Who nows about vacuum advance ?
Discussion
Depends... May or may not be. If you get a standrad one, you can always swap the weights and springs over.
Steve
www.tvrbooks.co.uk
Steve
www.tvrbooks.co.uk
As I understand it from ACT / Mark Adams, the only use for the vacuum advance is to lean out the mixture under cruising, to increase fuel consumption under these conditions. If it does not advance, you will just be burning more fuel than necessary on the motorway. If you have an MA chip, he compensates for this in the ECU programme - the ACT triple throttle body plenum has no vacuum advance take off, for example.
You can get a standard Rover distributor from various places but it won't necessarily have the same advance characteristics as the TVR modified one. To get the right advance curve, you would need to match the weights and springs that TVR used. One way to do this would be to strip both distributors and transfer the parts from the old one to the new one like Steve says.
Anyway, this is all unecessary if all you want is a new vac advance unit. I don't expect you'll have any trouble finding one, and in the mean time you can run quite happily without it as long as you block off the port on the throttle body which is normally piped up to it.
Edited to add - I mean, run with the vac advance unit fitted but not working. If you take it off completely you will need to lock the advance mechanism somehow.
>> Edited by greenv8s on Monday 9th August 12:59
Anyway, this is all unecessary if all you want is a new vac advance unit. I don't expect you'll have any trouble finding one, and in the mean time you can run quite happily without it as long as you block off the port on the throttle body which is normally piped up to it.
Edited to add - I mean, run with the vac advance unit fitted but not working. If you take it off completely you will need to lock the advance mechanism somehow.
>> Edited by greenv8s on Monday 9th August 12:59
starmist said:
As I understand it from ACT / Mark Adams, the only use for the vacuum advance is to lean out the mixture under cruising, to increase fuel consumption under these conditions. If it does not advance, you will just be burning more fuel than necessary on the motorway. If you have an MA chip, he compensates for this in the ECU programme - the ACT triple throttle body plenum has no vacuum advance take off, for example.
The vac advance doesn't affect the mixture directly, it only changes the ignition timing. Maybe Mark does something clever to lean the mixture off instead but I don't know anything about that and it doesn't sound likely to me. Is it true that the ACT tripple throttle plenum has no vacuum takeoff? The single throttle ACT plenum on mine certainly does have one, and I'd be surprised if it was omitted.
Rover V8 pre-GEMS distributor with vacuum advance has the following features:
Mechanical advance by bob weights and pre-load springs to match ignition timing in proportion to engine speed.
Usually two bob-weights and springs. The advance "curve" is a hybrid of the properties of each spring / mass pair and may be adjusted to suit the engine.
Vacuum advance exists to reduce ignition advance at cruise (i.e. part-throttle, high manifold depression).
Mechanical advance by bob weights and pre-load springs to match ignition timing in proportion to engine speed.
Usually two bob-weights and springs. The advance "curve" is a hybrid of the properties of each spring / mass pair and may be adjusted to suit the engine.
Vacuum advance exists to reduce ignition advance at cruise (i.e. part-throttle, high manifold depression).
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