What spark plugs should I use??

[Bonez8791]

Im needing a little advise as to which spark plugs I should use? Im running holley systemax heads with a vortech V1 S Trim with around 13lbs of boost. Any help is greatly appreciated.

[midnightrider]

Autolite 3923's or 4's. I kinda like the 24's for the street & 23's for the track. I've found that the 23's were too cold of a plug for street driving(Too low RPM's & they fouled out in short order)!!! Some folks have good luck w/the 23's though!!

[Bonez8791]

Originally Posted by midnightrider

Autolite 3923's or 4's. I kinda like the 24's for the street & 23's for the track. I've found that the 23's were too cold of a plug for street driving(Too low RPM's & they fouled out in short order)!!! Some folks have good luck w/the 23's though!!

Ok, Are those plugs I can get at a local Advance Auto or Napa? Or will I have to order them?

[midnightrider]

About ANY local parts store.. I just installed 8 of them. Cost from AZ was appx $19...

[Bonez8791]

Originally Posted by midnightrider

About ANY local parts store.. I just installed 8 of them. Cost from AZ was appx $19...

Ok awesome, Ill try to pick some up today. Are there different variations of this plug? Copper Core, Platinum, Double Platinum? If so which one do I want?

[GMundertaker]

I'm running NGKs and I like them so far. I've been using them for quite some time. Next time I come by I can give you 1 so you'll have the part # if you are interested? no biggie, I wouldn't discourage you from running autolites. I have been buying NGKs at advance.


Matt

[VORTECD]

Autolite copper core

[Bonez8791]

What are you guys gapping them at?

[VORTECD]

I wouldn't go over .030.

[boostdcoupe]

Originally Posted by GMundertaker

I'm running NGKs and I like them so far. I've been using them for quite some time. Next time I come by I can give you 1 so you'll have the part # if you are interested? no biggie, I wouldn't discourage you from running autolites. I have been buying NGKs at advance.


Matt

x's 2... bob k suggested them and ive never had a problem since.

[GMundertaker]

The ones I am running in my trick flow heads are Advanced Auto's SKU#20650564 NGK # 6364 On the porcelain they are marked BKR6ES NGK R in blue letters....


Matt

[boostdcoupe]

Originally Posted by GMundertaker

The ones I am running in my trick flow heads are Advanced Auto's SKU#20650564 NGK # 6364 On the porcelain they are marked BKR6ES NGK R in blue letters....


Matt

this is what bob told me, i got them at advance too...

NGK-R5671A-7... gap em at .025-.027

[Bonez8791]

Well I ended up picking up some Autolite 3924's today, ive always been a fan of autolites so I went with those. Would you gap them the same way?

[boostdcoupe]

Originally Posted by Bonez8791

Well I ended up picking up some Autolite 3924's today, ive always been a fan of autolites so I went with those. Would you gap them the same way?

yes... no more than .030

[Bonez8791]

Originally Posted by boostdcoupe

yes... no more than .030

Ok, thanks for the info.

[millhouse]

Originally Posted by midnightrider

Autolite 3923's or 4's. I kinda like the 24's for the street & 23's for the track. I've found that the 23's were too cold of a plug for street driving(Too low RPM's & they fouled out in short order)!!! Some folks have good luck w/the 23's though!!

That's why you are supposed to use a recessed tip racing plug. It will allow you to run a hotter plug (with a bigger gap) with a much lower risk of fouling (or spark blowout for that matter). Any time you have a higher compression (or forced induction) engine, the need for recessed tip racing plugs becomes quite apparent. Yes, you can "get away" with your typical projected tip autolite, but that doesn't mean it's going to be best suited for your application.

FYI, autolite sells recessed tip racing plugs as well.

[Bonez8791]

Originally Posted by millhouse

That's why you are supposed to use a recessed tip racing plug. It will allow you to run a hotter plug (with a bigger gap) with a much lower risk of fouling (or spark blowout for that matter). Any time you have a higher compression (or forced induction) engine, the need for recessed tip racing plugs becomes quite apparent. Yes, you can "get away" with your typical projected tip autolite, but that doesn't mean it's going to be best suited for your application.

FYI, autolite sells recessed tip racing plugs as well.

What is the part number for these plugs?

[millhouse]

Originally Posted by Bonez8791

What is the part number for these plugs?

Assuming the threads are the same as the other aftermarket aluminum heads...see below. It's worth noting that you can typically run one step hotter than normal with the recessed tip plugs (if you planned on running 2 colder, you can likely go with 1).

Per... Spark Plug FAQ.

Aftermarket aluminum heads (TFS, Edelbrock, AFR, Canfield, Brodix)

NGK Forced Induction

R5671-A8 Stock Number 4554, 1 heat range Colder (up to about 600rwhp)
R5671–A9 Stock Number 5238, for 18+psi, 2 heat ranges colder 650+ rwhp
R5671–A10 Stock Number 5820, for race cars.

Autolite Forced Induction and N/A

Autolite 3924's Naturally Aspirated Only
Autolite 3923’s 1 Heat Range Colder, good for approx 550rwhp
Autolite 3922’s 2 Heat Ranges Colder, good for approx 650rwhp

Autolie Race Series for aftermarket heads

Autolite AR3935 Naturally Aspirated Only
Autolite AR3934 1 Heat Range Colder
Autolite AR3933 2 Heat Ranges Colder

[Michael Plummer]

Originally Posted by millhouse

That's why you are supposed to use a recessed tip racing plug. It will allow you to run a hotter plug (with a bigger gap) with a much lower risk of fouling (or spark blowout for that matter). Any time you have a higher compression (or forced induction) engine, the need for recessed tip racing plugs becomes quite apparent. Yes, you can "get away" with your typical projected tip autolite, but that doesn't mean it's going to be best suited for your application.

FYI, autolite sells recessed tip racing plugs as well.

Hi Millhouse,
I thought a recessed plug was for racing application with a lot of boost and in street car applications they tend to foul easier than a projected tip spark plug. If anyone has problems with the flame being blown out get a better ignition system and a really good coil.

[millhouse]

Originally Posted by Michael Plummer

Hi Millhouse,
I thought a recessed plug was for racing application with a lot of boost and in street car applications they tend to foul easier than a projected tip spark plug. If anyone has problems with the flame being blown out get a better ignition system and a really good coil.

A recessed plug typically is beneficial in any application with extreme cylinder pressures, be it from a high compression n/a engine or forced induction. Because less of the tip is exposed to the chamber, the risk of pre-detonation is significantly reduced. This will allow you to run a hotter spark plug which in turn will allow carbon to more easily burn off. Speaking of carbon, because less plug is exposed, carbon will have a more difficult time accumulating on the porcelain.

Keep in mind, most people are running around with plugs 1-2 ranges colder than necessary when running even mild f/i applications. That's all fine and dandy when running down the 1/4 mile, but stoplight to stoplight those plugs are going to get carbon'd up. No amount of ignition upgrades is going to keep this from occurring, you simply need a hotter plug for the street and a colder one for the strip (or a recessed tip plug).

The final added benefit of course is pulling the spark out of the wind so to speak. While ignition upgrades typically will reduce or eliminate spark blowout, so will a $16 set of sparkplugs. You also get the added benefit of the above mentioned points.

[Michael Plummer]

Millhouse,
Thanks for the information but it differs from what I was told by Autolite techs and what was posted by Brandon (see below).


Posted by Brandon Peeler
Technical Support Representative
Aftermarket Division
NGK Spark Plugs (U.S.A.)


The theory is that typically for street driven applications a projected insulator will be beneficial as it positions the spark farther into the combustion chamber promoting better ignitiability as it will be closer to the densest part of the mixture. at low speeds it also helps keep the firing end of the plug hotter preventing fouling. This is helpful in high power cars that run very cold plugs on the street. Also as the intake valve opens and the fuel charge rushes in the plug has a greater area being exposed so as to cool down more.

The only downside is that by putting the plug into a higher turbulence area you may also raise the required voltage needed to fire the plug. In very high boost cars this can lead to misfire (spark blowout), especailly with a weak stock type ignition system or over heating of the ground electrode at high rpms (because the ground path is longer), especailly with a weak stock type ignition system. This can sometimes be helped by switching to a fine wire type iriidum plug which reduces that voltage requirement back down and also lowering the plug gaps.

I have also heard from drag racers on a couple applications that they were able to run a non-projected plug and add in a degreee or two of spark timing and pick up some substantial horsepower increases.

So really I would say if it is a street driven vehicle try to run a projected plug. If it is a all out race car you may benefit from a non projected type plug (or if running nitrous). Of course this rule is not always valid as cylinder head turbulence, quench area, etc can sometimes change this recommendation.

[Whitexc]

So.....which is it? Some valid points pointing in both directions. 3924's for some time now and they seem to work, however I am not opposed to other options.

EDIT: 3923's for some time, trouble free.....sorry.

[millhouse]

Michael,

It’s tough to argue with most of his points, as he is spot on (for most applications). I know from first-hand experience (as well as experience of many others) that suggest otherwise for the typical F/I mustang application.

The issue that we have for our applications is that our optimum, day to day heat range and WOT, down the drag strip heat range differ quite a bit. What is the first thing most people are told when selecting a spark plug for their newly F/I setup on their mustang? Pick a plug that is 1-2 steps colder (for mild setups). What is a main contributor to fouling of the spark plug? You got it, too cold of a plug for any given application. Combine that with the fact that quite a few of us run a bit safe (read, overly rich) tunes….or no tunes at all (possibly pig rich), and fouling is a real concern. While a protruded electrode most certainly has a better opportunity to burn off excess carbon, it also will accumulate more carbon. This is especially true on a colder plug that does not get hot enough. The carbon will begin to accumulate and viola…a fouled plug be the result.

This is precisely what was happening to me, as I needed a projected tip plug that was 2-steps colder than normal. A set of normal, projected tip plugs would last a few months (on a good tune mind you) before I would begin to notice excess accumulation of carbon on the ceramic. Switching to a racing plug drastically reduced/eliminated this behavior as I ran a hotter plug and what little carbon accumulated was burned off. I haven’t even mentioned yet that because a recessed tip plug is…well, recessed, that it is far less prone to fouling in the first place.

Of course, the spark break-up is what this post was all about…which is precisely what the recessed tip plug will prevent without having to invest any more $$$ into an upgraded ignition. Obviously, an upgraded ignition is the way to go in the long run, that won’t however negate the need for a recessed tip plug for many of us.

Again, I’m not disagreeing with his points…simply stating that many of our applications differ drastically.

[Michael Plummer]

Millhouse,
I respect and can agree with some of your points but we' will have to agree to disagree on whether a recessed spark plug is more prone to fouling. I believe it is when its in a daily driver with no issues going on inside combustion chamber.

I agree that a recessed tip spark plug will help with spark break up but if anyone is running an aftermarket igintion system and they aren't running the best coil for their particular ignition and setup then shame on them if there still experiencing spark break up.

When you see someone closing up their gap because of engine break up its because they have a less powerful ignition. Less powerful ignitions will require a smaller gap whereas more powerful ignitions will allow you to utilize a larger gap.

Myself and customers I work with use spark plug gaps between .030-.035 when they have a capacitive discharge type of ignition like a MSD. Care must be taken as to listen to what your engine is telling you. For example, too much spark plug gap can result in misfires and hard starting issues and too little gap can result in a loss of power.

Bottom line, experiment on your setup and find what works best for you.

[millhouse]

Fair enough.

Originally Posted by Michael Plummer

Millhouse,
I respect and can agree with some of your points but we' will have to agree to disagree on whether a recessed spark plug is more prone to detonation. I believe it is when its in a daily driver with no issues going on inside combustion chamber.

I agree that a recessed tip spark plug will help with spark break up but if anyone is running an aftermarket igintion system and they aren't running the best coil for their particular ignition and setup then shame on them if there still experiencing spark break up.

When you see someone closing up their gap because of engine break up its because they have a less powerful ignition. Less powerful ignitions will require a smaller gap whereas more powerful ignitions will allow you to utilize a larger gap.

Myself and customers I work with use spark plug gaps between .030-.035 when they have a capacitive discharge type of ignition like a MSD. Care must be taken as to listen to what your engine is telling you. For example, too much spark plug gap can result in misfires and hard starting issues and too little gap can result in a loss of power.

Bottom line, experiment on your setup and find what works best for you.

[blownholley50]

NGK-R5671A-7 here-- dig6 gapped at .025, w dig 7 they are gapped .028

[Bonez8791]

Originally Posted by blownholley50

NGK-R5671A-7 here-- dig6 gapped at .025, w dig 7 they are gapped .028

Do you drive yours on the street as well? Mine will be for both street and strip and I'm using a 6AL. With those work for me?

[Mercedez L.]

Originally Posted by VORTECD

Autolite copper core

Why Autolite copper core when we have all of these other kinds of plugs in platnum or iridium?

[blwn89hatch]

I was told platinums and boost is a big no no when i first put the blower on my back on 09.

[Mercedez L.]

Originally Posted by blwn89hatch

I was told platinums and boost is a big no no when i first put the blower on my back on 09.

Is copper a better conductor of electricity?

[slow87GT]

Im kind of surprised some of you are running the ngk 6's. I ran them for a while but came to the conclusion its bad advice. according to NOS you should run a 7 or colder(8,9,10). I cant see a blown combo liking a warmer plug than nitrous??

I could be wrong but Im pretty sure 3924 converts to ngk 7 and 3923 is ngk 8 and 3922 is ngk 9. iirc ngk 6 converts to 3925 which is stock heat range for na use with cast iron heads?

someone correct me if Im wrong

[slow87GT]

Originally Posted by millhouse

Assuming the threads are the same as the other aftermarket aluminum heads...see below. It's worth noting that you can typically run one step hotter than normal with the recessed tip plugs (if you planned on running 2 colder, you can likely go with 1).

Per... Spark Plug FAQ.

Aftermarket aluminum heads (TFS, Edelbrock, AFR, Canfield, Brodix)

NGK Forced Induction

R5671-A8 Stock Number 4554, 1 heat range Colder (up to about 600rwhp)
R5671–A9 Stock Number 5238, for 18+psi, 2 heat ranges colder 650+ rwhp
R5671–A10 Stock Number 5820, for race cars.

Autolite Forced Induction and N/A

Autolite 3924's Naturally Aspirated Only
Autolite 3923’s 1 Heat Range Colder, good for approx 550rwhp
Autolite 3922’s 2 Heat Ranges Colder, good for approx 650rwhp

Autolie Race Series for aftermarket heads

Autolite AR3935 Naturally Aspirated Only
Autolite AR3934 1 Heat Range Colder
Autolite AR3933 2 Heat Ranges Colder

this has been pretty much my findings

now can someone explain why Id want a hotter plug in a boosted app? It doesnt make any sense to me?

[blwn89hatch]

So ultimately what would be the difference from an autolite 3923 and an autolite 3934 race plug if they are both 1 heat range cooler?

[Sickfox]

Originally Posted by blownholley50

NGK-R5671A-7 here-- dig6 gapped at .025, w dig 7 they are gapped .028

This is the same plug I run, even gapped the same. Run 22 + psi, MSD-6, Mallory coil, 50%\50% race and street, 100% alky injection. Plugs are changed annually and look mint.

[Bonez8791]

Originally Posted by Sickfox

This is the same plug I run, even gapped the same. Run 22 + psi, MSD-6, Mallory coil, 50%\50% race and street, 100% alky injection. Plugs are changed annually and look mint.

Awesome. I think I'll pick some of these up. The ones I just bought are for N/A so they need to be replaced. Thanks for the info.