I am running a 355 with vortec heads. I am also running an msd 7al2 plus ignition box. According to the msd manual, for my compression ratio, it says to gap at .050-.060. Any other small block that I have ran I have always gapped them at .035. Any advice for this?

 

I've run my Vortec (and aftermarket versions) plugs at .050" with a 6AL box.
Others here say that despite the box, keep the gap at .035.
I've never had any trouble with the larger gap. All applications have been from 9-10.5:1 NA. Big cams and not so big cams. Racing, cruising, starting in extreme cold, idling in traffic, etc. Good performance and excellent fuel economy too.
I believe the issue the "others" have is in regards to boosted applications.

 

I to run .035 on just about everything. Always worked fine for me

my boosted stuff cruises around just fine with .020-.025 gaps.

 

0.035 for NA, 0.018 to 0.020 for boosted.

The large gap trick was for emissions. It is not useful for performance engines and is very hard on ignition components.

GD

 

Hey GD.
I read your other post on this subject.
Now, you mention emmisions. I can understand that in an OEM context.
But with reference to an aftermarket performance orientated ignition box I don't see the objective as being emmisions related. Is this some advertising bling from MSD to impress us?
FWIW, I've run the large gap forever in several engines and have never had any component of my ignition system fail. This isn't to stay it won't but so far and many miles later so good.

 

A large gap stresses everything in the high-voltage section that has insulation. Cap, rotor, wires, to some extent even the plugs themselves.

Given that there's basically nothing to gain from a super wide gap, and only opportunities for extra failure, I don't see much point in it. Anything "normal" for a modern ignition is fine; .035" - .045" is entirely adequate. Pretty much, how most of em come out of their box.

 

This is what the instructions say for my msd box. I ran them at .050 mainly due to them coming at I want to say .060 from the box.

 

MSD sells lots of caps, rotors, wires, and coils. Considerably more if they wear out faster. And they DO wear out faster at the higher voltages required to push the spark across a 0.060" gap. Further there is zero performance benefit in my experience to gaps larger than 0.020 to 0.035 other than possibly measurable benefit in emissions. I only surmise this because of the stock GM recommended gap of 0.060 on the Vortec.... Which was almost certainly for emissions.

I Dyno as many as 6-8 cars a day and we blow out spark on a very high percentage of them. We pull the plugs, swap them with new copper plugs gapped to 0.020 and finish tuning. No one has EVER complained that our plug gap was too tight and was somehow a problem. I don't see the use in stressing components anymore than necessary.

And what happens when that gap naturally expands to 65, 70 and beyond. That's a LOT of voltage

GD

 

I do know about the voltage. Even with my small blaster ss coil, it shocked the crap out of me when I was checking for spark at the track. Definitely agrees with the name blaster. So GD, would you just put them at .035 and call it a day?

 

You can certainly tolerate more but the question is: where's the advantage? I'd like to know MSD's angle on that.
Bigger gap. Bigger spark. Quicker initiation of the flame kernel and a faster flame spread?
I suppose you could tune to the plug gap. Open it up and see if less advance is required for best ET.
But at the end of the day, from this performance perspective, go with the tighter gap, save what is reported to be otherwise harder on parts and call it a day.
What say GD?

 

My tuner to friend of 17 years experience and I discussed the factors surrounding this thread......

He made the very cogent argument that NEVER, in 17 years, has he seen the occasion that a larger (or smaller) gap allowed a single additional degree of timing to be subtracted.

Timing is a measure of the time required to burn the fuel prior to the flame front reaching the face of the piston. If a larger gap were helpful it would result in less timing required for the flame to travel.... Ostensibly because it would result in a faster, more complete burn. But that simply isn't the case in practice. Changing the gap has no measurable effect on timing.

So from a tuning perspective it's useless. And only results in additional wear on ignition components. We routinely run gaps of 20 or less and have no issue doing it. In fact it's much easier on ignition components as it allows them to withstand higher cylinder pressures (forced induction) without blowing out the spark.

GD