So.....

On the last two blown motors, I was running NGK 7 plugs which are one point colder than stock. I also ran them at about .30. And both motors lost pistons.

So the current motor is running stock NGK 6 plugs, with stock .35 or so plug gap.

This motor pretty much running perfect (compared to the old motors) but it still does have the occasional hesitation and miss. Could this be because of the stock plugs and stock plug gap? I am leary of going to smaller gap and colder plugs because I had problems with them in the whole scenerio on the last two motors.

But, if colder plugs with smaller gap would actually do no damage, but improve things, I will install them on Friday.

Thanks.


Oh yeah,

8-10 psi on a NA block, NA ECU.

go grab some ngk bkr7e11 plugs. thats what i run in all my j-spec motors. stock number is 1283 at orielys.
if you have some hesitation and miss take the gap down to like 20-25. you pick up some power and lose the miss/hesitation.

holy 20-25, I wouldnt go below .26

The wider the gap with out hesitation the better.

true i agree that the wider the gap with out hesitation will be better. but my car hesitated like a lil bastard with 25 gap. i took it down to 20 and it damn near got rid of all the hesitation. still a bit left so i think im gonna knock it down a thousandth or two more.

You want to run the widest gap you can without misfiring at peak boost.

As you reduce plug gap you are reducing the surface area of the spark that is exposed to the combustion chamber. This makes it more difficult to properly ignite the mixture BUT....

... air is a great insulator. As you increase your plug gap, greater ignition coil voltages are needed to properly fire the mixture. As you start to run an engine under boost, more air molecules get shoved into that plug gap effectively increasing your plug gap.

Increasing boost also increases turbulence in the cylinder. Turbulence within the cylinder itself is a good thing, think of shaking a paint can to mix everything better. Downside is that as you get more turbulence you run into issues of actually blowing out the spark (think zippo in a huricane).

Finding the right gap takes a bunch of trial and error. The only totally fool proof way is to strap the car to a dyno with an oscilliscope to measure secondary ignition voltages at full boost. I had the opportunity to do this on my car and found a gap of .021 was ideal for the plugs I was using and the boost I was running (22psi). If you're a mere mortal without access to toys like this just run the widest gap you can without misfiring under full load.

As for plugs... the best I've found are the NGK copper plugs 1 heat range colder. When you go down a heat range you lessen the chances for detonation but the plugs foul easier. I was changing plugs at every other oil change (about 15,000 miles) which wasn't too fun. The motor liked it though. I don't have part #'s on these plugs handy but any good parts guy should be able to look it up for you.

hes back from the dead

OK, I gapped the stock 6s down to .28 from the orginal .34 gap or so.

So far.......it has less power off boost, but not much, and it kinda is hesitant while cruising, but on boost not any knock. Cross your fingers.

i am also that low
bkr7e at .19
but not running stock em

i as well am not running a stock ecu im running a mines tuned ecu.

The small plug gap seems (no proof, just seems) to have eliminated 99% of det. I was able to uphill haul ass in the passing zones and only got one knock out of about 5-6 runs.

All I need now is some engine management......

what did i tell you

You want to run the widest gap you can without misfiring at peak boost.

As you reduce plug gap you are reducing the surface area of the spark that is exposed to the combustion chamber. This makes it more difficult to properly ignite the mixture BUT....

... air is a great insulator. As you increase your plug gap, greater ignition coil voltages are needed to properly fire the mixture. As you start to run an engine under boost, more air molecules get shoved into that plug gap effectively increasing your plug gap.

Increasing boost also increases turbulence in the cylinder. Turbulence within the cylinder itself is a good thing, think of shaking a paint can to mix everything better. Downside is that as you get more turbulence you run into issues of actually blowing out the spark (think zippo in a huricane).

Finding the right gap takes a bunch of trial and error. The only totally fool proof way is to strap the car to a dyno with an oscilliscope to measure secondary ignition voltages at full boost. I had the opportunity to do this on my car and found a gap of .021 was ideal for the plugs I was using and the boost I was running (22psi). If you're a mere mortal without access to toys like this just run the widest gap you can without misfiring under full load.

As for plugs... the best I've found are the NGK copper plugs 1 heat range colder. When you go down a heat range you lessen the chances for detonation but the plugs foul easier. I was changing plugs at every other oil change (about 15,000 miles) which wasn't too fun. The motor liked it though. I don't have part #'s on these plugs handy but any good parts guy should be able to look it up for you.

Interesting post. What size piston are you running? .021 still seems on the tight side imo. (not that that's bad, just observation)

It'd be interesting to compare gaps between the 2.5's and the 2.0's. Out of curiousity do you know what's a common gap on smaller bore 4cyl's...say an sr20 (86mm iirc)

Do you think that suby's with their bigger bores and the fact that they already need rather large ign. advance numbers that an upgraded Ign. system would greatly benefit a build? Am i just overthinking this?

Louis

Well, my stock 2.2 NA gap is about .034 to .038, so i am really changing it ALOT!