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0.8mm gap instead of 1.1mm will I lose any power/response?

benl1981

By benl1981,
in Engines & Forced Induction

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benl1981 Grand Master

benl1981

Posted
Posted

About to put in some new spark plugs as I have a bit of hesitation. Engine RB25DET.

I don't want to put in spark plugs with gap 1.1mm to find out that they should have been at 0.8mm.

Car has full 3" exhaust. 10psi and R34 intercooler. ..i.e. small mods.

Question: If I get 0.8mm gapped plugs instead of 1.1mm will I lose any power/response?

WazR32GTSt Grand Master

WazR32GTSt

Posted
Posted

obviously smaller gap will lose power... otherwise all spark plugs would be gapped down very small

just run as large a gap as you can without getting any side effects (ie misfire)

i used to run 1.1mm gap on my rb20 running 12psi, and only dropped it to 0.8mm because when it can time for replacements (i use coppers) i couldn't find any 1.1mm ones so just got 0.8mm ones because they were in front of my face

but in the end... the difference may not be all that significant

benl1981 Grand Master

benl1981

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Thanks mate. Maybe from when it went through quarantine or whatever. The plug itself looked ok...

The gap was about 1-1.1mm. Might try some coppers at 0.8mm

Apparently the plugs that came out are expensive, but do they have any life left??

proengines Rising Star

proengines

Posted
Posted

We had a GTR on a dyno yesterday and it was showing signs of the ignition breaking down at around 7000rpm, the power curve flattened off at around 295kw and the line looked like a bush saw. We regapped the plugs from 1mm down to .8mm and it made 320kW with the power curve doing the same thing at the top end. It's a pretty good sign that the ignition system is on the way out and this one will be getting a new set of coils and plugs gapped to what they should be. This engine has the compression bumped up slightly and is running around 22psi from 4000ish onwards so it does place a lot more load on the ignition. It will be interesting to see what sort of power this engine makes with enough spark to make another useful 1500 or so RPM as the power curve was heading up at around 70ish degrees and it hit its peak torque at around 5500-6000ish and the line stayed almost horizontal until the ignition died off.

Usually if you have to close the plug gap up to stop ignition problems it means that you have an ignition problem further down the line and without fixing that first you will never make the power that the engine has the potential to. Because coils are expensive to replace, a lot of people ignore them and try to band-aid the problem by other methods but you'll never make the power that you should. Compared to the price of other mods, $7-800 for a new set of performance coils is really pretty cheap power.

gtst25 Proficient

gtst25

Posted
Posted

I guess heat range 6 should be ok for stockish car.

I doubt you'd have any problems going to heat range 7 though - I've had no probs even on cold mornings - I run .85mm gap, 15 psi, 210RWKW.

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