Jacobs ign? Plug gap?

[beached1]

What should my plugs be gapped at when running a HEI with a Jacobs pro street CDI and Ultra Coil? This is on my 427 BBC with the peanut plugs. Should I or can I still run my splitfire plugs that are in it now or should I just go get some Autolites? I was told by a friend that with the full Jacobs system that I now have I should gapped at 65 thou. Is that right? That sounds like alot.
Thanks

[stix818]

That sure seems a little high. We run a 7AL2 and only gap them at .045". I most likely wouldn't go to much further than that. If anyone else begs to differ give us some feed back.

[572Daytona]

.06 or higher was my recollection of the recommended gap when I installed my Jacob's ignition many years ago. I just pulled out Doctor Jacob's step by step guide to optimizing your engine and the recommendation in there is to increase the manufacturers suggested plug gap by .025 when installing a Jacob's ignition

[BOFH]

Ditto. The Jacobs setup means add .025 to what you needed before. The tricky part is figuring out what you needed before. If you went from points to electronic, you can add another .010, but if you added a blower, subtract .015, and so on.

[572Daytona]

What about other electronic ignitions, such as MSD, should the gap be increased with those as well? Or is the Jacobs that much different? Just wondering since I'm running an MSD on the Daytona and currently only running a .045 gap.

[Dennis Moore]

The only way you are going to increase the performance of any engine with an ignition modification is by increasing the plug gap. I would increase the gap to .060 but only with spark plugs that are capable of doing it. The ground strap has to be parallel with the electrode, not at an angle. Go through the spark plug catalogs and find a plug that is designed to be run with a large gap, good luck, there aren't many! AC Delco R43TS6 works good!
Please take this as FRIENDLY advice, carry a spare ignition with you, the Jacobs won't last long!
Sincerely
Dennis Moore

[*LS7*]

Last long?
Jacobs started in Costa Mesa CA. We had there 3rd unit ever sold for Marine Purposes. It only last 21 years before we decided to upgrade with the motor refreshening.
Now running a Jacobs Prro Street Modified unit for 9 years, not a glitch and hard mounted off a stringer.
Dennis, you might have had bad luck but to come on hear a suggest to another that he is going to be in trouble is UTTER BULLSHIT.
You know damn well for a company that WAS FIRST in selling EI's and still strong as ever MUST have quality parts.
I'm nit in a war of who has more performance gains or upgrade options, or acceseries. JUST CAN'T STAND POS PEOPLE "GLOBAL SLAMING" FOR NO REASON BUT THERE OWN!
[ September 13, 2002, 04:55 PM: Message edited by: *LS7* ]

[MikeF]

Dennis Moore:
The only way you are going to increase the performance of any engine with an ignition modification is by increasing the plug gap.This cannot be true. The coil can only supply x amount of voltage. If the plug gap is increased the amount of voltage available "time" is shortened. You want the biggest/hottest spark at the right time. Getting that hot spark throughout the R's is the key to increasing performance.
I agree w/ most of your other posts :) . Mike

[572Daytona]

I can't speak for all Jacob's owners but my experience has been great. I installed one on my Tahiti over 10 years ago and it is still working.

[beached1]

Hey thanks for all your input. I feel better about gapping them so much now. I'll post the results in a couple weeks with my GPS.

[XTRM22]

I had the Jacobs Marine pack on both a 454 mag, and a 350 mag. the 454 idled a little better but I could never tell the difference with the 350 over stock thunderboolt. The cool thing about the Jacobs system on your Mercruiser engine is if you carry the old coil wire you can over ride the Jacobs ( if it were to act up , mine never did) and use the existing thunderbolt. I never had any problems with the recommended gap, it seemed to work fine with the regular plugs but they specifically recomended not using split fires or the like.
Chuck

[Dennis Moore]

Dear Mike,
No matter what the capability of an ignition system is, the spark will always seek the easiest path to ground. In other words if you have a .035 inch plug gap the spark (voltage) will only build to a point to where it will jump (to ground) across the gap. Lets say that an engine only requires 15,000 volts to jump a spark across the gap (most engines). Even if the ignition is capable of 50,000 volts it will still jump the gap as soon as it reaches 15,000 volts. The ignition system can't say to itself "I can jump the gap now but I am going to wait until I build to 50,000 volts" The spark will jump the gap when it reaches 15,000 and then start the process all over again!(seeks the easiest path to ground). The only way to increase voltage from the ignition is to increase the resistance to ground by increasing the plug gap. Then you will be utilizing the full capabilities of the ignition. High voltage ignition systems and standard plug gaps still produce standard voltages. Almost all breakerles 12 volt ignition systems will work with .060 inch plug gaps. The reason why it is not recommended is because the rotor, cap, coil wire and spark plug wires are not up to the task. Instead of jumping to ground across the spark gap the spark may find an easier ground to some alternative place between the coil and the plugs (engine block, exhaust manifolds etc.). The new 496 engines have a standard 12 volt induction style ignition system but have .060 inch plug gaps. The reason why it works is because the engine doesn't have a distributor. It has 8 individual coils mounted close to the plugs on the valve covers with short high quality plug wires.
Hope this helps!
Sincerely
Dennis Moore
PS, Don't get me started on CD versus induction style ignitions. All of you guys that insist that your CD is the only way to go will be disappointed!

[DEL51]

spark current and duration are also big in the ignition scene. The book by Dr Jacobs is good.I would like to see a real ignition test to see at what point an aftermarket system truly makes a difference.
[ September 13, 2002, 10:22 PM: Message edited by: DEL51 ]

[MikeF]

Dennis Moore:
Dear Mike,
No matter what the capability of an ignition system is, the spark will always seek the easiest path to ground. In other words if you have a .035 inch plug gap the spark (voltage) will only build to a point to where it will jump (to ground) across the gap. Lets say that an engine only requires 15,000 volts to jump a spark across the gap (most engines).
The only way to increase voltage from the ignition is to increase the resistance to ground by increasing the plug gap.
Hope this helps!
Sincerely
Dennis Moore
I see what you're saying.
If the system can resupply the voltage needed to the coil @ higher R's then the fuel will be lit properly (most of our ign systems do not have a variable amperage module or dwell time adj to be able to resupply the coil w/ enough juice). If the voltage cannot be built up fast enough in the coil @ higher R's, the spark may not be able to jump the widened gap (yes/no).
If you have 8 coils....then you have all the time in the world to build up that secondary spark voltage (most of us do not have 8 coils).
Thanx for the reply!, Mike

[Fired Up]

Hate to be the party pooper. Put the third Jacobs system in my Motorhome over a year ago. The first one was bad. Second one was an exact replacement. Also bad. The third was a slightly different although new design. Still ran bad. Tried all their tech suggestions. Still ran bad. Jacobs would not respond to me about refunding me my $ nor would a supervisor return my calls. Maybe the marine system is better.

[*LS7*]

Care to post your original invoice number. They track everything and I would be currious.