plug gap suggestions

[pjc360]

I purchased a brand new crane cams hi-6 cd ignition the other day and i will be wiring it up to my 360 magnum next week some time, now i have been told that i will be able to run a larger plug gap once i have the crane ignition wired up, so whats a safe gap?
I currently have my plugs gapped at .035 with the stock mopar ecu ignition system, will i be able to run a .045 or .050 plug gap with the cd ignition? I know you dont wanna go to big, so whats most likely going to be the maximum that i will want to go? i'm thinking .050 would probly be the most i'd wanna go. but would .040 or .045 work better? i have a fairly rich mixture at idle because i'm running an edelbrock performer carburetor and they dont have much adjustability on the idle circuit. I have my idle mixture set the best it can be and it's still a little rich, so i was thinking a larger gap would help burn the mixture better, right?

 

[pjc360]

oh and i forgot to add, i will be running a crane cams lx91 e-core style coil to the crane cams cd box, if that makes a difference on what plug gap to choose.

 

[Abodybomber]

.040" to .050"seems to work well with multi spark boxes.Try .045" to .050" to start.

 

[pjc360]

I just figured if an hei ignition is strong enough for a .050 gap then a cd ignition should handle a .050 gap fine. but wasnt sure? i have always ran .035 gaps because this will be my first cd ignition.

 

[pjc360]

what will i see running a larger plug gap? better idle and thorttle response and fuel mileage is what i have been told? I have a fairly rich idle mixture becfause of my carburetor having zero adjustability on the idle circuit, so i'm hoping this cd ignition and a larger plug gap will help burn my mixture better at idle. I sometimes foul plugs because of it, but i'm also running the stock 4 pin mopar ecu ignition, i indexed my spark plugs and that seemed to help with fouling the plugs. I just think the ignition i have is on a very fine line of being able to burn my mixture at an idle, everywhere else in the rpm range it does just fine, it only seems to struggle at an idle....

 

[pjc360]

i think i might try the .045 gap first, cause after a few thousand miles that gap is going to open, and if i set it at .050 it might jump up to .055 wich seems a little too large. So i guess i could run .050 gap but i'd have to keep a close eye on the plugs and re-gap to .050 if they start increasing in gap size after a few miles.

 

[BillGrissom]

If you get the gap too big, it will mis-fire under high throttle at low speed, like getting on the freeway. That was my experience in my 96 Voyager 2.4 L. I suspected everything but the spark plugs until I ran across a TSB for the turbo version of that engine (PT Cruisers), where they recommended reducing the spark gap if a mis-fire problem. I went from maybe 0.055" to 0.045" and no more mis-fires.

It is harder the throw a spark at high pressure. An electronic ignition can throw a spark >1" at 1 atm pressure, but not at 200 psi cylinder pressure and why the TSB was for turbo owners. Verifying a spark in the air is not always assured and why an in-line spark tester is better.

 

[pjc360]

ya i have heard turboed engines and real high compression motors dont like having real big spark plug gaps.

 

[wjajr]

I have my idle mixture set the best it can be and it's still a little rich, so i was thinking a larger gap would help burn the mixture better, right?

Burning a rich mixture by making a larger spark won’t get the job done it will still be an incomplete burn of the air fuel charge. You need to get closer to ideal A/F mixture by adding air.

I’m guessing you are running a big loping idle cam with low idle vacuum characteristics. There are several ways to correct idle mixture when running non stock cams.

Leaning up idle mixture can be accomplished one way by progressive drilling holes in throttle plates. A place to start is to guess how much hole one needs is to uncap a manifold vacuum tap while engine is idling. If idle goes up from leaning out, calculate area of vacuum tap using its ID, divide that area by two, and drill a hole in each throttle plate opposite idle fuel passageway equal to that calculated half area. If this doesn’t work, just solder up the holes.

Secondly I’m not versed Eddlebrock / Carter meter rod stile carburetors, but perhaps you can adjust secondary throttle plate’s stop to open them a wee bit to add more idle air, in other words create a controlled vacuum leak.

Thirdly, do these carburetors utilize adjustable idle air bleeds? If so adding more air into idle circuit emulsion by changing to larger air bleed would lean out mixture. The so called idle mixture screws don’t regulate air fuel mixture, but instead meter out how much of a set air fuel emulsion passes through the idle circuit.

I would pick up an Eddlebrock / Carter carburetor tuning book for best methods such as this one for example:
http://www.amazon.com/Rebuild-Modify-Carter-Edelbrock-Carburetors/dp/1932494367

 

[pjc360]

no they dont have adjustable idle air bleeds, there is hardly any adjustability on the idle circuits of an edelbrock carburetor. just the two air fuel screws and thats basically it.
I know a larger plug gap and hotter ignition will not solve the richer mixture at idle, but it will help it untill i can afford a better carburetor, the carburtetor i am going to get is a quickfuel hot rod series 680cfm vaccum secondary carb that has changeable idle air bleeds and idle feed restrictions and a 4 corner idle. I'm just going with ignition first because it was a little cheaper to start plus i have always been told ignition first then carburetor.
But im hoping with a cd ignition and a little larger plug gap it will help burn the richer mixture at idle a little better then my current stock mop0ar ecu ignition system with .035 inch gap.