Smaller Plug Gap mean Greater MPGs?

07 Prerunner spark plug gap is about 39 thousandths to 43 i believe.

But say i gapped plugs at 35 instead of the above the spark would happen easier right so would this also mean the spark would combust more of the air fuel mixture and lead to greater fuel efficiency ??

 

Trust in the Toyota engineers. Stick to the specifications.

 

Life’s short, don’t let yourself get sidetracked by the minutia. Toyota isn’t infallible, but there’s no low hanging fruit to be found in terms of improving gas mileage on these trucks.

 

That's not how this works.

 

Does smaller gap make pre ignition or detonation more likely?

 

This.

 

I think it would decrease, smaller flame kernel /less combustion
but I know nothing

 

Bigger gap -> more exposure of spark to air/fuel mixture -> better power/efficiency

But only if you have enough ignition system to actually jump the larger gap.


I didn't know this 5 min ago, behold the power of google. Interesting question!

 

I think the fact that boosted cars have gap decreased supports this since the ignition is probably not powerful enough to jump the gap maybe also due to above ambient cylinder pressure so the gap must be decreased so the plug will be sure to fire at all.

 

Run it. Report back, always looking for volunteers at TW

 

Yeah pressure might have something to do with it. I don't know shit about boosted engines, but I did once build a spark gap switch for a project. It stored 25,000 volts in some capacitors, and had a spark gap to connect it to the load. The gap was in a little pressure cylinder. You cranked up the pressure before charging the capacitors, then released the pressure to fire it. The reduced air pressure in the gap allowed the electricity in the caps to arc across and fire a fat pulse into the load.

 

The reason boosted cars have a smaller plug gap is because it takes more voltage to jump across the plug gap as air pressure increases. So, instead of upping the spark voltage the reduce the plug gap.

 

This is correct, the higher the cylinder pressure the harder it is for the spark to jump the gap.

That's why secondary ignition misfires typically occur under higher engine loads because that's when cylinder pressure is the highest and electricity takes the path of least resistance, thus if the spark can find a path that's easier to jump than the plug gap it will go there.

I'd stick to OEM gap specs, increasing the gap will put more stress on the coils and could cause premature failure, decreasing the gap probably won't change anything but too small of a gap may cause misfires as there's not as much area for the spark to ignite the fuel.

 

Gap covers the resistance in the air mix which gets bigger with temp and pressure.

Rule is closest to oem spec is best mpg. Meaning as it wears the gap opens and has more resistance to jump across. Meaning more stress on coils.

Im gonna guess spec is 0.040 and anything over 0.045 starts running poorly

 

Send it.

 

Upping the spark plug voltage would require a new dizzy or at least a new coil id think. Changing plug gap can tell is the easiest solution.

 

over time, the gap will increase, so if you plan on leaving them for 100,000 miles, you should be all set.

 

If you buy NGK's. They come "pre-gapped" with a clear plastic tube at the base.

Leave it at that. You can compare with the other gaps on the rest of plugs.

More spark, more combustion

 

Im using Bosch double platinum checked them and did not much of a difference although only really have about 25K on these plugs i think so maybe was not even really time to check the gap.

 

I have to give Toyota credit.
I’d say the coils are pretty robust on the 4.0
I don’t get carried away with gap. I did my best to keep them at .040”
But a couple thousands off I’m not too worried about. I say keep it as close to the OE recommendation as possible.

Look at that gap……..