Use proper E30 leads for the M20 motor. This is what happened to me, a 15 year saga...
When I got my E30 in 2005 the first thing I did when doing the fluid change was also dump the ignition wires for a new set of expensive spiral core leads. After all, doing this on my previous cars had always made a positive difference to engine drivability and power.
But after I put them on I could swear it was not as good as before. But I dismissed this as being just in my head, and when you spend money on stuff that is supposed to be better, you start to fool yourself.
Earlier this year I had the engine rebuilt after the car being garaged for a long time. I purchased a lot of new parts, but the doubt about those leads stayed in my mind, so I purchased a new set of NGK blue leads which are widely available at local automotive chains for the M20 motors.
But afterwards, my engine builder told me he thought the leads were no good. I thought - bullsh###t, they are brand new - how could this be an issue?
But then a local BMW club specialist (who prepares E30's for the track) in fact laughed at me when I told him my setup - he said the first problem I have is those leads are never going to fire properly and you don't use spiral core leads on the E30....
So lo and behold after some research I had no idea the E30 uses leads with a special boot that has a 1000ohm network resistor inside (to give consistent near zero impedance across all spark plugs). Also it uses solid or stranded wire, not spiral core. The two new leads sets I purchased are just spiral core wire with standard boots.
So yesterday I had an OEM Bremi set installed and... finally this car drives like I expected it to after rebuilding the engine. Its not more power... but something else... previously when the car was under any sort of revs something seemed to be hesitant or missing. And under hard acceleration there was definitely misfires. But with these proper leads a general drivability is now back to where I remember it. Revving is more smooth.
So from this experience I can say use genuine leads or proper OEM leads.
Now there is something else to add here..... when doing my research I came across the Merc forums, because the guys with the classic 70's and 80's Mercs have spark issues, and there was a general consensus to now never buy Bosch leads. They used to be the premium, but apparently in recent years Bosch have moved production of the older classic stuff to cheap Chinese factories and they are garbage. So the Merc guys think that Bremi or Beru leads are far superior.
I don't know how true this is, but I did notice the Bosch was cheaper than the Bremi or Beru, so I got the Bremi which is considered OEM quality.
VAC Motorsport also make a custom premium set of leads that looks very good, using Moroso wire and Beru boots. I would have considered this set but they do not make a set for early style M20 motors.
When I got my E30 in 2005 the first thing I did when doing the fluid change was also dump the ignition wires for a new set of expensive spiral core leads. After all, doing this on my previous cars had always made a positive difference to engine drivability and power.
But after I put them on I could swear it was not as good as before. But I dismissed this as being just in my head, and when you spend money on stuff that is supposed to be better, you start to fool yourself.
Earlier this year I had the engine rebuilt after the car being garaged for a long time. I purchased a lot of new parts, but the doubt about those leads stayed in my mind, so I purchased a new set of NGK blue leads which are widely available at local automotive chains for the M20 motors.
But afterwards, my engine builder told me he thought the leads were no good. I thought - bullsh###t, they are brand new - how could this be an issue?
But then a local BMW club specialist (who prepares E30's for the track) in fact laughed at me when I told him my setup - he said the first problem I have is those leads are never going to fire properly and you don't use spiral core leads on the E30....
So lo and behold after some research I had no idea the E30 uses leads with a special boot that has a 1000ohm network resistor inside (to give consistent near zero impedance across all spark plugs). Also it uses solid or stranded wire, not spiral core. The two new leads sets I purchased are just spiral core wire with standard boots.
So yesterday I had an OEM Bremi set installed and... finally this car drives like I expected it to after rebuilding the engine. Its not more power... but something else... previously when the car was under any sort of revs something seemed to be hesitant or missing. And under hard acceleration there was definitely misfires. But with these proper leads a general drivability is now back to where I remember it. Revving is more smooth.
So from this experience I can say use genuine leads or proper OEM leads.
Now there is something else to add here..... when doing my research I came across the Merc forums, because the guys with the classic 70's and 80's Mercs have spark issues, and there was a general consensus to now never buy Bosch leads. They used to be the premium, but apparently in recent years Bosch have moved production of the older classic stuff to cheap Chinese factories and they are garbage. So the Merc guys think that Bremi or Beru leads are far superior.
I don't know how true this is, but I did notice the Bosch was cheaper than the Bremi or Beru, so I got the Bremi which is considered OEM quality.
VAC Motorsport also make a custom premium set of leads that looks very good, using Moroso wire and Beru boots. I would have considered this set but they do not make a set for early style M20 motors.
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