spark plug gap?

[thebeastjuggalo]

alright, i installed an accell 48,000v coil http://store.summitracing.com/partdetail.asp?autofilter=1∂=ACC%2D140011&N=700+42 94908171+4294908164+4294924755+4294925143+115&auto view=sku

and an accel performance distrib cap and rotor, autolite 7.5mm wires, acdelco platinum plugs at .040 stock gap...

i have been reading around and it would seem that i can increase the size of my gap for a larger spark since i have a higher output coil, what would you say i could increase the gap to?

[G.A.S.]

run the standard gap. To much of a gap will take too much juice away from the more powerfull coil.
The wider the gap, the more power it takes away.

[thebeastjuggalo]

but wouldnt making the gap bigger allow more fuel and air to be ignited at once, wich would in turn end up burning more of the fuel in the chamber? also increasing the gap should make the spark last longer to burn more of the fuel...

[old_master]

Too large of a gap and the mixture will ignite too rapidly, (before the piston reaches TDC) resulting in spark knock and a loss of power. Too small of a gap and the mixture will not be fully ignited when the piston reaches TDC, also resulting in a loss of power. The maximum voltage ever required to jump the spark plug gap is somewhere around 10KV to 15KV. OEM ignition coils are designed to produce in the neighborhood of 40KV, far more than enough voltage to jump the proper gap.

With certain parts, "High Performance" refers to the speed at which money needlessly leaves the wallet

[thebeastjuggalo]

well, guess that was a nice waste of $45 then

[old_master]

If it's any consolation, if the old coil was bad, you may have only paid a little more than necessary

Ignition timing, more accurately, spark timing, and spark plug gap, go hand in hand. With a smaller plug gap, more time is needed to fully ignite the fuel mixture. Advancing the timing accomplishes that. With a larger plug gap, less time is needed. Retarding the timing starts igniting the mixture later and gives it less time to fully ignite. Bottom line is the mixture must be fully ignited just as the piston reaches TDC to extract the most power from the expanding gasses. You can fool around with plug gap, timing, and fuel octane levels, but the manufacturers and engineers have already figured out what the specs need to be for the engine to run properly.

[ZL1power69]

The stock gap recomended on the 4.3 cpi i believe is .045. The stock coil is powerful enough to use on a 454 so firing the spark on our 4.3's is not an issue. i've always thought that the gap the factory recomends, .060 on 96+ 4.3's, is a bit to wide. Over time, the gap expands. I changed the plugs on my jimmy a month before it was totaled and the plugs i removed had a gap of .100 (i'm assuming the gap was .060 when they were installed). OM, in your personal opinion, is .060 really the optimal gap setting for the longevity of good performance? pulling the plugs every so often obviously on our engines is a pain.

[old_master]

Each engine has a parts and specification requirement called a "calibration level". The calibration for each model and year might be different even though it's the same displacement engine. The calibration level includes, a specific combination of camshaft, emission parts, ignition timing specifications, ECM programing, spark plug type and gap, etc etc, basically anything that affects the running of the engine. From time to time the manufacturer might change a spec after the vehicle is in the field. Any changes that are made are put in a technical service bulletin and distributed to the dealers. Depending on what changes were made, the bulletin may be released to aftermarket manufacturers so they can update their catalogs as necessary. To answer your question about gap, the absolute best way to know the most current specs that are best to use on any particular engine, is to check with the dealers TSB file.