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Please explain spark plug gap vs. tune

BAMF

Ready to race!
Location
Jacksonville, FL
Thank you everyone for the input, especially GIACUser for taking the time to get into the technical details.

One last question- assuming that there are no misfires occurring, is there any reason to not run the larger gap? My understanding, as was mentioned above, is that a larger gap will result in a more efficient burn. Are there any ill effects outside of misfires that I should keep an eye out for? I plan to log periodically just to keep an eye on things as I put some miles on the plugs and coils.
 

GIACUser

Master Wallet Mechanic
Location
SoCal
Thank you everyone for the input, especially GIACUser for taking the time to get into the technical details.

One last question- assuming that there are no misfires occurring, is there any reason to not run the larger gap? My understanding, as was mentioned above, is that a larger gap will result in a more efficient burn. Are there any ill effects outside of misfires that I should keep an eye out for? I plan to log periodically just to keep an eye on things as I put some miles on the plugs and coils.
Well you pulled this part out of context and there is a bit more coupled with it.

"My understanding, as was mentioned above, is that a larger gap will result in a more efficient burn."

From NGK

"A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. (we are using stock ignition) The added power allows them to open the gap yet still provide a strong spark.

With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think."



You should give different gaps a try and see what works best for you.
 

zrickety

The Fixer
Location
31709
Car(s)
09 GTI
May also be plug specific...for example I'm running Denso TT platinum and they come .040. I haven't touched them and the car runs great.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
Seems a lot of talk about plug gap and tunes...sure, increased boost and fuel can disturb a plug's arc. I do not see mention of coils. Oem coils are 3.3 ohm and work better with a larger gap because the arc is larger. R8 coils are 5.3 ohm and work better with a tighter gap because the arc is smaller. I use oem @ 0.028" or NGK PFR7B @ 0.028" without issue.

Coil Ohms;
Stock: 3.3 M ohms
5 cylinder coils: 4.75 M ohms
R8's: 5.31 M ohms
Okadas: 6.2 M ohms

What works for one tune, coil, and plug set-up may not be perfect for another. The best one can do is install a new set of plugs when all else is known to be good, drive it somewhat hard for a bit, then remove the plugs and check if there are signs of hot fouling or cold fouling. Also, you want to be sure the LAMBDA is good and fuel is being burnt thoroughly and not too rich or lean.

If you have just tuned for a bigger turbo or simply switched to a more aggressive tune and you notice some shaking or stumbling when you floor it...then you probably need to close the gap a bit if coils are known to be new and you are using oem plugs. PFR7B come with a gap of 0.028" and are a great plug with an aggressive tune and 'mas' boost...so you can use them if you do not want to mess with the gap. I use them when I have boost turned up to over 23 psi. Right now I have all WG preload off and I use oem plugs.

But if you prefer someone to say all of us should do the same because that one way is best...ummm, then stay tuned.
 

zrickety

The Fixer
Location
31709
Car(s)
09 GTI
Thanks for posting that. I had seen the ohm values before, and knew R8 coils were between stock and Okadas, but couldn't find the thread.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
I am shocked at the number of posts in multiple forums by people that are saying the 5.3 ohm R8 coils have a hotter spark than the 3.3 ohm coils. It is simply not true. More voltage is released to the plug with a lower resistance coil and requires a larger gap for better performance regarding ignition. The R8 coils are good when there is increased boost and resultant combustion that may disturb the arc of the oem coils. Then when a tighter gap is needed, is when the R8 coil may help because it works better with a tight plug gap. You can actually switch to a warmer plug with R8 coils due to the reduction of heat from its arc. The R8 typically uses a 6-heat plug because of this.
 

clockwise33

New York Giants Fanatic
Location
NJ
I am shocked at the number of posts in multiple forums by people that are saying the 5.3 ohm R8 coils have a hotter spark than the 3.3 ohm coils. It is simply not true. More voltage is released to the plug with a lower resistance coil and requires a larger gap for better performance regarding ignition. The R8 coils are good when there is increased boost and resultant combustion that may disturb the arc of the oem coils. Then when a tighter gap is needed, is when the R8 coil may help because it works better with a tight plug gap. You can actually switch to a warmer plug with R8 coils due to the reduction of heat from its arc. The R8 typically uses a 6-heat plug because of this.
The R8 coils (06E905115G) are paired with 8 range plugs in boosted OEM applications (3.0SC). These are the plugs that have worked best for my APR K04 tune (PFR8S8EG) gapped to about .025. I still get slight misses near red line but better than several different coil/plug combinations I tested.
 

ROH ECHT

K04 PLAY
Location
PDX OR
Car(s)
2007 MKV GTI
That makes sense because the R8's NA engines plug gap is what 0.031" and their heat range is 7? More boost would require tightening of the gap with their lower resistance coils and increasing the heat range if their coils are used on boosted cars.
 
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