Best type of spark plugs & Gap?

« **on:** May 19, 2014, 05:03:03 PM »

I've got a mild 396 steel crank forged internals with a Victor Jr. Intake & a Holley 750dp.
I need to do the plugs, is it worth getting "good"/"perormance" plugs especially if I'm still tuning my motor & what's a good plug gap?

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« **Reply #1 on:** May 19, 2014, 05:29:06 PM »

Quote from: Riverlife_ on May 19, 2014, 05:03:03 PM

I've got a mild 396 steel crank forged internals with a Victor Jr. Intake & a Holley 750dp.
I need to do the plugs, is it worth getting "good"/"perormance" plugs especially if I'm still tuning my motor & what's a good plug gap?

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I always run auto light plugs. what kind of ignition are you running? I would say around .35 to .40 is fine. i think most come out of the box at .45

« **Reply #2 on:** May 19, 2014, 05:31:54 PM »

It's just a MSD HEI 65k coil and 10.5mm wires nothing fancy

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« **Reply #3 on:** May 19, 2014, 05:38:34 PM »

Quote from: Riverlife_ on May 19, 2014, 05:31:54 PM

It's just a MSD HEI 65k coil and 10.5mm wires nothing fancy

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I would go with .40

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« **Reply #4 on:** May 19, 2014, 05:41:32 PM »

I'm at 35 with ngk ur7 series. Unilite dizzy with canister. BBF

« **Reply #5 on:** May 19, 2014, 06:33:47 PM »

Compression ratio has a lot to do with plug gap.

As long as the reach is proper and the right heat range, between .038" and .042" is good. The most important thing is that they are at least all the same.

I always laughed at people that thought something as simple as a spark plug can improve performance enough where you can tell by the seat of your pants.

If you saw a 1 HP gain from one plug to another, whether it cost $2.50 each or $15 ea. I would be more than a little shocked. So far, no one has been able to prove it.

Quicker starting, maybe, but how do you measure that?

GT

« **Reply #6 on:** May 19, 2014, 07:17:31 PM »

Quote from: GT Jets on May 19, 2014, 06:33:47 PM

Compression ratio has a lot to do with plug gap.

As long as the reach is proper and the right heat range, between .038" and .042" is good. The most important thing is that they are at least all the same.

I always laughed at people that thought something as simple as a spark plug can improve performance enough where you can tell by the seat of your pants.

If you saw a 1 HP gain from one plug to another, whether it cost $2.50 each or $15 ea. I would be more than a little shocked. So far, no one has been able to prove it.

Quicker starting, maybe, but how do you measure that?

GT

It's maybe 9.6-9.8:1 just a mild solid runner

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« **Reply #7 on:** May 19, 2014, 07:22:41 PM »

Quote from: Riverlife_ on May 19, 2014, 07:17:31 PM

It's maybe 9.6-9.8:1 just a mild solid runner

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Gap em' to .040" and rock it...

GT

« **Reply #8 on:** May 19, 2014, 07:47:53 PM »

Quote from: GT Jets on May 19, 2014, 07:22:41 PM

Gap em' to .040" and rock it...

GT

Will do, just off the top of your head what depth in the hole are my plugs , it's a 66-67 396. .460? .750?

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« **Reply #9 on:** May 19, 2014, 08:12:20 PM »

Quote from: Riverlife_ on May 19, 2014, 07:47:53 PM

Will do, just off the top of your head what depth in the hole are my plugs , it's a 66-67 396. .460? .750?

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You would need to provide the casting number of the head which is under the valve cover to determine which reach you need.

GT

« **Reply #10 on:** May 19, 2014, 08:22:16 PM »

« **Reply #11 on:** May 19, 2014, 08:24:00 PM »

They are oval port 206 casting

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« **Reply #12 on:** May 19, 2014, 08:41:59 PM »

It's a 396, simple, underpowered, overweight, and archaic. Use the cheapest plugs you can find that thread into the heads and are of the appropriate length. Set tha gap at .050 if your using an HEI...or at .030-.035 if running anything else.

« **Reply #13 on:** May 19, 2014, 09:19:56 PM »

Quote from: lbhsbz on May 19, 2014, 08:41:59 PM

It's a 396, simple, underpowered, overweight, and archaic. Use the cheapest plugs you can find that thread into the heads and are of the appropriate length. Set tha gap at .050 if your using an HEI...or at .030-.035 if running anything else.

Are we still talking about my motor?

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« **Reply #14 on:** May 19, 2014, 09:44:27 PM »

Yes

Don't take my post the wrong way. Simply put, there are small blocks with almost 75ci more displacement. There are big blocks with over 200ci more displacement. The best thing about a 396 is that it's a tank, and almost unbreakable...give it a good tune up, beat the shit out of it...it won't let you down, but it won't win any races.....unless Ray shows up. :-)

« **Reply #15 on:** May 20, 2014, 07:11:25 AM »

Quote from: lbhsbz on May 19, 2014, 09:44:27 PM

Yes

Don't take my post the wrong way. Simply put, there are small blocks with almost 75ci more displacement. There are big blocks with over 200ci more displacement. The best thing about a 396 is that it's a tank, and almost unbreakable...give it a good tune up, beat the shit out of it...it won't let you down, but it won't win any races.....unless Ray shows up. :-)

Who needs to win the race, it's all about being "fashionably late"... Haha

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« **Reply #16 on:** May 20, 2014, 11:12:37 AM »

Quote from: More2LifeThanMPG on May 20, 2014, 07:11:25 AM

Who needs to win the race, it's all about being "fashionably late"... Haha

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Haha true! Usually it's my wife that makes us late!!

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« **Reply #17 on:** May 20, 2014, 12:18:58 PM »

I'm enjoying my slow and reliable boat a lot more as time goes on.

« **Reply #18 on:** May 20, 2014, 12:28:20 PM »

I have been running Autolite 26 plugs with my blower and mechanical injection, gapped at .019 for a magneto, since 1992. They are resister plugs and I know for sure that it does shorten the life of the coil inside the mag. Autolite 26 plugs are one step hotter than stock to keep the plugs from fouling out while idling out of the marina with the mechanical injection tuned fat. Lately, I have been running the Autolite XP26 iridium plugs and have been rather impressed with their longevity.

The 26s may not be the correct plug for your head or the correct heat range for your application, just throwing out what I am using. Regardless, I think you can do no wrong going with even a simple Autolite plug. We ran them for many years in everything from stock up to 1000+ horsepower blown and injected cars and boats.

Meanwhile, here is some good reading that will keep you occupied for a while and hopefully help you learn your combination better while finding the right tune.

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

Cheers,

Joe

Riverlife_

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