The V8 Owners Forum -

Using your word the MSD will do the most "twiddling" (retard) at idle and therefore the rotor will have travelled nearly past the post before the actual spark occurs. , hence trailing edge at idle. "I thing"

Regards Denis

DEVONMAN wrote:Using your word the MSD will do the most "twiddling" (retard) at idle and therefore the rotor will have travelled nearly past the post before the actual spark occurs. , hence trailing edge at idle. "I thing"

Regards Denis

Hi Denis,

I think we are saying the same thing but in a criss cross fashion!

Yes, at tickover the trailing edge will be the edge that is in line with the post but only because of the "twiddling" that the MSD has done.

The MSD must get the signal to start the "twiddling" earlier than this (32 crank degrees earlier). Therefore the "commence twiddling" signal must come around the time that the leading edge of the rotor is in line with the post. As the revs rise the "twiddling time" will reduce which will mean that the leading edge ends up being the edge that lines up with HT post!

Are we mad?

Regards,

Pete

DEVONMAN wrote:

DaveEFI wrote:One gotcha when using a locked advance dizzy is you need to phase the relationship between rotor arm and plug lead contacts accurately, as it no longer varies with the spark advance.

I don't thing the relationship is affected by the bob weight position as the rotor, reluctor, pickup and cap have a fixed relationship. However the vacuum advance does change the relationship because the baseplate moves as does changing the pickup gap.

Regards Denis

It does - but that is lost when you use a programmable ignition unit, as the spark no longer occurs at the trigger point.

It can also be worthwhile cutting a hole in a gash dizzy cap and using a strobe to see the actual rotor arm position with the engine running.

DaveEFI wrote:It can also be worthwhile cutting a hole in a gash dizzy cap and using a strobe to see the actual rotor arm position with the engine running.

Yes that would have been a good idea when I was trying to solve a misfire under boost retard conditions. On the standard dizzy set up the rotor is set to spark near the trailing edge. Under vacuum advance the the spark then occurs nearer the leading edge. My misfire was due to the electronic boost retard causing the spark to occur just after the rotor had passed the post.
I solved it by adjusting the base plate in the dizzy relative to the cap.
I could have adjusted the rotor instead.

Regards Denis

Denis,

You mentioned that your dizzy is locked up, are you using the same MSD-A6 programmable unit that I intend to use? The reason that I ask is that I thought that it was the only unit that they sell where you can program in a curve.

I've had a reply from Summit, they reckon that the unit would work with just my pickup but I'm not so sure now. Mainly because the lead is going to be quite long and I can't see a milli-volt signal surviving the journey to the MSD box.

I've asked MSD themselves and just joined their forum, I'll post up anything that I find!

Cheers,

Pete

sidecar wrote:Denis,

You mentioned that your dizzy is locked up, are you using the same MSD-A6 programmable unit that I intend to use? The reason that I ask is that I thought that it was the only unit that they sell where you can program in a curve.

I've had a reply from Summit, they reckon that the unit would work with just my pickup but I'm not so sure now. Mainly because the lead is going to be quite long and I can't see a milli-volt signal surviving the journey to the MSD box.

I've asked MSD themselves and just joined their forum, I'll post up anything that I find!

Cheers,

Pete

I have in the past run a locked out dizzy and used a normal MSD 6 unit in combination with an MSD programable ignition control. I think your MSD unit is basically the same but in one box and now set up using a laptop instead of 3 knobs on the box.
I don't see why the pickup won't work in your case but certainly I would twist the wires together and screen them with aluminium tape.
Regards Denis

I'd tried it too run a MSD 6 Al on the Lucas leccy dizzy but whatever I tried it never worked so I replaced the leccy dizzy for the oldstyle Lucas points version which worked fine for years. Using points as a trigger you need to remove the condencer from the circuit.

Have to say.... did get issues with the old bob weights being old and so, out of control ( just worn out ) so I replaced it with a MSD Pro Billet dizzy which was the best investmend in the system. Easy to recurve whitin a minute to get the best performance ignition wise.

MSD 8548 Pro Billet is pre SD1 but when you swap gears for the SD1 drive ( very easy mod) it is a straight swap.

Yeah I know, it aint cheap, but horsepower never comes cheap.
MSD 8548 comes compleet with parts ( differend stops & springs) to get 24 differend ignition curves. So if you modify your engine further along the line is easy to recurve the lot to a more suitable ignition curve for your particular setup.

I'm running EDIS, and the pick-up is about 1.5 mtrs of cable away from the EDIS unit. Just use a good twisted pair screened cable.

DaveEFI wrote:I'm running EDIS, and the pick-up is about 1.5 mtrs of cable away from the EDIS unit. Just use a good twisted pair screened cable.

Now you've got me thinking again! I guess I could try both methods, it will only cost me some time and effort and one of those 4 pin ignitor jobbies!

I would say that my EDIS VR sensor is even further away due to the route I had to take.

The EDIS unit is in my battery box under the passenger seat (LR Defender) so a good way away from the sensor- no problems! Shielded cable, earthed to the battery.

I think "sidecar" is concerned that the output from the standard Rover in dizzy pick up has less output than the VR crank sensors that drive an EDIS box.
Regards Denis

DEVONMAN wrote:I think "sidecar" is concerned that the output from the standard Rover in dizzy pick up has less output than the VR crank sensors that drive an EDIS box.
Regards Denis

That's right, the signal must be very small. I'm not sure what a VR crank sensor is so I can not comment on that. (I guess it is just a coil pickup though)

Ah- sorry, so in effect using the reluctor and pickup in the dizzy as a triggerwheel and vr sensor?

Some bod on the MSD forum has answered the post that I wrote.
I think that he is something to do with "MSD"
He reckons that the Lucas reluctance wheel is very similar to an old Chrysler one which works OK with the MSD pickup. I think that what I'll do it fit a MSD pickup into a Rover dizzy!

I think that I'm indecisive but I'm not too sure now!