this SEEMS to have lessened the squatting...... hmmmmmmm..........

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white exec
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Re: GTI Turbo 'squatting under power

Post by white exec » 26 Nov 2019, 19:10

If air has got into the system (eg because of low fluid level) and worked its way towards the rear spheres, the back end will be abnormally soft, because the air is compressible.

The trapped air could act like "an additional sphere", bringing additional softness, just like the centre spheres switching in on Hydractive.

Have checked the CX repair manual, but cannot see any instruction for bleeding the suspension system, so I assume it is self-bleeding, given a good few Citrobics. Worth checking for air in the reservoir fluid (dip a sample, after a drive). If anything other than a few microbubbles, that needs sorting.

The CX sphere data I have...
(Volume/Pressure/Damping)
CX sphere data.JPG

Bilkob
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Re: GTI Turbo 'squatting under power

Post by Bilkob » 26 Nov 2019, 21:43

So it looks like the rear spheres are the same for saloon and turbo......