Anyone have any idea why the 1968 4bbl olds 350 (310hp) calls for R44s plugs and the 1969 calls for R45s plugs? I thought they were the basically the same heads and block?

I know the R44s are no longer available. I was deciding between NGK XR4 vs XR5.

Joe

 

Can't you get R44TS? They're gapped at .035.

 

R44TS is a tapered seat, extended tip plug. Won't work in an Olds motor.

 

Since the 4bbl motor is high compression, run the XR5 plugs.

 

Thanks, that was my initial plan, then became curious what the switch to the R45S in 69.

Joe

 

Maybe there was fouling issues with the colder plug, hard to say. Emissions were starting to become a concern as well.