View Full Version : 350 Mag Spark Plug / Timing Questions

05-15-2012, 09:52 AM
I have an '87 Magnum 350 (Z21) that I rebuilt last year and am trying to "sort out / tune" for this season. It has an older set of heads (all redone) and is running at about 10:1 compression with a CompCam (basiclly stock) cam. It has the stock Q-jet on a Weiand intake with through the hull exhaust. It is running a MSD Blaster coil on the stock ignition (Thunderbolt) with a rebuilt dist. Here are the questions that I have:

What gap should I have on the plugs? I have NGK BR6FIX and am thinking either: .035, .040, .044. Leaning toward .040. Any thoughts / experience?

What timing should I set it at? I am thinking at 10 degrees BTDC. Thoughts / experience?

Resistor for coil? I am "old" car guy and am use to some type of resistance for power to the coil (wire or ceramic). The boat wiring does not have one (nor show one in the wiring diagram). I am planning on leaving well enough alone if it is not going to cause any issues (I have not really check the coil temp once running for a while. It is mounted in the stock location on the intake near the dist). Thoughts / experience?

Thanks - Quick responses would be great as I am in the middle of the installing plugs, etc...


05-15-2012, 01:19 PM
I believe -8 degrees at idle and 28?? at 3000 rpm but not 100%

05-15-2012, 05:09 PM
Base timing is not as important as top time, your total top timing should be in the 30 to 32 range. As to your plug gap that depends on just how much spark the system can supply, I run .050 using stock ignition with a 60,000 volt coil. Most all of your current ignition systems are capable of .050 and higher.