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started replacing most of the rubber hoses as a couple seemed ready to split and needed doing , others seemed very brittle so thought 'in for a penny' as they say and set off to do the lot when I had a thought , the silicon seems a lot narrower internal dimensions than the rubber, but I got the stuff from Elkparts so should be OK shouldn't it?

Am I going to upset anything by doing this?

All knowledge appreciated!
 

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They should be fine. None of the hoses is sensitive to minor differences in diameter except the hose from the manifold to the MAP sensor which, according to Saab, is very sensitive to both the material used and the length. So don't replace that one. If it does need replacing (it looks like it might be silicone anyway), then get some of the right stuff from a Saab dealer. I don't think it costs a lot.
 

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Been considering a switch to silicone hoses myself, anyone know roughly (or exactly) how much it costs to retro-fit my 99 9-3S to silicone? Thanks!
 

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Originally posted by BillJ:
[qb]None of the hoses is sensitive to minor differences in diameter except the hose from the manifold to the MAP sensor which, according to Saab, is very sensitive to both the material used and the length. [/qb][/b]
Hmm, I've heard this before, but I did change mine for silicon for a while (before I heard this)then changed it back. I noticed no real difference. Also as I had thrown away the original MAP hose, I had to buy some more. I asked another 9000 owner to measure the exact length for me... and it was way too short for my car as they were different years. The hose itself is fairly rigid.

So, my own view is that as the MAP sensor requires accurate pressure information to work well, there should be no appreciable expansion/contraction under pressure or an overly long length of hose that would lead to sluggishness in the relaying of the pressure in the manifold to the sensor.
 

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So, my own view is that as the MAP sensor requires accurate pressure information to work well, there should be no appreciable expansion/contraction under pressure or an overly long length of hose that would lead to sluggishness in the relaying of the pressure in the manifold to the sensor.
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Not quite IMHO - its more a case that the system response will be mapped/modelled for a given hose length and compliance (expansion/contraction), if this is changed (increased or reduced compliance) the system damping/ time constant will change. Now I dont think you would notice this (unless a large change) however I suspect that particularly during transients the a/f and hence emissions will not be controlled as well as standard - Saab hence have to say its critical even if the owner will not notice a difference.

Back to the original question - I've just replaced all my hoseing with nice blue silicone stuff from those Elkpart guys - lovely. Only think I noticed is that silicon hose can easily split if kink at the metal connection (if that makes sense)
 

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I think we're saying much the same thing actually Adrian- that the system expects to "see" certain physical characteristics of the hose. It's quite rigid for it's size, so I'm assuming that the system is not tolerant of anything more than a little non-linear response in the tube.
 

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I've been told by a SAAB tech that he has noticed a difference when people replaced the hose with silicon (or rubber) but only when they've cut a very generous length rather than measure it accurately new for old. That said, I swapped my silicon hose back out for the original MAP sensor hose just in case.

[edit] And to answer the original question, 0.5mm either way seems to make no difference for the other hoses.
 
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