Spark Plug Quote of the Day

XR7 Dave

Registered User
Sorry guys, but if I have to repeat this one more time........;)

If you are running over 15psi you CANNOT run stock spark plugs or spark plug gap. It won't work reliably. Period, end of story.

You MUST run a cooler plug and you MUST gap it down. I have talked to, emailed, PM'd etc way too many people over the past months as we start to see more and more boost on these motors. The days of 250rwhp and 15psi are over. It is going to become very common to see 17-22psi boost with the new blowers and you just can not run an OE plug nor use OE plug gaps.

My recommendation to everyone running high boost is to simply purchase some Autolite 103 NON-PLATINUM spark plugs, gap them at .035", and go.

I fully understand that there may be a better plug and there may also be a place called "Heaven". But in the mean time, install a cooler plug that is known to work and get your car running correctly and tuned. Then, after you have that all taken care of you can experiment with something else if you want but in the mean time invest $16 in a set of the above mentioned plugs and gap them as directed.

Disclaimer: The above recommendation is only for people running high boost. If you run stock boost then if you want to run stock plugs that's fine. But you can't run stock plugs/gap at high boost. It doesn't work. ;)
 
Perfect timing Dave, I was planning on getting a new set of plugs and your post saves me from doing a bunch of searching and or posting to get information

Ken
 
Normal Driving

My only question is how does this plug and Gap combo work during regular cruising and driving while you are not pushing the high boost levels?

I usually put around 35-50 miles a day on my SC for work ( Yes I do get reimbursed for the mileage, plus I get to drive my own ride instead of a "company car").

Just curious if it tends to foul the plugs for not being hot enough over a long period of time?

I'm still following this recommendation, but was just wondering.

Smitty
 
AUTOLITE
APP 2544 DBL PLAT
XP 5144 IRIDIUM
the above /standard

autolite XP 103-colder
autolite XP 104-cold
605 1 heat range colder
104 2 heat range colder
103 3 heat range colder

the above 1/4" , less-protrusion into cyl.

Motorcraft
AWSF-34PP
AWSF-32PP-colder

Gap the new spark plugs between .052 - .056 ( Stock Gap )
rec / .035 - .045 gap

these are some of the plugs to be used ,also consider spark-plug wire condition and the resistance they carry ,lower resistance wire should have a hotter spark.
if the car is basic and not running the higher boost and not using a lot of boost ,a colder plug might not work to well ,depends on how the car will be operated

cheers
 
The Autolite 103 is an OE replacement plug for all other Ford supercharged applications. That should answer all your questions about daily driving etc.
 
OK then!

The Autolite 103 is an OE replacement plug for all other Ford supercharged applications. That should answer all your questions about daily driving etc.

Today is a good day!!!!! I learned something new. Thanks for the insight and information.

Smitty
 
Dave, doees that mean . . . . .?

Davee,

I have a '95 5-speed SC that I bought a couple of years ago. It has 27k on it and I don't drive it much. Here is my question: with SCP exhaust (stock manifolds), ported S-model SC, 75mm TB, 76mm MAF, 10% OD pulley, I notice that with the stock plugs, wires and injectors, that it pings when boost goes above about 10 PSI. What plugs/gap should I run? I also plan to replace the wires and eventually the injectors with 50s or so. Then a chip and a tune.

Thanks,

Don
 
103's with good low resistance wires
.035 is what he posted ,did mine at .045 ,everything seems to be happy
cheers
 
Last edited:
Davee,

I have a '95 5-speed SC that I bought a couple of years ago. It has 27k on it and I don't drive it much. Here is my question: with SCP exhaust (stock manifolds), ported S-model SC, 75mm TB, 76mm MAF, 10% OD pulley, I notice that with the stock plugs, wires and injectors, that it pings when boost goes above about 10 PSI. What plugs/gap should I run? I also plan to replace the wires and eventually the injectors with 50s or so. Then a chip and a tune.

Thanks,

Don
You have too much OD on the blower. If you want to run that much OD you need some serious IC upgrades and a tune. The car will make just as much power with a stock 89 pulley on the blower.
 
i HAVE USED THE it20 DENSOS AT OUT OF THE BOX GAP WITH UP TO 21PSI WITH NO FLAME BLOWOUT..THEY ARE SLIGHTLY COLDER AS WELL
 
hmm, haven't bought plugs for the 93 yet, so now I know what to get. It's nice when folks that have a good idea keep trying to beat it into our heads. Hopefully it'll stick someday.
 
You can gap your plugs at whatever you want. I think that you want to go as wide as you can before the spark blows out. Unfortunately, the Ford recommended gap is just too wide for a highly boosted motor. I think the way it works is that the increased boost pressure increases the density of the fuel-air charge so much that the resistance is too high for the spark to jump the wide gap. So Dave D. recommends a gap of 0.035 inches. I think that he is leaning toward the low side so that people aren't finding out by trial and error that they should have gone another 0.003", or having to change it every time they modify the car or retune.

By the way, I don't understand Autolite's naming system. My mom's Windstar 3.8 uses Autolite 765's (APP765 for the double platinum - worth it, because it's a pain to change the rear plugs). I compared pics to see what the difference was between the 765's and the 103's. It appears that they are the same length, except that the 103 is fully threaded and the 765 is only threaded partway down the body. What's the deal anyway?
 
You can gap your plugs at whatever you want. I think that you want to go as wide as you can before the spark blows out. Unfortunately, the Ford recommended gap is just too wide for a highly boosted motor. I think the way it works is that the increased boost pressure increases the density of the fuel-air charge so much that the resistance is too high for the spark to jump the wide gap. So Dave D. recommends a gap of 0.035 inches. I think that he is leaning toward the low side so that people aren't finding out by trial and error that they should have gone another 0.003", or having to change it every time they modify the car or retune.

By the way, I don't understand Autolite's naming system. My mom's Windstar 3.8 uses Autolite 765's (APP765 for the double platinum - worth it, because it's a pain to change the rear plugs). I compared pics to see what the difference was between the 765's and the 103's. It appears that they are the same length, except that the 103 is fully threaded and the 765 is only threaded partway down the body. What's the deal anyway?

The last digit is the heat range. xx5 is two heat ranges hotter than xx3. Stick a pin down beside the porcelin and measure the length.
 
O.k... I gotta ask. So I see the Autolite 3923 being used in the Ford Builder article... Is there some comparison of this one to the A103 plug.
 
O.k... I gotta ask. So I see the Autolite 3923 being used in the Ford Builder article... Is there some comparison of this one to the A103 plug.


Good question. The 3923s are one range colder than stock for use with 5.0 based motors running aftermarket heads like Trickflow, AFR ect... They don't have the taper made onto the plug, and use a crush type washer. That's what I'm using in my 347.

David
 
David (Dalke), does the .035" gap recommendation stand for those running a Screamin' Demon coil? Has there been any testing as to whether the gap can be widened to say .040".
 
Back
Top