Hello,
I got a new motor over the course of the winter, and made an attempt to increase performance somewhat. The 350 got a new set of pistons, and now the machine shop stated that my compression ratio is 9.8:1, up from 8.5:1 it was before the rebuild.

Anyway, when I put it back in the car, I got a new set of AC Delco R45TS sparkplugs, because that what was in the motor before.

Motor runs and drives great, exhaust is pretty loud, so it's hard to hear pinging, but I have't particularly noticed any.

My initial timing is set to 8* advanced, and I've put 113 miles on it, and had 93 octane in the tank. A few miles ago, I filled the tank again, but thought I'd try some 87 octane Trouble is, when the motor is good and hot, after I shut the ignition off, it will run on for maybe 1-2 seconds, barely noticible, but I know it does it. It did not do this with the 93

So I know part of my problem is that I put 87 in it, I'll put 93 in it from now on, but it got me thinking about plugs too.

With the increased compression, should I run a colder plug, maybe a R43TS

What is the difference between a CR43TS and a R43TS?

Thanks!

 

there's a chart on AC delco's webpage decoding their part #'s. I think Vader or Apeiron gave it to me on TGO, perhaps you can search here and find it. It's on my home computer and i'm not so...

I stepped down to a R42T (the lack of "S" means it's no an extended tip plug, and a very cool one), due to having 10:1 CR and iron heads. I think it'd be a good idea for you to try the R43's. Also, you can read you plugs to see if it's running lean or hot or something.

 

Temperature range of a spark plug is the plugs ability to remove heat. Normally a plug tip should be between 450C and 850C. Many things can affect that temperature such as compression ratio, fuel octane, ignition timing, cast or iron heads etc. Finding the proper heat range is almost trial and error. You want to run a cold plug but it still needs to be hot enough to burn off deposits. If it's too hot, the tip will burn off. If it's too cold, it will foul up.

Try a colder plug. If it fouls up, switch to one step hotter. Plugs are cheap but replacing them every 6 months because they're fouled up can get expensive.

My old 4x4 was an oil burner. 2 cylinders were always fouling plugs. I had R43's in 6 cylinders and R45's in the other 2 to help them burn off the extra oil. It worked for me until I was able to rebuild the engine.

Best reading about spark plugs
www.centuryperformance.com/spark.asp

 

so the wrong heat range plug can be masked by wrong mixture, and vice versa eh? hmm, more variables to consider...