Spark Plug Question

[James Keddie]

I want to change the spark plugs in my '70 350/300hp engine and am not sure which plug to use. The owners manual lists the R44 as OE, R45 for city driving and R43 for heavy duty? It has R43S plugs in it now and runs okay. I want to try the R45 plugs but there are a few AC Delco to choose from. They list R45, R45S (extended tip) and R45TS (extended tip with tapered seat). Does it really matter which R45 plug I use?
Thanks in advance.
Jim 42765

[Joe L.]

Re: Spark Plug Question

James------

You can't use the tapered seat plugs with your 70 cylinder heads.

You could try either the R45 or R45S. The extended tip design will allow for better burn off of electrode deposits.

On the other hand, if the car runs ok with R43S, why change? Since the R44S and R44 are no longer manufactured, you'd have to change by 2 heat ranges and go to the R45S or R45.

[James Keddie]

Re: Spark Plug Question

Thanks Joe. I didn't know the R44s were no longer available. I'll get a set of R45S's for the next tune-up.
Jim

[Donald T.]

Re: Spark Plug Question

R44 plugs are readily available on eBay. They usually go for around $20 or so.