widining spark plug gap??? Recommended or not?

[cpalmer]

So, know that I have my brakes in good order, (it's like a new car in corners), and I've taken my smog off, (not needed where I am) and the car runs a little better, but it's still a 530i....

I've have a few people tell me that I could open the gap on the plugs by .05 to lengthen the spark and have it burn cleaner.

What's the general consensus on this?

Just wondering what everyone thinks and if it is something I should do.

Hope everyone had a great 4th!

[GripGreg]

I've noticed that the factory gap is usually wider than what the book calls for. I've always wondered why. Good question to debate. Greg

[cpalmer]

When I put mine in last summer, I set them to what the manual said.

Guess I should go and check that number.

[GripGreg]

I prefer Bosch to whatever else. Did you have to re-gap them or just install? Greg

[cpalmer]

you know, they are Bosch and I remember putting them to the gap in the manual after about thinking I should just put them in.

Maybe I'll open them up a bit.

[Brian Smith]

Motors with weaker ignition systems require smaller plug gaps.
Raised compression ratios or forced induction adds additional difficulty to spark initiation.
While it might hold a theoretical advantage, for all out "BMEP," to use the largest spark gap you can manage, for most purposes, and certainly for street driven cars, you should probably use only the largest gap that permits zero detectable episodes of failure to ignite the compressed intake charge.
One unburnt cylindersworth of fuel out the exhaust equals less cleanly burning than miles of driving with a small plug gap that is theroetically not allowing as clean a burn as might be possible.
Does your 530i have electronic (non-points) ignition installed and an ignition distributor in known perfect working order? If not, those things hold the potential for a lot more fruit than spark plug gap.
I have no data to support these claims, but I do have 20+ years of tinkering and mildly tuning ignition systems from points-triggerred onward.

[cpalmer]

I switched out the points a few months ago to pertronix.

I was having some problems with them before and the dist. cap and rotor seemed to get some extra wear and tear on them during that time, although I replaced them last summer.

[T.Hanson]

Twenty years experience. Back to the old subject of forgetting there are millions of us who think gap is jeans.

What's a BMEP. How in horntoot would I ever know if a wider gap burn didn't ignite to release the unburned fuel less than a smaller gap one every three hundred miles. Like Jack Roush with his magnifying glass.

I mean no offense. Stock street 528i, L-jet, Bosch WR9DS. Every time I've changed them the gap was correct out of the box.

[GripGreg]

I agree with T-Han, what's a BMEP? I have the same stock set-up that T-HAN has. What is the differance between a weak/strong ignition system?
Does it start strong & become weak? Is this normal? I luv this type of debate! Greg

[GripGreg]

Sorry; but when I pulled my WR9D's from the box, I think they were gapped at .32. I took'um down to .26, I think. Would this make a differance? I still luv it,,,,Greg

[Brian Smith]

Twenty years experience. Back to the old subject of forgetting there are millions of us who think gap is jeans.

Ha. Right-o, not sure which side of the '80s the O.P. is coming from, and whether this was a serious inquiry or a coffee-can muffler dragger in the making, not that there's anything wrong with that, I suppose.

What's a BMEP. How in horntoot would I ever know if a wider gap burn didn't ignite to release the unburned fuel less than a smaller gap one every three hundred miles. Like Jack Roush with his magnifying glass.

I mean no offense. Stock street 528i, L-jet, Bosch WR9DS. Every time I've changed them the gap was correct out of the box.

BMEP - check across the hall, my apologies for even bringing up the term.
$10 extra to the board's paypal if someone comes up with something to claim as the meaning of that acronym that makes me laugh out loud. Other than that, forget I mentioned it.
As far as knowing when your spark doesn't ignite the fuel, I must admit that if an engine is failing to ignite the mixture due to a extra demand on the ignition system, the easiest way to "know" it is having experienced the same motor without the hindrance. Cold air temperatures, very low rpm, very high rpm...those are some conditions that even a good conditioned stock ignition system of our vintages have difficulty igniting the mixture, sometimes witnessed as a failure to run smoothly, or even to run at all! When the propensity to become unsmooth besets your engine, if you can identify the conditions under which it is unsmooth to a condition that is noted as being extra challenging for the ignition system, then it is a good hypothesis that perhaps the ignition system is not always doing its job well. Sometimes this failure to ignite produces the "rich mixture" scent.

I share the same experience with the Bosch plugs. I check the gaps, and they are, straight out of the box, almost always exactly what I had hoped them to be, or too close to be fit to modify.

I just think that anyone making a claim that a tiny bit of extra plug gap given to a stock engine is going to make anything run cleaner is, ah, without an electronic sniffer, talking out their bum. I could be wrong, but enough fiddling with motors makes me confident that larger design sacrifices can to be found (and improved) than plug gap.

Any mechanical advance distributor in a 530 with a pertronix retrofit would probably not benefit from a gap change away from Bosch factory gap setting in any positive way.

I think any car that is using an igintion distributor originally equipped with points can likely benefit from a new distributor cap and rotor with every tune up, which means probably at least once yearly. If the cap and rotor is a year old, I'd be replacing them and stowing the old parts someplace as "known working spares."

If I had noticed a positive change with the pertronix fitment, I'd also be getting curious about updating to the factory's style of electronic ignition in the the later e12 as a better long term solution.

The motronic stuff did so much to eliminate caps and rotors as tune up items that a single pair still work after 100k miles. If I ever get around to a programmable ignition system, I'll be very tempted to switch to one of those distributors.

[Brian Smith]

I agree with T-Han, what's a BMEP? I have the same stock set-up that T-HAN has. What is the differance between a weak/strong ignition system?
Does it start strong & become weak? Is this normal? I luv this type of debate! Greg
Sorry; but when I pulled my WR9D's from the box, I think they were gapped at .32. I took'um down to .26, I think. Would this make a differance? I still luv it,,,,Greg

Yes, Greg, you've got it.
That's what I meant, for the most part, between weak and strong. I'm calling the state of everything being factory fresh "strong," and what most of us have now....less strong.
These days a Toyota ECHO probably has a much stronger ignition system than the vast majority of us e12ers, so I don't strictly mean the system's condition, but I do mostly mean condition.
Is the factory spec for early M30 e12s 0.026"? If so, this is an example of the system strength being related not strictly to condition but also to the system's design. For the points distributor, I could imagine, the specified plug gap might be a smaller gap than the fully electronic later system received. The fully electronic system has fewer compromises than a points-triggerred system, and can be relied upon to spark across a larger gap in more varied conditions. Thus, the later fully electronic system could be released with a larger factory gap specification. My Chilton's (boo-hiss) shows the same gap spec. for both the 530i and the 528i.

Greg, I doubt that you are sacrificing anything to run the plugs at 0.026", and if someone with their plugs at 0.032" and the points distributor correctly adjusted and in good condition was experiencing an ignition problem under certain conditions, I'd probably suggest trying the plugs at BMW spec. instead of Bosch out of the box spec.

[T.Hanson]

Wow. O.K., don't ever be offended by me for being educated and experienced. I think you are called the best teachers.

Back to Jack Roush: I get the idea the best tuners are masters at reading spark plugs, because spark, ignition, fuel burn is the ball game.

[Brian Smith]

Wow. O.K., don't ever be offended by me for being educated and experienced. I think you are called the best teachers.

Back to Jack Roush: I get the idea the best tuners are masters at reading spark plugs, because spark, ignition, fuel burn is the ball game.

People who actually test things and have knowledge are a breed apart.
No offense taken here, for sure.
I just fumble around and have a "need" to optimize systems.
Somehow that doesn't stop me from forming firm opinions based upon what has worked or not worked for me.
I hope someone else can occasionally benefit from my findings as I have benefitted from those of others!

[Scott Bunn]

So, a user with points and stock set up should use which gap? 26 or 32?