So my 2012 IS350 that I recently bought has 56k miles and I decided to do the plugs that make the spark in the engine that makes the noise. So I was looking through threads and somehow came to the conclusion by someone’s post that seemed legit, or at least legit enough, that the gap was 0.039. The original plugs that I removed were gapped to 0.039. The OEM plugs that I bought off amazon were 0.043.

So I went ahead and gapped the iridium plugs to 0.039 and put the plugs in. Car started up, ran fine, no problems on the test drive, etc.

Came home, had the idea to check the owners manual to make sure. Bam... 0.043. So my question is...

Will having the plugs gapped to 0.039 as opposed to 0.043 really make that much of a difference? Gas mileage? Power?

Im new to the N/A scene but I know with tuning boosted engines it makes a massive difference. Any input would be great.

 

I think you will be ok. Tolerance gap difference is about +/- .003 or so.

 

Because they are none wearing plugs, over the course of 60,000 mi it is likely it would get a better burn and slightly better fuel economy if at spec. That said, unless you checked all of them and set them, even plugs we pay a premium for (think pre-gapped), I've found them all over the map. Like from .037 to .045".
Rule is check and adjust them as needed as out the box has variability.

 

Well I drove around for a day with them at 0.039 and it was a slight improvement. Definitely more pep and low rpm and smoother than before.

I then took out all the plugs and gapped them to spec, and WOW, huge difference in power, increased fuel economy by 2+mpg, engine was noticeably throatier. I’m glad I took the time to do it. Yea I agree, Increased gap means a bigger arc so more of a burn which explains the power and fuel economy. Not to mention my 56k plugs were worn out. Only takes an hour I encourage everyone to do it! Thanks for the input y’all.

 

For some reason I've never even looked at the gap of my "pre-gapped" Denso plugs. So this next round I'll actually check out before installing. Curious to see how close they actually are since they're supposed to be "pre-gapped".

 

Yep I noticed years back with my GS400. Members swore up and down that the Denso plugs where always gapped to spec. Before I installed them I checked gap, and they where all over the place.

 

Always found them more OFF than on spec. Use the 4705 at half the cost...