The V8 Owners Forum -

In my P6 the MS is in the boot, and the MAP sensor line is probably just under 4 metres long by the time is has snaked its way there from the engine bay.

Doesn't seem to cause me any issues.

Providing the tube doesn't collapse under vacuum then its length is utterly irrelevant.

Rossco wrote:Providing the tube doesn't collapse under vacuum then its length is utterly irrelevant.

So 100ft long ? 1000ft ? Even in electrical cables length matters, so for pressure readings it will too.

Signal will diminish and take time the longer the tube. Neither are good things. On a lazy old V8, there probably isnt a realistic length you could achieve on a car that would pose a problem though

But it is best practise to keep it short, much the same as it is best practise to keep wiring as short as practicable.

stevieturbo wrote:

Rossco wrote:Providing the tube doesn't collapse under vacuum then its length is utterly irrelevant.

So 100ft long ? 1000ft ? Even in electrical cables length matters, so for pressure readings it will too.

Signal will diminish and take time the longer the tube. Neither are good things. On a lazy old V8, there probably isnt a realistic length you could achieve on a car that would pose a problem though

But it is best practise to keep it short, much the same as it is best practise to keep wiring as short as practicable.

Ok, if we are being pedantic and I was assuming that not many cars use a 1000ft vacuum tube then eventually friction between the inside of the tube and the air will have an effect.

It also depends on how you're pulling the vacuum. If its by physically moving air (like a vacuum cleaner) then length has a very much greater effect as air flow inside the pipe causes friction. If the vacuum is being pulled and held then length is much less important.

Just a bit of an update.
Fitted a 2 bar Map sensor over the weekend and tweaked the ignition map as best as I could on the road (booked in for a RR session on the 9th Aug) but results were very good. Nice clean acceleration very smooth idle and best of all no detonation. TBH I have probably gone a little to much on retarding the ignition while on boost but better to be safe than sorry until its set up properly.
Thanks again for your help and advice
Chris

No experience of pressure charged engines, but on an NA one, the ignition vacuum unit is just used for economy. To advance the ignition under light engine load. The best maximum advance settings under full load would remain much the same.