Hey guys,

Some quick questions here: Are the R42TS AC-Delco plugs too cold for a ZZ4-cam 355 L98 with stock iron heads in 12 degree weather? I am having some bad idle problems after the engine rebuild. The "42's" I have in there are gapped at .35. I have about 9.9 to 1 compression as well, so do I need a special high-output coil and thicker wires? (I have 8mm accels in there now; stock coil). Basically Im looking to see what are the effects of a plug that is way too cold and weak spark accross the board on idle. Thanks!

 

An upgraded coil is certainly not a bad idea...but it's not gonna make a huge difference with plug selection.

Too cold a plug will foul out very quickly. It's similar to the effect of putting a glass of icewater out on a hot humid day. Carbon deposits will condense onto the plug. 42's are probably too cold with your app as well. I'd start with 45's and go from there.

 

R42TS plugs are only mildly cooler than the grocery getter
R45TS plug. I ran the same heat range all year round, and it was fine. Do a spark test, disconnect a plug wire from one cylinder
and atach a spare plug on the wire. Touch the ground electrode on the block and have someone crank the motor over. If you see a nice blue spark, the ignition system is ok. If the spark is anyway yellow, something is weak in the ignition.

These R42TS plugs were stock for 70's LT-1 corvettes and Z28's
and are the right plug for "performance driving" If all you do is commute back and forth to work and around town, then R45ts's
are probabily a better choice for your car.

I think your problem is elsewhere ( fuel management, ignition)
because R42ts plugs are not cold enough to cause low speed fouling, by themselves. By the way, once a set of plugs are fouled, reguardless of heat range, they will not cleanup. So you'll need to buy new ones.

 

Just wanted to thank you guys for your reponses. I am going with Champion Platinum power 3025's - stock replacement for '87 350 TPI (iron heads). This is just so I can have a standard plug so I can diagnose my idle problem. The injectors are known good Lt1 injectors -- the distributor is a rebuilt stock unit with new module inside. The wires I just bought yesterday (Accel 8mm). My Fuel pressure is set at 41 psi when engine is off and the fuel pump primes. My base timing is 6 degree BTDC. The engine itself is just rebuilt - I just finished putting it all together the day before yesterday. Basically, almost everything under the hood has been replaced except the radiator. Ahhhh troublshooting, its just not an annoyance, its an adventure!

 

41 PSi sounds low... most people get the best atomization and still love their FP's at 48 running psi... just a thought.

.35 also sounds pretty small... I run an Accel coil and am looking at .5 for my app... just another thought.

As for plugs not cleaning up if their fouled... soak them in gasoline overnight and take an old toothbrush to them and tell me the oil and carbon doesn't break down. Plut them in a car with a healthy ignition and mixture and they'll be fine. I have about 500 miles on a set of Bosch Plats that are kinda fouled... they'll be cleaned right after I finish up my ignition and installed...
Good luck with everything.