Spark plug choice ? please

[cj's mopar]

Hello, I have a question regarding my spark plug choice .
I have a 400! B block with Ross pistons small dish but set at zero deck height.
Running Stealth 440 heads .
Engine will be run with a six pack and a small roller cam . 2836 roller hydraulic from Hughs engines 525 lift .
Thinking about Running autolite 3924 .
Mainly because I have a new set on the shell from about ten years ago . Will these plugs be fine or should I use a colder plug?

 

[440rb]

I ran nothing but NGK's in my 446ci 10:1 race car and also in my hot 340 car. Never ran autolite but NGK 6's for hot street and 5's for strip, .030 thou with MSD ignition was best, forget all the giant gaps. Your 3924 should be equiv to NGK 6's.

 

[cj's mopar]

Ngk 6 ? Is that a 3/4 reach plug?

 

[Slap Stick]

3924s fit small blocks. You want an Autolite 85.

 

[RemCharger]

Ngk is a brand, 6 is a heat range.
Nothing about type/dimensions

Ngk 6 ? Is that a 3/4 reach plug?

 

[Slap Stick]

But the NGK 6 IS an extended reach plug. Wont work in a B/RB.
Just like the Autolite 3924.
Not everyone uses letters to designate plug reach like Champion.

 

[68 Sport Satellite]

3924s fit small blocks. You want an Autolite 85.

isn't it head dependent?

 

[Slap Stick]

isn't it head dependent?

Yep. 3924 is a long reach plug, like a N14Y. 85 is short and fits B/RB, like a J14Y.
The OP stated he wanted to use a 3924 in his 400. That won't work.

 

[Mackman]

May need long reach plugs with those heads.

 

[cj's mopar]

I checked on 440 Source web sight the said needs 3/4 reach plugs the sell for 29.00 but don't give part numbers

 

[68 Sport Satellite]

Yep. 3924 is a long reach plug, like a N14Y. 85 is short and fits B/RB, like a J14Y.
The OP stated he wanted to use a 3924 in his 400. That won't work.

But if he's using the 440 source heads, the reach may be different since those are aluminum, correct? I know my Eddy RPM heads take a different plug than stock.

 

[RemCharger]

IIRC, all, aluminum heads take the new style plug.
Never seen one that takes the old original style short fat plug for iron heads.

 

[Slap Stick]

Okay, well, an old dog learned a new trick today.
Thanks!

 

[383man]

IIRC, all, aluminum heads take the new style plug.
Never seen one that takes the old original style short fat plug for iron heads.

Yes all the aluminum heads I have worked with (Eddy , Indy , Stealth) all use the 5/8 plug. Ron

 

[beanhead]

Will these plugs be fine or should I use a colder plug?

Not unless your SCR is at least 11 to 1 or higher, and even then....testing different heat ranges is the only way to nail it down. Colder-than-needed plugs just get dirtier quicker without any positive benefit. I've gotten to like NGKs in a 5 heat range (BKR5E) but that's just personal choice, your 3924s will do fine.

 

[beanhead]

Yes all the aluminum heads I have worked with (Eddy , Indy , Stealth) all use the 5/8 plug. Ron

Yeah being able to use a 5/8" socket makes plug changes a breeze! Especially with TTI headers.

 

[cj's mopar]

Thanks to everyone for the Great Info I am getting close to dropping the new motor in and trying to all the pre break in boxes.

 

[Geoff 2]

A lot of misinformation here.
[1] Post 3#6. NGK6. 6 is the heat range, & is used for all thread length/diameters in the NGK range. Post #6. Champion does NOT use letters to denote heat range, they use numbers. 14 is hotter than 12.
[2] Errors in post #2. Sometimes a colder plug might be reqd, but for street use a hotter plug is needed.
[3] Unless this engine is going to be run at WOT for extended periods, 5 heat range in NGK is correct for street/strip.
[4] Use the biggest plug gap your ign can provide, not the smallest.

 

[68 Sport Satellite]

A lot of misinformation here.
[1] Post 3#6. NGK6. 6 is the heat range, & is used for all thread length/diameters in the NGK range. Post #6. Champion does NOT use letters to denote heat range, they use numbers. 14 is hotter than 12.
[2] Errors in post #2. Sometimes a colder plug might be reqd, but for street use a hotter plug is needed.
[3] Unless this engine is going to be run at WOT for extended periods, 5 heat range in NGK is correct for street/strip.
[4] Use the biggest plug gap your ign can provide, not the smallest.

I'm no expert, but I can't believe this is gospel for #3. It would also depend on fuel octane, wouldn't it? For my 10.2:1 451ci running California 91 octane with max timing set at 32 degrees total before it detonates, NGK 5 is too hot for my motor. I run NGK 7 with success on the street.

One other thing to remember for all is that NGK heat range goes backwards compared to other brands. NGK 5 is hotter than NGK 7, whereas Champion 5 is cooler than Champion 7.

 

[Geoff 2]

NGK 5 is what NGK recommends. How are you determining that 5 is 'too hot'? There are many causes of detonation, such as lean mixture, excessive engine temperature, etc. A too hot spark plug does not cause detonation, but it could cause pre-ign. Pre-ign & detonation are entirely different. Pre-ign occurs before the spark from the spark plug; detonation occurs after the plug has fired.