How about a NGK BKR6E?

 

Isn't that the same as what I'm running now? I think I need a non projected plug, too.

 

The 23 is cooler than the 24. I would try a standard autolite 3924 or 23 otb which are 0.45

Any oil getting into the combustion chamber? Bad seal?

 

I'm running an Eaton M112 with 11lbs peak tapering off to 7 lbs at higher rpms. When heatsoaked in winter weather, my ACT's are hitting 230 degrees. It's a new motor, and so far, everything looks good. If I get a chance, I'll sneak into the garage and pull the other 5 plugs today just to be sure (it is christmas, after all). I'm running a .030 gap. This is why I'm looking at cooler plugs - I feel the 23's are too hot, and the projected tip makes things worse.

 

I ran 3926, was too hot, ran 3924 worked ok, ran 3923, seemed similar to 3924. Went to BKR6E and I felt a SOTP difference.

Try a BKR7E if you want colder (crosses to Autolite 3922)

 

the higher the # the hotter the plugs.Autolite also makes a 3922 which is 1 step colder than the 3923 so you may want to try a set of those.Close up your gap to around .026 - .028

 

BKR6E worked great in my car with .027 gap running 11+ lbs of boost. I might actually go back to them as the car felt better with those vs. the 3923 for some odd reason. Same heat range though. The stock # at parts store is 6962 for box of 4. I had a .030 gap and was getting spark blowout so went down to .027 and it pulled clean to 6k with no issues.

 

This is all good info. I've been informed that projected tip plugs are not a good idea for blown apps. Also, I've opened up my chambers a bit, so the plug is less shrouded than before. I've also ran autolites for the last ten years, so I'm up for trying something different; and NGKs seem to be a favorite on the corral, so I'll give them a shot. The BKR7E's are projected tips, right? I'd rather err on the side of too cold, so I'm looking at NGK #4554 to start, if I can find them locally. Otherwise, I'm leaning towards 4091's, which I'll dub as the Kurgan plug, as he recommends them all the time. How much colder are 4091's? I'm also finding a build issue with the 3923's; I'll post some pics when I get them all out.

 

I think 2 heat rangers colder since it ends with -5, the higher the cooler. So R5671A-7 would be 2 heat ranges colder. I may be wrong but think this is correct. I may try these plugs too, why not. Not a lot of $$$.

 

Love my NGK 4091's. I get them from Napa for less than $2 each. Recessed electrode works great. I run .024 gap but 18 lbs boost.

NGK vs Autolites

 

Are the 4091 a resistor plug? The 3933 plugs are not and have been known to cuase issues on EEC cars.

 

NGK R5671A-7 4091 here w .028 gap. 7200_7500rpm. 24-26psi. 1k plus hp n no problems!!


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JustChuck - No, they're not. But I haven't run resistor plugs in years and never had an issue.

blownholley50 - Any ideas on what your air charge temps are? I think that's playing a role in my application.

I must be some sort of heathen, because I snuck out to the garage and pulled the plugs. To my (great) relief, they all looked the same. Here's a comparison between the AR3923's I've been running on the new motor (left) and the AR3934's from the old one (right):

Ignore the odd bits all over the 3934 - it was on my porting bench (read: table saw); I haven't cleaned it up yet since porting the heads.

I also found something a little unsettling. All of the AR3923's appeared to have some leakage outward between the plug body and the porcelain. None of the 3934's had this. I guess Honeywell = large corporation = crap applies here. Here's a random plug:

 

"Are the 4091 a resistor plug? The 3933 plugs are not and have been known to cuase issues on EEC cars."

The R-5671A-7 (4091) is a non resistor plug.

 

blownholley50 - Any ideas on what your air charge temps are? I think that's playing a role in my application.

300ish. No meth. No e85. Race fuel only.

 

LOL - and here I am worrying about 230 degree act's...

 

I ended up picking up some 4091's at Advance. For whatever reason, the 4554's are twice as much (ostensibly because, according to the parts counter genius, "It's a more powerful plug - it's an 8 instead of a 7." Sure thing there, buddy.) But for $2 a plug, it's certainly worth trying out the 4091's. If I get an opportunity, I'll test drive the thing tomorrow and report back.

 

She-ite muslin backdrops! I forgot to "report back." The NGKs are much, much better. Though didn't resolve the detonation issue completely. I needed to re-curve the distributor, too.

 

What is "much, much better" about them? Did you figure out how much colder they are than the 3923's?

The AR3923's have served me well, but I'm going up 3 points in compression too.

 

Much less detonation when lugging the engine. In fact, none, unless the engine is stoking hot and you hit it with 11 lbs of boost at 2,000 rpm in 3rd gear. I wasn't able to get the NGK's to ping until I bumped into a friend while out tuning. I let him drive the car, and he wasn't shifting the AOD at all; he was just putting around town and got it pretty hot, then rolled into it at two grand; that's when I heard it. The Autolites would ping a lot more.

I think the NGK's are about one heat range colder, but they're also non-projected tip, which I feel makes a significant difference. The engine also seems to run smoother and idle a bit better; but that's in the realm of "subjective." And the NGKs don't freakin' leak. For less than $2 a plug, I seriously doubt I'll ever run Autolites again (the AR's are like $4 each) - and I've been running them for 20+ years.

Hit up Bob Kurgan and see what he recommends. If he suggests these, go with 'em.