Trying to troubleshoot a problem which I believe to be electrical and curious if a coil could be the cause of the motor breaking up under a 3/4 to full throttle load. I have a new Firecore Dist and their wires, a MP chrome box, the coil on there now is an old MP unit from the conversion kit from 15 + years ago. No oil leaks from the coil. The car runs great until you bring the rpm's up. In park it revs to 6500 with no issues.

The initial timing is set @ 20 deg and I adjusted the advance slots in the dist to give it 38 deg. The advance springs are the ones as delivered from Firecore. The motor is a 10.5:1, Eddy head, 451, 254@50 solid cam.

if it's an oil filled coil i'd throw it in the bin & get an epoxy solid unit. oil filled coils & capacitors are becoming a thing of the past since they're prone to fail with age

Coils can definately be a problem... I had one once that would run fine until it was heat soaked then it would crap out. Once it cooled of it would fire again....

I am guessing its probably 17 years old now. Does Firecore offer such a coil like an MSD Blaster or better?

Simple answer is YES

Yes if its going out they tend to break up under load

OK, I have decided to replace the coil but not sure what direction to go. Like I said, I am running a Firecore dist set up and still have the ballast resistor. The MP electronic conversion is still in place but I did replace the orange box with a chrome one 4 or 5 years ago.

It could be the coil for sure.
I chased a similar problem years back ..... to the point of sending my 7 AL back to Texas to get checked out.
It was a weak valve spring.
The car pulled like normal till around 5100 and then it sounded like it was banging off the chip.....which I replaced first.
Checked wires , grounds , swapped my spare coil in ........ thought it has to be the box , which checked out fine.
Based on how it sounded ,everything pointed to ignition to me and a few other pretty savvy racers....... it wasn't.
And it ran the bottom of the track pretty much like it always did , but as load increases ( 2nd and 3rd ) the miss got more pronounced.
That was a strange one.

When I was testing coils and ignition boxes on the dyno, the best two coils I found to work with the MP boxes were the MSD blaster 2 and the Accel Super Stock. I have heard the newer Accel coils don't hold up like the older ones. If you want epoxy filled the Blaster 3 will do the job.
Keith

You don't say which motor or brand your running but on any Mopar BB, 426 Hemi or SB Mopar I would try backing the timing down to a true 30 BTDC total at or above 3500 RPM on the SB and 34 BTDC on the BB or Hemiroid first before changing any thing else I'm not sure how good or bad the weather is thier now but try the timing first How much use, miles or racing mintues, on the distributor and wires and what compression and fuel are you running? All the ignition coils I've seen fail usually go open on the internal windings or have cracks or a path for the electrical discharge to run to ground on the face of the coils I have worn out restistor type ignition wires, spark plug and coil wires, that would miss starting in high gear abot the 1000 lights (above 5000 RPM)

Its a 400 based B stroker (451), 10.5, Eddy head, 91 octane which is the highest pump you can buy here. The motor has less than 1500 miles on it now, never been on the track, and less than 400 miles or so street driven in a year. The distributor and wires have less than 300 miles or so on them now.

Which spark plug brand and part number are you using? Can you post a decent picture of one? That would help us see what they look like

The plugs are NGK FR5. I chose that plug based on the advice of a member here. I can get some pics of a couple of plugs in the next day or so. They looked like everything was burning nicely with a light tan color. I did use copper anti-seize on the threads when I put the plugs in. Is it possible that I used too much thus creating this high RPM break up situation?

I would not no be opposed at all to changing the plugs for a fresh set.

Neverseize is extremely conductive. If ANY gets near the end of the plug, it will be ruined. Been there, done that.

RIP

The NGK fives are way to hot for any fuel other than 100+ octane race gas Go buy a set of either NGK with 7 or 8 as the last number or aset of Champion RC9YC or a set of Autolite #23 and try them Look real closely with a 10x magnifier at the porclyn on your plugs, if there are either very small black or shiny dots on them your into detonation Most engine misses can be fix once the cause is determined and corrected Good luck, let us know what you find

Hey thanks Cab. I'll pick up a set of one that you mentioned and see if that changes things for the better.

A bad connection in the coil wire will also have the exact same symtoms. I know because I was tracking down the same problem. Only under load and at higher rpms the engine would misfire. Turned out to be the core of the wire was burning back from the connector inside the boot. Wire looked new on the outside. Engine also ran better when first started up but got worst the longer it ran.

I'll inspect the coil wire but it was replaced with the new Firecores. I ordered the #23 Autolites and will get them in in the next day or so.

Check rotor phasing. NAPA has an Echlin #MO3000 rotor with an .060" longer blade which can help with that (it'll reduce the radial distance but not the circumferential distance but both of those add up & if you're over the gap distance that your coil/ballast combo can handle then it will miss). It's worse at WOT when the required voltage is the greatest. Holler what it ends up being. A quick check is to cap the vac adv hose & see if it changes (gets better or worse) as only vac adv will alter RP (that's why Andy intro'd his machined reluctors way back) which you can do at home (just need a drill press/accurate measurements). Note that vac adv shifts phasing CW on a BB & CCW on a SB. See where it is at at rest (no vac)

I would like to believe that a new Firecore dist would not need a different rotor but anything is possible. The vacuum advance has never been connected.