Opening spark plug gap to .049 improves power... it is very noticeable.
 

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Originally posted by KGB
I just did mine today..its fairly easy if you are slightly mechanically inclined.
...changed the plugs in the Z today and boy what a pain? I guess "easy" is relative. It took me almost two hours. Oh well.

Here's how the plugs read:
Rear cylinder plugs: tan
Center cylinder plugs: tan with a little black soot (slightly rich condition)
Front cylinder plugs: tan with even more black soot (somewhat rich condition)

These readings are consistent with the design of the stock plenum in that it slopes down from the back to the front, making it more difficult for the middle and front cylinders to get their share of oxygen -- as Doug S. has stated.

Crawford's modified plenum, which I have but not installed, should improve this condition so that the air-to-fuel mixture is more consistent from front to rear.

I installed the new plugs with a gap setting of .049. My experience with after market high energy ignition systems (and I'm guessing that Nissan's direct ignition system has more energy than is typical) is that when the plug gap is too small the engine doesn't idle or run as smooth as it could. If the ignition system can support bigger spark plug gaps, more power and response can be had.

I'm going to reserve my comments for a couple of weeks to allow for carbon to build-up on the new plugs. An engine always runs better with new plugs, although my Z has only 7000 miles on it.

I can say that the idle quality and engine smoothness so far seem to be dramatically improved.

Stay tuned....
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I was going to wait a couple of weeks before commenting about the results of opening the plug gaps, but my Z seems to be running stronger than ever. Even in 95 degree heat, with the AC running.
I would estimate there's about an 8 to 10 horsepower increase. Believe or not! There is a very noticeable increase in low-end and midrange torque. The top-end, too, is improved, but it almost seems slightly overshadowed by the power in the low-end & midrange.

A few comments of note:
1) My exhaust tail pipes are showing telltale signs of turning brown. This is an indication that there's a more complete combustion taking place in the cylinders.

2) The sound of the exhaust note is noticeably tighter and much less boomy sounding. To many, the exhaust will seem quieter, but the Z just moves out without the drama of the boominess.

3) The engine has much less vibration and more of a willingness to rev. It is more responsive to throttle input across the entire rev-band and more readily accelerates (at any rpm) when you stomp on the gas. It feels good!


If everything I have said here holds up for the next month or so, I would say we have a “free” horsepower modification here. But if my Z, with only 7000 miles, has fallen away from “perfect” tune, all I have succeeded in doing is restoring lost horsepower.

I guess those open the gaps on their plugs will have to be the judges.

What plugs did you install, OEM or different?

whats the stock gap? 8-10 whp seems too much.....

I am very interested in this but don't know about spark plugs in the least. Can anyone give me some background here?

Dude, if you're gonna post a performance increase merely by changing spark plug gaps COME UP WITH A MORE SCIENTIFIC WAY OF PROVING YOUR RESULTS!!!! I "Felt" a difference might work in the Honda world, but not here. You MIGHT feel a 20rwhp increase, but sure as hell not a 2-8 rwhp. IT'S ALL IN YOUR MIND, until you prove otherwise.

Dan

Hey McDan... http://www.spacespider.net/emo/slap.gif

Be nice. Some of us want to hear if this actually works!

I would too, but I'd like to "know" if it works, not hear that it "feels" like it works. The way most people on this site determine if a mod works or not is flat out rediculous. Dyno test it, take it to the track, G-Tech time it, hell even run side-by-side with another Z, but don't tell me it "feels" faster!.... And I was being nice.

:p Sure.....I'll go test it on the dyno I keep in my garage. Or maybe my spare dyno that I keep out back in the shed with my big pile of money....

I think you guys need to be a little more realistic in your expectations....and maybe take another look at your definition of "nice."

:D

:icon18: :icon18: :icon18:

Nothing's ever good enough for some people.

If asking for ONE item of proof is too much to ask, then I guess I don't know what to say. You buy a $30,000+ car but can't afford a $50 dyno session? There are many other alternatives to at least make an attempt at proving your statement.

Hey McDork,
Leave the guy alone, he's trying to help and post some info for people so that others might be able to try it or research it and get to the bottom of it. Not everyone has a dyno near them. Try finding one near Pensacola for instance...

McDan: While there is some logic behind what you are saying, you could go about it in a much more friendly manner. No need to be a dick!

Yeah, I did this awhile back with a new four piston brake system. The system was way better than stock, more stoping power, more cooling, etc. with specs to prove it. All I got from a lot of people was "it hasn't been tested directly with Stoptech", It hasn't been track tested" and of course my favorite "it hasn't been dynoed" so of course the brake system to these people was basically BS or junk.

So your on point Jesse, nothing's ever good enough for some people. :confused: :confused:

Jeff

thanks KGB. I was planning on changing my plugs. I'll set the gap like you said and let you know how it turns out

Sorry maybe it is just me, but wtf does a dyno have to do with brakes? I mean, brakes = stopping power, dyno measures horsepower and ft-lb torque at the wheels, has nothing to do with brakes.

Also, Mcdan if you want proof it works, why don't you go regap your stock plugs yourself, and YOU pay the 50 bucks to see if it really shows a difference on the dyno. If you are too lazy, then YOU send the guy the money(btw, it is usually about 70 bucks for a dyno session with 3 runs) and I'm sure if he has time he wouldn't mind going if asked politely. Another thing, just because someone can afford a 26,000+ car doesn't mean they always have money to throw around to dyno every change they make to their car that effects horsepower and torque output.

Many things effect spark plug gap settings...
 

Spark plug gap should be made as small as possible, while still maintaining performance. A wide spark plug gap can cause hard cold starting, misfires during rich or lean fuel conditions, and reduction of upper rpm range. To maintain a good secondary spark (multiple spark) within a wider rpm range it is wise to run a narrower spark plug gap. It is better to precisely place two stable, consistent sparks than to fire one wider spark that may cause misfires under various conditions._

Compression Ratio: The higher the engine compression, the more voltage required to fire the plug, and the narrower the plug gap should be.

RPM: The higher the rpm's the less time the coil has to charge to break over voltage or complete saturation. A narrower spark plug gap will help high rpm stability.

Spark plugs with large side electrodes (ground straps) or spark plugs with split side electrodes are not recommended, they interfere with the flame front at the point of ignition.

Coil choice, fuel flow, intake velocities & fuel temperature are but a few additional factors that can effect spark plug gap.

http://www.powerarc.com/sparkplug.htm

JMS in TX

I agree with Silver Bullit II 100%. This is definitely an area where test and tune can shine. While your engine may like more gap, that doen't mean more is better in every situation. Thanks kgb for the post and I will keep watching to see what feedback comes from it.

I will probably leave the factory ignition system alone since I don't think that there is much we can do for it by way of MSD ignitions etc.

Ok Patssmmearr :rolleyes: (now that we've resorted to 3rd grade name calling). Can you f&cking read? I listed many other possible ways to show some sort of performance gain. Nice PT Cruiser by the way.:rolleyes:

Dan

Are you done? We are trying to have a good informational thread here. Thanks everone else BTW!

Thanks for your comments.
 

When I installed the grounding system a few months back, I noticed the improved smoothness and FELT there was about a 2 to 3 hp increase. Dyno results have been posted to confirm what I FELT, including confirmation from Turbo Magazine.

I stand by my earlier comments the wider gap setting has improved power of my Z. …and yes, the power increase is more noticeable the grounding system.