Vacuum units
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Vacuum units
hi there. I have got a slightly tuned engine with HIF38 carb, water heated inlet maifold, electronic ignition and K&N air filter, should i have the vacuum unit still connected as some people say to blank off the unit. What units do other people have that are fitted to slightly modified cars. Are they standard units as fitted on the minor or do they have differing vacuum characteristics, i.e when the units starts working, how much advance provided.
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Cam
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The vac unit is an economy device that advances the timing under partial load/no load. In pure race applications they are not needed as they are not operating for the majority of the time. It's up to you really, but I have kept mine on my tuned 1380 for economy reasons as it was my daily driver for a while.
Of course ideally you would need the advance curve set up on a dyno, but practically if your engine is in a 'light' state of tune then the original curve will be OK if not perfectly optimal.
Of course ideally you would need the advance curve set up on a dyno, but practically if your engine is in a 'light' state of tune then the original curve will be OK if not perfectly optimal.
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As said - it's for economy - so with current fuel prices - keep it on !
make sure it is working - they don't last long - suck the pipe and there should be no 'flow', and the end piece should move in to the diaphragm. Your ignition advance can be modified by filing away the extension on the bob weight - where it contacts the stop, and also by fiddling with the springs on the bob weights. It's a black art - can really only be confirmed with much rolling road testing. Just set your static advance forward until it 'pinks' slightly - then retard it till it stops pinking. And disconnect the water heating on the inlet manifold - it costs power !
make sure it is working - they don't last long - suck the pipe and there should be no 'flow', and the end piece should move in to the diaphragm. Your ignition advance can be modified by filing away the extension on the bob weight - where it contacts the stop, and also by fiddling with the springs on the bob weights. It's a black art - can really only be confirmed with much rolling road testing. Just set your static advance forward until it 'pinks' slightly - then retard it till it stops pinking. And disconnect the water heating on the inlet manifold - it costs power !
