Spark gap ?
 

I am curious just how much gap I can run, I read an article on some testing done on a stock 260ZX one of the thing that gave a slight gain was increasing the gap. I have 383 running 9.125 compression. I am using the Merc IV pack with a hot Jacobs coil my plugs are gapped at .050 it runs good. I get varied input, some say .035-40 which I feel is to small some say go as high as .065 on my setup. On my GMC Sub, the stock setting is .060. The new plugs came pre gapped at .080 I re gapped to .060, I asked a few other motor heads about the .080 they said some late auto apps run it with higher compression. Any input well appreciated!

Phil

Re: Spark gap ?
 

yes, larger gaps can yield gains due to additional charge molecules that lie between the gap. this could tax your ignition system and also cause misfires. and as you know it's harder for that gap to be bridged as your compression increases both dynamically and calculated.

as a side note, modern day vehicles can have ECU/EEC issues/errors due to the increased resistance seen in coil over spark-plug applications.

Re: Spark gap ?
 

I have a couple of circle track buddies running .065, but the load is different on marine. I am thinking of trying the .065 that my buds have recommended come spring, see how it runs and read the plugs to see if everything looks good if not I'll go back to .050 which is working fine.

Phil

Re: Spark gap ?
 

The Delco HEI system has more than enough available power to efficiently fire a .060 inch gap without any ill effects. However, the MerCruiser Thunderbolt system should not be gapped over .045 inch due to the problems mentioned by audacity. Increasing the gap increases resistance and you must have an ignition system that will not be adversely affected.

Re: Spark gap ?
 

I fully agree with .045 on stock IV the exception is that I am running a 60,000 volt coil, I believe the IV is 40,000. The literature for the coil had .050 or better, so I believe the coil I have will hold up. There is no extra strain on the pack being as it controls when the spark goes off.

Phil