Spark plug gap for FE on the 1.4T

I initially saw a massive spike in fuel mileage. I was getting 38mpg regularly, and right after opening the gap, that tank got me 45mpg. I averaged 54mpg for half the tank, of course have to take that computer average with a grain of salt. As of later tanks, I have been seeing 40-44mpg, which still is an improvement. But the butt dyno was more pleased. The response of the engine is much better.


But it isn't so simple to figure out the right gap for an engine. Definitely not a universal thing. I just toyed with an idea of boosted 4cyl, smaller displacement, engines that I am used to. Going by boost pressure also isn't a good factor, as cfm is the thing you need to know. Too many people see boost as boost, which is bad. The bigger factor is the cfm of the turbo over its map. Anyways, going with too big of a gap can potentially be blown out or not even spark. Going too small, it can cause poor combustion (sounds odd, as people may think a burn will burn everything) and could bridge over eventually. There is so much more to go on about, but I will just leave it short.

Simply, tuning the gap can make differences but sometimes is hard to find. If you really want to fine tune the ignition, then mess with the gap and also index the plugs to create the most complete burn possible with the stock engine components. Personally, too many factors can lead to how my results came about. It is a free thing to mess with, and is a reason I tried (plus I just felt the engine wasn't running right). Just be careful when doing this because the plugs are iridium, so definitely use feeler gauge (not that cheap round piece that isn't precise) when checking gap.

i guess they could be preparing for some wear down the road. a stock ls1 plug is .060. even with 1000+ boosted hp we dont go down to .029.

are the stock cruze plugs double platinum? if so i would think there is very little wear over the 100k lifespan.

i did some a little searching. didn't really find any scientific or tested data but the consensus is it is ok to up the gap by .010.

i have access to a mustang dyno. it is a loaded dyno so you can do all kinds of drive ability testing on it. i might try and do some somewhat scientific testing on some of these mileage ideas.

1st step would be to go out on a flat highway on a calm day and set the cruse at 60mph. record the injector duty cycle.

2nd step get on the dyno and set the cruse at 60mph and adjust the load until i see the same duty cycle.

3rd step pump up the tires from 35psi to 50psi and record the duty cycle at the same speed and load. wont be a great test since it will only be seeing one set of tires but it might show something and the fronts likely have 3/4's of the load/improvement if there is any.

4th, open the gap and retest

5th lean it out 5%, 10%, 15%... till it starts missing.

at some point maybe adjust the timing a little. now that i think about it all these test should be under a little more load like 75mph since the car gets stupid good mileage at 60mph as it is.

any other easy to test things that could be done on a dyno? i have always wondered if the actual speed goes up compared to the speedo when you air up your tires. if the car is going 1mph faster due to a larger diameter wheel than the computer thinks it is going we might be seeing more of an improvement in mileage with the higher air pressure than we thought.

many of these things could be done on the road if you did it on the right day. no wind and steady weather conditions. dyno would just make it a little easier.