Spark plug gap

[Mayhem]

350 Chevy, 10.5:1, 292/501 cam, aluminum heads, HEI distributor.

What would you gap your plugs at?

I was told .045, they came out of the box at .035, the old set were at .040-.041. Someone today said they thought .035, but everything I have read says .045.

However, it was screaming with the .040 set, and runs like crap with the .045. I do not want to do this again more than once.

What say you?

[Salvatore]

that much difference from .040 to .045? gap them at .040 again and stop reading. Have fun!!!

[PxTx]

Are you running any type of CD ignition? You do use up spark energy to "Jump" the gap, that is why a Mag has to run a tight gap- like .020 so while cranking the spark will actually jump.

I've found on CD systems, a larger gap works but on conventional .035 is a good place to start.

[Mayhem]

That is exactly what I was thinking. I just didn't want to find out it would be even better at .035.
The header makes it too much of a royal pain to keep messing with them due to the #6 plug being right behind the double tubes.
You have to pull the header to get to it at all. Also, the last rear header bolt on that side is practically up against the firewall.
I am putting Allen head bolts when I do this again. Thanks for the help.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: [email protected]</div><div class="ubbcode-body">that much difference from .040 to .045? gap them at .040 again and stop reading. Have fun!!! </div></div>

[PxTx]

Closing the gap actually affects your ignition timing. Closer the gap the more &quot;advance&quot; it gives you.

[Mayhem]

Accel HEI Dist. &amp; &quot;super-coil&quot; that mounts on the top of the cap.

You can kind of see it in this pic-

http://blueicehouse.com/n5ssi/IMAG0178.jpg


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">Are you running any type of CD ignition? You do use up spark energy to &quot;Jump&quot; the gap, that is why a Mag has to run a tight gap- like .020 so while cranking the spark will actually jump.

I've found on CD systems, a larger gap works but on conventional .035 is a good place to start. </div></div>

[Mayhem]

That's what I thought. You can definitely tell when driving at constant speed, like 45mph. Timing has changed.
I just REALLY want the right gap, and then I can tweak the timing from there for peak performance.
Thanks Paul.

Has anyone ever used the MSD Adjustable timing control that mounts inside, so you can fine tune while driving, as opposed to bumping the distributor a little and checking responsiveness?

MSD Ignition Control (http://www.msdignition.com/Products/RPM/Timing_Controls/Timing_Controls/8680_-_Adjustable_Timing_Control.aspx)

I prefer that fine tuning method, also for peak performance, or at least to know where it is in comparison to correct timing placement, for track setting.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">Closing the gap actually affects your ignition timing. Closer the gap the more &quot;advance&quot; it gives you. </div></div>

[Salvatore]

What is the timing at when the plugs are .040? Is it a big difference? You are right, you only want to do plugs once especially if they are really hard to get to.

[Mayhem]

It is recommended to be at 12-14 BTDC, but I honestly don't remember what it was at now.
I don't think it's a noticeable difference, maybe 2 degrees. But when driving, it now has an occasional miss, and not near the power it did.
I can put them back to .040 like the previous set, but I am being told .035 and .045, and really want to know which is right.
I can figure out what works best, but that involves a couple more plug R&amp;R sessions that I REALLY don't want to do.

[miket1]

Use an adjustable timing light so you can set total advance with timing all in on the top end, maybe 3000 to 3500 rpm or so, whatever rpm the advance is all in, then you will know your correct total timing advance, using different plug gaps.

[Mayhem]

Since I can't get an answer from anyone on specifically what the gap should be, I am regapping them back to .040 where the old set was. I can't believe .005 would make such a huge difference.

At least I know how well it ran at that gap. I still welcome input for what it should be.

Again: 350 1980 Corvette engine (apparently an L82), aluminum heads/intake, 292/501 cam, 10.5:1, 50/50 mix of pump gas and 111 leaded fuel.
(apparently the vette engine part makes a difference in plugs from all other 350's-not sure why).

I will likely buy the MSD dial adjustable timing setup later to fine tune it for different variations and temps.

Thanks all.

[Verne_Frantz]

Rather than asking everyone what the gap &quot;should&quot; be for your car, why don't you just set it where the car runs best???? Afterall, isn't that what you really want??

Verne <<GRAEMLIN_URL>>/rolleyes.gif

[Mayhem]

Yes, but as previously discussed, one of the plugs are a #$@!%!!! to change due to the header blocking it, and having to drop the header to get to it. If it were easy, I wouldn't even ask.

[VintageMusclecar]

I've found .035&quot; is a good all-around setting.

Bigger gaps can work with an arc welder ignition system, but the bigger the gap the more strain it puts on the ignition system, not something you want/need on the street--even with an HEI.

My $.02

[Mayhem]

Thanks. I set them back to .040 today, but it is cold &amp; rainy, so I can't test it out. I know it ran good before at this gap.
I will either get another set or regap these at .035 when it is warmer and I can test.

Thanks for the response.