Spark plug gap with MSD
 

598 cubes, 8.6 to 1, What plug gap should I run with MSD ignition ( 6M )

.035 would be fine.

The same as a any Cheby back in the day, funny how things stay the same as things change........035 is a universal gap, Chevy, Brigs&Straton lol

I like .035.
More gap will be harder on everything.

I like .040 with msd

Everyone is correct (IMHO and experience) above.

Save bigger gaps for the beach. Hah !

Gap depends on what heat range plug you are using.

Back in the day, if you had the "High energy ignition", you gapped the plugs at .060. If you didn't have the HEI, with a conventional ignition, you gapped them at .035 on most GM V8's.

I had several pontiacs, with factory HEI's. .060 was the recommended gap, never had an issue.

.035-.045 imo, is just fine for what you're doing. I've ran my plugs at both of those gaps, never seen an issue, or a difference either way, in my boat engines.

I agree if you have a large distributor cap you can go big gap but most guys here only run a 3" distributor cap no good for big gaps.

msd recomends 55 -60 for up to 10.5 c/r.35 to 40 will work every time up to 15 lbs boost.really no reason to widen the gap imo.

What does the gap have to do with heat range?

I know rule of thumb is , a larger gap, can put more strain on the cap, rotor, wires, and coil.

What about running a non resistor style spark plug, or a resistor style oem style plug, say with a 5k ohm internal resistor? Would a resistor style spark plug, combined with some high resistance anti RFI oem style plug wires, also put a big demand on the system?

most of all the OEM stock stuff is .45 and .60 Just saying

A motor that has higher cylinder pressure produces more heat than a lower cylinder pressure motor. A motor that produce more heat needs a colder spark plug. The reason for the colder plug is to transfer heat out of the combustion chamber into the head and through the cooling system. When you have a motor that has higher cylinder pressure/ heat in the combustion chamber you don't meet a big gapping gap to light the mixture why? Because you have more heat in the chamber. Everything is the opposite with a lower cylinder pressure motor. A hotter plug is used to keep temperature in the chamber and a larger gap to light the mix. The nice thing about plug manufacturers today is they gap the plugs for you based on the heat range of the plug and as long as they aren't damaged during shipping they should be properly gapped from the factory. An NGK -11 from the factory is gapped about .020" what's is a -8 plug gapped to .040"?

which do you mean, marine or auto

I disagree with the above.

The plug does not impact combustion chamber temps unless you get misfire from too cold of a plug which fouls because it doesn't stay hot enough to keep it's electrode and grand strap clean. Or is too hot where it causes pre-ignition because it 'glows red' igniting the air/fuel mix before the spark occurs. Those are the exceptions.

Heat range is all about the temperature of the plug itself. As noted above, it shouldn't run so cold that deposits and etc don't 'burn off' and stay clean, nor so hot that ot glows red and the a/f mix ignities before the plug sparks.

The amt of surface area of the plug is extremely small compared to the heads combustion chamber surface, the piston top, and the valve heads and thus doesn't really help cool or heat that system. It's all about the plug temp itself.

And thus why CDI systems and multiple spark systems (at low rpms) can be useful...if you need them....a motor that needs a certain temp rage plug for high rpm , high power (ie: high combustion chamber temps) but is too cold for low rpm and/or long idle time use in that motor. What do you do ? Use a multiple spark, high power ignition that will fire the plug that regular power, single spark systems couldn't do to fouling plugs.

Other needs for high power, multiple sparks at lower rpm is non or low quench engines, low swirl, large camshafts with reversion (exhaust gases coming back into comb chamber), low compression, bad comb chamber shape, and etc,etc that can/will create low mixture motion and and/or poor quality a/f mix to ignite. Much more on this but another subject.

Many, many different OE engines in the car world use NGK plugs with 1.1 MM plug gaps. This converts to .043" gap. You cannot say all these different engines (Audi, Toyota, Honda, Hyundai, etc,etc) all have same exact combustion chamber temps and etc as each other. Many different CC motors, NA, turbo, supercharger, and etc,etc......

Plugs use ceramic and other materials to insulate / transfer heat back into the cyl head, More or less of these materials controls how much heat it transfers. This determines it's manufacturer heat range designation so you can compare to other heat ranges of the same manufacturer and model of plug.

I think you just disagreed with what I posted and then reiterated (long form) what I said...?
I can tell you this from experience. If you have a motor with a ton of cylinder pressure 3000hp worth running a #11 NGK plug gapped at a tight .022 it runs perfect. Open your gap to .035 get ready cause the big boom is coming. So I ask why? Does the gap change the heat range of the plug? I would have to think so...

no,pressure changes how much the arc will jump to and from.Thats why I love the msd display,back the arc points out an inch and it will jump across it.But in a 1300-1800 nitrous fed small block,go any more than .026" and it won't fire.hummmm,yet in a low comp ratio engine you can have .060"
timing effects the band on the tip,not gap.I've tuned a few nitrous monsters.and this next season,twin turbo humungous block ford.:D

It might go boom because it cross fires under the distributor cap firing the wrong cylinder. Just a thought.

Pressure does not change how much the arc will jump. Resistance will. Air and fuel create resistance in the atmosphere between the electrode and ground strap. Forced induction creates a denser mixture of air and fuel and creates more resistance across the gap. More compression and other power adders do the same thing. It's not pressure.

Right from ngk
Pressure, compression call it you want what in the combustion chamber.they say

"A spark plug can deliver a weak spark (or no spark at all) for a variety of reasons...defective coil, too much compression with incorrect plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.
Slight misfires can cause a loss of performance for obvious reasons (if fuel is not lit, no energy is being created)"
And I went from memory on this.

http://vdlfuelsystems.com/?p=273.

Okay, we have enough info posted to basically end this thread....I think.

And since most boats are layed up for the winter, maybe some can chime in, I have a photo of different gaps, and was wondering which gap I'd run.

Hah !

http://thighgaphack.com/wp-content/u...3578cd1fe8.jpg

Those are the kind of gaps you die for!:hitit::pray:

:drink:[ATTACH=CONFIG]547121[/ATTACH]

#4

sorry 14 but im going with sb,s gap,lol.

all of them and would love them them to my death.:D

Gap Is A Good Thing!
Period.
Well Maybe not?