spark plug indexing

[putztastics]

Thanks Dave, very interesting.

Like you said it seems there would be two main reasons for "cycle to cycle varaition" involving ignition, "By mis-fire, I mean the flame front never started or the flame front began but was not completed. IE, the 'fire went out'. "

Here is a link to an interesting dropped spark test;

http://www.4secondsflat.com/a688dropcyltest.html

I don't know how dropped sparks are dectected but if there isn't a spark there will not be a fire, and like you mention you can't always hear it.

A seperate problem with some Mopar ignition boxes is timing retard with increasing RPM. Like 6 degrees retard in a 4000 RPM increase. (35 total @ 1200 29 total @ 5000 with a locked out distributor, MP Orange Box, FBO coil ignition.) You can imagine what that could do to the power. I dyno tested a Mopar 383 RB, the owner had a Mopar Performance Orange box, changing the ignition box only, made a 20 chp difference at 5000+ RPM.

Here is the graph;

http://www.revsearch.com/ignitiontest.jpg

There was not really an audible difference in the way the engine ran.

The coil was the FBO piece.

The intake was a cast iron dual plane that did not lend itself to easy fuel distribution mods, the cast iron exhaust manifolds probably didn't help either.

There should not have been dropped sparks with the FBO coil/Orange box combo until 5400 RPM so the problem was probably the RPM retard "feature" of the MP Orange box.

At about $2 per hp the FBO ignition box was a pretty good investment.

I've never dyno tested spark plug index but usually index them - grounding strap in line with the exhaust valve - the open part pointed to the exhaust valve.

I should try it sometime.

[NOwaterONLYair]

hello, new guy here posting. i dont know anything close to what you guys know but i wanted to ask this question.

what about trimming the tip of the ground strap to somewhat of a point rather then a square end? will that help in producing a more precise spark?

[Vengeance]

what about trimming the tip of the ground strap to somewhat of a point rather then a square end? will that help in producing a more precise spark?

Rounding it off would be okay, but you don't want it to be a "point" otherwise you could cause an unnecessary hot spot which could cause future pre-ignition...

[Unkl Ian]

We had a similar Box Retard problem,using some Ford box.
I forget the exact amount,but it was a LOT more
than 6 degrees in 4000 rpm.

Switching to an MSD box solved that problem.

A seperate problem with some Mopar ignition boxes is timing retard with increasing RPM. Like 6 degrees retard in a 4000 RPM increase. (35 total @ 1200 29 total @ 5000 with a locked out distributor, MP Orange Box, FBO coil ignition.) You can imagine what that could do to the power. I dyno tested a Mopar 383 RB, the owner had a Mopar Performance Orange box, changing the ignition box only, made a 20 chp difference at 5000+ RPM.