Spark plug gap

[grubby65]

I have relatively mild street 400/500 stroker motor. Here are some of the details:
Rear wheel hp 360
Rear wheel torque 390
MSD 6AL box, MSD distributor and wires
Aluminum Procomp heads
10-1 compression
91 octane gas
NGK 7 plugs
Smaller roller comp cam
I pulled the plugs and they were very black and even had some burnt carbon crunchies on them. I checked the gap and it was set at .028" which seems small. Called the motor builder and he said he sets them there because of pre-ignition. What are your thoughts

 

[HEMI-ITIS]

I use a 35 gap and it doesn't blow the spark out.

 

[fishmens67]

The plug could be a little cold.

 

[lewtot184]

start at .035" and go after the carb and ignition curve.

 

[68 HEMI GTS]

You could run a 6 with you’re combo. I’m 10.5 and run pump gas. .035 here and a 6.

 

[moparedtn]

Since the old points type ignitions were .035" on the plugs, I reckon it's safe to start there with electronic ignitions, eh?
You didn't mention any carb info on your setup?

 

[grubby65]

Carb is an 850 Edelbrock.

 

[grubby65]

The plugs are actually R5671A-7. I can't find a hotter plug. Not great at NGK stuff though

 

[68 HEMI GTS]

Brk6e

 

[lewtot184]

try an autolite 3924 and use .107" jets on the primary side of the carb.

 

[Cranky]

Man, even with a point system, I never started out with less than .032 but you supplied a very minimum amount of info......

 

[68 HEMI GTS]

I put autolites in my 3v truck. Replaced them plug by plug with MC over a few hundred miles as it lost cylinders. You couldn’t give me that garbage.

And I know a lot of guys swear by them, they just haven’t personally proved anything great to me.

 

[not so famous bob]

I put autolites in my 3v truck. Replaced them plug by plug with MC over a few hundred miles as it lost cylinders. You couldn’t give me that garbage.

wow, I`ve always ran .045 on my plugs w/ an MSD 6 !

 

[68 HEMI GTS]

wow, I`ve always ran .045 on my plugs w/ an MSD 6 !

I’ve played with gaps quite a bit. Never really seen an improvement going bigger than .035 power wise. On motors that create a bunch of cylinder pressure I’ve had to run smaller such as forced induction. My hemi will actually blow the spark out anything over .030 with the 6al and slow right down. Probably needs a 7 though in all fairness.

 

[not so famous bob]

I’ve played with gaps quite a bit. Never really seen an improvement going bigger than .035 power wise. On motors that create a bunch of cylinder pressure I’ve had to run smaller such as forced induction. My hemi will actually blow the spark out anything over .030 with the 6al and slow right down. Probably needs a 7 though in all fairness.

when we first put the old 6al on the hemi, (back in the day) we ran .035 but it had a higher comp. ratio than my 440/505. We were blowing the plugs out when I switched to s.stock, then went to the msd, it solved that problem. If not mistaken,MSD used to recommend .045 .

 

[Mike Gaines]

MSD still says .045

 

[HEMI-ITIS]

As we all know the "book" is a guideline and you need to find what your combo wants.