Magnecor

[Phil Payne]

I had a problem with an MB last week, and it's started me wondering about the suitability of Magnecor ignition leads.

See http://www.magnecor.com/magnecor1/7mm8mm.htm

This clearly documents a linear resistance of 3k Ohms/foot.

Audi's specification for the 10V I5 plug leads is 5k Ohm in the plug cap, close to zero in the lead, and 1k Ohm in the distributor plug for a total of 6k Ohm. And true to what you'd then expect, a new set of Audi leads measures out at close to 6k Ohm on each lead, irrespective of length. #1 and #5 are therefore the same.

Not so with a set of Magnecor leads purchased fully made up as a replacement (supposedly an 'improvement') for Audi stock leads. #1 measures as just over 6k Ohm, #5 as under 3k Ohm. That's exactly what you would expect if the plug cap and distributor plug had zero resistance and the Magnecor lead was 3k Ohm/foot.

I think having one plug lead with twice the resistance of another can only lead to problems.

[driftin jo]

[Pete Reeve]

I had a problem with an MB last week, and it's started me wondering about the suitability of Magnecor ignition leads.

See http://www.magnecor.com/magnecor1/7mm8mm.htm

This clearly documents a linear resistance of 3k Ohms/foot.

Audi's specification for the 10V I5 plug leads is 5k Ohm in the plug cap, close to zero in the lead, and 1k Ohm in the distributor plug for a total of 6k Ohm. And true to what you'd then expect, a new set of Audi leads measures out at close to 6k Ohm on each lead, irrespective of length. #1 and #5 are therefore the same.

Not so with a set of Magnecor leads purchased fully made up as a replacement (supposedly an 'improvement') for Audi stock leads. #1 measures as just over 6k Ohm, #5 as under 3k Ohm. That's exactly what you would expect if the plug cap and distributor plug had zero resistance and the Magnecor lead was 3k Ohm/foot.

I think having one plug lead with twice the resistance of another can only lead to problems.

What did Magnecor say when you told them of the problem Phil don't you think that you should give them a chance to put the problem right before you post?

[johne]

No, it won't.

More important than the resistance is the quality of the leads and for them not to breakdown under load.

The resistance is there to help supress radio interference but quite large variations won't have any effect on the spark delivered.

John

[Phil Payne]

No, it won't.

More important than the resistance is the quality of the leads and for them not to breakdown under load.

The resistance is there to help supress radio interference but quite large variations won't have any effect on the spark delivered.

John

I'm not questioning the quality of manufacture. It's one of the few things as a trained cable and wire engineer (Concordia, Long Eaton) I'm professionally qualified to talk about. And resistive leads do indeed reduce interference, though I've never known it be a problem on Audis.

There is variation in the spark - half the resistance means (very, very roughly) half the spark duration.

[Phil Payne]

What did Magnecor say when you told them of the problem Phil don't you think that you should give them a chance to put the problem right before you post?

It's phrased as a question, Pete. You were quite right when you said there are dozens (maybe more) quattro owners using them without apparent problems. I've found them under scads of bonnets and never had occasion to question them before.

[PeteRR]

I've got a set of 7mm ones on my MB quattro. I must say that they seem to be working perfectly so far.
I've also had a 7mm set and a 8.5mm set on my two previous RR quattro's. Again, with no problems.

(We also have them fitted to two Rangie's, and also have had them on two of our old Rover saloons in the family. They've been spot-on for me).

[johne]

I'm not questioning the quality of manufacture. It's one of the few things as a trained cable and wire engineer (Concordia, Long Eaton) I'm professionally qualified to talk about. And resistive leads do indeed reduce interference, though I've never known it be a problem on Audis.

There is variation in the spark - half the resistance means (very, very roughly) half the spark duration.

The leads are not the dominant resistance in the circuit. Spark size and duration are governed by the impedance of the coil, it's capacity to store magnetic flux and the spark plug impedance which changes as the spark forms and ebbs.

John

[Phil Payne]

I've got a set of 7mm ones on my MB quattro. I must say that they seem to be working perfectly so far.
I've also had a 7mm set and a 8.5mm set on my two previous RR quattro's. Again, with no problems.

Wouldn't expect problems with RRs or Rangerovers - their systems are different. In fact Magnecor's highest recommendations seem to come from Rangie owners.

I've just started looking at the system and it looks like there could be problems if the coil secondary is seriously out of specification, which does happen. Something to measure the next time I get to the car.

[caterpillar]

The leads are not the dominant resistance in the circuit. Spark size and duration are governed by the impedance of the coil, it's capacity to store magnetic flux and the spark plug impedance which changes as the spark forms and ebbs.

John

If the audi coil are 1 coil for 5 syl;( the old style 20v 5pot) and the tci one, you dont can use this... the coil vill break and goin bad