SIXt7

I have a completely stock 327/350. Which plug would run hotter.....
Delco R45 or 45S. Any problem with the extended tip getting spanked by the piston?

vark_wso

I'd recommend NGK B-4. These are non-resistor plugs in the same heat range & electrode depth as the obsolete AC-45. Both plugs you mention are of the resistor variety. Alternately, you can frequently find AC-45 at swaps or on eBay.

BarryK

Vark

funny you should say that.
I've developed a miss that I suspect is a plug issue from a voltage drop because of the resistor in the R45 plugs I use and I'm going to be getting and trying the NGK B4 plugs on Monday because they are a non-resistor plug.

magicv8

[QUOTE=vark_wso] Both plugs you mention are of the resistor variety. [QUOTE]
r45 is the resistor version.
45s is the extended tip which needs to be indexed to popup pistons.

I sold a half dozen sets of 45 plugs a year or two ago but I think I still have a set or two somewhere.

If you substitute r45 or any resistor plug for the nonresistor 45, I would not recommend using resistor (radio suppression) wires with an old original AC Delco coil, since the increased load could damage the coil.

NedP1

As to which plug would run hotter I believe the 45 is heat range and therefore they would be the same on the two plugs - R45 and 45S

saopm

So what does the “S” designate in R-45S?

Patrick67

I use Autolite 295 plugs in my stock 327/350. My car runs better now than with any AC plug. PT

67L36Driver

Way back when all SB Chebbys got plain old AC 44's. Given the number of them I can't hardly believe the 44's have been discontinued.

RoadVettes

"S" designates the extended tip. I have used these with good results. When I used the regular R-45 they fouled quickly. With the extended tip the carbon buildup burns off better, if you're having that problem (I was). I have a 327/300, no piston clearence problem at all, don't know about other motors.

Charlie

Ironcross

"S" means extended tip or electrode. They may interfere with a domed high compression piston {11-1 or more} when using the OEM GM steel shim gasket resulting in closing the gap and a miss-fire. To be safe I always recommend the R45. Real pain in the *** doing it twice and after it`s heated up.

BarryK

I believe the "4" is for 14mm and the "5" is the heat range.
compare plugs that are 43, 44, 45 - all 14mm but different heat ranges.

As has been mentioned, the "S" indicates the extended tip.