FAQ:Spark Plug Tech: Gapping, Indexing & Hot/Cold. Whats

[Gro Harlem]

Here's a lil info thread I typed up recently. Might as well share it here.

Spark Plug Gaps / Gapping Info

Gapping refers to the distance between the electrode tip & the electrode itself. The stock gap on a MX-3 is .044", and all brand-new OE-replacement plugs you buy for our cars will be pre-gapped to this spec. However, depending on your mods & future plans, changing this gap can help with throttle response/misfiring but WILL NOT INCREASE YOUR HORSEPOWER! It will simply "restore" lost power, so to speak.

Ever wonder why on crazily-modded turbo cars, you hear backfiring when they push in the clutch to shift? Simple...the car is misfiring. The air-fuel ratios during throttle transitions, such as shifting, RAPIDLY change, and the sparkplugs ability to ignite the mixtures is related to the gap (as well as strength of spark). Misfiring during shifting isn't necessarily a "bad" thing, but its an example of what is NOT optimal ignition efficiency. Some rally cars actually have a system that provokes backfiring to keep the turbo spinning (thus creating boost) during shifts. This reduces lag & is very beneficial, but again these systems are INTENTIONAL.

Generally speaking, on a high-compression engine (such as a motorcycle), you want BIGGER plug gaps due to the increased difficulty of igniting highly-compressed air/fuel mixtures. Think about it....a 12 air to 1 fuel ratio is harder to ignite than a 9:1...you need a bigger, stronge spark! The only problem with increasing the gap is the increased signal stregnth required to do so. An upgraded ignition coil (and plugwires, cept our car doens't use them), and ignition control box (like a MSD 6AL) are ways to increase the sparks strength. Our stock gap is 0.044". Increasing the gap to 0.050-0.052" if you have a modded NA KL-ZE with misfiring problems may eliminate the problem.

On a low-compression engine, such as one that is boosted, reducing the gap is extremely important to ensure proper running condition & reduction of misfires/detonation. Generally speaking, the air/fuel ratio is lower, even if the pistons weren't upgraded to low-comp versions, thus a smaller gap is needed. Generally speaking 0.028-0.032" is recommended for most turbo/supercharged applications on a 4-banger. Not sure for a V6 tho.

Scenario 1:
Say you have a stock freshly swapped KL-ZE GS with stock 0.044" plugs. You decide to install 14:1 pistons, crazy cams & upgrade the intake and replace the exhaust w/header/free-flo cat & 2.5" catback exhaust. You ignore your ignition system entirely and keep it as-is.

More than likely you'll be dissatisfied with the results of all that $$$ you spent on the mods. You may also have issues with misfiring at higher RPM's, or weak-feeling acceleration, particularly during lift. Solution? Install a MSD 6A ignition module, increase plug gap to 0.050". Result? MUCH improved throttle response, power, no more misfiring, happy owner who is satisfied with the results of $$$ spent

Scenario 2:
Stock RS B6-DE with 0.044" gapped plugs. Owner installs turbo kit w/3" exhaust, FMIC w/2.75" IC plumbing, goes with a megasquirt to tighten the fuel maps for optimal performance BUT ignores the ignition system. Result? Less power than expected, horrendous "lag", misfiring at low RPM. Difficulty idling. Solution? Install 6AL Ignition box & regap to 0.028". Result? MUCH more power, only lag present is turbo-related lag, no misfiring or detonation.

Re-Gapping, Often overlooked:
Every time your engine fires, a tiny bit of the metal of the electrode wears away. Over time the gap INCREASES so it is vital to regap your plugs. On my Celica GT...the previous owner NEVER replaced the stock iridiums and never regapped them. The electrodes were pretty worn. I never measured the gap but it was probalby over 0.060". Needless to say..I felt a HELL of a diff in throttle response when I replaced them.

Most electrodes are either platinum or copper or some form of nickel/copper alloy. Iridium is another, more expensive material. The thing to consider is ALL of these materials "wear" differently, thus re-gapping your plug is absolutely essential to keep your engine running at optimal efficiency.

NOTE: I don't care if you think "iridium is better for power" or "Platinums last longer". The materials vary in cost, life & signal stregnth. Its up to YOU to decide what to choose. I'm a cheap bastard & have never had bad luck with NGK copper V-powers ($1.98 each). I've used these in my turbo'd Mazdaspeed Protege, KL-ZE MX3 and now, my stock Celi GT w/great results.

TIP: If you are lazy, like me, you might plan ahead for this & regap your new plugs to 0.038" before installing. That extra 0.06" keeps you from having to regap the plugs as often, and doesn't really hurt performance on a lightly modded Celi.

[Gro Harlem]

Spark Plug Indexing:
Indexing is a "free mod" that can increase power, throttle response & fuel economy if done propely. Simply put, the premise behind indexing is to face the OPEN END of the spark plug electrode TOWARDS the intake valve(s). This theoretically increases the flow of air/fuel mixture to the area between the electrodes, making a stronger explosion & burning more of the mixture. There are multiple dyno-charts showing benefits, although there are also naysayers to this "mod". Use the tips below at your own risk!

The Wrong way to index: overtightening them until they are facing how you want them. You are risking stripping the threads in your head!

Using washers to "shim" the plug. This f'ks up the distance between the fuel nozzle, plug electrode & piston dish. It will decrease performance more than help. It is also difficult to determine how many "shims" you need. Sourcing washers thin enough is also going to cost you $$$ & time.

Alternative way to Index

Since the threads on every spark plug vary as far as how they'll face when tightened..what I did was buy 8 plugs instead of 4 when I went to the store.

I didn't buy iridiums, I'm pretty much an advocate of NGK V-power's (copper plugs that are 2$ each & perform damn well IMO), and since iridiums were "special order" and I knew I'd have to return 4 of them...I just got the V-powers for 1/5th the price.

Anyways, I used marks on my sparkplug socket extension to determine where the plug was facing. When tightening it you want it to face directly at the INTAKE SIDE (meaning towards front of car). Tighten to ~15-18 ft/lbs (which is not tight at all) and move onto the next plug.

If you tighten it & its facing the opposite direction..or to the side...remove it...put it back in its box & try the next plug until you get one that faces the right way. If your plug is slightly off, you can overtighten it a little bit to get it to where you want it but don't b---- at me if you strip your head! I'd say definitely never go above 35 ft/lbs or you'll risk the plug seizing in the threads (due to heat) making the plug difficult/impossible to remove w/out stripping the threads in the head.

Anyways..after all 4 are "indexed" return the remaining plugs (which should still look brand new since they were never fired) and reclaim the extra $$$ you spent and your done!


Benefits of indexing?
About 1-2whp in almost any car (even a crap 1.5L would experience these gains), noticeable increase in throttle response, slightly better efficiency (gas mileage). This can be argued by some, but I've yet to see any dyno results that don't show a gain (or favorable results) to cars with indexed plugs VS ones w/out.

IMO its a FREE mod that WORKS and gives 3 benefits (power/throt response/mpg's)

[Gro Harlem]

Cold vs Hot: Whats the difference?

The heat rating of a plug is related to the operating temperature of the tip of the plug. Colder plugs have less insulating materials on the inside of their tips, thus more heat is dissipated into the cylinder head over a hotter rated plug.

Generally speaking, too cold a plug will cause fouling & it won't fire properly. In other words, the fuel will form deposits on the tip eventually gunking it up. The tip must be hot enough to burn away (or repel) any fuel residue from attaching to the metal of the electrode tip.

Too hot a plug, especially in terms of high-performance engines, can cause detonation & misfiring which HURTS performance. Running a colder plug will ensure it fires properly & ensures the engine runs at optimal efficiency.

Simply put, getting colder or hotter plugs isn't going to net you any gains on a MX-3 , but could hurt your performance depending on your mods & goals.

The "hot" and "cold" ratings that plug manufacturers use varies from company to company. NGK, for example, uses a "6" as the recommended replacement heat rating for the MX-3. 5 is hotter than 6. Other companies numbers mean the opposite (5 is colder than 6). So check before you buy what the heat #'s mean.

For a MX-3, it shouldn't matter too much if you buy a 5 or 6 rated plug, but if you don't plan to do any mods past I/H/E going with the 5 is probably the best idea for drivability. If you plan to do NOS, supercharging or turbo you should definitely go with the colder 6-rated plug.

Again..you will NOT GAIN ANY HP if you change the heat range of your plugs...rather..if you are running a turbo & don't know why your engine misfires, getting colder plugs might be your answer! The purpose of the heat-ranges is to optimize the temperature of the tip of the plug for the particular application

[Tunes67]

Definitely FAQ material. I will add that running a cooler plug in a application that doesnt call for it will often result in unburnt fuel or carbon build up in the cylinders. This contributes to the running "Rich" condition that our engines are notorious for. Anyone that tells you Bosch 4+4 platinum plugs are good for our V6 engines is a moron and should be shot on sight. Granted that is for non boosted, naturally aspirated engines. If your Boosting a DE or ZE.. might try something cooler as Gro suggests.

Tunes67

[mx3autozam]

^^^^
That rule falls for almost all imports. For the best results just run NGK V-Power which is the same plug the manufacture puts in at the factory and its the cheapest!

Either way definitly FAQ Material.

[Gro Harlem]

Anyone that tells you Bosch 4+4 platinum plugs are good for our V6 engines is a moron and should be shot on sight.
Tunes67

/AGREE

i pissed away 30$ on some new +4 plats for my ZE (first plugs i put in it back in 2003) and YEA...they suck balls...I didn't realize it at the time but once I finally threw some 1/4-the-price NGK v-powers in tehre I was blown away at the diff in throttle response.

Bosch, while they are considered a great quality manufacturer of OE parts...I'd have to say their plugs aren't well-suited for our cars. Stick with NGK. High availability, cheap (v-powers run 2$ or less ea.) and rock-solid.

[mx3autozam]

Bosch work well in cars like VW and BMW. aka German built cars with German built plugs,. and even in those situations there not the +4's they are just "Bosch Super" but regarless in a Japanese made vehivcle I have to say NGK.

I even heard of a Honda B18C once wouldn't even start with Bosch +4's swapped in some V-powers and it fired right up..lol