plug wire resistance & 66 spark plugs

[Gary S.]

I remember reading a long time ago about how much resistance a spark plug wire has per linear foot. Unfortumately I don't remember this figure. Does anybody remember how to tell if a spark plug wire is good or has a short? In addition, I am looking for a near-stock spark plug for my stock 66 with 327/350. Any ideas on what is currently available in a heat range similar to what was in this car 34 years ago? This is an attempt to help eliminate possible causes of my miss/stumble and backfire through the tailpipe. I have eliminated the coil, condensor, timing, points, fuel filter & ballast resistor. I have pulled the carb and will go through it tomorrow and the distributor will be pulled and sent to a shop that still has a good testing machine and the knowledge on how to do this.

Thanks, Gary 21316

[Rich Garguilo #33425]

Re: plug wire resistance & 66 spark plugs

7000 ohms per foot !!

[Iron Duke NCRS #22045]

Re: plug wire resistance & 66 spark plugs

Gary - The original equipement plug in mid-sixties small blocks is the AC 44 for "town and country driving", but I and many others have found the hotter AC 45 to be a better choice for this style of driving. I personally don't care for the ACs because the black oxide coating on the shell has poor corrosion resistance, so I recommend Champions. They cross reference both the AC 44 and 45 to the J8C. The next hotter Champion is the J11C, which they cross reference from the AC 46. An extended tip plug will usually stay a bit cleaner so you might consider the J18YC, which they cross reference from the AC 45S. To the best of my knowledge, extended tip plugs will not interfere with the slight dome on your SHP engine.

Make sure your single point distributor end play is shimmed up to the fuel injection spec, which is .002-.008". The non-FI distributors were typically .060" to .120", which will allow the shaft to bounce up and down. Make sure the breaker plate sits firmly and does not wobble, and use the "heavy duty" 28-32 oz. breaker arm tension points such as Borg Warner A112HP. These are equivalent to the discontinued Delco D-112P heavy duty 28-32 oz. breaker arm tension points. With my distributor set up this way it tests good on a machine to 7000 and works fine on the car to the 6500 RPM redline. Old coils can act flaky when they get warm, so if the problem still persists, try another 12V coil to insure that your coil does not have some sort of thermal related degradation.

Duke

[Tom B.]

Re: plug wire resistance & 66 spark plugs

Gary,

Since you're eliminating the potential of problems one by one, and this is just a shot in the dark, but how old is your battery, are the connections good, and do you happen to be using a certain type of cut off switch? Just another check off the list. TBarr #24014

[Gary S.]

Re: plug wire resistance & 66 spark plugs

One year old battery, cables at least 10 years old, no cut off switch. Good thoughts here. I will clean all of the posts and cable connections. I am not sure how a cable can affect a car that will run well for 3-4 miles, then hesitate with a small tailpipe backfire. Nothing surprises me anymore though. Thanks Gary 21316

[Gary S.]

Re: plug wire resistance & 66 spark plugs

Thanks for the replies. I wlll be getting new plugs today and I will check the wires and replace as necessary. I did shim the distributor up a bit, because of excess play, when I had it out of the car. The funny thing is I ran this distributor for 9 years with only minor maintenance, such as points. When I had it out last week, I did shim it up a little bit. I put in a new heavy duty set of points and I swapped in a known good coil from my neighbor's 73. I am pulling the distributor to take it in for a complete physical at a shop that can test all of the functions such as indvidual plug firing and all of the advance stuff. Gary 21316

[ian paterson]

Re: plug wire resistance & 66 spark plugs

gary you also might want to check for a vacumn leak which would cause a lean backfire condition.plus make sure fuel supply is good thru filter and pump,i had a 59 that would hiccup and backfire after a few miles, floatbowl was running low, goodluck ian.

[Iron Duke NCRS #22045]

Re: plug wire resistance & 66 spark plugs

Gary - In case it hasn't been mentioned, replace the fuel filter. This happened once with my '63 SHP. At WOT it would literally quit, not just missfire, above about 4000 revs. Turned out to be a clogged fuel filter.

Duke

[Bill Clupper]

Re: plug wire resistance & 66 spark plugs

With respect to the plug wires, the original factory spec was 3000-5000 ohms per foot I believe, Chrysler used High resistance wire that was about 2000 ohms more throughout the scale. In reality, any wire reading less than 35000 ohms will work fine, the big problem is total opens