I'd like to make the switch from AC Delco R45S plugs to NGK. I had no idea how hard it would be to cross reference heat ranges, at least with the Delcos. I'd like to go one small step cooler than the R45S plugs. I'm looking at the NGK XR5/3332 and I've seen that some folks here on CO are using the same plug. The plug NGK recommends for my motor ('76) is a #4 heat range; and since 12 is their coolest, 4 seems pretty hot. Here are my specs:

455 .030 over
9.7 CR
Iron heads
HEI with Proform tune up kit
Taylor 350 ohm per foot plug wires, custom fit
Cam w/ .512 lift, 227/233 @ .050
Run 93 octane

 

The factory plugs for a 76 in AC Delco is a 46, so your 45 is probably close to the XR5. You could try the AC Delco in a 43, that is what part selector says is a replacement for a 1970 Oldsmobile. You could try for NGK a 5670-6 or 5670-7 racing spark plug. This BR6S is the resistor style and cheaper.
https://www.summitracing.com/parts/ngk-3522/
https://www.summitracing.com/parts/ngk-2746/
https://www.summitracing.com/parts/ngk-2891/

 

Thanks 307, I hadn't thought of looking up the stock AC plug for a '76 (although didn't I when I built this motor? I must have IBS, aging brain syndrome). I guess my question should be; what would be the proper heat range for my build? Since my '76 doesn't resemble a '76 motor other than the block, rods, and crank.
I want to get that AFR gauge and get it installed but thought an ignition makeover should come first.

 

The NGK R5670 looks pretty good. Many street/strip folks seem to be using them. But I still wonder if they're too cool. I'm running out if time this season for warm weather tuning. Is it common for an engine to love cool weather, say upper 50s to lower 60s? Or is that telling me something? I realize the outside air is more dense but what else?

 

Yes, the engine should run better with cooler ambient temps. Just make sure the choke is adjusted so it works correctly in the cooler weather.

 

Oh yeah, me and chokes are BFFs. Sigh, not really, but I got it good enough (it just opens a little too quickly).

So your answer begs the question, why? Is it just the denser/cooler air, hence the desire for an OAI hood (a working OAI hood)?

 

NGK XR5 gapped at .035.
Thry ran hotter plugs in ‘76 cuz they were lower compression and didn’t want to risk fouling causing a subsequent misfire as that would wreck the cats.

 

.035 with HEI? Not .045?

 

.035.

 

You da boss

 

Yes, denser/cooler air.

 

So, you're saying I should vent my AC into the carb!

 

Sure, why not. I heard there's some Mustang variant with a supercharger that uses the AC for the intercooler.

 

You know, after I wrote that joke, I started wondering if it wouldn't be a good idea. But it would be a little like adding more fuel to a rocket to propel the [more] fuel, wouldn't it.

 

Lookup Roadkill Boost Caboose

 

Hey, I love Freiburger and Finnigan! I'll look it up.