VX ignition timing ?

[3bar]

 Help please
trying to figure this out

Beta VX with supercharger and a distributor with a vacuum advance unit on it

I can set the timing off nbr 4 aiming for about ten deg at idle of 800rpm with the vacuum advance disconnected and the car runs like an absolute rocket - no audible pinking / knocking and running on modern high octane fuel 95/98 would be surprised to hear any but should the vacuum advance be connected up, but what would happen when the vacuum advance is under boost ? considering that most vacuum advance units reach max retard at atmo pressure ie heavy wot throttle and max advance at max vacuum ie light throttle loads  and being a supercharged engine its going to be close to atmo or positive pressure most of the time

to me the distributor has been swapped in the past - multiple owners blah, surely the vx ignition module on the inner wing controls the ignition timing advance ? I have searched and looked at many many vx engine bay and distributors and I cant "spot" the vacuum advance on others - but what other distributors would fit ?

The car has a possible over heating issue that i am trying to solve, previous owners fitted a big VW radiator and fan, they gutted the thermostat and i am just thinking if the ignition advance curve is out of whack that can also cause a wee bit of overheating - i dont want to throw more parts at it, unless i can be sure

already put new water pump, new thermal switch cutting in fan at 78 deg, new thermostat that opens at 77deg, when idling the fan cuts in and runs for a few minutes probably two, temps drop, fan switches off and it could literally idle like that all day long

so in short
1) do i hook up vacuum advance ?
2) what distributor should be on a VX ? and does the vx have a vacuum advance unit from the factory ?
3) do i mechanically disable the distributor vacuum advance and let the module handle ignition timing ?
4) how far out would timing need to be to cause a bit of overheating ? top 1/4 of the green segment on the gauge - is that actually overheating or what degrees does that relate to ? could it just be a failing temp sender ? and its not really overheating at all ?
5) does anyone have a diagram of the VX temp gauge and approximate celsius range ?

thanks all

[Neil-yaj396]

I can only really tick off 5. for you; the Beta instruments are not calibrated and generally not to be overly relied on. Having had 4 Betas anywhere around the middle is fine. If it hits the 3/4 the fan should kick in and pull it down.

Regarding 1. is there a take off fitting for the vacuum pipe on the carb or manifold? Someone might of swapped in a different distributor but it seems unlikely that they would have drilled either to fit the brass take off.

[JohnFol]

I am by no means an expert and have a 2l non-VX . . . . I have a vacuum advance and there is a T-piece joining it to the bottom of the carb and air filter box. It felt counter-intuitive as it lets atmospheric pressure into the vacuum. I was advised to run the vacuum pipe from distributor straight to carb.
. . . but your questions suggest you know a heck of a lot more than me

[peteracs]

Hi

Cannot answer any VX specific, but first establish if you have over heating issue by using one of the temp guns you can get online for relatively little money. They may not be super accurate, but you can get an idea from boiling kettle etc.

Then see what temp you are actually getting at the engine and rad and go from there.

Peter

[HFStuart]

As a general rule do not have the vacuum advance connected while setting the timing - simply disconnect at the dizzy and plug the hose.

[spydervx]

Hi

My spyder has a guy croft prepared volumex engine installed. 

I have not got access to the car at the moment and initially thought the distributor had a vacuum take off from the manifold as the photo below.  As Sanremo78 has correctly pointed out that is the brake servo take off.
 
In Guy Croft's workshop manual he says " the vacuum advance can be usefully retained on the Volumex tuned versions, but check for pre-ignition problems with it connected".

I can remember researching my distributor during the rebuild and believe it was possibly original. I think it is a Magneti Marelli SM808 -something - but I am away from the car at the moment and will try and confirm later in the week.  I have googled a couple of sites and it may be a SM808 PX? 

On the overheating issue; my spyder has a larger capacity radiator and the lower temperature cut in / off thermo switch like yours and it feels much safer with these margins.  If I let it idle the fan will cut in and out as you describe.

With its tuning the engine is very sensitive to plug temperature and I have found colder plugs help to manage the engine temperature.

Apologies if that just adds more confusion!

[SanRemo78]

I see a huge pipe coming off the right side (as viewed) of the manifold but would have thought that one fed the brake servo? Am I missing one in the photo?

I'm racking my brains to recall if any of the three VX cars (two HPE & a Stratos replica) had a vacuum advance or if it was bobweights. I may have to look at some old photo albums. I know the engine in the Stratos replica ran with a distributor from an injection engine as the original was smashed in the accident that killed the donor (or by the gorillas who removed it - they broke a cam pulley with a hook..)

Guy

[spydervx]

Hi Guy,

Apologies - I am sure you are correct given its size that is the servo take off.  I have the GC workshop manual here but not the car.  If the SM808PX is correct then in web photos it does not appear to have a vacuum connection.  I will correct my post above.

[squiglyzigly]

I’ll have to check my VX in the garage to be sure but these distributors come in various guises depending which models they originate from. They are also fitted on single cam Fiat and Lancias of the same period but obviously have different advance curves built into the bob weights and springs.
Some are vacuum advance and some not but the body of the distributor is the same. When I have rebuilt some in the past, I sometimes fit a new vacuum unit because the plastic side plate that holds the magnetic pickup inside is often split and on the edge of usability. I’ve rarely seen one of these side plates for sale but vacuum units are plentiful. And hence I rebuild them with a vacuum units to hold the magnetic pickup secure but do not connect it if the car doesn’t originally have one fitted.

I’ll get down the garage and check the VX I’m restoring to see if it’s fitted with vacuum advance or not.

Cheers
Ian

[WestonE]

I have been watching with interest here having moved away from clockwork ignition a long time ago now. However from the many conversations with Guy Croft over the years and my own modification of bob weight units. If you have a vacuum advance use it as it is the only way old fashion clockwork can respond to load adding advance when it is needed most e.g. lower revs climbing a hill. You always set static timing first and check advance curves with the Vacuum unit not connected and manifold pipe plugged. Careful modification of the stops for the bob weights can fix some wear that causes problems. Many VX Distributors have burnt out the wiring inside and have been replaced with whatever could be found often from Fiat Uno or Strada. On the VX the Vacuum unit cannot retard the ignition which highly tuned pressure charged engines must have. Fortunately the VX is not highly tuned in most cases (mine are). So the Vacuum advance is an asset provided you have no hint of pinking which is a warning for engine wrecking detonation.

If you look at what the capsule does it just overrides the movement of the advance base plate at lower revs. It does not normally add more to total advance. The figures for the VX are published in GCs first book. Unfortunately mine is still in a moving crate right now.

If you get serious with tuning a VX mapped ignition that can retard the ignition under high boost high load is essential and knock sensors that respond by retarding are highly desirable. I have these things via my Link Fury ECU, but this is not trivial to change to.

Eric     

[spydervx]

Hi 3bar.

I think Eric has summed it up perfectly. 

Just to complete my addition to this chain.  I checked my engine over the weekend it has:

Distributor: Magneti Marelli SM808 PX with vacuum connected to the manifold. 
I think this is an original VX distributor.

Ignition Module is Magneti Marelli AEI 300A.
Not sure if this is original, but is the same as the 2000ie according to the Fiat / Lancia Jan 82 Service manual.

Picking up Eric’s note about the GC Workshop Manual it states about the Volumex ignition data that a Marelli inductive discharge ignition with vacuum advance is employed with:
Static advance 10 degrees,
Centrifugal advance 25 degrees (+or-2 degrees)
Max vacuum advance 15 degrees (+or-2 degrees)

If your engine is standard, and you can get the vacuum advance and distributor working correctly, then it would be worth re connecting.