Blown 440 spark plug gap

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67charger383

67charger383

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Hey yall,

I’m trying to figure out what I should gap the spark plugs on my 440 (ported iron heads, forged pistons, 8-71 BDS blower running 15psi of boost)

I haven’t raced it yet and have only cruised it around at a few fairgrounds/cruise week events and I previously had the plugs set at .035 but I’ve had some problems with it popping at low throttle and when starting up. I’ve heard 2 different camps saying open it up or close it up.

What are y’all’s recommendations?
 
Been a long time, but if i recall, a hot ignition, non projected plugs and a .028ish gap was preferred back in my day with that kind of boost. Just another opinion...
 
Depends on the ignition system, and what fuel you’re using. You ain’t firing a .060 gap on methanol with points.
 
Maybe even tighter than stock. I'd try .035 and maybe go down to .020 and see.
 
.030 tops. Probably end up at .025 or maybe .028. I wouldn’t run less than a 7 box with what you have.

A magneto would probably be better.
 
Newbomb Turk said:
.030 tops. Probably end up at .025 or maybe .028. I wouldn’t run less than a 7 box with what you have.

A magneto would probably be better.
Click to expand...
You ever been hit by a mag? I have. Twice. Once in school fiddlin around with a friend's race car. Absolutely knocked my brains out. You'd thought I'd learned, but NOOOOOOO. I got one many years ago for my Ford 8N tractor. Found it at a local antique mall and just "HAD" to get it. It was a Wico Magneto. Put it on, got it running and it ran good. Only problem was it hit the hood a little and rattled while it was running. So I grabbed the hood to pull it away from the mag and "somehow" my arm touched the mag. I thought my elbows were gonna fall off. It really didn't fit that good, so I put the distributor back on it. LOL
 
I ran an Accel dual point and Super coil on my blown Rat motor 475 cu in, 21% overdrive on an 871 blower. I never gapped my plugs special, .032 or .035 as I remember. This was in a pickel fork jet boat. Ran and beat the hell out of it on the Mississippi River every weekend. I will still say that no special gap needed. On my airplane with an old magneto set up, .018 plug gap. Electronics are better.

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The gap is going to depend on how powerful the ign system is. A turbo or blown engine is going to be better off with a CD ign system, such as the MSD 6,7 boxes etc. The dedicated ign coils that can only be used with these CD ign systems pack the ign punch needed with these engines.
 
RustyRatRod said:
You ever been hit by a mag? I have. Twice. Once in school fiddlin around with a friend's race car. Absolutely knocked my brains out. You'd thought I'd learned, but NOOOOOOO. I got one many years ago for my Ford 8N tractor. Found it at a local antique mall and just "HAD" to get it. It was a Wico Magneto. Put it on, got it running and it ran good. Only problem was it hit the hood a little and rattled while it was running. So I grabbed the hood to pull it away from the mag and "somehow" my arm touched the mag. I thought my elbows were gonna fall off. It really didn't fit that good, so I put the distributor back on it. LOL
Click to expand...

Ouch lol!!
 
Close it up, .025-.028, my late model cars that are supercharged run .028.
 
kbr577 said:
Close it up, .025-.028, my late model cars that are supercharged run .028.
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How come? Your late model supercharged cars should have coil on plug and they’ll fire big gaps even on boost.
 
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