Interesting Problem....

[madbung]

I'm sorry but, 'feeling the difference' in top end?

Unless the tune was rooted before I can assure you that not only is there no power difference but, also this 'feeling' is peculiar only to cars that started out with a spark issue or were seriously 'under-gapped' for the density of the air/fuel mixture.

Smashing more power/rpm/boost into a motor and gapping down on the exsisting heat range is tuning 101( for all cars). If you get no joy in the top end after gapping down on the exsisting heat range you go to a colder plug etc.

For example, for most of the NA V8's I've tuned you can just about go off a rule of thumb that is gap down 4 thou for every 50hp added.

I've been doing this to alot of different cars over the years so 'luck' has nothing to do with it.

There are some serious horsepower GTST's & GTR's running around with factory coils as well. Splitfires do one thing well and thats make a cheap replacement for the expensive factory coils when they are shagged.

You have some strong convictions there...you can keep em. I don't use stop gaps unless necessary.

As I said "hey if 8 is your lucky number.... who am I to say different"

My car runs good on .8 and runs much better on 1.1, regardless of how it's tuned, I get more out of 1.1, the engine has been re-built and has never had stock coils on it.

The car had stock coils when I bought it...they were fine

Gapping down on stockers is done to adjust for the standard tune on 98ron...nothing to do with coils.

But hey thanks for the beer.

[rev210]

You have some strong convictions there...you can keep em. I don't use stop gaps unless necessary.

As I said "hey if 8 is your lucky number.... who am I to say different"

My car runs good on .8 and runs much better on 1.1, regardless of how it's tuned, I get more out of 1.1, the engine has been re-built and has never had stock coils on it.

The car had stock coils when I bought it...they were fine

Gapping down on stockers is done to adjust for the standard tune on 98ron...nothing to do with coils.

But hey thanks for the beer.

I don't use stop gaps either. I think you may not understand plug gapping in terms of how it fits in with a tune.

To clarify, I had suggested that 0.8mm is better suited to higher power/boost/rpm than 1.1mm on the same heat range of plug. I haven't suggested that you gap down to 0.8mm for the sake of it.

Nor have I said 0.8mm is the only gap I run. I have tried to give some insight into plug gapping by indicating when we go closing the gap a bit and why(not very well explained so far I guess)

When you decide to slap another 100hp into your motor you can re-test your 1.1mm theory 'if thats your lucky number' (our 'in joke'). You will find that due to the much higher charge density that equals the extra 100hp you will have a missfire that is simply fixed by re-gapping, or in the case of exceeding the heat range of the plug going to a colder plug.

So you aren't mislead; Gapping down is 'not' done to adjust for the standard tune on 98ron. It is only required when people up the boost/power (charge density).

As a side note the irridium and platinum varieties of plugs with thier smaller electrode allow for a 'longer' spark shape and tollerate a slightly wider gap. Makes sense as some of the Autolite plugs I used to use in my V8 days had smaller electrodes and seemed to go the same way.

Hope that explains a little better the plug gap rationale.

Actually maybe someone can look up the theory of spark plugs and post it up. Proving me wrong is always good fun and I get to learn something new too

Edited June 8, 2008 by rev210

[GeeTR]

*cough* ignition system bolstering CDI and 1.2mm gaps ftw *cough* Rev210, your theory is what i believe as well.

Edited June 8, 2008 by GeeTR

[turbo_brian]

Gapping (from my own experiences and not agreeing or dis-agreeing with anyone else) is for weaker or less able coil packs in cars.

When I have my POS 180sx, it was fine on 1.1mm plugs for a good 12 months, but then started mis-firing and causing problems.

After new plugs, and gapping to 0.9mm it was fine for a further 6 months before it went rough again, so took the plugs out and re-gapped to 0.8mm and it was again fine. Got 4 new coil packs, gapped the plugs back to 1.1mm and it was running perfectly fine again until I sold it.

If your ignition system can sustain the larger gap, I would be using it, as a larger gap usually = a hotter spark, which means better ignition of the air/fuel mixture.

Then you have other things to consider, such as ECU, tune, fuel type, etc but in it's most simplest form, the larger the gap, the hotter the spark, and the cleanest burn you can get.

B.

[madbung]

I do use the iridiums Rev...that could be the difference. Next time I'm stuffing around I'll try some coppers @ 1.1 and see.

Engine pulled 274kw when fresh, I'd like to try another 100hp and see how I go, but those extra hp will be costly

I understand exactly your methodology, but as I said I don't like to go about it that way if at all possible..If it can't be done in timing/tune, then yeah sure no problems. My ute, 289 windsor I run gapped down plugs to avoid pinging on u/l, because the mechanical dizzy won't allow enough advance to get her running right, when I change that over to a remapped electronic setup it'll be gapped to normal again. As it should be.

I know I do seem a tad pedantic on this shit..sorry and in no way am i saying the way you do yours is wrong, because I know it works fine that way also, I just prefer the other method.

p.s

8 is a lucky number

[rev210]

I think there is also 1 last thing that I should have clarified. A stronger spark from a boosted up CDI or in the old school NA V8s an MSD setup/magneto allows for a larger plug gap relative to a weaker coil system or on the skyline where the factory coils are on the way out. You still need to gap down as charge pressure increases regardless, although your starting point may begin higher. 7 is my lucky number.

[MBS206]

Running the same plugs, same coil packs, I went from a stock RB25DET to an RB25/30DET with a T04R off the side... Still running at 1.1mm gap with out an issue, and currently enough grunt to have 3rd gear spinning hard before I even hit full torque...