plug gaps

**sambb** · 15-03-2016, 06:27 PM

I was just reading a quote from an NGK FAQ where the advice was that in forced induction engines, you should reduce your plug gap by 0.1016mm for every additional 50HP you have added above stock.

The 1.8T comes with a recommendation for 28 thou (0.7112mm) gaps. Using my car as an example it is flowing 188-190g/s through the standard MAF which equates to roughly 230HP. The car is 150hp standard meaning I've added an additional 80hp.

So by doing a ratio that additional 80hp means I should be shrinking the plug gap by 0.16256mm. That would reduce my plug gap from 28 thou (0.7112mm) down to 0.54864mm which is still evn a bit less than 22 thou.

I had actually already brought mine down from 28 to 25 thou after doing a bit of reading that suggested slightly smaller gaps work better with auxillary water injection and to be honest the car did feel snappier and less prone to bogging.

I've always been happy to be a guinea pig on left of field things but 22 thou sounds awfully small. Has anyone else out there with the more mental engines experimented to this extent with shrunk plug gaps and have any feedback.

thanks

sam

**h100vw** · 15-03-2016, 07:45 PM

I don't think I'd go any smaller Sam. That's 12 thou under what the plugs come from the factory at.

I also think the starting hp should be higher for your equation, ie for every 50hp over 200 rather than 150. The car is well under performing as standard.

Gavin

**Blue9N3** · 15-03-2016, 07:54 PM

Correct me if I'm wrong,
But provider the car isn't suffering from misfires, isn't a larger gap better?

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**sambb** · 15-03-2016, 08:13 PM

yeah that had crossed my mind gav. It was made pretty anaemic in its 150hp form wasn't it. Yeah thats why I threw it out there cos 22 thou sounded a bit crazy. Are the 200hp spec 1.8T's on 28 thou too - its not just ours is it?
I'll crunch some numbers taking it from 200 hp. It'll probably come out at where I'm at now - a tight 26 thou

**h100vw** · 15-03-2016, 08:18 PM

Originally Posted by sambb

yeah that had crossed my mind gav. It was made pretty anaemic in its 150hp form wasn't it. Yeah thats why I threw it out there cos 22 thou sounded a bit crazy. Are the 200hp spec 1.8T's on 28 thou too - its not just ours is it?
I'll crunch some numbers taking it from 200 hp. It'll probably come out at where I'm at now - a tight 26 thou

The Polo Cup runs the same plugs at 132kw.

Gavin

**sambb** · 15-03-2016, 08:09 PM

basically you want to run the biggest gap you can provided its not being quenched by water, literally blown out by boost or misfiring due to inadequate ignition power. Go too small though and the spark kernel gets too small to light the fire properly and you loose power.

**sambb** · 15-03-2016, 09:39 PM

yep based on a 30hp increase over 200hp the reduction in gap would bring it to 25.6 thou - where I'm at now.

**nightphotographer** · 16-03-2016, 08:53 PM

I'm pretty sure I'm at 0.4" with the 2.0 TSI coil packs. I've not really tested it, I know I got the gap very wrong when I first installed the coils and it wouldn't run, and then I played around a little bit and now she's great. Unsure on any performance gains at all, but fuel economy is great and i wouldn't say it was a slow car.

**sambb** · 17-03-2016, 06:06 AM

you can really see how much cooling the ports, inlet valve and plug would get from the fuel air mix as the inlet charge rushes in. A direct injected engine would really miss out on that which is probably why they really rock with water injection added.

....and there's so much chaos in there its hard to believe that those super fine tip plugs that locate the spark in one tiny spot could improve things at all