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Old 01-21-2004, 04:56 PM   #1
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Question Gap for Spark Plugs???

I just picked up some NGK plugs (PN 6630) for my car. The guy at the shop said to set 'em at .045. Here's the engine details:

'91 302 (of course)
Stock lower end
Stock heads
Cobra Intake
B-Cam
24# injectors
65mm TB
75mm MAF
Underdrive Pullies
AFPR
CAI
MSD Cap/Rotor
FRPP 9mm Wires

Any other suggestions, or does .045 sound about right? Thanks for any advice!
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Old 01-21-2004, 06:58 PM   #2
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I've always (only) run Autolites and gap them at the recommended .054. The .045 the guy at the shop mentioned might be what NGK recommends with your application, but you should be able to verify this on NGK's web site.

Also, if you don't mind experimenting, you could try different gaps and see what works best with your combo.

Hope this helps.
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Old 01-21-2004, 08:41 PM   #3
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I always thought that you can open your gap up to .060 when you run an MSD ign,Boy was i wrong.I lot horsepower with a gap that wide so i regapped them down to .045 and it picked me right back up.So with that thought a .045 gap should do it.
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Old 01-21-2004, 10:43 PM   #4
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I just checked NGK's site and it says to set it at .054 gap. Is anyone running NGK plugs? What do you have your set at?
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Old 01-21-2004, 11:05 PM   #5
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I don't run NGK(NOT FOR AMERICAN CARS) I run autolite plugs and have them gapped at .045 now.
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Old 01-23-2004, 11:01 AM   #6
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NGK plugs

if that was true then why does my American gt-40 cast head only take the NGK-55R? If there is an autolite plug that will work please tell me the number because a stock 5.0 head wont fit it.
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Old 01-23-2004, 12:57 PM   #7
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quickstang91, if you're referring to FRPP iron GT-40 (not the P) heads, the Autolite part number that will work is 764.

You can also cross reference that with Motorcraft part # AWSF32C.

I ran GT-40 irons for about 4 years and always (well, almost always) ran Autolite 764s. They're tough to beat.

Spark plugs for stock 5.0 HO heads won't work because the threads aren't long enough. Been there, done that.

Hope this helps.
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Old 01-23-2004, 01:57 PM   #8
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to help you decide:

aftermarket ignitions usually say up to ~.060 with an otherwise stock motor.
higher compression kills the spark plugs ability to do its job, ie if you have a higher than stock c/r you won't be able to run as much gap.
~.045 - ~.054 seems like a pretty fair place to start. i was running ~.069 (from memory) at one point but it caused a slight miss at idle which in turn hurt emmissions. then i gave her a quick tune up and brought the gap down to ~.064 and she now runs like a champ.

-steve

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Old 01-23-2004, 04:55 PM   #9
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i've read all the above posts. All sound like good suggestions. What should I set the gap at on my Autolite Platinums with a 10.5 c/r. Thanks for the advice/help.
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Old 01-23-2004, 05:39 PM   #10
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Re: NGK plugs

Quote:
Originally posted by quickstang91
if that was true then why does my American gt-40 cast head only take the NGK-55R? If there is an autolite plug that will work please tell me the number because a stock 5.0 head wont fit it.

Sounds like the fella at your local parts store are all import boys and what to promote that plug....Thats just like a GM guy running ford motorcraft plugs in his motor because they make them for that car Bottom line: run motorcraft or autolite plugs in your car .
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With Help From:

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HarlandSharp
Whites pit's stop.
CenterForce Clutches.
JPC Racing.
AXLES ETC..Lansing, Ill
Moving Solutions..Belmont Mi.
SuttonHP..Matteson,Ill
Liss CarStar collision Center..crown point Ind.
PakMan MotorSports Inc, LockPort, Ill
Pro-Systems Carburetors..Spring Lake, Mi
Denso Iridium spark plugs.
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Old 01-23-2004, 06:02 PM   #11
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Lol.....Just like anti-freeze, oil filters, engine oil, etc..... these products are allmanufactured in very few assembly plants, The variance between brand is miniscule.

The only advantage to platnium is the gap does not erode so it remains the same for a long period of time. If your using for performance...... conventional plugs and regular changes is best.

Autolite was originally a derivitave of the manufacture line assembled for ford. But it is manufactured by the same plant and is a similar product to the champion plugs. Both are made at champion labratories....

THe motorcraft plug line is only available for ford engines, in original manufacture spec.....

NGKs are as fine as any other brand, and when talking about a "race" plug, the NGKs hold up far better than the champion race plug. 5 dyno pulls, and the champion plugs were all damaged, the porcaline didn't hold up to 1100 EGT temps, and 900HP.

The NGK race plugs, cadmium coated electrodes, held up fine to 1200 RGT temps and 1020hp.... pulled em out and all was well.

As for spark plug gap. Unless the compression has increased, its forced induction, or there is an N20 plan, stock gap will net you as much hp as anything else. .045 to .054 should not have much more than 1hp change. As compression/forced induction goes up the gap has to come down. You force more "air" molecules between the center and ground electrode and that is more resistance. As resistance increases the voltage has to increase to overcome it, and the amperage drops.... so there is LESS heat available to lite the fire.

Stock ignition systems, as well as the ole 6al box on a stock coil is about 18,000 volts.

A complete MSD system engine combination will be capable (blaster coil) of 40,000 volts.... a pro-power coil.... a 7al-2 etc... is a 54,000 volt system. The more volts the ignition system pushes at the spark plug, the more resistance can be overcome without sacraficing amperage and gap.


With all that said, with almost 18-1 compression, and N2O I had to nock my 54,000 volt system down to .026" gap to keep from blowing out the spark.
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