What is the correct spark plug and gap?

[88ZNX]

At least once a week I get asked what spark plug should I be using. First of all there is no magic spark plug. So I started researching this because it started making me second guess my self. After three days on the web reading and comparing and crossrefencing I made a chart of the plugs only for Buick V6s, I didnt get into other engine types to keep it simple. Because this info is based off of my opinion I invite anyone else's opinion also. This chart is for iron and allum. heads and the deferent brands and seat style. I chose the coldest number plug in each type because most racing applacions use a colder and stock plug and our engines are pushing 20,25,30,35 and 40 psi and an 8 to 1 compersion could be as high as 26 to 1 at full boost. You have to find the plug that works with your engine combo and tune. Will you be street driving mostly or track racing, cause an engine thats giong to be street driven on pump gas will need a medium heat rang plug if it only see boost every so often vs a hard core street and strip racer thats in the boost all the time, it will need a colder plug. But again according to the tune. Now the gap, this has been a rule of thumb thing a .035 gap plug should be closed up to around .025, then keep playing with it till you find the sweet spot. For example I allways ran .025 and wile on a chassis dino two yearys ago we pulled the plugs and closed the gap to .018 and picked up 36 RWH with no other change. That dosent mean yours will you just have to play with it.

Our iron heads only use a tapered seat with .450 leanth 14mm thread. There are several version of electrodes, counter sunk and extended, long groung straps and cut back groung straps. The cut back strap is for racing it exposes more spark to the chamber and has a tighter gap. There is a theory that the counter sunk electrode can with stand more boost with out loosing the flame vs an extended one cause it is more exposed to the tornado affect is the chamber. I couldnt find any thing to back this theory up. But it seam's logical.

Standerd counter sunk electrodes in the coldest heat rang I could find.
AC R42T AUTO LIGHT 144 AR132 CHAMPION 121 V59C NGK 5673-9


Extended electrodes in coldest heat rang.
AC R42TS AUTO LIGHT 23 AR55 CHAMPION V57C NGK 5674-10


After calling T/A and Champion I learned that T/A heads take washerd plugs and Champion will accept both tapered and washerd. The thread is 14mm leanth is .750


Standerd counter sunk electrodes with washers coldest heat rang.
AC ? AUTO LIGHT AR3932 CHAMPION C57CX NGK 5671-10 (4091)


Extended electrodes with washers coldest heat rang.
AC rapid fire 5 AUTO LIGHT 3910 3924 CHAMPION C57YC NGK 5672-10


Extended electrodes with tapared seat coldest heat rang.
AC ?? AUTO LIGHT 103 CHAMPION ?? NGK ??


Most spark plug manufacture heat rang is the higher number the hotter the plug. Example AC R42T is the coldest where the R45T is hottest. It seams only NGK is reversed. Example (4091) 5671-(5) is the hottest and 5671-(10) is the coldest.

Now that you know what is available you have to find out what your engine wants.
A plug that is to cold will normally foul out and miss fire but want cause engine damage in most cases. But a plug that is to hot can cause per ignition and detonation, and that will cause engine damage if not corrected.

Please fill in the gaps and give your opinion. List the plugs you are having good luck with.
Thanks Alan

 

[88ZNX]

More pics.

 

[88ZNX]

A great cross refernce chart.

Tech Tip: Spark Plug Heat Range Cross Reference

 

[88ZNX]

Where I got the best info from.

http://www.ngksparkplugs.com/docs/tech/Racing_Spark_Plugs_Performance_Applications.pdf

Good luck.

 

[22lbChevelle]

Great work!

 

[jasjamz]

Alan, you're getting sleepy... Cool info too!!

At least once a week I get asked what spark plug should I be using. First of all there. isn't magic spark plug. So, I started researching this because it started making me second guess myself. After three days on the web reading, comparing, and crossrefencing I made a chart of the plugs only for Buick V6s. I didn't get into other engine types to keep it simple.Because this info is based off of my opinion. I invite anyone elses opinions also. This chart is for iron and aluminum heads and the different brands and seat styles. I chose the coldest number plug in each type because most racing applications use a colder that stock plug. Our engines are pushing 20-40 psi and at 8:1 static compression could be as high as 26:1 at full boost. You have to find the plug that works with your engine combo and tune. Will you be street driving mostly or track racing? An engine thats giong to be street driven on pump gas will need a medium heat range plug if it only sees boost ever so often vs. a hard core, street/strip racer that's in boost a lot more often could need a colder plug. Again, watch the tune. Now, the gap is has been a rule of thumb thing at .035 gap Plugs can be closed up to around .025, then keep playing with it until you find the sweet spot. For example, I always ran .025 and while on a chassis dyno. Two years ago, we pulled the plugs and closed the gap to .018 and picked up 36 RWHP, no other changes. That does not mean yours will, you just have to play with it. Our iron heads only use a tapered seat with .450 length 14mm thread. There are several version of electrodes. Counter sunk, extended, long ground straps and cut back ground straps. The cut back strap is for racing, it exposes more spark to the chamber and has a tighter gap. There is a theory that the counter sunk electrode can with stand more boost with out losing the flame vs. an extended one because it is more exposed to the tornado affect is the chamber. I couldnt find anything to back this theory up, but it seem's logical.

Standerd counter sunk electrodes in the coldest heat range I could find.
AC AUTOLITE CHAMPION NGK
R42T 144 AR132 121 V59C 5673-9

Extended electrodes in coldest heat range.
AC AUTOLITE CHAMPION NGK
R42TS 23 AR55 V57C 5674-10

After calling T/A and Champion I learned that T/A heads take washer seal plugs and Champion will accept both tapered and washer seal. The thread length is .750 with 14mm.

Standerd counter sunk electrodes with washers coldest heat range.
AC AUTOLITE CHAMPION NGK
AR3932 C57CX 5671A-10(4091)

Extended electrodes with washers coldest heat range.
AC AUTOLITE CHAMPION NGK
rapid fire 3910 3924 C57YC 5672A-10
5

Extended electrodes with tapered seat coldest heat range.
AC AUTOLITE CHAMPION NGK
103


Most spark plug manufacturers heat range are, the higher number is hotter. Example AC R42T is the coldest where the R45T is hottest. It seems only NGK is reversed. Example (4091) 5671-5 is the hottest and 5671-10 is the coldest.

Now you know what is available you have to find out what your engine wants.
A plug that is to cold will normaly foul out and misfire, but won't cause engine damage in most cases. But, a plug that is too hot can cause pre ignition and detonation, and that will cause engine damage if not corrected.

Please fill in the gaps and give your opinion. List the plugs you are having good luck with.
Thanks Alan

 

[88ZNX]

I know I couldnt get off the phone long enuff to get this done untill 2am.:frown:

 

[GNVYUS 1]

The GN on gas always had great luck with AC Delco R43T gapped to .035 on Iron Heads with a newish Coil Pack and Alky Injection around 22-23psi. Plug always looked great = great MPG and no horse bucking up top. Would've gone to 42T if Psi was 25 or up consistently.

Went to E85, initially had R42T and then went to the E3's and it's also been great = pregapped, great start up and MPG (for E85) and 25psi at 25 degrees without any misses etc.

You didn't throw the Iridiums into play, ah, that would bring out the popcorn.

Have NGK BP7ES on my Talon (notice no R) gapped to .026 at 30psi, plug is great until it gets a bit of gap stretch around 1k miles (regap) and around 3k it's time for a new set.

 

[machinegun]

Please forgive me if I missed it above.

One plug I did not see mentioned is the CR4XTS

I usually use the CR as its electrode is slightly heavier or larger but all else is the same. I prefer to use these plugs as they do not seem to foul as much as the standard R4XTS.

Just someting worth mentioning.

Hope it helps.

I do have 1 question though, has anyone tried the diamond fire plugs in a TB?

I hate to be the first but have been a guienie pig before


Surprisinlgy my wifes 2003 mustang GT 4.6 with a few bolt ons and cat back actually idled smoother, got about .3 MPG more and seemed to run a little smoother in the uper RPM band.

 

[TTipe]

Iridium Plugs

I know Ken Duttweiller was experimenting with iridium plugs and found that internal plug resistance was lower.This could mean a larger gap given our high chamber pressures.I have seen first hand a turbo regal "auto igniting"(coil pack turned off) down the road.

 

[bison]

I have had the best luck with ac cr42ts with iron heads. The set in my blue car has been in there for 16 months. I never changed them one time. I've been running 28-30psi boost have over 100 dyne pulls and at least 10 minutes of wot time on the street. I've been running thus plug for at least 10 years with great results.

 

[The Darkside]

What about gap? I guess that depends on many factors, especially how much boost you're running....

 

[Razor]

I think plugs are over-rated

I've always thought of it this way. If you have a street car running around town.. you need a stock heat range plug. Maybe one step colder. Example R43 or R42. Gaps are dependant on boost levels run. The higher the boost.. the gap lessens. Typically I set mine to .032.

Thats basically it.. I have had great results with AC, NGK, and Autolite.

There are those 2000 HP applications you need to be on top of everything.. for the typical less than 700 HP Buick.. anything works.

 

[88ZNX]

Thanks for your in put, not everyone knows this basic info and this may keep a newbe from knocking a hole in a piston or a head gasket.
I didnt get in to the spark plugs with exotic metals because 99% of them are for cars with completly stock tunes that are supose to last 100k miles before changing them. It has been MY experience that these plugs do not last as long as a basic plug will in a richer/fatter tuned engine with out fowling out soon. They have never worked well for me.

 

[bison]

What about gap? I guess that depends on many factors, especially how much boost you're running....

I typically run high cylinder pressure so i usually gap around .025. I have not re-gapped the ones i was referring to in my earlier post. Spark plugs are overrated as Razor already said.

 

[Mike Licht]

For iron heads good old inexpensive autolight 23 or 24 has never let me down and nothing has run better
Mike