I know you guys have told me before, but I can't find the post and I bought new plugs today so... what is the appropriate gap for a lightly modified 289 with a MSD distributor and ignition coil? I seem to remember somebody saying the gap was supposed to be set at 40, but I don't recall.

 

Yeah, that is still under debate, but I would follow the MSD guide. If 0.040 is too much or too little, then adjust accordingly. My suggestion has always been to start with 0.040 and open the gap to see where the best gap is for your application. The MSD installation guide is your best resourse.

 

How can I tell if my gap needs to be adjusted?

 

Performance of the engine. If it runs crappy, the plug gap needs to be adjusted. The more you open the gap, the faster you will wear out the plugs though. I would suggest you follow the MSD guide for the best performance for your application. There are a ton of guys who suggest you gap the plugs to 0.032-38. They may be right, as they have good performance from their cars, but I disagree. Now, you see the query?

 

I'm one of the guys Glen mentioned, not that what I believe should be considered gospel. Keep in mind that wider gaps are generally needed if you are running lean (thats right, lean) as it takes more of a spark to light the fire. That's why the factory plug gaps got so wide in the mid-seventies when everything with a carburetor was leaned out to meet the tougher emissions laws. As long as your carburetor is tuned fairly well, a plug gap of .035 - .040 should be adequate. And as long as the spark is healthy and your plugs are the correct heat range, you should not have to worry about plug fouling. Just my $.02.

 

with more current avl. from the msd the gaps can be widen some.....glen how did you come up with wider gap means faster wear?...

 

If the gap is set too large, the ignition system will not be able to cope with the demands and a misfire situation will occur. Some wide gap spark plugs have a longer ground electrode to accommodate a wide gap setting. These must be used where specified, as opening up a standard plug to a wider gap setting may result in the electrodes not running parallel to each other. This could result in abnormal and premature electrode wear. The hotter the spark, the more wear on the electrodes, so either re-gapping or replacing the plugs will have to be performed more regularly with as wider gap setting. If used in a racing engine, then those guys perform this very regularly. But, as most of us have daily drivers, it would be impractical to have to re-gap or change the plugs very often. That's why it is important to find a happy medium for gap. Too little, foul plugs and loss of power...too big, faster wear on the electrodes.

 

First of all...what type of plugs are they? Depending on the type of plug and the ignition system depends on the gap....40 is a normal gap which works well in any situation...I just hope you didn't get platinum plugs...But in a worst case scenario, if you set them to .40 and your car doesn't run correctly....you can always just adjust the timing at the distributor to compensate..not the best way to fix it but it saves time pulling plugs.