Introduction: Save Gas and Incerase Horsepower by Side Gapping Spark Plugs

Picture of Save Gas and Incerase Horsepower by Side Gapping Spark Plugs

Side gapping spark plugs has been use in racing for years to increase horsepower by unshrouding the spark thus allowing the flame created to propagate faster resulting in a more complete burning of the fuel/air mix. Many manufacturers offer plugs deemed racing plugs that are side gapped but at inflated costs. By doing it yourself you can use a cheap .99 cent plug to save money and increase horsepower.

Step 1: Cuttting Ground Electrode

Picture of Cuttting Ground Electrode

Using a dremel with a cutoff wheel or a hacksaw you will need to cut the ground electrode even with the edge of the center electrode. You need to be careful not to hit the center electrode or the porcelain.

Step 2: Removing Burrs

Picture of Removing Burrs

Next you will need to use a file to remove any burrs left from cutting the ground electrode. If this step is not done the burrs could heat up until they glow red hot causing detonation. After the burrs are removed you will want to use some alcohol or starting fluid to thoroughly clean the plug to make sure there are no metal filings left.

Step 3: Setting the Gap

Picture of Setting the Gap

After all the burrs are removed you must set the gap. To do this you will need to find the manufactures setting for your vehicle and reduce that by 0.010". Example: manufacture setting 0.035" - 0.010" = 0.025". Then using a feeler gauge of the correct thickness insert it at a 45* angle to check and adjust as necessary until the gap is correctly set.

Step 4: Before & After

Picture of Before & After

Here are before and after photos of a non side gapped vs. sided gapped spark plug. With the side gapped plug the spark is now un-shrouded and is more exposed to the fuel/air mix. the flame created will now be able to spread faster resulting in a more efficient burn before the exhaust valve opens.


ThomasE82 (author)2017-03-12

Use caution increasing spark plug gaps. I did this on a Ford Ranger 3.0. It seemed to run OK but within a month the coil went bad and had to be replaced. It appears the coil has to work harder as the gap increases. I changed the gap back to factory specs.

MarkF136 (author)2016-04-14

The sparks are the same size in any plug configuration (side gap or regular) as the spark can physically only go from the center electrode to the ground electrode (hook portion) and does not throw past it.

Cutting the ground electrode gives you a smaller area for the spark to jump to eliminating reliability. The spark can only go from corner to corner, rather than having the ability to use the entire flat surfaces on both sides to find the best path when carbon deposits build up and hinder spark.

Check out the plugs on this page for an extreme version of this plug mod.

Taken from the link below: "A racing plug differs from a street plug typically by the heat range and expectation of durability. Also the long-life electrodes in the street plugs is designed for longevity. "

ChrisJ25 (author)MarkF1362016-09-19

I think you may have misread the article you cited. "Spark plugs with fine wire center and/or ground electrodes operate better for two reasons. First, a smaller center electrode requires less voltage to jump the gap. This means fewer misfires, which will be seen in higher mileage and more horsepower. The second reason is smaller center and ground electrodes reduce quenching." This means that the smaller area you mentioned actually makes for a better spark.

TurboYam (author)ChrisJ252017-01-10

I had a bid problem with my turboed 98 Yam R1 could just not get it to cold start had to send propane gas into the turbo and even so...So finally I found the solution, took out the resistances from the sparkplug caps (20 Kohms...!!)

and changed the CR9E plugs for nonresistor C9E spark plugs (5 Kohms) and now it runs great you can fell the bike has more power and starts up under all conditions. Absolutely no Rf inteference that all a joke to reduce emissions. Because to reduce pollutant emissions you have to have a not too good combustion like Guy Martin (TT champion and mechanic) explained in one of his videos

cowboycorvette (author)2014-11-06

The only thing side gapping will do is change WHERE the burn begins - not how much or how fast or how completely the mix burns. If anything, increasing the gap would theoretically increase the speed of the burn because you're igniting more fuel initially vs a shorter spark. Newer plugs are proven to burn better because they are producing a bigger (fatter), hotter spark. My question has always been - and why I found this - what happens when you simply increase the gap.

ChrisJ25 (author)cowboycorvette2016-09-19

Just increasing the gap will not make the spark better; it will actually weaken it. The air-fuel mixture has a much higher resistance than the metal of the electrodes so making the gap larger makes the resistance that much more. You would have to increase the power to the plug in order for the spark to be able to cross the increased gap. To learn more, please google basic electrical theory and how spark plugs work.

paul0008 (author)2016-07-06

Can this be applied in a motorcycle sir ?

MarkF136 (author)2016-04-14

Lastly, I googled "Top Fuel spark plug size comparison" and could not really find any major differences compared to your standard engine. The top fuel dragsters have much larger cylinders and 8000 hp (1000hp per cylinder) yet the spark plugs are not that different but use 2 plugs per cylinder and every other component is bigger and better, like the ignition/spark size. Their fuel economy can be 40 gallon per mile!

Look closely at the plug electrodes in the cylinder head picture I included. How big is your ignition/spark compared to the included photo.

MarkF136 (author)2016-04-14

Responding to a comment: what might acetone do to your fuel lines and plastic parts in your engine? What is acetone usually used for, nail polish remover, etc? What if acetone eats your fuel line and sends the bits of rubber or plastic into your engine and burns/cakes onto the plug? I don't know, maybe it will clean your engine and plug but may harm your oxygen sensor or catalytic converter or clean the oil off your cylinder walls removing the lubrication and causing more wear. Some octane boosters say they can harm engines and other parts but give more power.

MarkF136 (author)2016-04-14

Every car manufacturer uses different spark gaps and levels of spark energy. A Top Fuel racer is using a MUCH more powerful spark, completely different fuel and may use 11.2 gallons per second which is the same as a 747 plane.

Don't you think an engineer might know a bit more than the average home "bench racer"?

Speaking of different fuels racers use and additives like the guy who mentioned acetone, the cost of fuel is directly related to your MPG cost everyone is talking about. Acetone is much more expensive than gasoline and may be much more harmful to your car and pollution. Our gas prices are cheap compared to other fuels, you pay more for Hersheys syrup & laundry detergent than gas.

The Ethanol they put in our fuels is more harmful to our cars, especially older ones which were never meant to run it, which is why Ethanol is limited to 10-15%, and why there are Flex Fuel E85 (85% gas/15%Ethanol) designed vehicles. Ethanol pollutes less but also makes less power. There is more concern for pollution than your power output and life of your engine.

Are you really so desperate for 1% increase in horsepower (maybe with a plug) in your car which you can't detect anyway unless on a drag strip and at full throttle and worse MPG? Your HP is measured at full throttle, worst MPG and "perfect" conditions, new and at sea level. Calculate 0.01 of your power and MPG. If you have 200hp x 0.01 = 2hp max under perfect conditions! An air intake and exhaust upgrade is a more realistic upgrade with much higher gains.

read these articles to understand more.

MarkF136 (author)2016-04-14

I would think a side gap would wear the smaller corner of the spark plug electrode faster needing more adjustment and replacement more often.

If you have good air/fuel mixture in your cylinder the spark obviously still ignites it from any angle if your engine is functioning properly.

As ZakC2 mentioned, dirty, fouled plugs may not be as efficient having a weaker spark. Many people don't study the different types of plugs and may be using the wrong type, especially if they have made modifications.

read these articles to understand more.

ZakC2 (author)2015-11-17

When running your automobile and the plugs always seem to be black and oily when you check them, they are fouling because your engine is either burning a lot of oil, or your mixture is too rich, or because you need to be running "hotter" spark plugs. Running too cool a plug causes fouling, which inhibits a good spark. Running the right plug optimizes the spark. Running too hot a plug may cause pinging, or just melt the spark plug.

picbuck (author)2008-05-27

But...if it were that easy to increase mileage and horsepower...wouldn't the manufacturers be doing it? And bragging about it in Superbowl ads? Well...just a thought.

galeb (author)picbuck2015-05-13

Follow the money, auto companies and oil companies have the same board of directors or related ones.

eskimojo (author)picbuck2008-09-12

Not necessarily, commercials(especially those showcased during the superbowl) are dictated by trends and marketing plans. There have been plenty of technologies that have gone basically unnoticed by the general population simply because they are unpopular or don't fit into the "American Way"(basically quick/easy/cheap).

picbuck (author)eskimojo2008-09-13

My reference to the Superbowl was, of course, a metaphor. Meaning a manufacturer who comes up with a better way tends to shout the news from rooftops (also metaphorically). On a more basic level, the media--both print and electronic--have long since fallen into bash-America mode. But the view that "they" (any they) are better than America is mistaken. Europe curses us for what they call our effete central heating and air conditioned cars. But we don't want to keep such things to ourselves, we want Europeans to have them too. Compare the two ethical stances, and decide which is better. While in the East, Japan and China--among others--have a more productive view. They want to be us. The American Way can be very simply stated: you're as good as the next guy, and you can take your shot the same as anybody else. If anybody can find fault with this view then they are, as far as I'm concerned, welcome to their opinion. That's another thing about the American way: you can have your opinion, you can state it as loudly as you like, and all Americans band together to protect your right to do so.

Cjern (author)2015-04-30

Ever try 100% pure acetone? I've read some stuff on it and tried it and noticed a crazy increase in mpg and some power. 5oz to 10 gallons. Thought it was BS so I tried it on my wife's RDX and couldn't believe the difference. Had it in the dealer and asked them to check the fuel system while it was in there and they said there was nothing wrong with it. I just wanted to be sure. Also a buddy of mine tried it on his Dodge pickup with I think it's a 5.7 hemi. He said his mpg went up 6mpg and said it seemed a lot smoother. It's only said to help the gas vaporize better so it ignites faster and more complete. Just throwin that in to see if anybody's ever tried that? Want to try it on my car to see if I notice a difference. Didn't mean to change the subject.

stevem3 (author)2014-08-22

Side gapping has been used going back to the First Days of Indy Racing. The Grandson of 1st Indy Winner in 1911 Ray Harroun (Bill) use to come to the Circle Burner Motorcycle and Sprint Car Races locally. He mentioned numerous times when racers were doing plug checks or changing heat ranges about how they side gapped their Sparkplugs back in the day.. If it didn't work then nobody would have continued doing it. It's more than a 100 years later and it's still being used....So There!

cowboycorvette (author)stevem32014-11-06

People back in the day also thought the earth was flat until someone came up with some hard evidence to disprove that ;-) Lots of "experts" do lots of things in lots of fields for long periods of time that are complete BS. I'm a Dr - there are so many medical myths that Drs and nurses get passed on and will never stop - they're complete BS and have no fact basis but they still do it and it gets passed on!! Ever read on an ER direction sheet to keep your stitches "clean and dry" - absolute worst thing to do for any wound!! Keeping it dry CREATES a much bigger, nastier scar and delays the healing process by at least 40%. We base our decisions on hard facts - not just because someone claims it works and its being done by everbody ;-)

cowfy (author)2014-11-02

plus a 5 gas sample before and after should give black and white indication.

cowfy (author)2014-11-01

i am not groking this.why can't any evidence be shouild be a simple matter.just compare burn time before and after cutting the plugs.does that make sense?

bmj67 (author)2007-09-30

If it didn't work then why would just about all spark plug manufactures offer the plug in one form or another. Here are a few links to some of the plug makers.




Those are just a few manufacturers but they all look just about the same as what my modded plug looks like with the exception of the bosch platinum 2.

LasVegas (author)bmj672007-10-01

Those plugs are designed/intended for single use. They are replaced between every race. They're also made using platinum or nickel to handle the higher heat. Standard plugs use steel. The last (Bosch) plug actually has more than double the spark area of a standard spark plug! That one I might consider experimenting with.

frankalbergo (author)LasVegas2014-05-21

@LasVegas, The only racers that use this tec is Pro Stock and they do not remove the plugs. They run them for the entire weekend All of the other Pro classes use some form of power adder and tune the car based on in part what the plugs look like.Also note they are making around 1600 HP on motor only and every little bit counts.

wiccanman82 (author)LasVegas2009-03-02

Im not sure about the whole one use thing, i have a 02 chevy SS pickup that i have done extensive work to and i use only bosch platinum in it and i only change my plugs once a year (not every time i run the truck) i never had any problems with them

bmj67 (author)LasVegas2007-10-01

Where do you see that it says they are to be replaced after every race. Also racing engines take more stress than a normal engine so theres not a big need for the more exotic metals in a stock engine. Spark plugs Do Not produce heat read for yourself HERE that is ngk's site.

bumsugger (author)bmj672007-10-05


balloondoggle (author)bmj672007-10-02

Simple greed. If they make them with shorter electrodes they use a bit less material (less cost). THen the marketing guys come up with the spin and the accountants mark up the price to match the hype. That said, I don't know if it would work or not, but the cynic in me says this is a case of marketing hype backed by Dollar Lust.

trebuchet03 (author)bmj672007-10-01

Again, it's more important to see data in a non racing application. Low compression, lower voltage/amperage ignition system, very low comparative engine speed. It doesn't really matter if they make them or not - it would be more compelling if they were OE equipment ;)

bmj67 (author)trebuchet032007-10-01

The only data that I have is that I pickup 1-2 mpg compared to stock and I feel improved acceleration. Do a Google search and see what other people have to say as well I'm not the only one. I'm not going to go out and spend hundreds on dyno testing. The whole point of this is to get better gas mileage and improve performance without spending a ton. Like i said before I replace my plugs often and this is just my experience with side gapping. You can do what you want no one is forcing you to cut your plugs. But I for one will not pay $5-$6 for a spark plug that won't be in my engine over a year anyway. OEM are cheap they just do the bare minimum to maximize profit.

trebuchet03 (author)bmj672007-10-01

Do a Google search and see what other people have to say as well I'm not the only one.

I have ;) We're also not the only one's that are asking for empirical evidence... The people making claims don't really have empirical evidence :p Unfortunately, most of the anecdotal evidence is base don people that are changing plugs anyway - so any gains are very likely a result of going from an old plug to a fresh one.

The only data that I have is that I pickup 1-2 mpg compared to stock and I feel improved acceleration.

"Feel" is too subjective - the key factor of the psyche wanting a result after invested effort... And 1-2mpg is well within driving style and environmental error (even station pump error :p). Not nearly enough to call it a result. However, a dyno isn't needed ;) You can do A-B-A testing and get a decent result. ABA Testing.

The whole point of this is to get better gas mileage and improve performance without spending a ton
That's completely fine - there's several communities dedicated to just that :p But if you can't prove or repeat a result, you didn't have one ;) All we have to go on at the moment is a manufacturer's claim that you won't have any increase.

I'm not saying it's not worth testing - my point is, if anyone is going to make a claim, they better have objective, empirical (not anecdotal) data and need to explain their methods so others can test and confirm. Frankly, this is cheap enough that I'll probably be testing it - but that likely won't happen until summer :p

bmj67 (author)trebuchet032007-10-01

Most other people are like me and don't want to spend the money to get the empirical evidence. :) I know what you mean about going from old plugs to new. Some people never change spark plugs because they think plugs last forever.

I know feel is different for everyone and that the placebo effect doesn't just apply to just pills.

I'm not saying it's not worth testing - my point is, if anyone is going to make a claim, they better have objective, empirical (not anecdotal) data and need to explain their methods so others can test and confirm. Frankly, this is cheap enough that I'll probably be testing it - but that likely won't happen until summer :p

For the price if it works for you good if not your out maybe $10 and a little bit of time.

This is a very good instructable, and I know for a fact that it increases horsepower about %20 per cylinder due to me testing this a bit in one of my hot rods on the dyno. I would suggest making the gap even just a little bit bigger too.

Pizzapie500 (author)2010-11-19

Set the gap? What does that mean?

bmj67 (author)Pizzapie5002010-11-26

You need to set the gap between the side and center electrode by first measuring and then bending the side electrode in or out.

suzukikatana (author)2010-04-23

Advance the timing and have the thing ping its head off great. Duh

james.mcglashan (author)2009-09-19

can you please update the video it doesnt work???

OBar (author)2009-08-06

I drive a four cylinder Chevy S-10 in desperate need of an oil change. ( I dunno why I felt the need to inform you of that) I used to work for a man who built and drove race cars, and he said that for a daily driver car, regular maintenance and care goes a long way.

joeofloath (author)2009-04-03

Does this work for 2 strokes? I have an old quad I'm converting (instructable coming :)) and it might need some more power...

ajilitee (author)2008-09-22

What about those fuel additives? I am getting desperate my commute is getting out of hand.

DamionLee (author)ajilitee2009-01-27

Fuel additives are fine if you want to add something occasionally to clean your engine, but you would be better off using a product like 10K for that. With regards to performance, fuel additives add elements to your fuel which will not burn as well as the petrol. What happens with most fuel additives is that you lose horse power. They are a great scam in that regard.

gin_road (author)2008-11-06

Hey, my Kawasaki ZRX-1100 uses this technology. It uses an NGK plug#CR8EK. This plug not only uses the side gap technology, it doubled it!!!, It has two ground electrodes on the plug placed 180 degree's apart. Only one downside, 8 to 10 bucks a piece.

trebuchet03 (author)2007-10-01

From the horses mouth:

There are some exceptions, though. Extremely high compression cars or those running exotic fuels will have different spark plug requirements and hence NGK makes spark plugs that are well-suited for these requirements. They are classified as "specialized spark plugs for racing applications". Some are built with precious metal alloy tips for greater durability and the ability to fire in denser or leaner air/fuel mixtures. However, installing the same spark plugs Kenny Bernstein uses in his 300+ mph Top Fuel car (running Nitromethane at a 2:1 air/fuel ratio and over 20:1 dynamic compression) in your basically stock Honda Civic (running 15:1 a/f ratios with roughly 9.5:1 compression) will do nothing for you! In fact, since
Kenny's plugs are fully 4 heat ranges colder, they'd foul out in your Honda
in just a few minutes.


Some of these "specialized racing plugs" are made with precious metal alloy center/ground electrodes or fine wire tips or retracted-nose insulators. Again, these features do not necessarily mean that the spark plug will allow the engine to make more power, but these features are what allow the spark plug to survive in these tortuous conditions. Most racers know screwing in a new set of spark plugs will not magically "unlock" hidden horsepower.

I'm also more inclined to believe a company that makes an anti-claim over one that makes a claim (Especially without data to back it up):
NGK as a company tries to stay clear of saying that a racing spark plug (or ANY spark plug) will give you large gains in horsepower. While certain
spark plugs are better suited to certain applications (and we're happy to counsel you in the right direction) we try to tell people that are looking to "screw in" some cheap horsepower that, in most cases, spark plugs are
not the answer.

pyrotmaniac (author)trebuchet032008-09-21

This rings very true, in one of the first hot rods I built in the early '90s being at the time just a teenager. I thought that I had done enough to warrant changing to specialized plugs of this sort. Simply adding a larger carb. and exhaust to an engine will not even bring you into the ball park of needing this type of spark plug. The car I was building at the time never ran 100% untill I replaced the $10.00 spark plugs for some good old champion $.99 units. sure you change them when you change your oil (well almost that often) but who cares. For your daily driver you should be popping the hood every couple of weeks just to check on everything anyway.

bmj67 (author)trebuchet032007-10-01

I never said you had to just use the plug in your car or truck. There are many motorcycles and atvs that have compression rations above 10:1 stock. Also there are cars that come from the factory with turbos and superchargers. They are not your average Honda civic.

trebuchet03 (author)bmj672007-10-01

That's fine and all - but again, I stand that a claim requires empirical evidence to be believable ;) There are cars that have dynamic compression - these are the minority on the road as with higher compression engines.

Finally, I'll reiterate the NGK statement to the purpose of this modification...
Some are built with precious metal alloy tips for greater durability and the ability to fire in denser or leaner air/fuel mixtures...
(running Nitromethane at a 2:1 air/fuel ratio and over 20:1 dynamic compression)...
these features are what allow the spark plug to survive in these tortuous conditions.

nibbler125 (author)2008-09-21

ill try this i have a 3 wheeler that likes to miss and load up allot

Tightwad (author)2007-10-23

Ok, lots of people seem confused by various Spark Plug terminology. First: Hotter/Colder- The spark is not "hotter" or "colder"'s a spark. Gap size is set/determined by the ability of the ignition coil to bridge the gap. The stronger the Coil, the wider the gap can be...wider is better because it opens up firing area a bit more. Hotter/Colder actually refers to the plugs ability to bleed of heat. If you look down into the spark plug, you will see that the ceramic inslator portion is different lengths on different plugs. This is what determines the "heat" range. Having a hotter/colder plug is not better/worse...rather you need a plug that will run at the optimal temperature for your application....Motors that run hot using Alcohol or similar need "colder" plugs to help reduce the change of the spark plug turning into a glow plug. Spark Gap/indexing...this mod- This will, for 99.5% of the people out there, have no positive effects in their applications. This doesn't make it bad, or false advertising, simply not beneficial. There are so many other places you lose power and effeciency that making up for it in this one place will not be noticable. This would be the LAST thing you do after you have upgraded/improved everything else along the way. Opening up the ignition area, or indexing your plug relative to the Intake Valves works, but is only quantifiable in high-performance applications where everything else is already optimized. Downsides to this mod - As others have pointed out, you will get more wear from this mod, and thus will need to adjust/change your plugs more often. There are no negative side effects otherwise, simply shorter life span of the plug and gap setting. Regular plugs will NOT work better than plugs correctly modded this way. "But I felt a difference"- Sorry, but there isn't anyone short of a seasoned racer that could feel the difference that JUST this mod makes. You can't feel a 1-2 HP increase(if you even get that) by the seat of your pants....1-2 HP is less than 2% gain. Tightwad ASE Certified spoilsport

eskimojo (author)Tightwad2008-09-12

Thank you for clearing that up, it's good to hear a voice of reason every once in a while on the internet, even on this site.

Malaachi (author)2007-10-25

Won't they foul faster?

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