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MG MGF Technical - How Much Can I Raise an MGF by Hydragas Pressure?

I am considering the use of an MGF for car trials. Whilst most motor sport calls for lowering of the suspension, one of the requirements for trials would be for increased ground clearance. Can anyone tell me if the hydragas suspension pressure can be safely increased beyond normal levels and what sort of ride-height gain could be achieved in this way before the suspension ceased to work, became rock-hard (or exploded)? Many thanks, Alan.
Alan Jux

I do a bit of marshalling on classic trials and have often wondered why there aern't any MGF's in it considering how cheap they are to buy. Fit a sump guard and pump up the hydrospastic suspension and you are there. Tyres might be the problem - will the rules let you fit narrower ones. Put some spares in the boot an you should have perfect weight distribution for trailing. The engine is powerful and torquey enough especially a VVC.
Paul Hollingworth

AFAIK the maximum 'safe' pressure of the hydragas circuit is 500psi, but I'd not be confident that elderly hoses/joints/spheres wouldn't start letting go before that figure was reached, and I reckon the ride would be pretty jittery too...

You could raise the ride height without changing the pressures/characteristics by extending the pins between the knuckle joints & the hydragas spheres. The shorter Trophy pins are IIRC 10mm shorter than standard, and that results in circa 20mm lower ride height, so attaching 10mm of shims to the bottom of standard pins could give you +20mm with no change to the pressures of the spheres.
bandit

I agree with Bandit. The extra pressure upto say 500 psi will not raise the suspension too far and will stiffen it up beyond what you will require for trialing.

A far better solution would be to machine new shafts to fit between the spheres and the suspension points. If you make these long enough you could actually reduce the pressure of the suspension and keep a higher suspension which IMO would be perfect for such an event.
Robert (Bob) Midget Turbo

Hi,
no good idea to using a non-modified MGF suspension for car trials.
The working range is restricted by upper and lower stops.
500 psi will push and rest the upper arm to the lower stop. I think it will happen already with 450psi, resulting in 400mm ride hight.

All gets clear if you drain the suspension and measure the working range. I did 10 years ago, but forgot the values unfortunately. (May be in the archives 1999, search for "working range")
From memory it might be 4 inches in total.
Only some other figures are here
http://www.mgfcar.de/pump/guidopump.html
(see the 380mm mark). I recall
Other information can be found there.
http://www.mgfcar.de/hydragas/index.htm

Avoid adding pressure to the hydragas system.
If you can't resist, then add washers of 5mm thickness between displacer and suspension knuckle. Pump it to 400 psi and see how it performs. If it is what you want then machine the longer rods, as suggested.

Regards
Dieter
Dieter

Agreed with above - it's not just the static pressure you're worried about but the pressure peaks as 'shocks' are absorbed by the suspension system. As you are planning to trial the car, the loads put through the suspension are going to be greater as a consequence - so the alternative is to look at other ways of raising the suspension height rather than increasing the static pressure to 500psi...
Rob Bell

As others have said, not a good idea to run the spheres at significantly higher pressures. Not only would this not give much additional clearance, but it will adversely affect the effectiveness of the suspension. You would be better off maintaining the standard pressure and machining some spacers that you can fit between the body and the hydragas spheres.
Ralph Gadsby

Many thanks for your words of wisdom guys. It seems that increased gas pressure is not the way to go, but that it may not be too difficult to raise the car mechanically as suggested, possibly then running with the pressure set normally or even slightly lower than normal. Food for thought - but you have answered the basic question. Thanks again, Alan
Alan Jux

This thread was discussed between 04/01/2009 and 08/01/2009

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