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What is the gap on the spark plugs supposed to be? I've heard at least two conflicting numbers, so I'd like to get it cleared up before replacing mine. TIA.

-Brian

in the Owner's manual (of my 1992 turbo leg.) , the gap has to be between 0.039" and 0.043"

What would be the benefits or side effects of having a bigger or smaller plug gap? i am curious!

Bigger gap =
Positive side: larger spark, better ignition.
negative side: your spark can get "blown out" by the air passing by

smaller gap =
negative: not enough spark, bad ignition, stuttering
positive: your spark is hard to blow out.

-Jason

Would a bigger gap, like say .07 make it hard for a car to start on a cold morning?

probably......that's a massive gap.........

that's what they were at when i replaced them. Problem solved!

hey.

how big gap should i use with 1 bar as highest boostlevel? ngk vx bkr6evx. also ordered a new o2 sensor today, bosch. i hope plugs n sensor will lower my fuel use a bit

The stock gap is fine, 1.0 - 1.1 mm

Legacy777 wrote:The stock gap is fine, 1.0 - 1.1 mm

I didnt gap it when i installed, is that bad? lol stock NGK gap?

JasonGrahn wrote:Bigger gap =
Positive side: larger spark, better ignition.
negative side: your spark can get "blown out" by the air passing by

smaller gap =
negative: not enough spark, bad ignition, stuttering
positive: your spark is hard to blow out.

-Jason

than why do they recommend a smaller gap and colder plugs with turbo cars?

Airgne wrote:than why do they recommend a smaller gap and colder plugs with turbo cars?

Because the presence of boost increases resistance across the gap so a smaller gap is easier for the spark to jump and the resulting higher combustion chamber temps require a colder plug to keep head and piston temps within spec.

smaller gap =
negative: not enough spark, bad ignition, stuttering

Unless the gap is way too small, these negatives don't really apply. My Scion XB came with .044 gapped plugs but after installing a turbo it runs great with 1-step colder plugs gapped at .032. It's also worth mentioning that too wide a gap can result in a weaker spark and misfires. Personally I'd rather have the gap on the small side of the oem spec than wider.

BTW, since aftermarket Subaru plugs come pre-gapped to .044 it's a good idea to re-gap them to .039-.040 since the gap increases with wear.

SubaruFred wrote:

Airgne wrote:than why do they recommend a smaller gap and colder plugs with turbo cars?

Because the presence of boost increases resistance across the gap so a smaller gap is easier for the spark to jump and the resulting higher combustion chamber temps require a colder plug to keep head and piston temps within spec.

smaller gap =
negative: not enough spark, bad ignition, stuttering

Unless the gap is way too small, these negatives don't really apply. My Scion XB came with .044 gapped plugs but after installing a turbo it runs great with 1-step colder plugs gapped at .032. It's also worth mentioning that too wide a gap can result in a weaker spark and misfires. Personally I'd rather have the gap on the small side of the oem spec than wider.

BTW, since aftermarket Subaru plugs come pre-gapped to .044 it's a good idea to re-gap them to .039-.040 since the gap increases with wear.

i know that, i wanted to see if he did. he gave half the info to ppl.

Airgne wrote:i know that, i wanted to see if he did. he gave half the info to ppl.

Sorry but I don't know what you do or do not know. I usually answer forum questions with the assumption that they are genuine and with the purpose of offering accurate, useful info to all potential readers.

Since you already knew the answer to your question, may I ask your opinion on a related topic? I had some left over ND spark plugs laying around from a Scion turbo project that are correct for my Legacy but one heat range colder. What is your opinion on running 1-step colder plugs on a 173k mile EJ22 that burns very little oil? My thoughts are that they might actually help with knock due to increased compression from existing combustion chamber carbon deposits but OTOH being colder, they could also potentially contribute to increased carbon deposits from inadequate CC temps. Conventional wisdom on the subject is to run hotter plugs to combat oil fouling but that's not an issue here. What's your opinion?

Airgne wrote:i know that, i wanted to see if he did. he gave half the info to ppl.

You quoted a post from 2002.....he hasn't been on the board in a while to see that. There's no reason to play the testing game. If you can be of help in a post, great, otherwise no need to post and play games.

SubaruFred wrote:Since you already knew the answer to your question, may I ask your opinion on a related topic? I had some left over ND spark plugs laying around from a Scion turbo project that are correct for my Legacy but one heat range colder. What is your opinion on running 1-step colder plugs on a 173k mile EJ22 that burns very little oil? My thoughts are that they might actually help with knock due to increased compression from existing combustion chamber carbon deposits but OTOH being colder, they could also potentially contribute to increased carbon deposits from inadequate CC temps. Conventional wisdom on the subject is to run hotter plugs to combat oil fouling but that's not an issue here. What's your opinion?

I'll give you my opinion on the colder plugs. It stems from the old hot rod days where they would run colder plugs to help keep the plugs from overheating on high horsepower/compression engines. Turbo cars are very similar, which is why some respond well to colder plugs. However there is a big difference between the old hot rod days and now....much much better engine controls, ignition, fueling, etc. With that better control you can get away with running the correct heat range and not overheat the plugs.

On non-turbo cars, especially factory cars, there's no reason to run colder plugs. The car will run worse, trust me. A friend of mine in Houston did some mod to his 99 RS, and ran colder plugs for a little bit. Engine ran worse, and had less power. Swapped back to the correct heat range....engine ran better.

Are you experiencing knock on your current engine? If so, you need to fix the problem that is causing knock, not necessarily put a band-aid on to fix the symptom. If you have carbon deposits try some sea foam through the PCV valve, and/or the Italian tune-up.

Legacy777 wrote: I'll give you my opinion on the colder plugs. It stems from the old hot rod days where they would run colder plugs to help keep the plugs from overheating on high horsepower/compression engines. Turbo cars are very similar, which is why some respond well to colder plugs. However there is a big difference between the old hot rod days and now....much much better engine controls, ignition, fueling, etc. With that better control you can get away with running the correct heat range and not overheat the plugs.

On non-turbo cars, especially factory cars, there's no reason to run colder plugs. The car will run worse, trust me. A friend of mine in Houston did some mod to his 99 RS, and ran colder plugs for a little bit. Engine ran worse, and had less power. Swapped back to the correct heat range....engine ran better.

Are you experiencing knock on your current engine? If so, you need to fix the problem that is causing knock, not necessarily put a band-aid on to fix the symptom. If you have carbon deposits try some sea foam through the PCV valve, and/or the Italian tune-up.

Thanks. On my custom-turbo Scion I agree that I could probably get away with std heat range plugs due to superior EMS and basically relying on the knock sensor to pull timing when heat induced knock is present. However, it would likely mean running less igntion timing advance and subsequently reduced hp/tq to compensate for the increased combustion chamber temps.

On my old Subaru, I definitely agree that std heat range plugs should be optimal but I installed the colder plugs because I had them laying around and the existing plugs were worn out. It's been a few thousand miles now so I'll pull them soon ad see how they look. Thus far they have been a big improvement over the worn out correct heat range plugs although I pretty much expect that the colder plugs will be fairly sooty. In which case I'll install the std heat range plugs.

BTW, what is an "Italian tune-up"?

An italian tune-up is just going out and flogging the motor, driving agressively, that kind of stuff. Some people, including myself probably do this on a daily basis, while others never get above 4,000 rpm. Those are the cars you see with a little puff of black smoke when they get on the gas. Built up carbon

Legacy777 wrote:An italian tune-up is just going out and flogging the motor, driving agressively, that kind of stuff. Some people, including myself probably do this on a daily basis, while others never get above 4,000 rpm. Those are the cars you see with a little puff of black smoke when they get on the gas. Built up carbon

Thanks! I've been doing those for years but didn't know it. Another trick I've used for removing carbon buildup is injecting water into the carb or TB. I use a spray bottle to mist water into the intake air after the filter and rev the engine. The steam helps to loosen carbon buildup.

Yup, the water vapor trick works too. Sea foam in the intake also helps, and can make a nice big smokey cloud

I want to like Seafoam because of all the great reviews but so far it hasn't done anything for me that Wally World Super-Tech FI cleaner didn't do. Speaking of which, I find it very annoying that I can't find any decent comparative reviews for popular carb/FI cleaners. They range in price from $2-10 and all contain generic "petroleum distillates" and I have no idea which ones are worth the money.