sstanford you are exactly correct. If the engine and ignition are original, keep the same plug as factory. What the plug mfg don't tell you is although most of the specs are the same, different brands of plugs have different internal resistances. Therfore, they fire at different tip temps (not the same as heat range) and different burn times. Once you go to modified engines or ignition systems, you will get different results, and a bit of trial and error may be in order. Best to talk to someone who has used your combination. It could save a lot of failures. Most of the aftermarket ingition builders are willing to help, and have a lot of data to fall back on.

I've been running AC/Delco Rapidfire's in my vette for three years now without a problem. I think that they are a good step up from the regular AC's.
And that's my .02 cents
Sarge

I have posed the same question to MSD and I am waiting for a reply, will post when received! Thanks Everyone!!

i use accel header plugs shorter then normal lets my wires live in the header area without burning up
mine is a 300+ hp daily driver and ive had no problems frpom the accels

I like the Accel sparks plugs. I ran them before I installed the Vortec heads, and in other cars. I have not been able to find an Accel spark plug for the Vortec heads. For the spark plug to seat into the combustion chamber, it has to be a little longer. That is why I run the A/Cs, but no complaints with them.

Hi Gerry
The theory behind plugs like Split Fire is that if you
expose the spark to the load in the combustion chamber,instead of shielding it behind the ground electrode, you will get better combustion.
My friend had a 1913 model T and said it made more
power with the original side gap plugs than with replacement Champions with the wrap around ground electrode! We're talking about a noticeable difference
in a 90 year old engine with about 25 horsepower!
I'm trying HALO plugs (Halo.com) which have an open spark
in my 78 and will give you an update in the spring when
I can drive the car again.
Steve

I have posed the same question to MSD (AGAIN)and I am waiting for a reply, will post when received! Thanks Everyone!!

I wouldn't hold my breath waiting for MSD to give a specific recommendation. When I've spoken with them, they're great at providing info on their products. General questions usually get a "check with that manufacturer" or "experiment with different setups" response. I guess they don't want to make any enemies by favoring one product over another.

This is the answer I received (in 3 days)fm MSD
If you are happy with the plugs that you are currently using then you can remain with them. The gap can be increased to .045 to .050; this will help get a better burn to the air/fuel mixture.
Thanks,
msdtech2
tHANKS EVERYONE!!!!!