What should my gap be?

[OLD MAN]

I run MSD Blaster coils in both my E21's and have always gaped the plugs at .045", both cars run great and both have the stock electronic ignitions in them.

[jego]

Terry, misfiring at part throttle can indicate a lean mixture. But you probably already knew that.

[Rushfan1]

Searching the E21 forum, there has been a tremendous amount of discussion on spark plug gap. For a stock 1980, is the consensus to ignore the manual/Haynes and go larger with the .030 gap?

Also, what would you choose, Champion Copper or Platinum (only $1.50 more per plug). NGK-G Power Platinum are also available. I would rather go with Platinum unless there is a recommendation against it.

[320iAman]

Table of the Conductive Order of Metals

This list of electric conductivity includes alloys as well as pure elements. Because the size and shape of a substance affect its conductivity, the list assumes all samples are the same size. In order of most conductive to least conductive:

1. Silver
2. Copper
3. Gold
4. Aluminum
5. Zinc
6. Nickel
7. Brass
8. Bronze
9. Iron
10. Platinum
11. Carbon Steel
12. Lead
13. Stainless Steel

I use Bosch WR9DS-silver coated electrode, Factory Spark Plugs, as to gap 0.024, 6mm. 6mm is stamped on WR9DS Bosch retail box as gap, for the 320i 80-83- bosch transistorized ignition system. If your burning oil, increasing the gap helps somewhat, I'd stick with what the manufacturer has as stock gap for a stock build unless it is proven by theory and then application results another gap is better.. Better results are not I think, it seems, I believe, it sounds, ect its better,,,, measured gas mileage, better dyno results and so forth are application results.

Randy

[GDAus]

Searching the E21 forum, there has been a tremendous amount of discussion on spark plug gap. For a stock 1980, is the consensus to ignore the manual/Haynes and go larger with the .030 gap?

Also, what would you choose, Champion Copper or Platinum (only $1.50 more per plug). NGK-G Power Platinum are also available. I would rather go with Platinum unless there is a recommendation against it.

Hi ...

The whole plug gap issue between the points ignition cars and the electronic ignition models I suspect, was a mix of conservatism with new technology and wanting to avoid any mix ups with having different plug gaps for the different types.
When I first got my E21 I did think that that the specified gap was a bit small for an electronic system. But when I found out that the earlier E30s were still using the M10 engine, I wondered if they we different. Turns out they used the same ICU/coil combinations as the E21s, but the plugs gaps are specified with a 0.8 mm gap .. a bit under 0.032".

I ran NGK plugs with the 0.8 mm gap for a number of years without any problems.

AS to running platinum plugs .. there has been a bit of discussion on the forum here about that .... and different people have tried them with pretty indifferent results. I was curious as to why these types of plugs didn't seem to work too well in the M10.

I finally had a chance to do some digging into Bosch's technical info about their R&D for their different products. The platinum plugs were designed for new lean burn technology engines in the late 1980's to meet new emission standards worldwide.

Simply put .. Platinum/Iridium etc plugs were designed for newer Late 1980's lean burn engines with HEI and they can take the higher combustion temperatures and the erosive effects of higher spark plug voltages. It's more about thermal conductivity and hardness than electrical conductivity ... just so the electrode tips don't melt and that the plugs have a decent service life.

So the standard E21 electronic ignition doesn't put out a higher enough voltage for these plugs to work effectively.

However ... I've been happily using Bosch platinum plugs for about 4 years now in my M10 ... the simple fix is to change the standard coil for a later "transformer" type coil. Mine came off ebay for $8 ... and was for a Nissan RB30E 6 cylinder engine which used a 1.5 mm plug gap! These types of coil (sometimes called E-core or C-core) are orders of magnitude more efficient that the older cylinder coils and they produce way more energy for less current. Mine is barely warm after an hours worth of high speed cruising on the motorway. The standard electronic ICU can handle up to a touch over 8 amps compared to about 4 amps for a points system and Bosch do 2 types of universal transformer coil .. one for points .. one for electronic systems.

IT was part of an upgrade to get rid of everything with those Beru type pin connectors. SO .. earlier type distributor cap ... Transformer type coil ... ended up with Bosch super sport inductive type plug leads. After that, the first time I started it, the engine burst into life before I finished turning the key all the way in the start position. Even with the NGK plugs at 0.8 mm there was a noticeable difference. I did try them up to 1.5 mm .... worked nicely on the motorways but there was a little low speed hesitation. But I was still sorting out my k-jet at the time ... so that was more likely the culprit there.

I lucked into a set of Bosch Platinums because a mate bought a set and they turned out to be the wrong type for his car .. and I found that Bosch actually listed them as right for an M10, so a few beers later they were mine. Out of the box they were gapped at 0.9 mm .. I didn't bothered changing them .... and haven't found the need to experiment with them since

The pic is the type of coil I am talking about .. I was still using resistor type leads at that stage .. but the inductor type leads are much tougher and stand up to handling better.

Sorry this got a bit wordy ... but sometimes simple questions have complex answers

Cheers

[cgifool]

Thanks for the tip! What, if any, resistor would be used for this kind of coil?

I'm generally of the mindset that "upgrades" rarely are, and a big fan of the "vintage experience", but this sounds like something I would seriously consider.

regards
David

[epmedia]

Thanks for the tip! What, if any, resistor would be used for this kind of coil?

I'm generally of the mindset that "upgrades" rarely are, and a big fan of the "vintage experience", but this sounds like something I would seriously consider.

regards
David

Good question for GDAus, especially if it can be adopted to work for the 'points' type of ignition. I like the idea of better spark at less energy. Those old style oil-filled coils can get a bit hot.

[GDAus]

Good question for GDAus, especially if it can be adopted to work for the 'points' type of ignition. I like the idea of better spark at less energy. Those old style oil-filled coils can get a bit hot.

At the moment I don't have an answer to that .. but I suspect the universal points type transformer coil would be a straight 12 volt coil (not needing a ballast resistor). It would simplify matters and the newer type coils are so much more efficient that the reduced voltage during starting wouldn't have too much of an effect on the output voltage.

I know I seen these universal types on the shelf at a local parts store ... but I don't know if I managed to find any info about them online. I downloaded a ton of stuff a couple of years ago .. I'll have to spend a bit of time having a look.

But certainly for the electronic systems .. the coil I have been using is a Bosch BIC800 so I know that definatley works. I has the standard type female socket for the plug leads and I did have to fit a plug for the 2 spade connectors on it.

cheers

[GDAus]

Just a bit of an update....

I sorted out all the ins and outs of K-Jet and got it running to factory specs and I was able to experiment with Plug gaps!
The Bosch Platinums I was using came out of the box gaped at 0.9 mm and I tried different values up to 1.5 mm

At motorway speeds 1.5 mm gap was giving improved fuel economy but there was a bit less torque available to get up some long hills in 5th gear.

In the end I settled on 1.2 mm which gave one touch starting and good hill performance in 5th gear.

I mentioned in some of the posts here about Bosch " Universal" Replacement Transformer Coils. I don't know if they were something Bosch Australia was doing locally here, but they have disappeared of the shelves here and there is no reference here to them in any catalogues.
Also Bosch has changed the design of their transformer type coils so they do look different from the one I am using.

Cheers

[82Kashmir]

Looks like a Good upgrade worth exploring lots of them at the junkyard. That coil type looks like a lot of 90's cars ignition setups, plug gap at 1.2mm makes sense Standard Hei plug gap of that era.

[GDAus]

Looks like a Good upgrade worth exploring lots of them at the junkyard. That coil type looks like a lot of 90's cars ignition setups, plug gap at 1.2mm makes sense Standard HEI plug gap of that era.

I did a fair bit of experimentation with fuel mixture /plug gap combinations.
I was getting better fuel economy with a leaner mixture with a gap of 1.5 mm but on long hills at motorway speeds in 5th gear it would slow down too much for my liking.
But with a slightly richer mixture and 1.2~1.3 mm gap it would pull to the top of the hills

The coil I'm using has a
Primary resistance = 1.6 Ω
Secondary " = 8.86 kΩ

Cheers